A developmental disorder affecting the growth and development of the proximal end of the femur (thigh bone) near the hip joint characterized by avascular necrosis of the femoral head, cystic changes of the femoral head, and/or sclerosis of the femoral head. It is a relatively milder form of the other skeletal disorders associated with COL2A1. [ https://orcid.org/0009-0003-2127-3550 https://clinicalgenome.org/affiliation/40065/ ]