Pseudoachondroplasia

Disease Overview

Summary

Pseudoachondroplasia (PSACH) is a type of short-limbed dwarfism characterized by disproportionate short stature, normal facial features and head size, and early onset osteoarthritis; intelligence is normal. There is marked laxity in the fingers, wrists, elbows and knees. Joint pain is common at all ages; osteoarthritis occurs in early adulthood and affects all the joints. Scoliosis or abnormal curvature of the spine and cervical spine instability are complications. Pseudoachondroplasia is caused by a change (variant) in the COMP gene and follows an autosomal dominant pattern of inheritance. Thirty percent of affected people have an affected parent and 70% of affected people have a random, new (de novo) variant in COMP with no previous family history.

Introduction

Pseudoachondroplasia was first described in 1959 by Drs. Maroteaux and Lamy and was originally considered to be a type of spondyloepiphyseal dysplasia. In the newest classification for skeletal dysplasia it is classified under the  group “pseudoachondroplasia and the multiple epiphyseal dysplasias” as COMP-related pseudoachondroplasia.

The COMP-related skeletal dysplasias include pseudoachondroplasia and multiple epiphyseal dysplasia type 1.

In the past, pseudoachondroplasia was divided into four different types based on severity and inheritance pattern but now, pseudoachondroplasia is known to be a single, distinct disorder caused by variants in the COMP gene.

COMP-PSACH was referred to as pseudoachondroplastic dysplasia in older medical literature.

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Synonyms

• PSACH
• COMP-related pseudoachondroplasia
• pseudoachondroplastic dysplasia (formerly)
• pseudoachondroplastic dysplasia
• pseudoachondroplastic spondyloepiphyseal dysplasia

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Signs & Symptoms

The signs and symptoms and severity of pseudoachondroplasia (PSACH) can vary even among members of the same family.

Babies with PSACH look completely normal at birth with normal weight and length, so the condition may not be noticed at first.

The most common early signs and symptoms include:

• Slowed growth that starts between 9 and 12 months of age first affecting body length and then height
  • Children with PSACH usually fall behind the average growth curve by about two years
• Disproportionate short stature (short height where the arms and legs are shorter than the torso) that becomes more noticeable as a child gets older
• Abnormal walking
  • Children typically start walking between 12 to 18 months, but their walk may look different, and it is often described as “waddling” due to problems with how the hip bones are formed
• Face that looks slightly angular but without any major facial differences
• Arm and leg problems (usually noticeable by ages 3–5)
  • Arms and legs are shortened especially compared to the body
  • Hands and toes are very short and may have extra skin folds
  • Loose joints (joint laxity) meaning that the joints are very flexible
    • Loose knee joints may result in:
      • Bowed legs (knees bend outward) called genu varum
      • Knock knees (knees angle inward) called genu valgum
      • Windswept deformity where one leg bows outward and the other angles inward
  • Elbow that does not fully straighten which is the opposite of the looseness seen in other joint
• Spinal problems are common and may include:
  • An S-shaped curve in the spine (scoliosis)
  • An exaggerated inward curve in the lower back (lumbar lordosis)
  • A rounded upper back or “hunchback” appearance (kyphosis)
  • Underdevelopment of a small bone in the upper spine (odontoid hypoplasia) that can cause:
    • Neck instability
    • Higher risk of spinal cord injury (cervical myelopathy)
      • If this happens, surgery to fuse the top of the spine may be required
• Pain that can start in early childhood and often worsens with exercise or activity
  • Early joint pain may be due to inflammation from problems in the cartilage-forming cells (chondrocytes)
• A type of joint wear and tear (osteoarthritis) that usually starts in early adulthood
  • Leads to chronic joint pain (arthralgia) especially in the hips, ankles, shoulders, elbows and wrists
  • Joint damage tends to get worse over time (degenerative joint disease) and may eventually require surgery often starting with hip replacements and followed by replacements in other joints as needed
• Short stature with an average adult height about 3’8” (116 cm) for females and about 3’9” (120 cm) for males with some individuals reaching up to 4’10”

Intelligence is normal and life expectancy is not affected. Most people with pseudoachondroplasia lead active, fulfilling lives, raise families and work in many different careers.

