Familial hypomagnesemia with hypercalciuria and nephrocalcinosis in 2 sisters

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a rare autosomal recessive tubular disorder characterized by excessive renal magnesium and calcium wasting, eventually, progressing to renal failure. It has been recently attributed to a mutation in the Claudin 16 (CLDN 16) gene of the Paracellin-1 (PCLN-1) tight junction protein. Herein, we report 2 sisters with FHHNC. Both sisters presented at an early stage with hypomagnesemia and hypocalcemia. The first patient was initially mislabeled and treated as a case of hypoparathyroidism, while the second patient was diagnosed retrospectively after the diagnosis of her sister. The 2 patients developed end stage renal disease.