Saturday, September 11, 2010

Genetically Transmitted Diseases/Disorders

A genetic disease can be the result of mutation in a gene. According to online library there are currently more than 4,000 known genetically transmitted diseases with more being discovered every year. Genetic diseases can be inherited from parents by children. Some genetic diseases are extremely rare, while some genetic diseases are more widespread. 

People who are curious as to their chances of inheriting or passing on a genetic disease can get genetic testing.

Cystic Fibrosis

  • Cystic fibrosis affects more than 30,000 children and adults in the United States today, according to the Cystic Fibrosis Foundation. It is also life-threatening as it causes mucus to build up and clog organs in the body. Mucus and bacteria build up in airways and cause severe swelling that can lead to lung damage.

    According to the Cystic Fibrosis Foundation in order to inherit the disease one must inherit two copies of the defective cystic fibrosis gene. This means the individual must inherit a copy of the defective gene from both parents.

  • Chronic Granulomatous Diseases

  • Chronic granulomatous diseases are genetically transmitted diseases in which the immune system is affected and compromised. The immune system cells are not able to efficiently form compounds that are necessary to kill pathogens. This inefficiency leads to granulomas which are ineffective at fighting disease and infection. A granuloma is essentially a small tumor or small area of inflammation. Usually the inflammation is caused from a tissue injury or infection, however in patients with CGD the granulomas are chronic.

    According to a study in 2004 conducted by Dr. Maryland Pao, et al., chronic granulomatous diseases affect one in 200,000 people, and there were an average of 20 new cases each year.

    Symptoms of CGD can include but are not limited to superficial skin infections, abscesses of the skin tissues and organs, arthritis and pneumonia.

  • Mucopolysaccaridosis Diseases

  • Mucopolysaccaridosis diseases are genetically transmitted diseases that affect the functions and abilities of the enzymes to break down sugars. The inability to break down the sugars leads to a build up in the cells and the blood which leads to permanent cellular damage.

  • Phenlketonuria

  • Phenlketonuria is a genetically transmitted disease in which the body's ability to metabolize phenylalanine is compromised. When left untreated this genetically transmitted disease can lead to brain damage as well as mental retardation.

    When discovered early enough in childhood a special diet can be maintained, and the child can grow with normal brain development. A special diet includes limited amounts of breast milk, cheese and other dairy products as well as limited amounts of meat and chicken, nuts and fish.

  • Turner's Syndrome

  • Turner's syndrome is a series of genetically transmitted diseases that affect the chromosomes. There are many different types of syndromes depending upon the chromosomal makeup the individual has inherited. Symptoms of Turner's syndrome can include swelling of the hands and feet, a short stature and broad chest, a low hairline and low set ears, and being reproductively sterile.

    It is common for a fetus with Turner's Syndrome to spontaneously abort.

  • Celiac Disease

  • According to the Celiac Spruce Association, one in 133 people are affected by celiac disease. The disease can lay dormant until triggered by gluten in food. It is not uncommon for gluten in food to set off a response in a person's body which causes damage to the small intestine which leads to the small intestine being unable to absorb nutrients in food and causing malnutrition.

    Contrary to popular belief, celiac disease is not a food allergy and is not age-dependent. Celiac disease can appear or become active at any age

  • Jewish genetically transmitted diseases

    That only effect the Jewish people? The list is near endless but here’s a small sample of ailments, quite a few are exclusive to their people. Chosen for disease one might say? If there are any explanations or theories behind this I would like to know.
    Alpha 1-anti-trypsin Deficiency
    Amyotrophic Lateral Sclerosis
    Aut. Dom. Optic Atrophy
    Aut. Dom. Retinitis pigmentosa
    Bardet Biedl syndrome
    Berger’s Disease
    Bloom Syndrome
    Canavan disease
    Celiac Disease, or Sprue
    Con. Stat. Night Blindness
    Congenital blindness
    Congenital deafness
    Corneal Dystrophy
    Crohn’s Disease
    Cystic fibrosis
    Hereditary Hearing Loss
    Kaposi’s sarcoma
    Lactose intolerance
    Leber’s congenital amaurosis
    Lipoamide Dehydrogenase-
    Early rheumatoid arthritis, often
    occurring in childhood
    Elephant man’s disease- Proteus
    Fabry Disease
    Factor XI deficiency
    Familial Dysautonomia
    Familial Hypercholesterolemia
    Familial hyperinsulinemia
    Familial Mediterranean fever
    Fanconi Anemia
    Gaucher Disease
    dehydrogenase deficiency
    Glycogen storage disease type 1a
    Glycogen storage disease type III
    Machado Joseph Disease
    Malformed limbs
    Maple syrup urine disease
    Mucolipidosis IV
    Multiple Sclerosis
    Muscular Dystrophy
    Nemaline Myopathy
    Niemann-Pick disease
    Non-Classical Adrenal Hyperplasia
    Non-syndromic sensorineural
    Psychotic disorders- abnormally high incidence of
    Rib cage misaligned
    Stargardt disease
    Tay Sachs
    Temperature intolerance
    Torsion Dystonia
    Type III Glycogen Storage disease
    Usher Syndrome Type 1F
    Vitelliform Macular Dystrophy
    Wilson disease

    What is genetic screening?

    What is newborn genetic screening?
    Newborn genetic screening is a health program that identifies treatable genetic disorders in newborn infants. Early intervention to treat these disorders can eliminate or reduce symptoms that might otherwise cause a lifetime of disability.
    Who performs newborn screening?
    Newborn genetic screening programs are conducted worldwide. In the United States, newborn screening programs are developed and run by individual states. Each state decides which disorders to test for and how to cover the costs of screening.
    Who is screened?
    In most cases, newborn infants are automatically screened in the hospital shortly after delivery.
    Who pays for screening?
    Individual states in the United States finance their newborn screening programs in different ways. Most states collect a fee for screening, which ranges from less than $15 to nearly $60 per newborn. Health insurance or other programs can pay this fee for the newborn's parents.
    Often, the fee charged does not fully cover the cost of screening, so public health system funding is used to supplement the program. Financing a screening program comes with an expectation that the benefits of testing - early detection and treatment - will equal or exceed the cost.
    Who decides?
    Lawmakers in each state have enacted legislation that defines the state's newborn screening program. From time to time, these programs need review and revision to incorporate new technologies, address financial issues and ensure that the screening program is meeting the needs of the state's residents.
    When developing a policy, lawmakers must consider the following questions
    • Which disorders should be included in the screening program?
    • Who pays for the screening program, and how?
    • Who should be screened?
    • Who has access to test results?
    • Who benefits from the screening program?
    • What are the potential risks of screening?

