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Inherited Disorders and Birth Defects

Genetics and Genetic Counseling

Genes and Chromosomes

Genes are the tiniest piece of human information. They serve as the body's blueprint of heredity. Genes are made of DNA, which are double stranded molecules (like beads on a string) of protein within our cells. These proteins contain four letter codes, A, G, C, T, that interlock to form different sequences. The body has about 25,000 genes. Together, they make up the plans that determine how the body will develop, grow and function.

Genes do not float freely in the body. They are housed in molecular compartments known as chromosomes. If genes are the blueprints, chromosomes are the binders that hold the pages together and keep them organized. Humans have 46 chromosomes. There are 2 sex chromosomes and 22 pairs of non-sex chromosomes. Females have 2 X chromosomes and males have 1 X and 1 Y chromosomes. The chromosomes are housed within the nucleus of the human cell.


Since the beginning of time, people have recognized the concept of inheritance - that is, traits that are passed down from generation to generation. In most situations, those traits are looked at with pleasure, "she's got her father's eyes." However, when there is a genetic condition in the family that causes disease, illness or birth defects, there is usually great concern. Genetic disorders, while individually not very common, make up a significant portion of health care concerns. There are more than 6,000 known genetic disorders.

Any individual or family with an actual or potential concern about a diagnosis, recurrence risk, treatment or surveillance regarding a specific condition or birth defect often may seek guidance and counseling from a genetic counselor.

Genetic Counseling

Genetic counseling is the process of providing individuals and families with a medical history or increased personal risk for a genetic condition, or those at risk for having a child with a birth defect or genetic condition:

Medical geneticists and genetic counselors are health professionals with specialized training and experience in human and medical genetics and counseling who can give information and supportive counseling concerning many disorders or abnormalities. Genetic specialists should have certification from the American Board of Genetic Counseling or the American Board of Medical Genetics.

Genetic counseling is not about preventing the occurrence of a genetic disorder. Rather, the objective is to provide education and counseling about the possible risks, complications, and implications of genetic conditions. Counseling also is designed to provide support and educate families about available resources. Persons at risk for a genetic disorder, or those at risk for giving birth to a child with a birth defect or genetic disease, may feel overwhelmed sorting through other factors that may affect a person's decision making process including:

By providing expert information and helping individuals consider and explore the possibilities, genetic counselors can reduce confusion and promote informed decision-making. In addition to helping to educate and facilitate, the counselor also serves as an advocate, offering support regardless of the choices made. The goal is to help you arrive at a decision with which you are comfortable.

What You Can Expect From a Visit to a Counselor

During the visit, depending on the issue or condition, you may be asked to supply:

If the issue relates to the diagnosis of a genetic condition, the members of the genetics team will discuss how the condition can be managed and what the long-term implications are of having the condition. The genetic counselor can educate you about tests that determine whether or not a person is a "carrier," that is, someone who has an abnormal gene that could cause birth defects or disease in her children. If you are a carrier, genetic counseling can help determine the likelihood of passing on an abnormal gene. If you have a disorder or carry genes that may increase the chance you could develop a genetic disorder, genetic expertise can help determine the likelihood (recurrence risk) of the disorder arising in other family members or in yourself.

Family Tree or Pedigree

The family tree or pedigree is similar to a road map back into time that can help shed light on the future. Thus, discovering whether someone is at risk for a genetic disorder requires knowing with great accuracy your health history and that of your family.

When used in medicine, the pedigree is a historical diagram that traces family genetic characteristics, health problems, and disorders. Because charting a pedigree involves keeping track of many pieces of information, a diagram is made using symbols. The symbols distinguish males and females, show blood relationships among family members, and indicate relevant individual genetic traits.

Properly diagrammed, the pedigree will provide helpful details about each individual in the family and how the extended family (grandparents, uncles, aunts, grandchildren, in-laws) fared health-wise over time. Details provided by the pedigree include:

It is helpful to obtain some of this information before coming to the genetics clinic. This typically involves calling on certain relatives to ask them questions about the health of your grandparents, spouses, siblings, sons, daughters, etc.

To learn more about genetics and genetic counseling, please visit:




  1. Gelehrter TD, Collins FS and Ginsburg D. (1998). Principles of Medical Genetics. 2nd ed. Baltimore: Williams and Wilkins Publishing.
  2. National Society of Genetic Counselors (1995). Genetic Counseling: Valuable Information for You and Your Family. Wallingford, PA: National Society of Genetic Counselors, Inc

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Last Reviewed: Nov 10, 2009

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University