Pathophysiological mechanisms proposed for DPHL have included Arylsulfatase A (ARSA) deficiency because of the histologic similarities between DPHL and metachromatic leukodystrophy, but subsequent studies showed ARSA deficiency to be neither necessary nor sufficient for the development of DPHL [4–6]. The gene discussed is ARSA; the disease is hyperinsulinemic hypoglycemia, familial, 4.