    Genetic Research

    Research advances in genetics are in the news almost every day. Many of these news reports tell of the discovery of a gene that causes a disease or other medical problem. While these reports are often exciting and provocative, it is often not easy to understand exactly what has been discovered and how that discovery will help the people with that disorder. There are a number of studies on the genetics of stuttering now in progress. Findings from these studies are beginning to appear, and there is much hope that more discoveries, telling us more important information about stuttering, will soon be made. What exactly are these studies, and what do scientists hope to learn from them?
    Several of the current genetic studies on stuttering, including our NIH Family Research Project on Stuttering, are technically known as linkage studies. In linkage studies, scientists attempt to find genetic markers that are co-inherited with stuttering in families. This co-inheritance in families is known as linkage. When a marker or markers show co-inheritance with stuttering, scientists know that these markers lie very close to the gene or genes that help cause stuttering in those families. Since scientists already know the location of each marker they test, discovering linkage to a marker tells them the location of the gene(s) involved. If scientists can find the location of these genes, they can learn a great deal about the contribution of each one of those genes to stuttering. In addition, they can use the information on where the genes are located to find, isolate, and study these genes.
    What are these genetic markers? Anything that shows inherited differences in people is a genetic marker. A good example is your blood type. A personþs blood type can be type A, type B, or type O, and each person inherits their blood type from their parents. The gene which specifies blood type resides on chromosome number 9. One of the first examples of linkage ever demonstrated in humans was co-inheritance of ABO blood type with a rare and unusual disease called nail-patella syndrome, in which people have abnormal fingernails and kneecaps. Knowing that the gene causing nail-patella syndrome is linked to the ABO blood type gene told scientists that the nail-patella syndrome gene is on chromosome number 9 as well. This information on where this gene is located allowed scientists to find this gene and to see how it was different in people with nail-patella syndrome. This discovery revealed new information on how fingernails and kneecaps develop, and how these two parts of the body are actually related to each other. The goal of linkage studies on stuttering are exactly the same.
    Scientists hope to find the genes that can cause stuttering, to see what these genes do, both in normally fluent people and in those who stutter. How will this help people who stutter? First, despite decades of effort by dedicated researchers, no underlying cause of stuttering has been found. While many stuttering therapy methods have proven to be helpful, understanding the underlying causes of stuttering will be a tremendous aid in designing new and better therapies. Even before this point, however, having good genetic markers for stuttering could help with stuttering diagnosis, identifying those that stutter because of genetic factors. These could help identify individuals at risk in families, and help get early intervention started in those who need it most. It's an exciting time in stuttering research. We have good reason to hope for better understanding of

    chromosomal disorders|chromosomal diseases

    Most human cells contain 46 chromosomes, or 23 pairs of homologous chromosomes. Each chromosome of the pair is the same shape and size and has the same genes in the same location. Chromosome disorders occur due to two types of alteration in the chromosomes. Chromosome disorders can be caused by an alteration in the number of chromosomes in the nucleus, or by an alteration in the structure of a chromosome.

    Syndrome caused by chromosome abnormality. Normally, humans have 23 pairs of chromosomes, including one pair of sex chromosomes. Any variation from this pattern causes abnormalities. A chromosome may be duplicated  or absent; one or more extra full sets of chromosomes can be present (see ploidy); or part of a chromosome may be missing (deletion) or transferred to another (translocation). Resulting disorders include Down syndrome, intellectual disability, heart malformation, abnormal sexual development, malignancies, and sex-chromosome disorders (e.g., Turner syndrome, Klinefelter syndrome). Chromosomal disorders occur in 0.5% of births; many can now be diagnosed before birth by amniocentesis.

    Sex cells, or gametes, have only 23 chromosomes. When the sex cells are produced, chromosomes separate and move to opposite ends of the cell. Sometimes a chromosome moves to the same end of the cell as its pair, instead of the opposite end. This extra chromosome is incorporated into the nucleus of the daughter cell, causing it to have an extra chromosome, a nondisjunction. As a result, one of the gamete cells will have two copies of the chromosome and the other will have none.

    During fertilization, a sperm cell merges with an egg cell producing a zygote with two copies of each chromosome. If a nondisjunction has occurred, and a gamete with the wrong number of chromosomes unites with another, the resulting cell will have the wrong number of chromosomes. If the cell has too many chromosomes, it is said to be polyploidy. Often, the cell only has one extra copy of a chromosome, or three in humans, so it is called a trisomic cell. If the cell only has one copy of a chromosome, it is called a monosomic cell.

    Nondisjunctions in human cells are relatively high. The results are often lethal to the developing fetus though, so it usually doesn't survive. Chromosome disorders caused by nondisjunctions that do result in children being born are:

        * Down syndrome – An extra chromosome 21 is present so it is also called trisomy 21. The affects range from moderate to severe and those with Down syndrome have characteristic facial features, a short stature and heart defects. They often suffer from respiratory diseases, have a shorter life span and some degree of mental retardation.

        * Patau syndrome – This syndrome results from a trisomy of chromosome 13. It causes severe eye, brain and circulatory defects. Cleft palate is often a result and the children rarely live longer than a few months.

        * Edward’s syndrome – Children with Edward’s syndrome rarely live longer than a few months, as all of their organs are affected in some way. This condition is caused by trisomy 18.

        * Klinefelter’s syndrome – Individuals with this syndrome have multiple copies of the X chromosome, XXY, XXXY or XXXXY. These individuals are male, but the presence of extra X chromosomes causes body proportions that are female and smaller testes with no sperm development. The greater the number of X chromosomes, the more marked the condition.

        * Turner’s syndrome – Children with Turner’s syndrome have only one X chromosome, so they have only 45 chromosomes in total. This is the only non-lethal monosomy in humans, but most do not survive the pregnancy. Those that are born are female, but they are small in stature and do not mature sexually.

    Changes in structure are what cause the other chromosome disorders. There are four changes that can occur in chromosome structure to cause chromosome disorders – deletions, inversions, translocations and duplications. These structural changes are due to chromosomes breaking and then not reattaching correctly.

    During a deletion, a part of the chromosome is lost. As a result, this can cause a loss of the genes on that portion of the chromosome. Losing genes can significantly affect an organism’s development and can often prove lethal. Cri du chat is a chromosome disorder caused by the deletion of part of chromosome 5. It results in severe mental retardation, a very small head with unusual features and the child makes a distinct cry that sounds like an upset cat.

    During an inversion, a portion of the chromosome is reattached in the inverted position, causing the sequence of the genes on this portion to be reversed. While the overall genetic information is the same, the characteristics affected by the genes may be changed. If a portion of a chromosome is reattached at a different point on the same chromosome, or to a new chromosome, a translocation has occurred. Like an inversion, this can also cause changes in the characteristics of the individual depending on how, where and what was moved.

