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Pseudoachondroplasia
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Pseudoachondroplasia

Pseudoachondroplasia is an inherited disorder of bone growth characterized by short stature and various skeletal abnormalities, distinct from achondroplasia.

Overview

Pseudoachondroplasia is an inherited disorder of bone growth. It was once thought to be related to another disorder of bone growth called achondroplasia, but without that disorder's characteristic facial features. More research has demonstrated that pseudoachondroplasia is a separate disorder.

All people with pseudoachondroplasia have short stature. The average height of adult males with this condition is 120 centimeters (3 feet, 11 inches), and the average height of adult females is 116 centimeters (3 feet, 9 inches). Individuals with pseudoachondroplasia are not unusually short at birth; by the age of two, their growth rate falls below the standard growth curve.

Other characteristic features of pseudoachondroplasia include short arms and legs; a waddling walk; joint pain in childhood that progresses to a joint disease known as osteoarthritis; an unusually large range of joint movement (hypermobility) in the hands, knees, and ankles; and a limited range of motion at the elbows and hips. Some people with pseudoachondroplasia have legs that turn outward or inward (valgus or varus deformity). Sometimes, one leg turns outward and the other inward, which is called windswept deformity. Some affected individuals have a spine that curves to the side (scoliosis) or an abnormally curved lower back (lordosis). People with pseudoachondroplasia have normal facial features, head size, and intelligence.

Frequency

The exact prevalence of pseudoachondroplasia is unknown; it is estimated to occur in 1 in 30,000 individuals.

Causes

Mutations in the COMPgene cause pseudoachondroplasia. This gene provides instructions for making a protein that is essential for the normal development of cartilage and for its conversion to bone. Cartilage is a tough, flexible tissue that makes up much of the skeleton during early development. Most cartilage is later converted to bone, except for the cartilage that continues to cover and protect the ends of bones and is present in the nose and external ears.

The COMP protein is normally found in the spaces between cartilage-forming cells called chondrocytes, where it interacts with other proteins. COMP gene mutations result in the production of an abnormal COMP protein that cannot be transported out of the cell. The abnormal protein builds up inside the chondrocyte and ultimately leads to early cell death. Early death of the chondrocytes prevents normal bone growth and causes the short stature and bone abnormalities seen in pseudoachondroplasia.

Learn more about the gene associated with Pseudoachondroplasia

  • COMP

Inheritance

Pseudoachondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

In some cases, an affected person inherits the mutation from an affected parent. Most cases result from de novo mutation in the gene and occur in people with no history of the disorder in their family.

Other Names for This Condition

  • PSACH
  • Pseudoachondroplastic dysplasia
  • Pseudoachondroplastic spondyloepiphyseal dysplasia syndrome

Frequently Asked Questions

major long-term complication is the early onset and progression of osteoarthritis, particularly in the hips and knees, leading to chronic joint pain and reduced mobility. Management often includes pain relief, physical therapy to maintain joint function, and sometimes surgical interventions like joint replacements to address severe osteoarthritis or correct significant limb deformities.
Yes, managing daily life often involves physical therapy to improve muscle strength and joint flexibility, occupational therapy for adaptive strategies, and pain management for joint discomfort. Regular, low-impact exercise is encouraged to maintain mobility without excessive joint stress. Avoiding activities that put undue strain on joints can help slow the progression of osteoarthritis.
Growth rate typically falls below the standard curve by age two, which is often when short stature becomes noticeable. Diagnosis usually involves a physical examination, X-rays to identify characteristic skeletal changes, and genetic testing to confirm mutations in the COMP gene.
Pseudoachondroplasia is inherited in an autosomal dominant pattern. This means only one copy of the altered COMP gene is needed to cause the condition. If a parent has pseudoachondroplasia, there is a 50% chance with each pregnancy that their child will also inherit the condition. Genetic counseling can provide detailed risk assessments and discuss family planning options.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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