Adult-Onset Hypomagnesemia With Secondary Hypocalcemia Caused by a Novel Variant in TRPM6 Gene: A Case Report.

Hereditary hypomagnesemia with secondary hypocalcemia (HSH) is a rare autosomal recessive disorder caused by biallelic variants in the transient receptor potential melastatin 6 (TRPM6) gene, typically presenting in infancy. Currently, there is a lack of reports in the literature on adult-onset cases. This case report describes a 51-year-old male with adult-onset HSH, presenting with limb weakness, muscle spasms, and electrolyte imbalances, including severe hypomagnesemia (0.28 mmol/L). Genetic testing revealed a novel heterozygous variant in the TRPM6 gene (c.4914del, p.E1638Dfs*8), classified as likely pathogenic. The patient's symptoms significantly improved following magnesium supplementation, and his electrolyte levels gradually normalized. This case highlights the importance of considering HSH in patients with unexplained hypomagnesemia and emphasizes the role of genetic testing in confirming the diagnosis. The findings also suggest that magnesium supplementation can effectively alleviate symptoms and improve the quality of life in patients with adult-onset HSH. Early recognition and treatment are crucial to prevent potential complications, such as neurological damage.