    Tay-Sachs Disease

    Tay-Sachs Disease is one of the most lethal genetic disorders The causes of Tay Sachs disease lie in a mutation in a single gene (monogenic genetic disease). The mutation that is responsible for the disease lies in the gene Hex A. This gene codes for the enzyme hexaminidase A and is found in the chromosome 15. The normal protein catalyzes the degradation of some fatty acids called gangliosides. Tay-Sachs Disease is a devastating and fatal illness caused by the lack of the enzyme hexosaminidase A (hex A). Tay-Sachs is of genetic origin. All who have Tay-Sachs get it from two parents who carry a recessive gene for the disease. These parents do not have Tay-Sachs because the disease in both its most common forms, infantile and juvenile Tay-Sachs result in mortality before children reach adulthoodThe most important ganglioside for Tay-Sachs is the Ganglioside GM2. This material is found in the nerve cells of the brain and especially in the cell membranes. In the case of Tay-Sachs Disease there is no enough activity of the enzyme and the gangliosides are accumulated with destructive results.
    Answering to the question whether there is only one specific mutation that leads to Tay Sachs or not, we have to say that the mutations can happen to more than one site of the gene. A large number of HEXA mutations have been discovered, and new ones are still being reported. These mutations reach significant frequencies in several populations.

    The cause of this deterioration is that hex A is not present to break down fatty tissues in the brain and nerves. Failure to metabolize these substances gradually results in the above symptoms and death, since the brain and nerves become more and more impaired by fatty tissues.

    Juvenile Tay-Sachs causes affected children to develop symptoms around the age of three, though this can vary anywhere from two to five. The progression of the disease is very slow, taking up to 12 or 13 years for death to occur. Parents are heartbroken to see their children gradually lose previously acquired functions like talking and walking. Children with juvenile Tay-Sachs may still have the ability to understand, but speech if it exists will be slurred and unintelligible in late stages. Juvenile Tay-Sachs is also associated with more pain, as frequent muscle spasms and cramps occur.

    On rare occasions, an adult will develop a hex A deficiency. His or her disease will be similar in course to those affected by juvenile Tay-Sachs. Predictors for this deficiency in adults are not well defined.

    Tay-Sachs is often associated with European Jews. They do have the highest rate of being carriers of the gene responsible for Hex A deficiency. However, not only Jewish children get Tay-Sachs. The existence of the illness has been noticed in some French Canadians. As well, those whose have Cajun ancestry are more at risk.

    One parent, who is a carrier, has a 50% chance of passing the carrying gene to children. When both parents are carriers each child has a 25% chance of being born with Tay-Sachs. Each child also will inherit a gene to carry the disease. Tay-Sachs can be diagnosed with chronic villus sampling during the early part of pregnancy. Many who then receive a positive diagnosis are faced with the difficult decision of whether to end a pregnancy and the life of their child at this point, since the outcome of the disease is likely fatal.

    Blood Diseases

    Because the functions of blood are many and complex, there are many disorders that require clinical care by a physician or other healthcare professional. These conditions include benign (non-cancerous) disorders, as well as cancers that occur in blood.

    A blood disease is a disease which affects the blood. Many blood diseases are congenital, the result of inherited genetic disorders. Others may be acquired, typically in response to some sort of stress in the body. Blood diseases or blood disorders as they are sometimes called are distinct from blood-borne diseases, diseases which are carried in the blood. One of the key differences between a blood disease and a blood-borne disease is that blood diseases are not contagious
    There are four types of blood disease. Coagulopathies are disorders which concern bleeding and clotting, such as hemophilia. Anemias concern the lack of hemoglobin, a substance in red blood cells which is vitally necessary for oxygen transport. Hematological malignancies like leukemia are cancers which affect the blood and bone marrow, while hemoglobinopathies are blood diseases which have to do with the structure of red blood cells. Sickle cell anemia is a classic example of a hemoglobinopathy.

    In the case of a blood disease that is caused by genetics, the treatment for the disease is usually focused on managing the symptoms to keep the patient comfortable and help him or her lead a normal life. In hemophilia, for example, the patient is provided with clotting factors so that the blood clots normally. These diseases cannot be cured, but they can often be managed very effectively. With the use of gene therapy in the future, it may be possible to address the underlying cause of such disorders.

    Blood diseases with external causes such as disease leading to anemia can be treated by addressing the cause, which also clears up the disease. In the case of blood malignancies, the blood may be treated with chemotherapy and radiation to kill the malignant cells, with more extreme procedures like marrow transplants and blood infusions being used in particularly aggressive cases.

    Many blood diseases are identified early, because the symptoms can be very debilitating for the patient. In the case of genetic diseases, people who know that their children are at risk may request testing shortly after birth to see if the genetic disorder is present, and some parents use genetic testing in assisted reproduction to select embryos which are free of the genetic disorder. In other instances, people go to the doctor for symptoms like fatigue, pale gums, excessive bleeding or clotting, joint pain, and so forth, and the blood disease is diagnosed with the assistance of medical tests.

    Blood disease breakthroughs begin here

    Many of the most significant advances in the treatment of leukemia, lymphoma and other blood diseases began here at the Hutchinson Center. These accomplishments pave the way for the future of cancer care.

    Mini-transplants deliver big results for more patients
    We have developed a milder blood stem-cell transplant that relies on the power of donor immune cells to fight cancer and eliminates the need for painful chemotherapy and radiation. The mini-transplant typically involves no hospitalization and is extremely successful for treating older patients with blood cancers who are unable to tolerate chemotherapy and radiation. At the Hutchinson Center, we're testing the procedure's effectiveness in children as well as young women who wish to preserve their fertility.

    Harnessing the immune system to fight cancer
    Our Nobel Prize-winning work on bone-marrow transplantation revealed the remarkable cancer-fighting power of the immune system. Today, we lead a revolutionary new field called immunotherapy that yields powerful cancer treatments with far fewer side effects than conventional drugs, radiation or surgery. This innovative approach uses antibodies called T-cells that deliver chemotherapy and radiation directly to cancer cells. It also includes cutting-edge vaccines to stimulate the immune system to fight cancer relapse.

    Preventing relapse and predicting prognosis
    We were the first to develop a molecular test to detect cancer recurrence that is sensitive enough to find one blood-cancer cell among a million normal cells — an accomplishment that saves lives. This test allows doctors to quickly prescribe new therapy at the first hint of possible relapse. We're developing similar tests that can predict a patient's response to treatment so that doctors can customize therapy and ensure the best chances for survival.

