Achondroplasia

The most common form of short stature with disproportionately short limbs — dwarfism with short arms and legs. Achondroplasia is caused by mutation in the fibroblast growth factor receptor-3 gene (FGFR3), which is located on chromosome 4 in chromosome band 4p16.3. Aside from short arms and legs, the fingers are short and the ring and middle fingers diverge giving the hand a trident (three- pronged) appearance. There is a typically large head with prominence of the forehead (frontal bossing), underdevelopment (hypoplasia) of the midface with cheekbones that lack prominence, and a low nasal bridge with narrow nasal passages. The brain is normal and intelligence is entirely normal in achondroplasia. However, the complications of achondroplasia can impinge on the brain and the spinal cord. Achondroplasia is inherited as an autosomal dominant trait affecting boys and girls equally. The parents of children with achondroplasia are more often than not normal. Most cases of achondroplasia are due to new mutations that appear for the first time in the affected children. Achondroplasia can be diagnosed before birth by molecular means.

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This chondrodystrophy, characterized by an abnormality in conversion of cartilage to bone, is the most common form of short-limb dwarfisim; characterized by short stature with rhizomelic shortening of the limbs, large head with frontal bossing and midface hypoplasia, exaggerated lumbar lordosis, limitation of elbow extension, genu varum, trident hand, characteristic radiographic skeletal findings, and neurologic symptoms complicating hydrocephalus and spinal canal stenosis. Autosomal dominant inheritance with most cases sporadic, caused by mutation in the fibroblast growth factor receptor 3 gene (FGFR3) on chromosome 4p. [G. a- priv. + chondros, cartilage, + plasis, a molding]

- homozygous a. severe a. caused by inheritance of two a. alleles, one from each parent; usually fatal in the first year of life.

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achon·dro·pla·sia .ā-.kän-drə-'plā-zh(ē-)ə n a genetic disorder disturbing normal growth of cartilage, resulting in a form of dwarfism characterized by a usu. normal torso and shortened limbs, and usu. inherited as an autosomal dominant compare ATELIOSIS

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n.

a disorder, inherited as a dominant characteristic, in which the bones of the arms and legs fail to grow to normal size due to a defect in both cartilage and bone. It results in a type of dwarfism characterized by short limbs, a normal-sized head and body, and normal intelligence.

• achondroplastic adj.

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achon·dro·pla·sia (a-kon″dro-plaґzhə) [a-¹ + chondroplasia] an autosomal dominant disorder caused by mutation in the fibroblast growth factor receptor 3 (FGFR3) gene (locus: 4p16.3), which encodes a transmembrane receptor protein-tyrosine kinase that binds fibroblast growth factor and inhibits proliferation of chondrocytes within the growth plate, causing ligand-independent activation of the gene. It is characterized by disturbance of epiphyseal chondroblastic growth and maturation, causing inadequate enchondral bone formation and resulting in dwarfism with short limbs, normal trunk, small face, normal vault, lordosis, and trident hand. See also achondroplastic dwarf, under dwarf. achondroplastic adj

Child with achondroplasia showing short stature, short limbs and fingers, normal length of the trunk, a relatively large head, prominent forehead, and depressed nasal bridge.