GNAS and Fabry disease: GNAS mutations in FD are gain‐of‐function alterations, which constitutively activate adenylyl cyclase (AC) to generate excess cyclic adenosine monophosphate (cAMP) through loss of GTPase activity of GTP‐bound Gαs (Landis et al., 1989) and abnormal activation of GDP‐bound Gαs (Hu & Shokat, 2018), resulting in abnormal proliferation and differentiation of mutation‐bearing BMSCs (Marie, 2001).