HTT and neurodegenerative disease: Huntington’s disease is one of nine CAG trinucleotide repeat disorders, a group of inherited neurodegenerative diseases (Zoghbi and Orr, 2000; Nakamura et al., 2001) and is caused by a CAG repeat (codes for glutamine, Q) mutation in exon-1 of the huntingtin (HTT) gene, which results in an elongated polyglutamine [or poly(Q)] stretch of the protein – giving rise to the term mutant HTT (mHTT) (McColgan and Tabrizi, 2017).