HTT and choreatic disease: This autosomal dominant inherited neurodegenerative disease is the most common genetic cause of abnormal involuntary movements called chorea, and is characterized by mutations in the huntingtin gene (HTT) that result in abnormal expansion of the cytosine–adenine–guanine (CAG) trinucleotide repeats in the HTT gene, encoding a polyglutamine (polyQ) tract at the N-terminal region of the huntingtin (Htt) protein.