HTT and juvenile Huntington disease: So began a new age of Huntington’s disease: armed now with certainty of the cause of every past, present and future case of Huntington’s disease, researchers could focus their efforts on understanding the gene, studying the protein in its wild-type and mutant forms, elucidating the mechanisms through which mutant huntingtin (mHTT) causes disease, and working on therapies targeting the mutation and its known effects.