Question: What is (are) Familial avascular necrosis of the femoral head ?
Answer: 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: GARD

Question: What are the symptoms of Familial avascular necrosis of the femoral head ?
Answer: What are the signs and symptoms of Familial avascular necrosis of the femoral head? The Human Phenotype Ontology provides the following list of signs and symptoms for Familial avascular necrosis of the femoral head. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Autosomal dominant inheritance - Avascular necrosis of the capital femoral epiphysis - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.
Source: GARD