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Causes

Pseudoachondroplasia is caused by changes (variants) in the COMP gene. Genes provide instructions for creating proteins that play critical roles in many functions of the body. When a gene variant occurs, the protein product may be faulty, inefficient, or absent. Depending upon the functions of the protein, this can affect many organ systems of the body. COMP gene variants specifically affect chondrocytes in the growth centers which are the cells that specify for linear growth. The articular cartilage at the ends of all the long bones also contains chondrocytes and is easily eroded causing osteoarthritis and painful joints.

Pseudoachondroplasia follows autosomal dominant inheritance. Dominant genetic disorders occur when only a single copy of a disease-causing gene variant is necessary to cause the disease. The gene variant can be inherited from either parent or can be the result of a new (de novo) changed gene in the affected individual that is not inherited. The risk of passing the gene variant from an affected parent to a child is 50% for each pregnancy. The risk is the same for males and females.

Thirty percent of affected people have an affected parent and 70% of affected people have a random, new (de novo) variant in COMP with no previous family history.

Recurrence was reported in a few families in what appeared to be autosomal recessive inheritance. These cases were the result of parental germline mosaicism for a COMP variant. Parental germline mosaicism refers to a situation where a gene variant is present in some of a parent’s sperm or egg cells, but not in other cells of their body. This means a parent may not be affected by a genetic condition, but can still pass on the variant to their child, who may then be affected  As a result, one or more of the parent’s children may inherit the germline COMP variant, leading to pseudoachondroplasia, while the parent does not have this disorder because the variant is not present in sufficient number of body cells. The likelihood of a parent passing on a mosaic germline variant to a child depends upon the percentage of the parent’s germ cells that have the variant. There is no test for germline variants prior to pregnancy. Testing during a pregnancy for familial cases with a known variant is commercially available and should be discussed with a genetic specialist.

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Affected populations

The exact birth prevalence of pseudoachondroplasia is unknown but estimated vary from 1 in 30,000 to 1 in 100,000. Males and females are equally affected.

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Disorders with Similar Symptoms

Symptoms of the following skeletal dysplasia disorders can be similar to those of pseudoachondroplasia and are considered in the differential diagnosis.

Clinical exams, X-rays and genetic testing may help differentiate these disorders.

Achondroplasia is the most common skeletal dysplasia, similarly to PSACH, and is characterized by short stature, joint issues and spine abnormalities. However, head and facial differences are very prominent in achondroplasia. These include a large head (macrocephaly), a flat nasal bridge and a bulging forehead (frontal bossing). These are not seen in PSACH. Limb shortening in achondroplasia affects the upper parts of the arms and legs more, trident hands (where the fingers spread in a three-pronged shape) are common in achondroplasia but not in PSACH. Both conditions may have joint stiffness and spinal curvature, but spinal narrowing (stenosis) is more frequent and more severe in achondroplasia.

Multiple epiphyseal dysplasia (MED), a group of disorders that, like PSACH, affects the growth centers (epiphyses) of bones as early-onset hip and knee pain, waddling gait and joint deformities. There are two main types of MED:

• Autosomal dominant MED which can also be caused by variants in the COMP Differently from PSACH, stature is typically only mildly short or in the low-normal range, spinal X-rays are usually normal in AD MED, while PSACH commonly involves spinal abnormalities like scoliosis or kyphosis, arthritis tends to start later and is generally milder in AD MED and PSACH is typically more severe overall in both joint damage and height impact
• Autosomal recessive MED (AR MED), which includes joint pain in hips and knees, skeletal abnormalities of hands, feet, and knees and scoliosis. Differently from PSACH, pain and joint issues often begin later in childhood, stature usually remains within the normal range until puberty and is only slightly reduced in adulthood (150–180 cm) and about half of individuals with AR MED show symptoms at birth (like clubfoot or unusual finger shapes), which are not seen in PSACH, and functional ability is often better preserved in AR MED.

Spondyloepimetaphyseal dysplasias (SEMD) are a group of skeletal conditions that involve abnormalities in the spine (spondylo), ends of the bones (epiphyseal) and the growing part of the bone shaft (metaphyseal). These can look similar to PSACH on X-rays, especially in severe cases.

There are also advanced tools like the dREAMS database that help specialists compare radiographic features of different skeletal dysplasias.

 

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Diagnosis

The diagnosis of pseudoachondroplasia is based upon identification of characteristic clinical and radiographic findings, detailed patient history and genetic testing. The diagnosis is rarely made at birth because short stature is not present. The distinctive features develop over time, and this sets it apart from other short stature conditions.

