Primary idiopathic hypomagnesemia in two female siblings

Two female siblings with primary idiopathic hypomagnesemia, born to consanguineous parents, are described. Both presented at 6 weeks of age, with convulsions and persistent hypocalcemia (calcium 1.5 adn 1.6 mmol/l; normal range (NR) 2.2-2.6 mmol/l), which could not be controlled with anticonvulsants and/or calcium gluconate. On further investigation they were also found to have hypomagnesemia (magnesium 0.17 mmol/l and 0.22 mmol/l; NR 0.65-1.05 mmol/l). Convulsions and the low serum calcium and magnesium levels were first managed by im and then by oral administration of magnesium supplements. A burst in circulating parathyroid hormone levels to well above the physiological range was observed at the start of therapy. Serum magnesium values of the mother and father were just below the normal range, with normal serum calcium. This type of infantile primary hypomagnesemia appears to be a hereditary disease with autosomal recessive characteristics, although a partially penetrant X-linked or autosomal dominant trait cannot be excluded.