Pseudoachondroplasia

Pseudoachondroplasia (PSACH) is a rare skeletal dysplasia characterized by disproportionate short stature, joint laxity, and early-onset osteoarthritis. It is sometimes referred to as pseudoachondroplastic dysplasia or pseudoachondroplastic spondyloepiphyseal dysplasia. Unlike achondroplasia, individuals with pseudoachondroplasia have normal facial features and head size. The condition is caused by mutations in the COMP (cartilage oligomeric matrix protein) gene located on chromosome 19p13.1, which encodes a protein essential for normal cartilage and bone development. The disease is typically not apparent at birth, with affected children appearing normal in length and proportions. Short stature and limb shortening usually become noticeable around age 2 to 3 years, when the child begins walking and growth deceleration becomes evident. Key skeletal features include short limbs (particularly the proximal segments), a waddling gait, lumbar lordosis (exaggerated inward curvature of the lower back), brachydactyly (short fingers), and generalized joint hypermobility, particularly at the knees and fingers. Windswept deformity of the legs (valgus or varus angulation at the knees) is common. Spinal abnormalities may include platyspondyly (flattened vertebral bodies) and anterior beaking of vertebrae. Adult height typically ranges from approximately 82 to 130 cm (about 2.7 to 4.3 feet). Early-onset osteoarthritis, particularly affecting the hips and knees, is a significant source of morbidity and pain, often requiring joint replacement surgery in adulthood. There is currently no cure or disease-modifying therapy for pseudoachondroplasia. Management is supportive and multidisciplinary, focusing on orthopedic surveillance and intervention. Treatment may include surgical correction of lower limb malalignment, management of spinal complications, physical therapy to maintain joint function and muscle strength, and pain management for osteoarthritis. Limb-lengthening procedures may be considered in some cases. Regular monitoring by an orthopedic specialist experienced in skeletal dysplasias is recommended throughout life. Genetic counseling is important for affected individuals and their families.

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