GCM2 and familial hypoparathyroidism: Genetic defects affecting GCM2 are rare in FIH: a study of 20 unrelated FIH cases (10 familial and 10 sporadic) found several polymorphic variants, but did not find GCM2 mutations that segregated with the disease and/or led to loss of function (Maret et al., 2008).