In the last few years, a great effort has been devoted to understanding how the deregulation of the phosphatase STEP61 contributes to the pathophysiology of various neuropsychiatric disorders such as AD, Huntington’s disease, schizophrenia, X-fragile syndrome, and in the pathological changes associated with aging [17,28,29,49,51,77,78]. The gene discussed is PTPN5; the disease is juvenile Huntington disease.