Pseudoachondroplasia

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

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 (hyperextensibility) 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.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the COMP gene 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.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

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 one affected parent. Most cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Disproportionate short-limb short stature · Very frequent (99-80%)

A type of disproportionate short stature characterized by a short limbs but an average-sized trunk.

Joint hypermobility · Very frequent (99-80%)

The capability that a joint (or a group of joints) has to move, passively and/or actively, beyond normal limits along physiological axes.

Abnormal form of the vertebral bodies · Frequent (79-30%)

Abnormal form of vertebral body, which is the central cylindrical portion of the vertebra that together with other structures such as the vertebral arch, pedicles, laminae, spinous process, transverse processes, and articular facets makes up a vertebra.

Arthralgia · Frequent (79-30%)

Joint pain.

Brachydactyly · Frequent (79-30%)

Digits that appear disproportionately short compared to the hand/foot. The word brachydactyly is used here to describe a series distinct patterns of shortened digits (brachydactyly types A-E). This is the sense used here.

Distal joint hypermobility · Frequent (79-30%)

Lack of stability of a distal joint (e.g., finger).

Generalized joint hypermobility · Frequent (79-30%)

Joint hypermobility (ability of a joint to move beyond its normal range of motion) affecting many or all joints of the body. In individuals with Joint hypermobility at multiple sites (usually five or more), the term generalized joint hypermobility is preferred.

Irregular epiphyses · Frequent (79-30%)

An alteration of the normally smooth contour of the epiphysis leading to an irregular appearance.

Knee joint hypermobility · Frequent (79-30%)

The ability of the knee to move past its normal range of motion, (knee hyperextension is greater than 10 degrees).

Limb undergrowth · Frequent (79-30%)

Limb shortening because of underdevelopment of one or more bones of the extremities.

Lumbar hyperlordosis · Frequent (79-30%)

An abnormal accentuation of the inward curvature of the spine in the lumbar region.

Metaphyseal irregularity · Frequent (79-30%)

Irregularity of the normally smooth surface of the metaphyses.

Metaphyseal widening · Frequent (79-30%)

Abnormal widening of the metaphyseal regions of long bones.

Osteoarthritis · Frequent (79-30%)

Degeneration (wear and tear) of articular cartilage, i.e., of the joint surface. Joint degeneration may be accompanied by osteophytes (bone overgrowth), narrowing of the joint space, regions of sclerosis at the joint surface, or joint deformity.

Other findings in the same source

From: Orphanet

Additional reported features include Platyspondyly (Frequent (79-30%)); Short long bone (Frequent (79-30%)); Short phalanx of finger (Frequent (79-30%)); Shortening of all metacarpals (Frequent (79-30%)); Waddling gait (Frequent (79-30%)); Wind-swept deformity of the knees (Frequent (79-30%)); Delayed epiphyseal ossification (Frequent (79-30%)); Increased laxity of fingers (Frequent (79-30%)); Abnormality of femoral epiphysis (Occasional (29-5%)); Acetabular dysplasia (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Pseudoachondroplasia is Orthopaedics, with a orthopaedic specialist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• What explains the change in pain, movement or function?
• Which activities need adjustment while the diagnosis is being clarified?
• What are the roles of rehabilitation, observation and surgery in this situation?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Pseudoachondroplasia. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.