Friday, May 27, 2011

Autosomal Recessive Disorders

I know many friends and family are still a little confused on what an "autosomal recessive" disorder is; and how you get it.  I am going to try my best to describe what that is here.  I hope it answers a lot of your questions.

Okay; so as many of you know already; each person inherits 23 pairs of chromosomes.  1 pair from mom, and 1 pair from dad.  These chromosomes make up who we are.  On these chromosomes there are 20,000 plus genes.  The genes determine more specific traits such as what color eyes we have, how tall we are going to be, etc.  As our Geneticist put it: if you were a book; your chromosomes are the pages of the book, and your genes are the words that are written on the pages.  So for example, if there is a gene in your family that gives the trait of blue eyes......the chromosome is responsible for making sure you have eyes and that they work, and the gene is responsible for where your eyes are placed on your head, the shape, how big they are, and if yours are blue or not.  Now what determines this.....dominant and recessive genes.

Each person has dominant and recessive genes that they carry.  For all the specific traits about us.  Male baldness, a hairy back, a bump in your nose.  Those are all traits.  Now back to the blue eye thing.  If both of your parents have blue eyes; you are not guaranteed to have blue eyes.  This where recessive traits come in.  You may have a grandparent with brown eyes, etc.  So even though blue eyes are the dominant trait; brown may be the recessive trait that your mother carries.  Say your father also happens to be blue eyed but carries a brown eye recessive trait too.  This means there is a 25% chance that each child could have brown eyes.  The same is for Macy's disease.   The recessive trait is where her disease lies.  All of her chromosomes are normal (all of her pages in her book are there---there are not any duplications or deletions which is what causes syndromes like Downs Syndrome, etc.) but the words written on one of her pages is not normal.  And it happens to be the one that is responsible for the cluster of proteins that repair DNA in your blood; so it leads to bone marrow failure and cancer.  This is also why some children are born with anomalies.  Since DNA cannot be repaired in the blood; things can go wrong when the embryo is forming.  In Macy's case; her kidneys and thumbs did not form correctly.  She is actually pretty lucky because many kids are much worse off.

To break it down even further; there have been 15 genes identified on that particular chromosome that are responsible for FA (so 15 different words on that page if not correct can cause FA).  Each of those 15 groups are called complementation groups. We need to find out which one is the one responsible for Macy's FA.  Even though each one is Fanconi Anemia; each type or complementation group is prone to different types of cancers and complications, etc. so it is good to know which one she has to better her course of treatment.  FANC-A is the most common, followed by FANC-C and FANC-G and so on.  For example, FANC-D is more prone to breast cancer than the others so this info is good to know because if she has that kind; me being a carrier would also increase my chances of breast cancer.  The more we know; the better we can screen for particular complications.  Now to the part on how she got it.

Our Geneticist said that everyone carries about 8-10 diseases on our recessive genes ( too!).  Think of a disease as merely a mutation on a gene---a word that is not written correctly on a page.  Everyone has them; no one's are perfect and most are not significant enough to affect us unless two of the same are put together.  My husband and I just happen to have the same page with the wrong words, and therefore, carry one of the same diseases.  Fanconi Anemia.  It is very rare, and we are both carriers, and happen to be the one's to find each other and have a baby.  So each one of our children would have a 25% chance of having the disease. The disease will only show up if BOTH parents are carriers.  That is why it has never shown up in either family before.  Even though one of Adam's parents is a carrier, one of mine; one of each of our grandparents, etc.  You won't have the disease itself unless both parents are carriers.  And even then it is a 25% chance with each child.  Macy is our only child and she just happens to be that 25%.  

So, Fanconi Anemia and all other recessive disorders are not something you can "catch" or develops later in life.  Although complications may not show up till later in life for some; it is something you are born with.

We are very lucky we found out when we did.  We were planning on getting pregnant with our 2nd child this month.  Now that we know what we know; we are not willing to take a chance because 25% is high when it comes to the seriousness of this; so we are going to have to find another way to have other children.

I hope this answers some of your questions on her disease.  And I hope everyone has a great weekend!

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