GNAS and Fabry disease: Fibrous dysplasia (FD) is a rare, genetic but noninheritable bone disorder caused by a postzygotic mutation of GNAS located on chromosome 20q13.3 (Weinstein et al., 1991), which presents in three forms: monostotic FD, which occurs in one bone; polyostotic FD, which involves multiple bones; and McCune–Albright syndrome, which simultaneously contains polyostotic FD, skin hyperpigmentation and hyperfunctioning endocrinopathies (Collins et al., 2012).