Huntingtin gene CAG repeat numbers in Chinese patients with Huntington's disease and controls

Huntington's disease is due to a CAG triplet repeat elongation in the huntingtin gene. Boundaries in CAG numbers have been found between healthy people with and without risk to pass the disorder to the next generation, and between people without, with a mild, or with a fully penetrant phenotype. These data have been generated in western populations and it is not clear whether they are also valid amongst Chinese.

In order to establish normative data in the huntingtin gene for Chinese people, 966 chromosomes from normal controls were tested. Further, the range of CAG repeats was examined in a cohort from six centres and a total of 368 patients with the disease were included.

The CAG triplet repeat range in normal controls was between 9 and 35 (mean 18.9, SD 2.57). Triplets in the range between 26 and 35 were found in 2.5%. In the patient cohort, triplet repeats in the shorter allele were between 8 and 37 (mean 17.7, SD 1.6). In the longer allele, a range between 36 and 120 was found. There was a negative correlation (-0.65, r = 0.42) between age at onset and the number of triplet repeats in the larger allele. The mean age at onset was 38 years, with a range between 2 and 70 years. In 23 patients (6%) a childhood or juvenile onset was noted.

These data show comparable ranges of huntingtin gene CAG triplet repeats in normal people and in patients with Huntington's disease as in western populations.