Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) familial osteochondritis dissecans ?
    ### Response:
    Familial osteochondritis dissecans is a condition that affects the joints and is associated with abnormal cartilage. Cartilage is a tough but flexible tissue that covers the ends of the bones at joints and is also part of the developing skeleton. A characteristic feature of familial osteochondritis dissecans is areas of bone damage (lesions) caused by detachment of cartilage and a piece of the underlying bone from the end of the bone at a joint.
    