Achondroplasia – Causes, Symptoms and Treatment
Achondroplasia is the most common form of dwarfism, caused by a mutation in the FGFR3 gene. It leads to shortened limbs with a normal-sized trunk and is the most frequent genetic skeletal dysplasia worldwide.
Things worth knowing about "Achondroplasia"
Achondroplasia is the most common form of dwarfism, caused by a mutation in the FGFR3 gene. It leads to shortened limbs with a normal-sized trunk and is the most frequent genetic skeletal dysplasia worldwide.
What is Achondroplasia?
Achondroplasia is the most common genetic cause of short stature (dwarfism) and belongs to a group of conditions known as skeletal dysplasias – disorders that affect normal bone development. The name derives from Greek and roughly translates to "without cartilage formation." The condition affects the conversion of cartilage into bone (ossification), resulting primarily in shortened long bones of the arms and legs, while the trunk remains relatively normal in size.
Causes and Genetics
Achondroplasia is caused by a mutation in the FGFR3 gene (Fibroblast Growth Factor Receptor 3), which plays a key role in regulating bone growth. The mutation causes the FGFR3 receptor to be permanently overactive, which abnormally inhibits bone growth.
- In approximately 80% of cases, the mutation occurs spontaneously (de novo), meaning neither parent is affected.
- In approximately 20% of cases, it is inherited in an autosomal dominant pattern: one affected parent has a 50% chance of passing the mutation to each child.
- If both parents have achondroplasia, there is a 25% chance the child will inherit two copies of the mutation, resulting in homozygous achondroplasia, which is not compatible with life.
Symptoms and Clinical Features
The features of achondroplasia are distinctive and typically recognizable at birth:
- Short stature: Average adult height of approximately 120–130 cm
- Rhizomelic shortening: Disproportionate shortening of the proximal limb segments (upper arms and thighs)
- Large head circumference (macrocephaly) with a prominent forehead
- Midface hypoplasia: Flat nasal bridge and underdeveloped midface
- Trident hand: Characteristic spacing of the fingers into a trident-like shape
- Lumbar lordosis: Exaggerated inward curvature of the lower spine
- Normal intelligence and life expectancy in uncomplicated cases
Possible Complications
Although people with achondroplasia generally have normal intelligence and life expectancy, various complications can arise:
- Spinal stenosis: Narrowing of the spinal canal, which can cause nerve pain or weakness
- Foramen magnum stenosis: Narrowing of the opening at the base of the skull, particularly dangerous in infancy
- Sleep apnea: Breathing interruptions during sleep due to anatomical features
- Recurrent ear infections and hearing loss due to altered anatomical structures
- Hydrocephalus: Increased fluid pressure in the skull (rare)
Diagnosis
Achondroplasia can be diagnosed before birth or shortly after:
- Prenatal diagnosis: Ultrasound from around week 24–28 of pregnancy can reveal shortened limbs; genetic testing (amniocentesis, chorionic villus sampling) can confirm the FGFR3 mutation.
- After birth: Clinical examination and characteristic appearance, skeletal X-rays, and a genetic blood test to confirm the FGFR3 mutation.
Treatment and Management
There is currently no cure for achondroplasia. Treatment focuses on managing complications and improving quality of life.
Medical Therapy
Since 2021, vosoritide (Voxzogo) has been approved in the EU – a C-type natriuretic peptide (CNP) analogue that counteracts the overactive FGFR3 receptor and promotes bone growth in children. It is administered as a daily subcutaneous injection and has been shown to significantly increase growth velocity.
Surgical Interventions
- Decompression surgery for spinal canal stenosis or foramen magnum stenosis
- Limb lengthening surgery: A controversial procedure to surgically extend the limbs
Supportive Therapies
- Physical therapy to strengthen muscles and improve posture
- Occupational therapy to support daily living skills
- Regular orthopedic and neurological monitoring
- ENT care for ear and hearing issues
Living with Achondroplasia
People with achondroplasia typically lead full, independent lives. Adaptations such as accessible housing, modified vehicles, and ergonomic aids can significantly enhance independence. Support organizations like Little People of America (LPA) provide valuable community and resources.
References
- Ornitz DM, Legeai-Mallet L. Achondroplasia: Development, pathogenesis, and therapy. Developmental Dynamics. 2017;246(4):291–309.
- Hoover-Fong J et al. Lifetime impact of achondroplasia: Current evidence and perspectives on the natural history. Bone. 2021;146:115872.
- European Medicines Agency (EMA). Voxzogo (vosoritide) – Summary of product characteristics. EMA, 2021. Available at: https://www.ema.europa.eu
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