Patient 4 (P4) was subject to diagnostic trio WES after candidate gene screening for possible causal variants in genes associated with hypomagnesemia (CLDN16, CLDN19, CNNM2, EGF, FXYD2, KCNA1, SLC12A3 and TRPM6), which identified only a single possible pathogenic SLC12A3 variant (XomeDx Slice, Genedx). This evidence concerns the gene FXYD2 and familial primary hypomagnesemia.