    Cord-blood transplants extend lifesaving options to more patients
    About a third of all blood-cancer patients who could benefit from a transplant are unable to find a compatible donor, a number that is much higher for patients with rare tissue types or who are of mixed ethnicity. We're pioneering new transplants based on umbilical-cord blood, which does not need to be as stringently matched to a patient's tissue type as other sources of blood stem cells.

    Quality of life counts
    We house the world's leading long-term follow-up program for blood-cancer patients, which provides outstanding ongoing medical and psychosocial support for the unique needs of transplant survivors. The program's research has yielded major reductions in complications following treatment and helps survivors adjust to life after cancer therapy.
    The future is brighter with your help

    Every day brings us closer to new discoveries that will benefit more blood-cancer patients like Steve Ross—and private donations are essential to our progress.


    Genetic Analysis

    What is Genetic Analysis
    Genetic analysis is the overall process of studying and researching in fields of science that involve genetics and molecular biology. There are a number of applications that are developed from this research and these are also considered parts of the process. The base system of analysis  revolves around general genetics. Basic studies include identification of genes and inherited disorders. This research has been conducted for centuries on both a large-scale physical observation basis and on a more microscopic scale.

    Much of the research that set the foundation of genetic analysis began in prehistoric times. Early humans found that they could practice selective breeding to improve crops and animals. They also identified inherited traits in humans that were eliminated over the years.

    Modern genetic analysis began in the mid-1800s with research conducted by Gregor Mendel. Lacking the basic understanding of heredity, Mendel observed various organisms and found that traits were inherited from parents and those traits could vary between children. Later, it was found that units within each cell are responsible for these traits. These units are called genes. Each gene is defined by a series of amino acids that create proteins responsible for genetic traits.

    Certain advancements have been made in the field of genetics and molecular biology through the process of genetic analysis. One of the most prevalent advancements during the late 20th and early 21st centuries is a greater understanding of cancer's link to genetics. This research has been able to identify the concepts of genetic mutations, fusion genes and changes in DNA copy numbers.

    DNA sequencing is essential to the applications of genetic analysis. This process is used to determine the order of nucleotide bases. Each molecule of DNA is made from adenine, guanine, cytosine and thymine, which determine what function the genes will posses. This was first discovered during the 1970s.

    A variety of other types of research associated with genetic analysis. Cytogenetics, the study of chromosomes and their function within cells, helps identify abnormalities. Polymerase chain reaction studies the amplification of DNA. Karyotyping uses a system of studying chromosomes to identify genetic abnormalities and evolutionary changes in the past.

    Hereditary Cancer and Cancer Genetics

    Cancer genetics has for many years focused on mutational events that have their primary effect within the cancer cell. Recently that focus has widened, with evidence of the importance of epigenetic events and of cellular interactions in cancer development. The role of common genetic variation in determining the range of individual susceptibility within the population is increasingly recognized, and will be addressed using information from the Human Genome Project. These new research directions will highlight determinants of cancer that lie outside the cancer cell, suggest new targets for intervention, and inform the design of strategies for prevention in groups at increased risk.

    What is Hereditary Cancer ?
    Everyone has two copies of each gene, one from each parent. Most people are born with two normal copies of each gene. Hereditary cancers occur when a person is born with changes or mutations in one copy of a damage-controlling gene which normally protects against cancer. In the majority of these cases, the changes were inherited from the mother or father.
    People with an inherited gene change also have a 50% chance to pass the mutation to each of their children. These changes can increase the risk for cancers in different parts of the body. The changes do not increase the risk for every type of cancer and not everyone who is born with a gene change will develop cancer. The medical community uses the term "genetic susceptibility" to describe the increased risk for cancer that occurs in people with an inherited mutation.

    Cancer is a common disease, so most families will have some members who have had cancer but that does not mean the cancer in that family is hereditary. We don't know the cause of most cancer, but experts believe that about 10% of most cancer types are due to inherited gene changes. Cancer that does not appear to be caused by inherited genes is called "sporadic cancer." It is believed that most perhaps 90%of all cancers are sporadic. This means even if cancer does not run in a family, a family member can still be at risk for some type of cancer in his or her lifetime.

    All cancers are caused by changes to materials in our bodies called “genes.” These are units of information in every cell of our bodies. Genes tell our bodies which proteins to make based on the type of cell and its needs. Some genes tell our bodies how to fix damage accumulated over time from normal aging, environmental toxins, sun exposure, dietary factors, hormones, and other influences. These damage-controlling genes can repair cells or tell cells when to stop growing and die if there is too much damage to repair.
    When genes themselves are damaged, they can develop changes called “mutations.” When mutations occur in the damage-controlling genes, cells can grow out of control and cause cancer.
    For most people who develop cancer, the cancer-causing gene mutations happen over the course of a lifetime, leading to cancer later in life. Some people are born with a gene mutation that they inherited from their mother or father. This damaged gene puts them at higher risk for cancer than most people. When cancer occurs because of an inherited gene mutation, it is referred to as "hereditary cancer."

