Exome sequencing identifies a novel frameshift variant causing hypomagnesemia with secondary hypocalcemia

Hypomagnesemia with secondary hypocalcemia is a rare autosomal-recessive disorder characterized by intense hypomagnesemia associated with hypocalcemia (HSH). Mutations in the TRPM6 gene, encoding the epithelial Mg2+ channel TRPM6, have been proven to be the molecular cause of this disease. This study identified causal mutations in a 2-month-old male patient of hypomagnesemia from a consanguineous marriage. Biochemical analyses indicated the diagnosis of HSH due to primary gastrointestinal loss of magnesium. Whole exome sequencing of the trio (i.e. proband and both parents) was carried out with mean coverage of > 150×. ANNOVAR was used to annotate functional consequences of genetic variation from exome sequencing data. After variant filtering and annotation, a number of single nucleotide variants (SNVs) and 2 bp deletion at exon26:c.4402_4403delCT in TRPM6 gene were identified. This deletion which resulted in a novel frameshift mutation in exon 26 of this gene was confirmed by Sanger sequencing. With these investigations in hand, the patient was managed with magnesium sulphate. The patient remained asymptomatic and was developmentally and neurologically normal till his last follow up.