Achondroplasia is an inherited disorder of bone growth that causes the most common type of dwarfism. Besides that achondroplasia also one of chondodystrophies, in which the development of cartilage, and therefore, bone is disturbed. The disorder appears in approxamitely one in every 10,000 births. The average height of adult males with achondroplasia is 52 inchies ( or 4 feet, 4 inchies ). The average height of adult females with achondroplasia is 49 inches ( or 4 feet, 1 inch ).
Diagnosis is often made at birth due to the characteristically short limbs, and the appearance of a large head. X – Ray examinitation will reveal a characteristic appearance to the bones, with the bones of the limbs appearing short in leght, yet broad in width. A number of measurements of the bones in x – ray images will reveal abnormal proportions.
Achondroplasia is inherited as an autosomal dominant trait. Those with the genetic mutation for achondroplasia have a fivty percent chance of having a child of their own with the disorder. If two achondroplasia dwarfs have a child together they have a 50% chance of having a dwarfs baby, a 25% chance of having a baby of average height, and a 25% chance that the baby will have what is commonly reffered to as “ double dominance” achondroplasia. This last form is always fatal in infancy. Babies born with double dominance suffer from very small rib cages, as well as serious brain abnormalities.
Achondroplasia is caused by an abnormalily in a gene located on chromosome 4, called fibroblast growth factor receptor ( FGFR3). Sometimes the child inherits achondroplasia from a parent who has the condition, but in about 80 per cent of cases the problem result from a new mutation of a gene. In achondroplasia, the mutated from of the receptor is constitutively active and this leads to severely shortened boned bones.
Achondroplasia is noticeable at birth. The baby has an appropriate-sized trunk but his arms and legs are short, his head large, and his fingers and toes are stubby. The baby with achondroplasia is slow to sit, stand, and walk alone, but is not mentally retarted. After he starts walking he may become bow-legged. He may have ear infections during childhood and develop a sway-back(lower back lordosis). Adults may have trouble with pain in the legs, even paralysis that prevents walking. Surgery can relieve the pressure in the spine (from stenosis) causing these symptoms.