Variation in the number of CAG repeats in the Machado-Joseph disease gene (MJD1) in the Japanese population.

Variation in the number of CAG repeats in the Machado-Joseph disease gene (MJD1) was examined by polymerase chain reaction and denaturing polyacrylamide gel electrophoresis analysis of 2134 normal and 135 affected chromosomes of Japanese individuals. The number of repeats ranged from 14 to 47 in normal alleles and from 61 to 84 in disease-associated alleles. The most frequent and lowest number of repeats was 14. The size distribution of normal MJD1 alleles did not fit a normal distribution curve, but was tetramodal. Repeats from 14 to 17, 18 to 23, 24 to 25, and 26 to 47 units were designated groups A through D, respectively. When examined Hardy-Weinberg equilibrium by chi-square analysis of goodness of fit: no evidence of significant deviation from the Hardy-Weinberg equilibrium was observed [x2=4.248<16.919 (P=0.05), df=9]. The observed distribution peak of normal MJD1 alleles corresponding to peptides containing 10, 15, 20, and 24 glutamine suggests that stretches of 5 and 10 glutamine might constitute a functional domain of human MJD1.