Achondroplasia By Kait Keaveny

Achondroplasia Autosomal Dominant Disorder. Affects about 1 in 25,000 people. About 98% of those with achondroplasia have a point mutation in the FGFR3 gene at 4p16.3 that encodes fibroblast growth factor receptor 3.

The penetrance of the gene is 100% The protein made by the FGFR3 gene is a receptor that regulates bone growth by limiting the formation of bone from cartilage (a process called ossification), particularly in the long bones. Researchers believe that mutations in the FGFR3 gene cause the receptor to be overly active, which interferes with ossification and leads to the disturbances in bone growth seen with this disorder.

There are 4 nucleotide substitutions in Achondroplasia. It can be inherited but more than 80% of the cases are results from a mutation that occurred during development. Compression of the spinal cord and/or upper airway obstruction increases the risk of death in infancy. Homozygous achondroplasia, caused by the presence of two mutant alleles at nucleotide 1138 of the FGFR3 gene, is a severe disorder with radiologic changes qualitatively different from those of achondroplasia. Early death results from respiratory insufficiency because of the small thoracic cage and neurologic deficit from cervicomedullary stenosis

Clinical Features nonproportional dwarfism shortening of the proximal limbs (called rhizomelic shortening) short fingers and toes a large head with prominent forehead small midface with a flattened nasal bridge spinal kyphosis (convex curvature) or lordosis (concave curvature) varus (bowleg) or valgus (knock knee) deformities frequently have ear infections (due to Eustachian tube blockages), sleep apnea (which can be central or obstructive), and hydrocephalus

Diagnosis: The physical features are usually sufficient for an accurate diagnosis. Radiology, ultrasound, and other imaging techniques are used to observe the skeletal abnormalities. A DNA-based test is available for new- borns before the symptoms appear in atypical cases.

Treatments All treatments are supportive. In newborns, because of the large head and weak neck muscles, positions that could block breathing must be avoided. Infections of the inner ear in children is common. Preventative measures must be taken against apnea, cessation of breathing during sleep. Excessive weight gain must be controlled in children. Orthopedic surgery to elongate limb bones, growth hormone therapy, and psychiatric help are often taken to deal with the short stature.

References pg pg ia/details.html ia/details.html bin/carddisp?FGFR3 bin/carddisp?FGFR3 a a Pasternak, Jack J. 2nd ed. Hoboken: John Wiley & Son, Inc,