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Achondroplasia
It is the most common form of short-limbed dwarfism, primarily affecting the long bones in the arms and legs. This condition is present from birth and impacts individuals across all populations.
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Overview
Achondroplasia is a genetic disorder characterised by abnormal bone growth, specifically affecting the growth plates in the long bones. This leads to significantly shortened arms and legs, a short stature, and certain distinctive facial features, such as a prominent forehead and a flattened nasal bridge [PMID:33679872]. Despite these physical characteristics, intelligence is typically unaffected in individuals with achondroplasia.
This condition is the most frequent cause of disproportionate short stature, where the trunk is of average length but the limbs are noticeably shorter. It is usually diagnosed at birth or shortly after, and while it presents with distinct physical traits, the overall health and wellbeing of affected individuals are typically managed through regular medical care and support [PMID:16220556]. The estimated prevalence of achondroplasia ranges from 1 in 15,000 to 1 in 40,000 live births.
Symptoms & clinical features
The primary clinical features of achondroplasia are evident from birth. Individuals typically have short stature, with an average adult height around 131 cm for males and 123 cm for females. The limbs, especially the upper arms and thighs, are disproportionately short compared to the trunk. Hands are often broad and short, with a characteristic separation between the ring and middle fingers, sometimes called a 'trident hand' [PMID:16220556].
Other common physical findings include a large head (macrocephaly) with a prominent forehead, a flattened bridge of the nose, and a common appearance of bowed legs (genu varum). Spinal curvature, such as lordosis (an inward curve in the lower back) and kyphosis (an outward curve in the upper back), can also develop. Some infants may experience episodes of apnoea (temporary cessation of breathing) due to a narrowed opening at the base of the skull, which can compress the brainstem [PMID:33679872].
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Affected organs
Achondroplasia primarily affects the skeletal system, particularly the development of bones that form from cartilage templates (endochondral ossification). This process is crucial for the growth of long bones, vertebrae, and the base of the skull. The abnormal bone growth impacts the long bones of the limbs, leading to their characteristic shortening.
Beyond the limbs, the spine can be affected, potentially leading to issues such as spinal stenosis (narrowing of the spinal canal) or kyphosis. The skull base can also be narrower than typical, which may cause compression of the brainstem or spinal cord at the foramen magnum. This can sometimes lead to breathing difficulties or other neurological symptoms in infants. Ear structures can also be impacted, increasing the risk of middle ear infections, which, if chronic, may lead to hearing difficulties.
Risks & severity
The severity of achondroplasia can vary, but it generally leads to a consistent pattern of physical features and associated health considerations. Complications can arise, particularly in infancy and early childhood. A significant risk in infants is compression of the brainstem at the base of the skull, which can cause central apnoea and may require surgical intervention. Hydrocephalus (excess fluid in the brain) can also occur, though it is often mild [PMID:33679872].
Throughout childhood and adulthood, individuals with achondroplasia are at increased risk for orthopaedic issues such as bowed legs, spinal stenosis (narrowing of the spinal canal), and recurring middle ear infections. Weight management is also an important consideration, as obesity can exacerbate spinal and joint problems. With appropriate medical management and monitoring, most individuals with achondroplasia lead full and productive lives, although life expectancy may be slightly reduced, primarily due to cardiovascular or respiratory complications [PMID:16220556].
Genetic causes
Achondroplasia is caused by pathogenic changes in the FGFR3 gene. This gene provides instructions for making a protein called fibroblast growth factor receptor 3. This protein plays a crucial role in regulating bone growth, particularly in cartilage cells (chondrocytes) that develop into bone [PMID:16220556].
The FGFR3 protein acts as a negative regulator of bone growth; it signals to slow down the proliferation and differentiation of cartilage cells. Pathogenic changes in FGFR3, specifically in achondroplasia, lead to the protein being overactive. This overactivity results in excessive suppression of cartilage growth, particularly in the long bones of the arms and legs, leading to their characteristic shortening [PMID:33679872]. The vast majority of individuals with achondroplasia have the same two common pathogenic variants in the FGFR3 gene.
- FGFR3 fibroblast growth factor receptor 3The FGFR3 gene provides instructions for making fibroblast growth factor receptor 3, a protein crucial for regulating cell growth, differentiation, and especially skeletal development.
Inheritance pattern
Achondroplasia is inherited in an autosomal dominant pattern. This means that only one copy of the altered FGFR3 gene is sufficient to cause the condition. In about 80% of cases, achondroplasia results from a new (de novo) pathogenic variant in the FGFR3 gene, meaning the variant occurred spontaneously and was not inherited from either parent [PMID:16220556]. In such instances, neither parent carries the pathogenic variant.
