Table 1.

Genetic modifiers implicated in HD onset and progression.

Genes	Effect
FAN1	FAN1 depletion in animal models and humans accelerates repeat expansion [48]. Increased expression promotes CAG repeat stability and is associated with delayed disease onset [49,50,55]. Variants that delay or hasten disease onset [10,53].
MLH1	The MLH1 gene is associated with brain CAG instability in Htt knock-in mice [61]. MLH1 delays disease onset [59].
MSH3	Promotes somatic CAG expansions, thus contributing to an earlier onset [62,63,64]. Variants are implicated in disease progression [11].
PMS1, PMS2, LIG1	Variants alter disease onset [12].