Several genes are implicated in diseases caused by dysregulated ionic/pH homeostasis (Slc9a8), linked to lupus (Uhrf1bp1), linked to taupathy (Mark1), increased expression linked to Alzheimer’s (Soat1), overexpression linked to Huntington’s disease (Arfgef2) and linked to mental retardation in Down’s Syndrome (Sim2). The gene discussed is ARFGEF2; the disease is juvenile Huntington disease.