Avascular necrosis of the femoral head
(ANFH) is a degenerative condition which causes the upper ends of the thigh bones (femurs) to break down due to an inadequate blood supply and deficient bone repair. It can lead to pain and limping and cause the legs to be of unequal length. The prevalence of ANFH is unknown but around 15,000 cases are reported each year in the United States, with most cases being associated with mechanical disruption (hip trauma or surgery), hypofibrinolysis (a reduced ability to dissolve clots), steroid use, smoking, alcohol intake, hemoglobinopathies and hyperlipidemia (an increase in the amount of fat - such as cholesterol and triglycerides - in the blood). Familial forms of ANFH appear to be very rare, with only a few families reported in the medical literature. Age of onset in these familial cases ranges from 15-48 years (as opposed to between 3rd to 5th decade of life for other forms of ANFH). Transmission in familial cases is autosomal dominant and mutations in the type II collagen gene (COL2A1) have been detected in affected family members. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.