    Common Genetic Diseases

    Common genetic diseases



    The discovery and the spread of the various genetic diseases have today gained gigantic proportions in the world all around us. Though studies are still on in order to ascertain the causes behind these diseases as well as to deduce some form of cure for them, the pain and suffering which are still caused by the presence of some of these common genetic diseases in the human body remains as before – manifold. Some of the common genetic diseases include:
    Cystic Fibrosis
    A common form of hereditary genetic disorder, the advent of Cystic Fibrosis in the human body is responsible for pushing the individual to a stage of progressive degeneration, which in turn can cause various disabilities as well as in certain severe cases, death. The disease is caused by a scarring of the pancreas or fibrosis, an act which has given rise to a part of the name which is designated for the disease. It is after this that a cyst is formed in the pancreas, which can give rise to a difficulty in breathing as well other symptoms, which can include:
    • Sinus Infections
    • Poor Growth
    • Diarrhea
    • Infertility
    Down syndrome
    One of the best known forms of genetic diseases, the Down syndrome has been studied to be caused by an extra 21st chromosome, even when the entire chromosome structure other than this remains intact. The most important feature of this syndrome is that it interferes with the various growth processes of the victim’s mental and physical developments. The Down syndrome is accompanied by a characteristic visual appearance which can easily allow doctors to immediately identify the cause of the disease. Some of the main symptoms which are identified by Down syndrome include:
    • Congenital Heart Defects
    • Gastroesophageal Reflux Disease
    • Recurrent Ear Infections
    • Obstructive Sleep Apnea
    • Various forms of Thyroid Dysfunctions.
    One of the more widely spread forms of the diseases caused by the various kinds of genetic disorders, Haemophilia is a term given to a condition in which various groups of genetic disorders create conditions through which the body loses its ability to process blood coagulation or control or begin the process of the clotting of blood. A form of the X chromosome related genetic disorder; the symptoms of Haemophilia can only be seen in the bodies of the human males.
    One of the most common symptoms of Haemophilia is prolonged bleeding or the restarting of bleeding even after it had stopped complete. This can cause serious damages in the cases of those patients who have a history of internal bleeding. The involvement of females in this disease can only be in the forms of carriers as they are never really seen as to be victims suffering from the malady. Some of the symptoms associated with the disease include conditions of:
    • Deep internal bleeding
    • Joint damage
    • Transfusion transmitted infection
    • Poor reactions which can result from the treatment of the clotting factor
    • Intracranial hemorrhage
    Sickle-cell disease
    A dreaded form of the manifestation of a typical genetic disorder, the Sickle-cell disease is a term that is given to a condition in which the Red Blood Corpuscles or RBCs of the patient’s blood can transform or become mutated to change their shape from the regular shape of their cells to a special sickle shape, which is the cause being the nomenclature used for the malady.
    The main resultant factor of the transformation of the blood cells of the human body into the shapes of sickles is that they cause an immense decrease in the flexibility of the cells, which in turn can result in severe major complications and also reduce the immunity of the body’s natural system.
    Some of the treatments that are generally suggested as a part of the relief process of the Sickle-cell disease includes:
    • Cyanate
    • Vaso-occlusive treatments
    • Folic acid and penicillin
    • Acute chest crisis
    • Hydroxyurea
    • Bone marrow transplants
    Turner syndrome
    First discovered in the year 1930, Turner Syndrome is the name given to the medical condition which is specific only to human females. In this condition, the victim in question possesses a genetic structure in which one or many parts of the X chromosome remains absent in the cell formation. There are certain visual signs which can readily indicate the presence of the Turner Syndrome in a victim’s genes. Notable among the various external signs include a marked short stature. Other symptoms include:
    • Small fingernails
    • Horseshoe shaped kidney
    • Low Hairline
    • Poor body development
    • Increased weight
    • Absence of a menstrual cycle
    • Sterility of the reproductive organs.

    Genetic Testing For Breast Cancer

    Breast Cancer and Genetic Testing

    Intensive genetic counseling is required before undergoing genetic tests for breast cancer. During this educational counseling session, the health care provider can fully explain the benefits and risks of genetic testing and answer any questions you may have.

    You will also be required to sign a consent form prior to participating in any genetic tests. The form is an agreement between you and your doctor, showing that you have discussed the test and how its results might affect your family.

    Here are some questions to consider when thinking about genetic testing:

        * Am I prepared to cope with the result? Are my family members also prepared, including my children and my spouse?
        * What are my goals for testing?
        * How would I use my test results? What will I do differently if the results are positive, or if they are negative?
        * Whom will I share my results with?
        * Would a positive test result change relationships with my family?

    What Happens During Genetic Testing?

    Most importantly, you'll need to obtain a family pedigree to determine if there is a cancer development pattern within your family. A family pedigree is a chart that shows the genetic makeup of a person's ancestors, and is used to analyze inherited characteristics or diseases within a family.

    After outlining the family pedigree, a blood test can be given to determine if you have a breast cancer gene. Keep in mind that the vast majority of breast cancer cases are not associated with a breast cancer gene. In addition, scientists do not know all of the genes that can cause breast cancer, so doctors can only test you for the known genes.

    When someone with a cancer diagnosis and a family history of the disease has been tested and found to have an altered BRCA1 or BRCA2 gene, the family is said to have a "known mutation." If an association between the development of breast cancer and a breast cancer gene is made, then all family members willing to participate in genetic testing are asked to give a sample of blood. For many people, knowing their test results is important, because this information may help to guide future health care decisions for themselves and their families.
    How Do I Interpret the Genetic Test Results?

    A negative genetic test means that a breast cancer gene mutation was not identified. If genetic testing has previously identified a mutation in your family, then a negative test means you do not carry the specific mutation that was identified in your family. Therefore, you would have the same risk as the general population. If a BRCA1 or BRCA2 mutation has not been previously found in your family, a negative result should be interpreted cautiously.

    In such cases, there is still a chance you are at an increased risk to develop breast cancer due to potential mutations in genes other than those we currently can test for.

    A positive test result means that a mutation known to increase the risk of breast and ovarian cancer was identified. Knowing your cancer risk may help guide important health care decisions for you and your family.

    DNA Genetic Testing

    DNA Genetic testing


    Genetic testing involves taking some of a person's DNA, generally from a swab of saliva or a sample of blood. The sample is then searched for signs of mutations or irregularities in the DNA code. But diseases are complex and the test results can be difficult to interpret.
    In the case of some diseases – such as Huntington's disease and cystic fibrosis – the cause is almost 100 per cent genetic. Testing for these kinds of illnesses has been around for some years now and is able to provide a clear diagnosis.
    But other diseases are far more complex and need multiple genetic markers to be present. These diseases are also affected by environmental factors such as diet and lifestyle, for example cardiovascular disease and diabetes. Predictive genetic testing, which is a relatively recent practice, can give you some idea of your risk of developing these types of diseases.
    When performed appropriately, genetic testing is "very powerful and useful", says Ron Trent, a professor of molecular genetics at the University of Sydney who has been involved in the field for more than 20 years. "But if not used appropriately, it is a waste of time."
    If you think you might benefit from a test, you'll need advice on which test (if any) is appropriate and where to get it. Your GP may be able to help or you can go to a specialist centre.
    "Within our public hospital system we have lots of clinical genetic units," Trent says. "They are a very good first point of call. In the clinical genetics units, the counsellors and the clinical geneticists can assess the risk and can refer the patient on for testing or refer them onto another specialist."

    Genetic Mutation

    Every organism has a set of genes and half of the genes of that organism come from each parent. The combinations of the genes causes the variation of individuals within the species. The genes of a butterfly, an ape or a fowl carry the code that determines the appearance and the character of the butterfly, the ape and the fowl. The genetic code allows an overwhelming variety within the species of the kind. However, a mutation of the gene will not break through the barrier of the species or the kind. A mutation is basically a gene that has an abnormality in relation to its normal configuration. The abnormality can then be passed to successive offspring, thereby producing a marked difference. There are many different types of mutations. The smallest possible genetic mutation is a 'point-mutation'. This occurs in the DNA when the base-pairs combine with the 'wrong' partner. Multiple point-mutations are common and are found to increase substantially by the effect of mutagens. Mutations are, of course, heritable and these can extend to whole or part chromosomal mutations. Because many genes are affected by a chromosomal mutation, these often have drastic ramifications on the offspring.

