Camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP) is a rare condition which causes joint abnormalities that begin at birth or during early childhood. The name comes from the main symptoms, including permanent bending of the fingers (camptodactyly), joint disease (arthropathy), and changes in the hip joint resulting in shortened legs and a possible limp (coxa vara). Some people with CACP also have too many cells between their joints (synovial hyperplasia) and too much fluid around the heart (pericardial effusion) or lungs (pleural effusion).

Camptodactyly-arthyropathy-coxa vara-pericarditis syndrome is caused by a mutation in the PRG4 gene. This gene is responsible for making a protein that lubricates the joints.The condition is inherited in an autosomal recessive manner. CACP may be at first confused with juvenile idiopathic arthritis because the two diseases have similar symptoms.

Diagnosis is based on clinical findings (symptoms which the doctor notices on a physical exma) and a biopsy of the fluid between the joints (synovial fluid).Genetic testing can confirm the diagnosis. Treatment options such as physical therapy and pain medication focus on relieving symptoms of the disease. The medication for juvenile idiopathic arthritis is not helpful for those with CACP.

Camptodactyly-arthropathy-coxa-pericarditis syndrome is caused by a change (mutation) in the PRG4 gene. This gene provides the instructions for making lubricin, a protein (part of synovial fluid) that lubricates the joints. In other words, lubricin works like oil in a hinge and is needed so the joints can bend easily without a lot of force or causing damage to the bones. Lubricin also works as an lubricant between the two layers of the thin sac which surrounds the heart (pericardium). The pericardium holds the heart in place and helps it work properly. In addition lubricin keeps the thin coverings of tendons (tendon sheaths) from sticking to the thin fibrous coverings (sheaths) of muscles and organs as well as controls cell growth of special cells (synovial fibroblasts) which are part of the thin covering (synovial membrane) surrounding the synovial fluid within joints.

PRG4 gene in each cell. People with CACP inherit one mutated copy of the gene from each parent, who is referred to as a carrier. Carriers of an autosomal recessive condition typically do not have any signs or symptoms (they are unaffected). When two carriers of an autosomal recessive condition have children, each child has a:

• 25% chance to be affected (have CACP)
• 50% chance to be an unaffected carrier like each parent
• 25% chance to be unaffected and not a carrier

Diagnosis of CACP is based on clinical findings (symptoms which the doctor notices during a physical exam), X-rays of the joints, cardiac ultrasound (also called an echocardiogram), and a biopsy of the fluid between the joints (synovial fluid). Genetic testing can confirm the diagnosis. CACP may at first be confused with juvenile idiopathic arthritis (JIA) because the two diseases may have similar symptoms.