Letter re: Huntington disease reduced penetrance alleles occur at high frequency in the general population.

Abstract

There is general consensus that the presence of 40 or more CAG repeats in the Huntington gene ( HTT ) confers Huntington disease (HD). In their study on CAG-HTT in 7,315 people, Kay et al.1 estimated that 0.246% of the general population have low-penetrance expanded (36–39) CAG repeats and 6.2% have intermediate (27–35). The latter is similar to the 5.1% (50/983) frequency of intermediate CAG repeats in the Prospective Huntington at Risk Observational Study (PHAROS) study and 2.5% (50/1985) in the Cooperative Huntington's Observational Research Trial (COHORT) study.2,3