Familial hypomagnesemia with secondary hypocalcemia is a rare autosomal recessive disorder characterized by very low serum magnesium levels. Hypocalcemia is a secondary consequence of parathyroid failure and parathyroid hormone resistance as a result of severe magnesium deficiency. The disease typically manifests during the first months of life with generalized convulsions or signs of increased neuromuscular excitability, such as muscle spasms or tetany. Untreated, the disease may be fatal or lead to severe neurologic damage. Treatment includes immediate administration of magnesium, usually intravenously, followed by life-long high-dose oral magnesium. [From OMIM]