Clinical phenotype in a girl with familial hypomagnesemia with hypercalciuria and nephrocalcinosis

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a rare autosomal recessive disorder of the renal tubules caused by mutations in the CLDN 16 or CLDN19 genes encoding the proteins claudin-16 and claudin-19. CLDN 16 or CLDN19 play an important role in the cellular transport of magnesium and calcium in the thick ascending limb of the loop of Henle and are responsible for most of the tubular magnesium reabsorption. FHHNC is characterized by hypomagnesemia, hypercalciuria, medullary nephrocalcinosis, and eye involvement, and progresses to chronic renal failure requiring dialysis and kidney transplantation, mainly in young adults. A clinical case of rapidly progressive renal function decline in a patient with mutations in the CLDN19 gene without ocular involvement is demonstrated.