The disease is caused by loss‐of‐function mutations ofCLDN16 (previously known as PCLN1) (type 1), (Simon et al., 1999) or CLDN19 (type 2).The majority of Spanish patients with FHHNC are homozygous for CLDN19 founder mutation p.(Gly20Asp), and they also have severe ocular defects (Konrad et al., 2006, Claverie‐Martin et al., 2013; Martin‐Nuñez et al., 2015). The gene discussed is CLDN19; the disease is familial primary hypomagnesemia with hypercalciuria and nephrocalcinosis.