HTT and juvenile Huntington disease: Huntington’s disease (HD) is an inherited autosomal dominant neurodegenerative disorder characterized by progressive motor dysfunction, cognitive decline, and psychiatric disturbances, primarily due to expanded cytosine-adenine-guanine (CAG) repeats in the huntingtin (HTT) gene, which result in the production and aggregation of mutant huntingtin (mHTT) protein in neurons1,2.