Familial primary hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a form of familial primary hypomagnesemia (FPH), characterized by renal magnesium (Mg) and calcium (Ca) wasting, nephrocalcinosis, kidney failure and, in some cases, severe ocular impairment. Two subtypes of FHHNC are described: FHHNC with severe ocular involvement (FHHNCOI) and without severe ocular involvement (FHHN).