PTPN11 and Osteochondroma: Metachondromatosis (METCDS, MIM: 156250) is a rare autosomal-dominant skeletal disorder, characterized by enchondromas and osteochondromas primarily in the iliac crest and tubular bone metaphyses.79–81 These lesions are usually asymptomatic and either regress spontaneously or transform into chondrosarcomas.82PTPN11 variants that cause METCDS represent a new category of PTPN11 loss-of-function (LOF) variants.