A complete set of X-rays (radiographs) establishes the diagnosis by revealing abnormal growth centers (epiphyses) and other characteristic skeletal findings. The diagnosis is made clinically and by radiographs. More advanced imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT) scans can be used later to assess skeletal health, particularly before surgery to correct skeletal malformations.

Genetic testing identifying a COMP gene variant can confirm the diagnosis.

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Standard Therapies

Treatment
There is no cure for COMP-PSACH. Management focuses on supportive care to improve quality of life, maintain function and prevent complications. A multidisciplinary team approach is recommended. The team includes geneticists, pediatricians, specialists in treating skeletal disorders (orthopedic surgeons), neurologists, physical and occupational therapists and other healthcare professionals who will systematically and comprehensively plan needed treatments.

After the diagnosis of pseudoachondroplasia, a thorough initial evaluation is important to understand the extent of the disease and guide care planning.

Recommended assessments include measuring height and plotting it on PSACH-specific growth chart. Skeletal evaluations should cover joint laxity, arthritis and structural abnormalities. A skeletal survey with specific views of the hips, knees, hands and spine is typically done.

Because cervical spine instability is a serious risk, affected people, especially those showing neurological symptoms, should have flexion/extension X-rays or MRI of the cervical spine.

Genetic counseling is recommended to help families understand the genetics and natural history of pseudoachondroplasia and to provide psychosocial support.

Depending on the specific symptoms, treatment may include the following:

• For joint pain, analgesics may be used, though no formal studies confirm which pain medication is the most effective.
• Physical activities are encouraged but should be chosen carefully to avoid worsening joint degeneration, since cartilage is often severely compromised in affected individuals.
• Osteotomies are frequently required during childhood to correct lower limb misalignment, and revisions may be needed later due to joint instability.
• Scoliosis rarely requires surgery but when it is severe, surgical correction can be effective.
• People presenting with odontoid hypoplasia and signs of cervical spine instability or spinal cord compression may need C1-C2 fixation to stabilize the spine.
• Total hip replacement surgery (total hip arthroplasty) is done for more than 50% of individuals.
• Extended limb lengthening has been attempted in a few people, but outcomes are uncertain, and the procedure is rarely performed.
• Emotional and social challenges related to short stature, including stigmatization and discrimination, should not be overlooked.
• Ongoing monitoring is important throughout childhood and beyond. Height should be measured regularly and tracked on a PSACH growth chart. Orthopedic assessments should be conducted at least annually to monitor joint mobility, limb alignment, scoliosis, and signs of joint degeneration. Radiographs of the spine or joints should be done as needed.
• Neurological checks are also essential, particularly in young children, to look for signs of spinal cord compression. Imaging the cervical spine (via X-ray or MRI) should be done if symptoms suggest instability. In addition, psychosocial assessments should be done routinely to identify and address any issues related to self-esteem, social challenges, or discrimination.
• People with PSACH who have odontoid hypoplasia should avoid activities that involve extreme flexion or extension of the neck due to the risk of spinal cord injury.

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Clinical Trials and Studies

There was one clinical trial designed to test the efficacy of resveratrol, an antioxidant, in adults with pseudoachondroplasia. The study was terminated because they did not find enough participants. In a mouse model of pseudoachondroplasia, resveratrol has been shown to decrease inflammation, restore some long bone growth and likely decrease pain.

A case report described a five-year-old child with pseudoachondroplasia who had less joint pain after taking two over-the-counter supplements: CurQ+ and resveratrol. Before starting the supplements, the child had trouble walking to school because of joint pain. After taking them, they could walk without help or complaints. These results are encouraging, but more research is needed to see if the supplements are safe and effective for other children with pseudoachondroplasia.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: [email protected]

Some current clinical trials also are posted on the following page on the NORD website:
https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/

For information about clinical trials sponsored by private sources, contact: www.centerwatch.com

For information about clinical trials conducted in Europe, contact: https://www.clinicaltrialsregister.eu/

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References

TEXTBOOKS
Jones KL, Jones MC, del Campo Casanelles. Eds. Pseudoachondroplasia. In: Smith’s Recognizable Patterns of Human Malformation. 7th ed. Elsevier Saunders, Philadelphia, PA; 2013:464-465.

