HTT and juvenile Huntington disease: Huntington’s disease is an inherited neurodegenerative disorder that manifests with psychiatric disturbances, movement disorders and cognitive decline.1 It is caused by a cytosine, adenine and guanine (CAG) repeat expansion in exon 1 of the huntingtin (HTT) gene that encodes a polyglutamine (polyQ) tract in the huntingtin protein (HTT).