A novel PCLN-1 gene mutation in familial hypomagnesemia with hypercalciuria and atypical phenotype

Familial hypomagnesemic hypercalciuria and nephrocalcinosis (FHHNC [MIM 248250]) is a rare renal tubular disorder characterized by impaired reabsorption of magnesium and calcium in the thick ascending limb of Henle's loop (tALH), causing renal magnesium wasting and hypercalciuria. Patients with FHHNC usually present with recurrent urinary tract infections, polyuria, nephrolithiasis (NL) and nephrocalcinosis (NC) with many progressing to chronic renal failure (CRF). We have shown recently that loss of function mutations in paracellin-1 PCLN-1/claudin-16, a renal tight junction protein located in the TAL, are causative of FHHNC. We present clinical and molecular studies on a highly inbred family with FHHNC in association with an unusual phenotype in that all affected members were extremely short. Affected individuals were found to be homozygous for marker D3S1314 on chromosome 3q. Sequencing of the PCLN-1/claudin-16 gene revealed a previously unknown point mutation at S235Y on exon 4 on the 4th transmembrane domain, providing additional evidence that inactivating mutations in the PCLN-1/claudin-16 gene result in FHHNC.