HD is a rare autosomal dominant neurodegenerative disease caused by the unstable CAG repeat expansion in the Huntington (HTT/IT15) gene and presenting with motor, cognitive, and psychiatric symptoms [423] When the HTT/IT15 gene holds 39 to 180 CAG repeats, the translated polyglutamine-containing mutant HTT protein (mHTT) complexes with and disrupts the normal function of several transcription factors, thereby altering the activities of neurons, astrocytes, and microglia. Here, HTT is linked to Huntington disease.