Interestingly, a similar combination of rapid onset psychiatric disturbance with marked regression and catatonia has been described in Down syndrome [42, 43] and subsequently labeled “Down syndrome disintegrative disorder.” A recent case series [44] documented a role for immunotherapy in restoring function and stability in these individuals, although it is also recognized that cognitive decline in Down syndrome relates to amyloid precursor protein gene triplication [45–47]. The gene discussed is APP; the disease is Down syndrome.