Embryology · Skeleton, muscles, limbs and skin
Achondroplasia (FGFR3) !
- Malformation
The most common cause of short stature with short limbs: an overactive gene slows the growth of cartilage in the long bones.
Updated 2026-11-01
See it in 3D: Humerus · Femur · Base of the skull · L4 vertebra · Spinal cord
What it is
Achondroplasia is the most common skeletal dysplasia, about 1 in 15,000 to 40,000 births. It is caused by a mutation that leaves the FGFR3 receptor overactive, which slows chondrocyte proliferation in the growth plate. It affects bones that ossify by the endochondral route: the limbs and the skull base. Intelligence is normal.
Embryological cause
- FGFR3 is a normal brake on cartilage growth; the gain-of-function mutation leaves it permanently switched on.
- Almost all cases are due to the same mutation (G380R) in the transmembrane domain.
- Autosomal dominant inheritance; about 80 % are new mutations, linked to advanced paternal age.
- It affects endochondral ossification (long bones, vertebrae, skull base); the membranous vault grows normally.
- Two mutant copies are usually lethal; other FGFR3 mutations cause thanatophoric dysplasia (lethal) and hypochondroplasia (mild).
Markers
- FGFR3
- G380R
- Autosomal dominant
How it presents
- Rhizomelic shortening: upper arms and thighs shorter than forearms and legs.
- Macrocephaly with frontal bossing and midface hypoplasia.
- Trident hand, marked lumbar lordosis and bowed legs.
- Narrow foramen magnum: risk of brainstem compression, apnoea and hydrocephalus in early childhood.
- In adults: lumbar spinal stenosis.
Diagnosis
- Third-trimester ultrasound: short femur with a large head; usually not visible before week 24.
- X-ray: characteristic pelvis and vertebrae, with the distance between pedicles narrowing downwards.
- Molecular testing of FGFR3 confirms the diagnosis.
Test yourself
Think of the answer, then tap the question to see it.
Which gene causes achondroplasia, and what does the mutation do?
FGFR3; the mutation makes it overactive and slows chondrocyte proliferation.
Why is the skull vault normal in achondroplasia?
Because it forms by intramembranous ossification, which does not depend on the cartilage growth plate.
Which early neurological complication is most feared?
Brainstem compression from a narrow foramen magnum, which can cause apnoea and hydrocephalus.
Which parental factor is linked to new FGFR3 mutations?
Advanced paternal age.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Skull: neurocranium, viscerocranium, sutures and fontanelles
- Limb development: the apical ectodermal ridge, ZPA and limb rotation
- Craniosynostosis
- Prenatal diagnosis: ultrasound, serum screening, cell-free DNA, CVS, amniocentesis
- Congenital hydrocephalus: aqueductal stenosis
- Vertebrae: resegmentation of the sclerotomes
Related conditions
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Achondroplasia: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Langman's Medical Embryology, 13th ed., ch. 10: The Axial Skeleton (Wolters Kluwer, 2015).
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Representative model, for educational purposes only.