RÉSUMÉ
Huntington's disease (HD) is an inherited neurodegenerative disorder characterized by chorea and progressive dementia. The mutation causing the disease has been identified as an unstable expansion of a trinucleotide (CAG) n at the 5' end of the IT 15 gene on chromosome 4. We have analyzed the distribution of CAG repeats in 71 Iranian individuals (34 patients and 37 unaffected family members) belonging to 31 unrelated families thought to segregate HD. We found one expanded CAG allele in 22 individuals (65%) belonging to 21 unrelated families. In these HD patients, expanded alleles varied from 40 to 83 CAG units and normal alleles varied from 13 to 36 CAGs. A significant negative correlation between age at onset of symptoms and size of the expanded CAG allele was found (r= - 0.51; P=0. 1). In addition, we genotyped 25 unrelated control individuals (total of 50 alleles) and found normal CAG repeats varying from 10 to 34 units. In conclusion, our results showed that molecular confirmation of the clinical diagnosis in HD should be sought in all suspected patients, making it possible for adequate genetic counseling. This Study is the first report of molecular diagnosis of Huntington disease among Iranian population and ever in Middle East and with regard to high frequency of consanguinity marriage in this region.