Trinucleotide repeat elongation in the huntingtin gene in Huntington's disease patients from 85 French families. The French HD Research Group.

IT15 is a new gene encoding a protein named huntingtin; a polymorphic CAG repeat in the proposed open reading frame of IT15 has been characterized, and an elongation of this repeat has been correlated to Huntington's disease (HD). We have investigated the CAG repeat in the huntingtin gene in 85 unrelated French families with Huntington's disease. In 79 patients (from 60 families, where at least one HD DNA was available) we found repeat lengths of 37 to 100 units, in contrast to 11 to 35 CAG's on normal chromosomes. Comparison of repeat length and age at onset of disease symptoms in 71 individuals confirms an inverse correlation (r = -0.51 for p < 10(-4)) between the age at onset and the number of CAG repeat units.