“…In humans, loss of the remaining wild-type allele of EXT has been detected in approximately 40% of sporadic and multiple osteochondromas (Hameetman et al, 2007b;Reijnders et al, 2010;Zuntini et al, 2010). In sporadic osteochondromas, we have described homozygous deletions of EXT1 in B80% of the cases (Hameetman et al, 2007b;Reijnders et al, 2010;Zuntini et al, 2010). It was shown recently that during the formation of osteochondromas, chondrocytes with functional EXT from the growth plate or the neighboring tissue are being integrated into the cartilaginous cap, generating a mosaic mixture of wild-type cells and cells with homozygous inactivation of EXT1 or EXT2 (de Andrea et al, , 2011Jones et al, 2010;Matsumoto et al, 2010).…”