Most FHHNC patients have been found to carry CLDN16 mutations, although in the South of Europe (mainly Spain and France) CLDN19 mutations are more prevalent and a specific CLDN19 so-called Hispanic founder mutation (c.59G>A; p.G20D) has been described [9,10]. Here, CLDN19 is linked to familial primary hypomagnesemia with hypercalciuria and nephrocalcinosis.