What is achondroplasia?
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.
How common is achondroplasia?
Achondroplasia is the most common type of short-limbed dwarfism. The condition occurs in 1 in 15,000 to 40,000 newborns.
What genes are related to achondroplasia?
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.
How do people inherit achondroplasia?
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.
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Management
Treatment of Manifestations
Recommendations for management of children with achondroplasia were outlined by the American Academy of Pediatrics Committee on Genetics [AAPCG 1995]. The recommendations of the committee are meant to supplement guidelines available for treating the child with average stature. The recommendations include, but are not limited to, the following:
Monitoring of height, weight, and head circumference using growth curves standardized for achondroplasia [Horton et al 1978]
Measures to avoid obesity starting in early childhood. Hunter et al (1996) recommend that children with achondroplasia stay within one standard deviation of the mean weight on the achondroplasia growth curves [Horton et al 1978].
Careful neurologic examinations, with referral to a pediatric neurologist as necessary
MRI or CT of the foramen magnum region for evaluation of severe hypotonia or signs of spinal cord compression
Obtaining history for possible sleep apnea, with sleep studies as necessary
Evaluation for low thoracic or high lumbar gibbus if truncal weakness is present
Referral to a pediatric orthopedist if bowing of the legs interferes with walking
Management of frequent middle-ear infections
Speech evaluation by age two years
Careful monitoring of social adjustment
Obstructive sleep apnea. Treatment may include adenotonsillectomy, weight reduction, continuous positive airway pressure (CPAP) by nasal mask, and tracheostomy for extreme cases. Improvement in disturbed sleep and some improvement in neurologic function can result from these interventions [Waters et al 1995]. In rare instances in which the obstruction is severe enough to require tracheostomy, surgical intervention to advance the midface has been used to alleviate upper airway obstruction [Elwood et al 2003].
Short stature. Growth hormone (GH) therapy has been proposed as a possible treatment for the short stature of achondroplasia. Initial skepticism about the utility of this approach was based on normal GH levels in children with achondroplasia and a concern that the abnormal growth plate cartilage would not respond. However, studies have shown that growth velocity increases with GH therapy, especially during the first year of treatment. A number of studies suggest increased growth rate over a one- to two-year period of treatment [Shohat et al 1996 , Weber et al 1996 , Key & Gross 1996 , Stamoyannou et al 1997 , Tanaka et al 1998]. The usefulness of GH treatment in achondroplasia will be known only when individuals in the current studies reach their adult height.
Early experience with surgical limb-lengthening procedures resulted in a high incidence of complications including pain, pin infections, and neurologic and vascular compromise resulting from rapid lengthening. However, more recent experience has been more favorable and increases in height of up to 12-14 inches may be obtained over an 18-24 month period [Peretti et al 1995 , Ganel & Horoszowski 1996 , Yasui et al 1997]. Although some have advocated performing these procedures at as early as six to eight years of age, many pediatricians, geneticists, and ethicists have advocated postponement of such surgery until the young person is able to make an informed decision.
Suboccipital decompression. The best predictors of need for suboccipital decompression include lower-limb hyperreflexia or clonus, central hypopnea demonstrated by polysomnography, and reduced foramen magnum size, determined by CT examination of the craniocervical junction and by comparison with the norms for children with achondroplasia.
Spinal stenosis. The exaggerated lumbar lordosis frequently observed in persons with achondroplasia undoubtedly contributes to symptoms of spinal stenosis. Correction of the sacral tilt during femoral limb lengthening reduces the severity of the lumbar lordosis and may result in improvement of symptoms [Park et al 2003].
Thomeer & van Dijk (2002) determined that about 70% of symptomatic individuals experienced total relief of symptoms following decompression without laminectomy. The L2-3 level most commonly required decompression.
Kyphosis. Young children with achondroplasia often have kyphosis at the thoracolumbar junction. Typically, this kyphotic curve remits after the child develops increased truncal musculature and begins to walk. Bracing and sitting modifications are usually sufficient to prevent persistence of the thoracolumbar kyphosis. If the kyphosis persists, spinal fusion may be necessary to prevent further progression of the kyphosis and neurologic complications [Ain & Shirley 2004]. Sarlak et al (2004) described an alternative surgical approach.
Socialization. Because of the highly visible nature of the short stature associated with achondroplasia, affected persons and their families may encounter difficulties in socialization and school adjustment. Support groups, such as the Little People of America, Inc (LPA), can assist families with these issues through peer support, personal example, and social awareness programs. Information on employment, education, disability rights, adoption of short-statured children, medical issues, suitable clothing, adaptive devices, and parenting is available through a national newsletter, seminars, and workshops.
Prevention of Secondary Complications
Cephalo-pelvic disproportion may necessitate delivery by Caesarian section when the mother is of average stature and the fetus has achondroplasia.
Mothers with achondroplasia must always be delivered by Caesarian section because of the small size of the pelvis in affected women.
Surveillance
Because adults with achondroplasia are at increased risk for spinal stenosis, a clinical history and neurologic examination is warranted every three to five years once the person with achondroplasia reaches mid-life.
I'd like to ask one question : Is it letal or fatal ???
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