    Genetic mutation  may be a stronghold of science fiction and comic books, but its presence is very real, and still not always understood. At a basic level, mutation causes a gene or genetic  sequence to change from its original or intended purpose. It can be caused by a variety of internal or external sources, and the effects can be positive or negative for the organism that undergoes mutation.

    There are several factors that can cause genetic mutation to occur. In the normal process of cellular division, mutation can occur when gene properties do not copy properly to the new cell. Radiation, such as that from ultraviolet sources, can also cause mutation. Radiation-caused mutation can be very dangerous, but has also been harnessed for medical use, as in treating malignant tumors. Viruses, which attack an organism on a cellular level, can also be responsible for genetic mutation.

    Mutation is essential to the evolution of a species. Some genetic mutations can be beneficial to a species, serving a purpose like increasing immunity to a common disease. The introduction of mutation into a species encourages gene pool variations that can result in beneficial adaptations. Negative mutations will often be destroyed through natural selection, as weaker or less adaptable specimens are less likely to survive and pass on their detrimental genetics to another generation.

    Depending on what type of cell is affected by mutation, results can be positive, negative, or neutral. Hereditary diseases, for instance, are a result of a mutated or damaged cell that passes on the mutation to each new cell it creates. Similarly, cancer is the result of malignant growth of mutated cells. However, one common mutation in humans, the CCR5 base pair, can give added resistance to some diseases including HIV.

    The concept of mutation has inflamed imaginations for generations, as its potential power to change or harm humans is enormous. One popular comic book series, X-Men, takes the concept to an extreme, creating a parallel universe in which some of the population is granted super-powers due to extreme genetic mutation. While the limits of genetic mutation remain unexplored, it appears unlikely that anyone will begin sprouting horns or flying due to mutation any time soon.

    Types Of Genetic Diseaseas|Genetic Disorders

    Genetic disorders are caused by the mutations or abnormalities that occur in a chromosome or genome. These abnormalities may appear phenotypically at any time of a human life. It is being estimated that there are around 4,000 genetic disorders which affect the human life. But this number keeps changing as we know more about our gene and genome. Types of mutations like single nucleotide mutation, chromosomal aberration, mitochondrial genome and also environmental factors play a role in inducing these genetic disorders in humans. 
     As per the available information on genetic disorders, these disorders can be broadly classified into four different categories, which are as follows:

    1. Single-gene Disorders: Also known as Mendellian or monogenic disorders, these occur when the changes or mutations occur in only a single gene. Some well-known examples of single-gene disorders include cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington's disease and hereditary hemochromatosis. Single gene disorders can be further classified into autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive and Y-linked disorders. For example Cystic fibrosis is an example for single gene disorder. Cystic fibrosis condition is caused by a mutation in chromosome 7 gene known as cystic fibrosis transmembrane conductance regulator (CFTR). The mutation in the gene CFTR produces the abnormal non-functional protein, which affect the movement of sodium chloride in the body cell. This leads to the formation of abnormal thick mucus in the lungs. This in turn makes it difficult for patients to breathe and digest. This is also an example for recessive genetic disorder. Recessive genetic disorders are the one when both the alleles of a gene are defective then only the condition occur phynotypically. That is both the parents should pass the defective gene to their offspring then only this condition appears in once life.

    2. Multifactorial Genetic Disorders: Multifactorial genetic disorders are caused by combination of many factors like gene mutation, small variations in the chromosome structure and also environmental factors. Cancer, heart conditions or disease are best examples for this type of genetic disorder.

    A single mutation in the gene will not induce skin cancer. Rather multiple DNA mutations caused by environmental factors like X-ray or UV rays may increase the chances of developing skin cancer. This type of genetic disorders is very difficult to diagnose, treat.
    These disorders are really complex, difficult to analyze and hard to treat. Some examples of multifactorial disorders include autism, coronary heart diseases, cleft palate, mental retardation, cancer and diabetes.

    3. Chromosomal Disorders: These diseases occur as a result of abnormalities in the chromosomal structure such as missing or presence of extra copies of chromosomes. The most well-known chromosomal disorder is the Down syndrome or Trisomy 21 where a person has three copies of chromosome 21. Other examples include Klinefelter syndrome, Cri-du-Chat syndrome, Turner Syndrome and Williams' syndrome.

    4. Mitochondrial Disorders: These disorders occur when there are mutations in the mitochondrial DNA or the non-chromosomal DNA of the cell. These disorders are maternal in origin as only egg cells contribute mitochondria in a developing embryo. One very good example of a mitochondrial disorder is the Leber's Hereditary Optic neuropathy.

    Genetic Testing and cost

    Genetic tests are tests on blood and other tissue to find genetic disorders. About 900 such tests are available. Doctors use genetic tests for several reasons. These include
    • Finding possible genetic diseases in unborn babies
    • Screening embryos for disease
    • Testing for genetic diseases in adults before they cause symptoms
    • Confirming a diagnosis in a person who has disease symptoms
    People have many different reasons for being tested or not being tested. For many, it is important to know whether a disease can be prevented or treated if a gene alteration is found. In some cases, there is no treatment. But test results might help a person make life decisions, such as career choice, family planning or insurance coverage. A genetic counselor can provide information about the pros and cons of testing.

    Genetic testing has developed enough so that doctors can often pinpoint missing or defective genes. The type of genetic test needed to make a specific diagnosis depends on the particular illness that a doctor suspects.
    Many different types of body fluids and tissues can be used in genetic testing. For deoxyribonucleic acid (DNA) screening, only a very tiny bit of blood, skin, bone, or other tissue is needed.

    Genetic Testing During Pregnancy

    For genetic testing before birth, pregnant women may decide to undergo amniocentesis or chorionic villus sampling.
    Amniocentesis is a test performed between weeks 16 and 18 of a woman's pregnancy. The doctor inserts a hollow needle into the woman's abdomen to remove a small amount of amniotic fluid from around the developing fetus. This fluid can be tested to check for genetic problems and to determine the sex of the child. When there's risk of cesarean section or premature birth, amniocentesis may also be done to see how far the child's lungs have matured. Amniocentesis carries a slight risk of inducing a miscarriage.
    Chorionic villus sampling (CVS) is usually performed between the 10th and 12th weeks of pregnancy. The doctor removes a small piece of the placenta to check for genetic problems in the fetus. Because chorionic villus sampling is an invasive test, there's a small risk that it can induce a miscarriage.

