TCERG1 and Huntington disease: 73 However, none of these genes generated significant onset modification signals in our large scale unbiased genetic analysis.14,15,49,74 Interestingly, one candidate modifier that showed a trend of association66,75 and was replicated by GWAS is TCERG1, which harbours a complex coding hexamer repeat that appears to be the source of the influence on HD age-at-onset.76 Unfortunately, the hexamer repeat with potential association was not imputed in our data because this repeat was not present in the imputation reference panel that we used.