CNNM2 and familial primary hypomagnesemia: Based on the severity of the neurological manifestations, CNNM2 pathogenic variants may manifest either as a mere hypomagnesemia syndrome with mild neurological manifestations (autosomal dominant renal hypomagnesemia 6, HOMG6, MIM# 613882) or a syndrome of hypomagnesemia, seizures, and mental retardation (HSMR1 MIM# 616418), frequently associated with obesity and autism.