This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Familial hypomagnesemia with secondary hypocalcemia is a disease characterized by very low magnesium levels in the blood. The disease begins during the first months of life with generalized and recurrent seizures which do not improve with usual treatment. Additional features include tetany (spasms of the hands and feet, cramps, spasm of the voice box (larynx), and overactive neurological reflexes), failure to thrive, restlessness, tremors, muscle spasms, and bluish skin around the mouth (perioral cyanosis). Abnormal heart rhythm (cardiac arrhythmia) may be observed. The low levels of magnesium result in low levels of parathyroid hormone (PTH) and in low levels of calcium in the bloods (hypocalcemia). It is caused by mutations in the TRPM6 gene. Inheritance is autosomal recessive. Untreated, the disease may be fatal or lead to severe neurologic damage. Treatment involves giving magnesium, usually in the vein (intravenously), followed by life-long high-dose oral magnesium.
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