Huntingtin is the protein coded for by the HTT gene. Autosomal dominant mutation in the Huntingtin (Htt) protein is the cause of Huntington’s Disease (HD). In HD, the polyglutamine (polyQ) domain in the N-terminal sequenceof the protein is expanded beyond a threshold of 36 glutamines. mutant polyQ expansion strongly correlates in an inverse manner to disease age of onset.