Pseudoachondroplasia is a type of skeletal dysplasia occurring due to mutations in the cartilage oligomeric matrix protein (COMP) gene, resulting in the appearance of a short stature, extensive laxity of the joints and ligaments, and an early onset of degenerative arthritis. A comprehensive clinical and radiologic workup is necessary in order to distinguish between several disorders presenting with similar symptoms, and genetic studies are required to confirm the diagnosis.
Signs and symptoms of pseudoachondroplasia (PSACH) arise because of mutations in the COMP gene that codes for a family of proteins essential for numerous physiological processes in the extracellular matrix of chondrocytes and other soft tissue cells . These mutations lead to premature death of chondrocytes during bone growth, resulting in the transformation of cartilage into bone and subsequent impairment in musculoskeletal growth . Unlike many disorders of insufficient growth in which symptoms present from birth, pseudoachondroplasia (PSACH) is distinguished by a slightly delayed onset of symptoms, as newborns and infants suffering from this condition do not exhibit any signs until early childhood  . Short stature, often severe enough to be termed dwarfism, appears during the second year of life, along with various musculoskeletal abnormalities   . Deceleration of linear growth, lower extremity bowing and a waddling gait, all lead to rhizomelic dwarfism, while the adult heights range between 82-130 cm with shortening of limbs   . In addition, joint changes include profound laxity, pain and a significant reduction in mobility due to osteoarthritis, a cardinal feature of PSACH that affects all joints, particularly the shoulders, elbows, and hips . In fact, severe joint pain and degenerative osteoarthritis in PSACH frequently require hip replacement . Brachydactyly, a knock knee, lumbar lordosis, scoliosis, ulnar deviation of the hands are other notable signs of this genetic disease  . Normal head circumference and size, the absence of facial changes and preserved mental growth are important characteristics of PSACH, as craniofacial and intellectual abnormalities are more common in other similar disorders (for eg. achondroplasia)  .
The diagnosis of PSACH is difficult to make at birth and during infancy due to the absence of typical features, but when signs of short stature and accompanying joint-related symptoms appear, a detailed workup is necessary to determine the underlying cause . Firstly, a thorough patient history is necessary, primarily to assess the appearance of symptoms and their course. A family history, however, may be vital, as autosomal dominant (but also recessive) patterns of inheritance have been assumed, but because many mutations arise de novo (sporadically), the absence of a positive family history should not rule out PSACH from the differential diagnosis  . Physical examination of the child can provide sufficient details to form valid clinical suspicion, in which case radiographic studies should be advised. Plain radiography of all bones in the body must be carried out, as prominent shortening of the proximal segments of long bones (the humerus and femur are predominantly affected), flared and irregular metaphyses, flattened femoral heads, incomplete formation of the acetabulum, a widened pubic symphysis, kyphoscoliosis and a normal radiography of the skull are notable features on X-ray  . When clinical and radiologic findings point to PSACH as a probable cause, genetic studies are indicated, when mutations in the COMP gene, mapped on chromosome 4q35, are identified through molecular analysis  .