Achondroplasia
Incidence
Incidence: 1 in 16,000-25,000 live births.Genetics: Autosomal dominant inheritance predicting a 50% recurrence risk for affected individuals.
Clinical Characteristics
It is a pattern of skeletal changes including short stature with disproportionately short limbs, prominent forehead, shallow nasal bridge, lordotic posture, broad hands and feet. Genetics: Autosomal dominant inheritance predicting a 50% recurrence risk for affected individuals; achondroplast couples also have a 25% risk for severely affected homozygotes. About 75% of achondroplastic patients represent new mutations, explaining why the majority of patients have a normal family history. Sudden infant death (5%). Risk for depression in older individuals. There is short stature (males average 130 cm, females average 123 cm). The term \\\\\\\\\\\\\\\"achondroplasia\\\\\\\\\\\\\\\" refers to a condition with short stature, distinctive facial appearance, and short limbs. Hypochondroplasia is a similar disorder with a relatively normal face and milder skeletal changes than patients with achondroplasia. The incidence of achondroplasia is between 1 in 16,000 and 1 in 25,000 births, while that for hypochondroplasia is about 10-fold less. Both disorders result from mutations in different portions of the fibroblast growth factor-3 receptor gene. Thanatophoric dysplasia and homozygous achondroplasia are lethal forms of dwarfism that result from mutations in the same gene. Differential diagnosis involves the separation of achondroplasia from other forms of short-limbed dwarfism. Patients with achondroplasia have rhizomelic (proximal) limb shortening, prominent forehead with shallow nasal bridge, and characteristic splayed or \\\\\\\\\\\\\\\"trident\\\\\\\\\\\\\\\" fingers. Skeletal radiographs will demonstrate characteristic changes in the lumbar vertebrae (spine) and pelvis (e.g., unusual iliac wings). Thanatophoric dysplasia can be distinguished at birth by its more severe facial changes, limb shortening, and chest narrowing that results in death. The diagnosis of achondroplasia is made by clinical examination and skeletal x-rays. DNA analysis can be pursued in uncertain cases, but this is not usually required.
Natural History and Complications: These children have normal intelligence, normal lifespan, and remarkable physical adaptation. . It is important to realize that all children with achondroplasia have some degree of low muscle tone and developmental delay; these problems are unusually severe in children with spinal cord compression. The lower spinal canal is also narrow, producing spinal cord and nerve root compression from changes in the spinal bone or discs later in life. In achondroplasia, the spinal canal narrows as one progresses to the lower spine, causing spinal curvature in 7-20%. Limbs may become bowed due to joint, resulting in bow legs (15%) or curved feet. . Compression of the upper spinal cord and medulla oblongata of the lower brain may present as recurrent apnea (cessation of breathing), central sleep apnea, low muscle tone and developmental delay, or sudden death. This compression may also be associated with hydrocephalus, causing increased intracranial venous pressure by interference with venous flow out of the brain.
Laboratory diagnosis: DNA analysis to demonstrate characteristic mutations in the fibroblast growth factor-3 receptor. The diagnosis of achondroplasia is increasingly made by fetal ultrasound, allowing earlier planning for and acceptance of a child with short stature.
Precipitants
none
Provocation Tests
none
Diagnostic Procedures
The diagnosis of achondroplasia is made by clinical examination and skeletal x-rays. DNA analysis can be pursued in uncertain cases, but this is not usually required.
DNA analysis to demonstrate characteristic mutations in the fibroblast growth factor-3 receptor. The diagnosis of achondroplasia is increasingly made by fetal ultrasound, allowing earlier planning for and acceptance of a child with short stature.