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Achondroplasia is a disorder of bone growth. Although achondroplasia literally means "without cartilage formation," the problem is not in forming cartilage but in converting it to bone, particularly in the long bones of the arms and legs.
All people with achondroplasia have short stature. The average height of an adult male with achondroplasia is 131 centimeters (4 feet, 4 inches), and the average height for adult females is 124 centimeters (4 feet, 1 inch). Characteristic features of achondroplasia include an average-size trunk, short arms and legs with particularly short upper arms and thighs, limited range of motion at the elbows, and an enlarged head (macrocephaly) with a prominent forehead. Fingers are typically short and the ring finger and middle finger may diverge, giving the hand a three-pronged (trident) appearance. People with achondroplasia are generally of normal intelligence.
Health problems commonly associated with achondroplasia include episodes in which breathing slows or stops for short periods (apnea), obesity, and recurrent ear infections. In adulthood, individuals with the condition usually develop a pronounced and permanent sway of the lower back (lordosis) and bowed legs. Older individuals often have back pain, which can cause difficulty with walking.
Achondroplasia is the most common type of short-limbed dwarfism. The condition occurs in 1 in 15,000 to 40,000 newborns.
Mutations in the FGFR3 gene cause achondroplasia.
The FGFR3 gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. This protein limits the formation of bone from cartilage (a process called ossification), particularly in the long bones. Two specific mutations in the FGFR3 gene are responsible for almost all cases of achondroplasia. Researchers believe that these mutations cause the protein to be overly active, which interferes with skeletal development and leads to the disturbances in bone growth seen with this disorder.
Achondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. About 80 percent of people with achondroplasia have average-size parents; these cases result from a new mutation in the FGFR3 gene. In the remaining cases, people with achondroplasia have inherited an altered FGFR3 gene from one or two affected parents. Individuals who inherit two altered copies of this gene typically have very severe problems with bone growth, and are usually stillborn or die shortly after birth from respiratory failure.
'''Achondroplasia''' is a type of genetic disorder that is a common cause of dwarfism. People with this condition have short stature, usually reaching a full adult height of around 4'0" (1.22 meters). The disorder is a result of an autosomal dominant mutation in the fibroblast growth factor receptor gene 3 (FBFR3), which causes an abnormality of cartilage formation. It occurs at a frequency of about 1 in 20,000 to 1 in 40,000 births. Clinical features of the disease: * dwarfism (nonproportional short stature) * shortening of the proximal limbs (termed ''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 deformity (bowleg) or valgus deformity (knock knee) deformities * frequently have ear infections (due to Eustachian tube blockages), sleep apnea (which can be central or obstructive), and hydrocephalus People with achondroplasia have one normal copy of the fibroblast growth factor receptor 3 gene and one mutant copy. Only one copy of the gene needs to be present for the disorder to be seen. Thus, a person with achondroplasia has a 50% chance of passing on the gene to their offspring, meaning that 1 in 2 of their children will have achondroplasia. However, in 3 out of 4 cases, people with achondroplasia are born to parents who don't have the condition. This is the result of a new mutation. New gene mutations are associated with increasing paternal age (over 35 years). Studies have demonstrated that new gene mutations are exclusively inherited from the father and occur during spermatogenesis (as opposed to resulting from a germline mosaicism). Achondroplasia can be detected before birth by the use of prenatal ultrasound. A DNA test can be performed before birth to detect homozygosity, where two copies of the mutant gene ... [ Read More ]
Achondroplasia - Article from eMedicine.
Pediatric Oncall - Offers information about achondroplasia, the most common type of disproportionate short stature.
Achondroplasia - Information, pictures of people with the condition, and an open forum.