CTSK and metachondromatosis: Some studies examined the detailed pathogenesis of metachondromatosis by deleting PTPN11 specifically in monocytes, macrophages, and osteoclasts (lysozyme M-Cre; LysM-Cre) or in cathepsin K (Ctsk)-expressing cells using PTPN11flox/flox and Cre recombinase transgenic mice (Yang et al., 2013).