HTT and Huntington disease: In Huntington disease (HD), Ogg1 (and/or Neil1)-initiated repair of 8-oxoguanine (8-oxoG, or oxidized pyrimidines) in CAG triplets is proposed to trigger iterative oxidation–excision cycles that contribute to the somatic instability of the huntingtin gene, through a CAG repeat expansion [12,13,14,15].