X-linked hypophosphatemia (XLH), also called X-linked dominant hypophosphatemic rickets, X-linked vitamin d-resistant rickets, is an X-linked dominant form of rickets (or osteomalacia) that differs from most cases of rickets in that ingestion of vitamin D is relatively ineffective. It can cause bone deformity including short stature and genu varum (bow leggedness). It is associated with a mutation in the PHEX gene sequence (Xp.22) and subsequent inactivity of the PHEX protein. The prevalence of the disease is 1:20000. The leg deformity can be treated with Ilizarov frames and CHAOS surgery.