Late-onset Huntington disease with intermediate CAG repeats: true or false?

Huntington disease (HD) is a neurodegenerative disorder associated with an expanded CAG trinucleotide repeat length in the huntingtin gene. 'Intermediate alleles' with 27 to 35 CAG repeats generally do not cause HD but are unstable upon germ-line transmission. Insights in CAG repeat mosaicism and enhanced trinucleotide expansion in postmitotic neurons indicate that in the intermediate range, other factors than the CAG repeat length in diagnostic tests have to be considered. Here, we report two patients with mild, late onset HD and an intermediate repeat allele. The authors anticipate that intermediate repeats can cause late-onset HD due to disease modifiers and may be more common than previously stated.