Familial osteochondritis dissecans
Familial osteochondritis dissecans is a joint condition caused by abnormal cartilage, leading to bone lesions, pain, and early-onset osteoarthritis.
Overview
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. People with this condition develop multiple lesions that affect several joints, primarily the knees, elbows, hips, and ankles. The lesions cause stiffness, pain, and swelling in the joint. Often, the affected joint feels like it catches or locks during movement.
Other characteristic features of familial osteochondritis dissecans include:
- Short stature
- Development of a joint disorder called osteoarthritis at an early age (characterized by the breakdown of joint cartilage and the underlying bone)
Frequency
Familial osteochondritis dissecans is a rare condition, although the prevalence is unknown. Sporadic osteochondritis dissecans (which is not inherited and typically involves a single lesion) is more common; it is estimated to occur in the knee in 15 to 29 per 100,000 individuals.
Causes
Mutation of the ACAN gene can cause familial osteochondritis dissecans. The ACAN gene provides instructions for making the aggrecan protein, which is a component of cartilage. Aggrecan attaches to the other components of cartilage, organizing the network of molecules that gives cartilage its strength. In addition, aggrecan attracts water molecules and gives cartilage its gel-like structure, enabling the cartilage to resist compression and protect bones and joints.
The ACAN gene mutation associated with familial osteochondritis dissecans results in an abnormal protein that is unable to attach to the other components of cartilage. As a result, the cartilage is disorganized and weak. Researchers suggest that a disorganized cartilage network in growing bones impairs their normal growth, leading to short stature.
Inheritance
This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.