HTT and Huntington disease: Growing evidence from cellular and animal models shows that phosphorylation or pseudophosphorylation of Ser13, Ser16, Ser434, or Ser536, in HTT reduces the toxicity of polyQ-mHTT, and levels of phosphorylation are weakened by polyQ expansion,424–426 suggesting that phosphorylation state of HTT tightly links to toxicity in HD pathogenesis.