Etiology:- Activating mutation in fibroblast growth factor receptor 3 gene (FGFR3) → inhibited chondrocyte proliferation → reduced endochondral ossification- New mutations in ∼80% of cases; autosomal dominant inheritance in ∼20% of cases (homozygosity is lethal)

Epidemiology:- Most common type of skeletal dysplasia and disproportionate short stature - The probability of new mutations increases with the father's age at the time of conception.

Clinical features:- Short stature: average standing height of 131 cm in males or 124 cm in females- Average-sized torso; short, plump extremities- Macrocephaly, prominent brow, midface retrusion, flattening of the nose- Normal intelligence

Diagnostics: X-ray- Lateral skull: midface hypoplasia, frontal prominence- Spine: abnormally narrow interpedicular distance → spinal canal stenosis; scoliosis- Extremities: bones are short and broad; short fingers

Therapy:- Early administration of growth hormone (1-6 years)- Surgical corrections: spinal stenosis, secondary scoliosis, genu varum, foramen magnum decompression