HTT and Huntington disease: The role of HTT PTMs in ameliorating pathological phenotypes in HD mouse models is well supported by the findings that phosphor-mimetic mutations at residues associated with phosphorylation (e.g., S13/S16 and S421) can significantly affect mutant HTT biology (Gu et al, 2009; Kratter et al, 2016; Xu et al, 2020).