    Why Doctors Recommend Genetic Testing

    A doctor may recommend genetic counseling or testing for any of the following reasons:
    • A couple is planning to start a family and one of them or a close relative has an inherited illness. Some people are carriers of genes for genetic illnesses, even though they don't show, or manifest, the illness themselves. This happens because some genetic illnesses are recessive — meaning that they're only expressed if a person inherits two copies of the problem gene, one from each parent. Offspring who inherit one problem gene from one parent but a normal gene from the other parent won't have symptoms of a recessive illness but will have a 50% chance of passing the problem gene on to their children.
    • An individual already has one child with a severe birth defect. Not all children who have birth defects have genetic problems. Sometimes, birth defects are caused by exposure to a toxin (poison), infection, or physical trauma before birth. Even if a child does have a genetic problem, there's always a chance that it wasn't inherited and that it happened because of some spontaneous error in the child's cells, not the parents' cells.
    • A woman has had two or more miscarriages. Severe chromosome problems in the fetus can sometimes lead to a spontaneous miscarriage. Several miscarriages may point to a genetic problem.
    • A woman has delivered a stillborn child with physical signs of a genetic illness. Many serious genetic illnesses cause specific physical abnormalities that give an affected child a very distinctive appearance.
    • A woman is pregnant and over age 34. Chances of having a child with a chromosomal problem (such as trisomy) increase when a pregnant woman is older. Older fathers are at risk to have children with new dominant genetic mutations (those that are caused by a single genetic defect that hasn't run in the family before).
    • A child has medical problems that might be genetic. When a child has medical problems involving more than one body system, genetic testing may be recommended to identify the cause and make a diagnosis.
    • A child has medical problems that are recognized as a specific genetic syndrome. Genetic testing is performed to confirm the diagnosis. In some cases, it also might aid in identifying the specific type or severity of a genetic illness, which can help identify the most appropriate treatment.
    In the United States, Myriad Genetics performs all commercial BRCA1 and BRCA2 testing. They report results within a month. (Abnormalities in other genes have been associated with breast cancer risk. Right now, these appear to be a less common cause of breast cancer than BRCA1 and BRCA2 mutations, although research is ongoing. If you want to be screened for those, talk to your doctor and genetic counselor about where to be tested.) The cost of the BRCA test ranges from about $300 to $3,000, depending on whether you get the limited test, in which only a few areas of the gene are evaluated, or the full test, in which hundreds of areas are examined on both genes.

      Friday, September 3, 2010

      List of Genetic Diseases

      Genetic disease can be defined as an ailment which is the result of abnormalities in genes or chromosomes of an individual. On a common level, in case of genetic disorders, the abnormalities are present in all cells of the body, since the time of conception of a child. Diseases such as cancer, which are caused by genetic abnormalities acquired in a few cells during life, are usually not classified as the same. While some of the genetic disorders are the result of chromosomal abnormalities, others occur during the production of germ cells by the parent(s). Till date, 4,000 genetic diseases have been discovered by doctors, with possibility of more being there. In the following lines, we have given the list of some of the most common genetic disorders.
      List of Genetic Diseases 
      • Achromatopsia (inability to see color)
      • Adrenal Hypoplasia Congenita (reduction in adrenal gland function)
      • Adrenoleukodystrophy (progressive brain damage)
      • Aicardi Syndrome (partial or complete absence of a key structure in brain)
      • Albinism/Hypopigmentation (no melanin pigment in eyes, skin and hair)
      • Alexander Disease (neurodegenerative disease)
      • Alpers' Disease (degenerative disease of the central nervous system)
      • Alpha-1 Antitrypsin Deficiency (decreased A1AT activity in blood & lungs)
      • Alzheimer's (degenerative disease starting with memory loss)
      • Amblyopia (poor or indistinct vision)
      • Angelman Syndrome (intellectual and developmental delay, seizures)
      • Anencephaly (absence of a major portion of the brain, skull, and scalp)
      • Aniridia (underdevelopment of the eye's iris)
      • Anophthalmia (congenital absence of one or both eyes)
      • Ataxia Telangiectasia (immunodeficiency disorder)
      • Autism (brain development disorder)
      • Bardet-Biedl Syndrome (obesity, pigmentary retinopathy, polydactyly, mental retardation, hypogonadism, and renal failure)
      • Barth Syndrome (metabolism distortion, delayed motor skills, stamina deficiency, hypotonia, chronic fatigue, delayed growth)
      • Batten Disease (fatal, autosomal recessive neurodegenerative disorder)
      • Best's Disease (progressive vision loss)
      • Bipolar Disorder (a category of mood disorders)
      • Bloom Syndrome (breaks and rearrangements in the chromosomes)
      • Branchio-Oto-Renal (BOR) Syndrome (autosomal disorder of kidneys, ears, and neck)
      • Canavan Syndrome (progressive damage to nerve cells in the brain)
      • Carnitine Deficiencies (metabolic disorders)
      • Cerebral Palsy (physical disability in human development)
      • Charcot-Marie-Tooth Disease (loss of muscle tissue and touch sensation)
      • Cleft Lip/Cleft Palate (abnormal facial development during gestation)
      • Coffin Lowry Syndrome (mental retardation and delayed development)
      • Coloboma (hole in one of the structures of the eye)
      • Color Blindness
      • Congenital Heart Defects
      • Congenital Hip Dysplasia (Dislocation)
      • Connective Tissue Disorders
      • Cooley's Anemia/ Thalassemia (formation of abnormal haemoglobin molecules)
      • Corneal Dystrophy (non-inflammatory, bilateral opacity of cornea)
      • Cornelia de Lange Syndrome (severe developmental anomalies)
      • Cystic Fibrosis (progressive disability due to multisystem failure)
      • Cystinosis (autosomal recessive disorder of the renal tubules)
      • Developmental Disabilities
      • Diabetes
      • Down Syndrome (impairment of cognitive ability, physical growth & facial appearance)
      • Duane Syndrome (inability of the eye to turn out)
      • Ehlers-Danlos Syndrome (defect in collagen synthesis)
      • Epidermolysis Bullosa (extremely fragile skin & recurrent blister formation)
      • Familial Dysautonomia (disorder of the autonomic nervous system)
      • Familial Mediterranean Fever (inflammatory disorder)
      • Fanconi Anemia (short stature, skeletal anomalies, bone marrow failure)
      • Fibrodysplasia Ossificans Progressiva (disease of the connective tissue)
      • Fragile X Syndrome (X-linked mental retardation)
      • G6PD (Glucose-6-Phosphate Dehydrogenase) Deficiency Anemia
      • Galactosemia (inefficient metabolism of the sugar galactose0
      • Gaucher Disease (deficiency of the enzyme glucocerebrosidase)
      • Gilbert's Syndrome (high levels of unconjugated bilirubin in bloodstream)
      • Glaucoma (diseases of the optic nerve)
      • Hemochromatosis (excessive absorption of dietary iron)
      • Hemoglobin C Disease (abnormal hemoglobin)
      • Hemophilia/Bleeding Disorders (inefficient control over blood clotting or coagulation)
      • Hirschsprung's Disease (enlargement of the colon)
      • Homocystinuria (disorder of the metabolism of the amino acid methionine)
      • Huntington's Disease (abnormal body movements)
      • Hurler Syndrome (deficiency of alpha-L iduronidase)
      • Klinefelter Syndrome (small testicles and reduced fertility)
      • Krabbe Disease (fatal degenerative disorder of nervous system)
      • Leber Congenital Amaurosis (loss of vision)
      • Leukodystrophies (progressive degeneration of the white matter of brain)
      • Long Q-T Syndrome (heart problem)
      • Macular Degeneration (loss of central vision)
      • Marfan Syndrome (disorder of the connective tissue)
      • Marshall-Smith Syndrome (unusual accelerated skeletal maturation)
      • McCune-Albright Syndrome (disorder of bones, hormones & skin pigmentation)
      • Menkes Disease (disorder that affects copper levels in the body)
      • Metabolic Disorders
      • Mitochondrial Disease
      • Mucolipidoses
      • Mucopolysaccharide Disorders
      • Muscular Dystrophy (progressive muscle weakness)
      • Neonatal Onset Multisystem Inflammatory Disease (uncontrolled inflammation in multiple parts of the body)
      • Neurofibromatosis (grow of tumors in nerve cells - Schwann cells)
      • Niemann-Pick Disease (disorder affecting lipid metabolism)
      • Noonan Syndrome (heart malformation, short stature, learning problems)
      • Optic Atrophy (loss of some or most of the fibers of the optic nerve)
      • Osteogenesis Imperfecta (no protein - collagen, or the ability to make it)
      • Peutz-Jeghers Syndrome (benign hamartomatous polyps in gastrointestinal tract)
      • Phenylketonuria (PKU) (deficiency in enzyme phenylalanine hydroxylase)
      • Polycystic Kidney Disease (multiple cysts in both kidneys)
      • Pseudoxanthoma Elasticum (fragmentation and mineralization of elastic fibers in tissues)
      • Progeria (accelerated aging)
      • Ptosis (drooping upper eyelid or breasts)
      • Rentinitis Pigmentosa
      • Scheie Syndrome (absence or malfunctioning of lysosomal enzymes)
      • Schizophrenia (impairments in the perception or expression of reality)
      • Severe Combined Immunodeficiency (SCID) (crippling of adaptive immune system)
      • Sickle Cell Anemia (abnormal, rigid, sickle shape of red blood cells)
      • Skeletal Dysplasias (abnormal bone and cartilage development)
      • Smith-Magenis Syndrome (developmental disorder)
      • Spherocytosis (production of bi-concave disk shaped red blood cells)
      • Spina Bifida (incompletely formed spinal cord)
      • Spinocerebellar Ataxia (progressive in-coordination of gait)
      • Stargardt Disease (Macular Degeneration) (progressive vision loss)
      • Stickler Syndrome (disorders affecting connective tissue, mainly collagen)
      • Tay-Sachs Disease (usually affects nervous tissue of the brain)
      • Treacher Collins Syndrome (craniofacial deformities)
      • Tuberous Sclerosis (causes benign tumors in various body parts)
      • Turner's Syndrome (only one X chromosome in each cell of a female)
      • Urea Cycle Disorder (deficiency of one of the enzymes in the urea cycle causing irreversible brain damage and/or death)
      • Usher's Syndrome (deafness and a gradual vision loss)
      • Velocardiofacial Syndrome (deletion of a small piece of chromosome 22)
      • von Hippel-Lindau Disease (abnormal growth of tumors in body parts)
      • Werner Syndrome (premature aging)
      • Williams Syndrome ("elfin" facial appearance, with a low nasal bridge)
      • Xeroderma Pigmentosum (deficient ability to repair damage caused by ultraviolet (UV) light)
      • XXX Syndrome (an extra X chromosome in each cell of a female)
      • XYY Syndrome (an extra Y chromosome in each cell of a male)

