High Quality Content by WIKIPEDIA articles! Hypomagnesemia with secondary hypocalcemia (HSH) is an autosomal recessive genetic disorder affecting intestinal magnesium absorption. Decreased intestinal magnesium reabsorption and the resulting decrease in serum magnesium levels is believed to cause lowered parathyroid hormone (PTH) output by the parathyroid gland. This results in decreased PTH and decreased serum calcium levels (hypocalcemia). This manifests in convulsions and spasms in early infancy which, if left untreated, can lead to mental retardation or death. HSH is caused by mutations in the TRPM6 gene.