The three reported cases with isolated OC (i.e., superficial heterotopic ossification without AHO or hormone resistance) and a GNAS mutation were all infants (aged 1, 3, and 6 years) [Elli et al., 2013a; Huh et al., 2014], so it remains to be confirmed whether this is a true GNAS-associated phenotypic category or rather the first manifestation of POH. This evidence concerns the gene GNAS and pseudohypoparathyroidism type 1A.