      Genetic Diseases


      One of the most important threats for human’s health is, undoubtedly, the genetic diseases. What a genetic disease is? It is a disorder caused by genetic factors and especially abnormalities in the human genetic material (genome). There are four main types of genetic disorders. Of course, some of these changes in genome can cause interesting advantages in specific environments (Darwinian Fitness). But there is no doubt that all these abnormalities (disorders) bring destructive results to a living being in the present environment.
      The four types of (human) Genetic diseases are:
      1) Single-gene/monogenic Genetic Diseases: 
      In this category the starting point is a mutation/change in one gene. The next question is how a change in the sequence of a single gene can cause severe disorders. Genes code for proteins which are some of the most important tools for the living beings, and also take place in the structures of the cells. The results of a mutation that happens in a part of gene that codes for a functional part of a protein are unwelcome
       Lungs of a patient suffering from cystic fibrosis 

      The protein is no more functional and as a result, many severe consequences take place. Almost 6000 single gene disorders are known and it is estimated that 1 of 200 newborns face a single gene genetic disorder. Some of these are sickle cell anemia, cystic fibrosis, Aicardi Syndrome, Huntington’s disease.

      2) Multifactorial/Polygonic Genetic Diseases:
      The second type of human genetic diseases is caused by mutations in more than one genes. The environment combines with these mutations in order these diseases to appear. We can easily conclude that polygenic disorders are more complicated than the previous type (single gene diseases). These abnormalities are also difficult to analyze, because there are many factors that researchers should take into consideration in order to reach to some useful conclusions. Many well known chronic diseases are Multifactorial Genetic Diseases. Everybody knows Alzheimer, diabetes, obesity and arthritis. Besides many cancer types are caused by multi mutations.

      3)Chromosomal Genetic Diseases:
      Chromosomes are big DNA molecules composed from genes. The chromosomes are located in the cell nucleus. Abnormalities in the structure, number (and not only) of the chromosomes can cause some of the most dangerous genetic disorders. This type of disorders seem to be much easier to observe because they are, sometimes, detected by examination with microscope. Down Syndrome is the most well known disease caused by chromosomal abnormalities. In this disorder there is a third copy of chromosome 21 (there are two copies of each chromosome in the cells of healthy humans). Chromosomal diseases can be also caused by segments and joins of parts of chromosomes.

      4) Mitochondrial Genetic Diseases:
      It is not a common situation. Mitochondrial DNA is a DNA molecule found in the mitochondria (out of the nucleous) – a necessary organelle for cellular respiration. Mutations in the mitochondrial DNA can also cause undesirable abnormalities. In the following pages you can find more info about some of the most dangerous human genetic diseases and also reveal the secrets of some rare disorders.