Last update: 12/12/2007
Background to disease
OMIM 229300 (gene OMIM 606829)
Friedreich ataxia (FRDA, Friedreich ataxia 1, FA) is the most common inherited ataxia in European populations with a prevalence of 1/50,000 and carrier frequency of 1 in 90. It is the only autosomal recessive triplet repeat disorder. Neurodegenerative symptoms include progressive gait ataxia, lack of tendon reflexes in the legs, loss of position sense, hypertrophic cardiomyopathy (in 80 % of patients) and impaired glucose tolerance. There is an increased incidence of diabetes mellitus in friedreich ataxia patients. Symptoms usually start before age 25, with patients often becoming wheelchair-bound by late 20’s. There is intra- and inter-familial variability in the phenotype.
The disease is caused by expansion of a GAA repeat in intron 1 of the frataxin (FRDA) gene at 9q13. 98% of all FRDA chromosomes have the GAA repeat expansion while the remaining 2% have a point mutation.
Repeat size ranges are*:-
Allele |
(GAA)n |
|
Normal |
8 – 33 |
|
Premutation |
34 – 100 |
|
Affected |
90 – 1300 |
*EMQN guidelines, 2001.
Laboratory Analysis
Analysis for this disease is now carried out by the Northern Genetics Laboratories under a reciprocal arrangement (GENLYNC). Please contact them directly regarding information regarding turnaround time and sensitivity. Local samples should still be sent via the Yorkshire Regional Genetic Laboratory where they will be forwarded as whole blood as appropriate. DNA from these samples can be stored in the Yorkshire Regional Genetic Laboratory if it is anticipated that future tests may be required (please indicate clearly on referral card if required).