As evidence, SUMO1 modification promotes solubility of α-synuclein (PD) and huntingtin (HD) [7,136], while SUMO2 modification of ataxin-1 and ataxin-7 (SCA type 1 and 7, respectively) promotes degradation by recruiting RNF4 [35,138]. Here, RNF4 is linked to Huntington disease.