Achondroplasia

Achondroplasia is a disproportionate short-limb dwarfism, by far the most common of the human chondrodys-plasias. It occurs in three of 100,000 live births. Achondroplasia is inherited in an autosomal dominant manner. Over 80% of individuals with achondroplasia have parents with normal stature and have achondroplasia as the result of a "de novo" mutation of a gene, localized to the distal short arm of chromosome 4.

In infancy, hypotonia is typical, and acquisition of developmental motor milestones is often delayed. Intelligence and life span are usually normal. Compression of the spinal cord and upper airway obstruction increase the risk of death in infancy.

Mean adult height in males is 131  5.6 cm, and in females 124  5.9 cm (Figs. 1.9-1.16).