FAN1 and Huntington disease: Indeed, both could contribute to the HD disease pathology but recent evidence from genome-wide association (GWAS) studies of HD have found many genes that are involved in DNA damage repair in neurons (e.g., FAN1, LIG1, MLH1, MSH3, PMS1, and PMS2) as strong modifiers of age at onset and disease severity (Genetic Modifiers of Huntington’s Disease [GeM-HD] Consortium, 2015; Maiuri et al., 2019; Tabrizi et al., 2020), suggesting that impaired or defective DNA repair mechanism is mechanistically linked to HD pathomechanism.