When one parent has achondroplasia, there is a 50% chance with each pregnancy that their child will inherit the pathogenic variant and therefore also have the condition. If both parents have achondroplasia, the inheritance pattern becomes more complex, with a 25% chance of the child having two copies of the pathogenic variant (homozygous achondroplasia), which is a much more severe and often life-limiting form of the condition. There is also a 50% chance of the child having one copy (heterozygous achondroplasia, like the parents) and a 25% chance of the child not having the condition.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
Diagnosis & testing
Achondroplasia can often be suspected before birth based on findings from prenatal ultrasound scans, which may show shortened limbs or other characteristic skeletal features. After birth, a clinical diagnosis is typically made based on the distinctive physical features. These include disproportionately short limbs, a large head with a prominent forehead, and a flattened nasal bridge.
Confirmation of achondroplasia is achieved through genetic testing, specifically looking for pathogenic variants in the FGFR3 gene. This testing can be performed using a blood sample and is available through the NHS Genomic Medicine Service (GMS) pathways. Referrals for genetic testing and counselling are typically made by paediatricians, orthopaedic specialists, or clinical geneticists. The relevant NHS National Genomic Test Directory R-code for testing achondroplasia is R99.
Management & lifestyle
Management for individuals with achondroplasia is focused on monitoring growth and development, addressing potential complications, and providing supportive care. Regular check-ups with a multidisciplinary team, which may include paediatricians, orthopaedic surgeons, neurologists, and genetic counsellors, are important. Monitoring for complications such as spinal cord compression, hydrocephalus, and middle ear infections is crucial, particularly in infancy and early childhood.
Orthopaedic interventions, such as surgical correction for bowed legs or spinal issues, may be considered if necessary. Physical therapy can also help improve mobility and strength. Growth hormone treatment is generally not effective for increasing final height in achondroplasia, although some emerging treatments are being researched. Lifestyle considerations include maintaining a healthy weight to reduce stress on joints and the spine, and adapting the home and workplace environment for better accessibility.
UK care pathway
In the UK, individuals with suspected achondroplasia are typically referred to clinical genetics services or specialist paediatric clinics within the NHS. Genetic counselling is an integral part of this pathway, providing information about the condition, inheritance patterns, and reproductive options. Genetic testing for achondroplasia, looking for pathogenic variants in the FGFR3 gene, is available through the NHS Genomic Medicine Service (GMS). The testing is typically initiated by a clinician using the National Genomic Test Directory R-code R99.
Following diagnosis, care is usually coordinated by a paediatrician, often in collaboration with a specialist multidisciplinary team. This team may include orthopaedic surgeons, neurosurgeons, audiologists, and physiotherapists to address the various aspects of the condition. Genetic counsellors remain a key resource for families throughout the individual's life.
Frequently asked questions
Will my child's intelligence be affected by achondroplasia?
No, intelligence is typically unaffected in individuals with achondroplasia. They generally have normal cognitive development and intellectual abilities.
Is achondroplasia always inherited from a parent?
No, in about 80% of cases, achondroplasia is caused by a new genetic change (de novo variant) that occurs spontaneously and is not inherited from either parent. In the remaining cases, it can be inherited from a parent who also has the condition.
Are there treatments to make children with achondroplasia grow taller?
While growth hormone therapy is not generally effective for increasing final height in achondroplasia, some newer treatments are being developed and researched. Management focuses on addressing complications and supporting overall health.
What health problems should we look out for in a child with achondroplasia?
Key concerns include potential breathing difficulties in infants due to a narrow skull opening, hydrocephalus, recurrent ear infections, and orthopaedic issues like bowed legs and spinal problems. Regular medical check-ups help monitor for these.
How is achondroplasia diagnosed in the UK?
Achondroplasia can be suspected during prenatal ultrasound or diagnosed clinically at birth. Genetic testing for the FGFR3 gene confirms the diagnosis and is available through the NHS Genomic Medicine Service following a referral from a specialist clinician.
References
- Pauli RM. Achondroplasia: a comprehensive clinical review. Orphanet journal of rare diseases. 2019. PMID: 30606190
- Leiva-Gea A, Martos Lirio MF, Barreda Bonis AC. Achondroplasia: Update on diagnosis, follow-up and treatment. Anales de pediatria. 2022. PMID: 36347803
- Savarirayan R, Hoover-Fong J, Yap P. New treatments for children with achondroplasia. The Lancet. Child & adolescent health. 2024. PMID: 38485412
- Savarirayan R, Ireland P, Irving M. International Consensus Statement on the diagnosis, multidisciplinary management and lifelong care of individuals with achondroplasia. Nature reviews. Endocrinology. 2022. PMID: 34837063
- Hoover-Fong J, Scott CI, Jones MC. Health Supervision for People With Achondroplasia. Pediatrics. 2020. PMID: 32457214
- Murton MC, Drane ELA, Goff-Leggett DM. Burden and Treatment of Achondroplasia: A Systematic Literature Review. Advances in therapy. 2023. PMID: 37382866
- Merchant N, Hoover-Fong J, Carroll RS. Approach to the Patient with Achondroplasia-New Considerations for Diagnosis, Management, and Treatment. The Journal of clinical endocrinology and metabolism. 2025. PMID: 39813116
- Adam MP, Bick S, Mirzaa GM. Achondroplasia. 1993. PMID: 20301331