JOURNAL ARTICLES
Hecht JT, Barreda-Bonis AC, Posey KL. CurQ+ With Resveratrol Diminish Joint Pain in a Child With Pseudoachondroplasia: A Case Report. Cureus. 2025;17(3):e81195. Published 2025 Mar 25. doi:10.7759/cureus.81195

Posey KL, Coustry F, Hecht JT. Cartilage oligomeric matrix protein: COMPopathies and beyond. Matrix Biol. 2018 Oct;71-72:161-173. doi: 10.1016/j.matbio.2018.02.023. Epub 2018 Mar 9.PMID: 29530484 https://pubmed.ncbi.nlm.nih.gov/29530484/

Posey KL, Hecht JT. Novel therapeutic interventions for pseudoachondroplasia. Bone. 2017 Sep;102:60-68. doi: 10.1016/j.bone.2017.03.045. Epub 2017 Mar 21.PMID: 28336490 https://www.sciencedirect.com/science/article/abs/pii/S8756328217301151

Posey KL, Alcorn JL, Hecht JT. Pseudoachondroplasia/COMP – translating from the bench to bedside. Matrix Biol. 2014;37C:167-173. https://www.ncbi.nlm.nih.gov/pubmed/24892720

Jackson GC, Mittaz-Crettol L, Taylor JA, et al. Pseudoachondroplasia and multiple epiphyseal dysplasia: a 7-year comprehensive analysis of the known disease genes identify novel and recurrent mutations and provides an accurate assessment of their relative contribution. Hum Mutat. 2012;33:144-157. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3272220/

Li QW, Song HR, Mahajan RH, Suh SW, Lee SH. Deformity correction with external fixator in pseudoachondroplasia. Clin Orthop Relat Res. 2007;454:174-179. https://www.ncbi.nlm.nih.gov/pubmed/16957646

Kennedy J, Jackson G, Ramsden S, et al. COMP mutation screening as an aid for the clinical diagnosis and counseling of patients with a suspected diagnosis of pseudoachondroplasia or multiple epiphyseal dysplasia. Eur J Hum Genet. 2005;13:547-555. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2673054/

INTERNET
Briggs MD, Wright MJ. COMP-Related Pseudoachondroplasia. 2004 Aug 20 [Updated 2023 Nov 30]. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1487/ Accessed May 21, 2025.

Pseudoachondroplasia. Orphanet.Nov 2008. https://www.orpha.net/en/disease/detail/750?name=Pseudoachondroplasia&mode=name  Accessed May 21, 2025.

McKusick VA., ed. Online Mendelian Inheritance in Man (OMIM). Baltimore. MD: The Johns Hopkins University; Entry No:177170; Last Update: 01/09/2024. Available at :https://omim.org/entry/177170 Accessed May 21, 2025.

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Patient Organizations

Human Growth Foundation

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Related Rare Diseases: Recessive Multiple Epiphyseal Dysplasia, Schimke Immuno-Osseous Dysplasia, Pseudoachondroplasia, ...

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Restricted Growth Association

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Related Rare Diseases: Spondylothoracic Dysplasia, Recessive Multiple Epiphyseal Dysplasia, Pseudoachondroplasia, ...

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More Information

The information provided on this page is for informational purposes only. The National Organization for Rare Disorders (NORD) does not endorse the information presented. The content has been gathered in partnership with the MONDO Disease Ontology. Please consult with a healthcare professional for medical advice and treatment.

GARD Disease Summary

The Genetic and Rare Diseases Information Center (GARD) has information and resources for patients, caregivers, and families that may be helpful before and after diagnosis of this condition. GARD is a program of the National Center for Advancing Translational Sciences (NCATS), part of the National Institutes of Health (NIH).

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Orphanet

Orphanet has a summary about this condition that may include information on the diagnosis, care, and treatment as well as other resources. Some of the information and resources are available in languages other than English. The summary may include medical terms, so we encourage you to share and discuss this information with your doctor. Orphanet is the French National Institute for Health and Medical Research and the Health Programme of the European Union.

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OMIM

Online Mendelian Inheritance In Man (OMIM) has a summary of published research about this condition and includes references from the medical literature. The summary contains medical and scientific terms, so we encourage you to share and discuss this information with your doctor. OMIM is authored and edited at the McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine.

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