Studies of linkage in 12 FHHNC kindreds found the disease locus to be on chromosome 3q27, and positional cloning studies identified mutations in the gene encoding paracellin-1 (PCLN-1), which is also referred to as claudin 16 (CLDN16) [72]. Here, CLDN16 is linked to familial primary hypomagnesemia with hypercalciuria and nephrocalcinosis.