Hypomagnesemia 5, Renal, with or Without Ocular Involvement, also known as fhhnc with severe ocular involvement, is related to hypomagnesemia 3, renal and primary hypomagnesemia with hypercalciuria and nephrocalcinosis. An important gene associated with Hypomagnesemia 5, Renal, with or Without Ocular Involvement is CLDN19 (Claudin 19), and among its related pathways/superpathways are Sertoli-Sertoli Cell Junction Dynamics and Cell junction organization. Affiliated tissues include eye and kidney, and related phenotypes are nystagmus and abnormality of retinal pigmentation