DNA testing for Huntington disease in the Turkish population.

Huntington disease (HD) is an autosomal dominant inherited disease, characterized by involuntary movements, behavioral and personality changes and dementia. Although the mean age at onset is about 40 years, onset varies from 5 to 79 years. Therefore, at-risk individuals are never sure to have escaped the disease. The genetic defect is a CAG trinucleotide repeat expansion at the 5' end of the IT-15 gene on chromosome 4. In this study, we analyzed 127 patients with HD and 122 healthy controls. The numbers of CAG repeats varied from 38 to 78 (median: 42) in 127 HD patients, while in healthy controls we observed only 10-35 CAG repeats (median: 18). The length of the CAG repeat expansion in Turkish HD patients and normal controls was similar to that reported from other populations. Negative correlations (r = -0.67) were also found between age of disease onset and repeat length.