Mutations in the TNFRSF11A gene, which encodes for RANK, were the first to be associated with isolated PDB cases and other, so called, PDB-like disorders, such as familial expansile osteolysis (FEO) and expansile skeletal hyperphosphatasia (ESH) (Hughes et al., 2000). This evidence concerns the gene TNFRSF11A and familial expansile osteolysis.