Hypomagnesemia with Secondary Hypocalcemia Linked to a Novel TRPM6 Gene Mutation

Hypomagnesemia with secondary hypocalcemia (HSH) is a rare inherited disorder, characterized by extremely low levels of serum magesium associated with symptomatic hypocalcemia. HSH manifests in the new born period with neurological symptoms, including generalized seizures, which are refractory to anticonvulsant treatment. In this disorder, the basic abnormality is the defective intestinal absorption of magnesium. Mutations in TRPM6, the gene encoding the transient receptor potential cation channel subfamily member 6 have been found to be responsible for this disease. We report on a four-month-old Tunisian girl who presented with convulsions. Laboratory evaluation yielded extremely low serum magnesium levels, low calcium levels, and abnormal PTH levels. The diagnosis of HSH was confirmed by mutation analysis which identified the novel mutation c.1307A >G in exon 11 of TRPM6 (Lys436Arg). Our patient was homozygous for this mutation. Prenatal diagnosis was done during second pregnancy. DNA from trophoblast biopsy showed the same mutation as the proband.