GNAS and fibroma: Although mice with chondrocyte-specific ablation of Gnas exhibit ectopic cartilage formation within the metaphyseal region of the tibia [28] and those with targeted heterozygous disruption of exon 2 of Gnas (GnasE2 −/+) [9] develop subcutaneous fibromas or angiofibromas with associated calcifications [29], there has not been a mouse model that recapitulates the SCO found in AHO in humans until now.