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Inherited Disorders and Birth Defects

Ataxia

09/10/2009

Question:

This isn`t a question but I noticed you have a woman aged 17. This is not the youngest case. I grew up with a boy who was diagnosed with the disease at age 9-10 we are now both 19. I find it extremely courageous what the guy has been through. Could you share some information on the gene side of the disease? More depth into chromosome 9 please?

Thanks

Answer:

I believe you are asking about the genetics of Friedreich ataxia, which is a genetic disorder that is inherited in an autosomal recessive manner.

As you know, Friedreich ataxia (FRDA) is a progressive disease that causes ataxia (unsteady gait and balance) starting in childhood or in the early teens. It usually starts with poor balance when walking, followed by slurred speech and upper-limb ataxia. The mean age of onset of symptoms is between 10 and 15 years of age. However, it has been reported to be diagnosed as early as the age of 2 and as late as 60’s in a few people.

Friedreich ataxia (FRDA) is caused by a mutation (change) in a gene called frataxin that is on chromosome 9. Among people with FRDA, almost 98-99% will have a gene change in frataxin. This mutation causes a problem known as a triple-repeat expansion. In FRDA the expansion is a GAA triplet-repeat expansion. An expansion is an area of the gene that repeats the same nucleotide sequence over and over and over again. It’s like a vinyl record which has a scratch in it – the record gets stuck and keeps repeating itself. When this happens, the gene cannot make the protein it codes for and the person has the disease. So in FRDA a person has hundreds of GAAGAAGAAGAA ------------------------

As I mentioned, it is inherited in an autosomal recessive manner – that is both parents are carriers for the gene (they have no problems), but have a 25% chance of both passing the mutated gene on at the same time and having an affected child.

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

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