Progressive pseudorheumatoid arthropathy of childhood (PPAC) also called Progressive pseudorheumatoid disyplasia (PPD, SEDT-PA) is a joint disease that worsens over time. This condition is characterized by breakdown (degeneration) of the cartilage between bones (articular cartilage). This cartilage covers and protects the ends of bones, and its degeneration leads to pain and stiffness in the joints and other features of PPRD.
PPRD usually begins in childhood, between ages 3 and 8. The first indications are usually an abnormal walking pattern, weakness and fatigue when active, and stiffness in the joints in the fingers and in the knees. Other signs and symptoms that develop over time include permanently bent fingers (camptodactyly), enlarged finger and knee joints (often mistaken as swelling), and a reduced amount of space between the bones at the hip and knee joints. Hip pain is a common problem by adolescence. Affected individuals have flattened bones in the spine (platyspondyly) that are abnormally shaped (beaked), which leads to an abnormal front-to-back curvature of the spine (kyphosis) and a short torso. At birth, people with PPRD are of normal length, but by adulthood, they are usually shorter than their peers. Affected adults also have abnormal deposits of calcium around the elbow, knee, and hip joints and limited movement in all joints, including those of the spine.
PPRD is often mistaken for another joint disorder that affects young people called juvenile rheumatoid arthritis. However, the joint problems in juvenile rheumatoid arthritis are associated with inflammation, while those in PPRD are not. It may initially be mistaken for juvenile rheumatoid arthritis, however people with this condition do not have the laboratory test results of juvenile rheumatoid arthritis.
- Stiff joints (contractures)
- Short stature
- Widening of the ends of the finger and toe bones as well as other tubular bones.
- Bony widening at the fingers' joints progresses leading to permanent bending of the fingers (camptodactyly)
- Spine involvement results in short trunk and hunching of the back (kyphosis)
- Abnormality of the hip bone
- Limitation of joint mobility
- Abnormal gait
- Hip anomalies
- Restricted joint mobility
- Abnormal vertebral size
PPD is caused by a mutation in the WISP3 gene and is inherited in an autosomal recessive pattern. The function of the protein produced from this gene is not well understood, although it is thought to play a role in bone growth and cartilage maintenance. The WISP3 protein is made in cells called chondrocytes, which produce and maintain cartilage. This protein is associated with the production of certain proteins that make up cartilage, but its role in their production is unclear. WISP3 may also help control signaling pathways involved in the development of cartilage and bone and may help regulate the breakdown of cartilage components.
WISP3 gene mutations lead to an altered protein that may not function. Loss of WISP3 protein function likely disrupts normal cartilage maintenance and bone growth, leading to the cartilage degeneration and joint problems that occur in PPRD.
There is still no cure. Treatment may include pain medication and hip and knee joint replacement surgery at an early age.
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