Define Achondroplasia. Describe its clinical features, management, pathophysiology and prognosis.

Definition

• Achondroplasia is the commonest skeletal dysplasia causing disproportionate short stature.
• It is autosomal dominant (most cases are new mutations, linked to advanced paternal age) due to a FGFR3 gene mutation affecting endochondral bone growth.

Clinical Features

• Rhizomelic (proximal) short limbs with a relatively normal trunk length.
• Large head with frontal bossing and a depressed nasal bridge; 'trident' hand.
• Lumbar lordosis, and normal intelligence.

Complications & Management

• Foramen magnum stenosis (risk of cord compression/apnoea), hydrocephalus, spinal stenosis, and obstructive sleep apnoea.
• Supportive/multidisciplinary care; monitor for neurological complications; genetic counselling (50% risk to offspring).

Pathophysiology

An activating FGFR3 mutation inhibits chondrocyte proliferation at the growth plate, impairing endochondral ossification (long bones) while membranous ossification (skull vault) is relatively preserved — hence short limbs with a large head.

Management Detail

• Monitor head circumference and neurology in infancy; polysomnography if sleep apnoea suspected.
• Address spinal stenosis in later childhood/adulthood; psychosocial support; emerging targeted therapies.

Genetics & Counselling

• Achondroplasia is autosomal dominant with a 50% risk to offspring; two affected parents risk a lethal homozygous form.
• Most cases are de novo mutations associated with advanced paternal age.

Prognosis

With normal intelligence and appropriate management of complications (foramen magnum/spinal stenosis, sleep apnoea), individuals with achondroplasia have a near-normal life expectancy and can lead independent lives.