Achondroplasia

In achondroplasia affected bones include those of the limbs and trunk, face, cranial vault, spine, and hand. Classic (heterozygous) achondroplasia is a relatively common type of dwarfism of autosomal dominant inheritance, evident at birth and compatible with a long life span. Affected patients have short limbs (rhizomelic micromelia) and stubby, trident hands. Radiographic findings include a large cranium with a small foramen magnum. The interpediculate distances of the lower lumbar vertebrae, which normally increase from the proximal to distal direction, remain the same at all levels or decrease in the lower lumbar region. The iliac bones are squared with small sacrosciatic notches and flat acetabular angles. The ribs and small tubular bones are also shortened. Thoracolumbar kyphosis is seen in infancy, and exaggerated lumbar lordosis with prominent buttocks is present in children and adults. Persons with achondroplasia may develop compression of the spinal cord, lower brain stem, cauda equina, and nerve roots as a result of constrictions of the basicranium, foramen magnum and spinal canal.

Homozygous achondroplasia is a lethal, extremely rare type of congenital short-limbed dwarfism causing death within the first days or weeks of life. The abnormalities are more severe than those in the classic heterozygous form.

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