Pseudoachondroplasia
A skeletal dysplasia causing short stature from COMP gene mutations.
Pseudoachondroplasia is an inherited disorder of bone growth, classified as an osteochondrodysplasia that results in mild to severely short stature due to inhibition of skeletal growth primarily in the limbs. It is a genetic autosomal dominant disorder linked to mutations in the COMP gene located on chromosome 19. The condition is generally not discovered until 2–3 years of age, as growth is normal at birth, and is typically first detected by a drop in linear growth, a waddling gait, or lower limb deformities.
Quick Facts
- Specialty
- Medical genetics
Facts from the source article.
Lore & Background
Pseudoachondroplasia is caused by a heterozygous mutation in the COMP gene, which encodes cartilage oligomeric matrix protein. This protein is an extracellular calcium-binding protein involved in chondrocyte migration and proliferation. In pseudoachondroplasia, COMP is not secreted but collects inside chondrocytes, ultimately poisoning and killing them, leading to significantly reduced growth in the limbs while the face and torso remain unaffected. Studies by Hecht et al. suggest that type IX collagen also accumulates within pseudoachondroplasia chondrocytes, indicating that pathogenesis involves interactions between mutant COMP gene products and specific cartilage components.
Reader's Guide
Pseudoachondroplasia is one of the most common skeletal dysplasias, affecting all racial groups, though precise incidence figures are not available. It is clinically and genetically distinct from achondroplasia, despite similarities in nomenclature. The condition is characterized by disproportionate short stature, lower limb deformities, short fingers, and ligamentous laxity, with normal intelligence and craniofacial features. Radiographic findings include rhizomelic limb shortening, epiphyseal-metaphyseal changes, oval vertebrae with anterior beaking, and normal widening of interpedicular distances (differentiating it from achondroplasia). The disorder is inherited in an autosomal dominant manner, with offspring of affected individuals at 50% risk of inheriting the mutant allele. Prenatal testing is available if the mutation is known in the family. The identification of the COMP gene in 1995 by a research team led by Dr. Jacqueline Hecht was a key milestone in understanding the molecular basis of this disorder.
Did You Know?
- Pseudoachondroplasia is caused by mutations in the COMP gene on chromosome 19, which encodes cartilage oligomeric matrix protein.
- Average adult height is about 120 cm for males and 116 cm for females.
- Plasma COMP levels are significantly reduced in patients, providing a reliable diagnostic method.
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