|
|
|
| ACHONDROPLASIA |
Dr Ira Shah
M.D, DCH(Gold Medalist), FCPS, DNB
Q: What is achondroplasia ?
A: Achondroplasia is derived from Greek and it means "without cartilage formation". Though patients with achondroplasia have cartilage, only a small amount of cartilage in the growth plates of the long bones turns into bone and short stature. It is the most common type of disproportionate short stature.
Q: What are the clinical features of achondroplasia?
A: The patients have a disproportionate short stature- with a normal trunk, short arms and short legs. There is proximal shortening of the limbs (rhizomelic dwarfism). The average adult height is 4 feet. The head appears larger than the body, with a prominent forehead and flattened bridge of the nose. Teeth may be crowded with poor alignment. Spine is usually straight in the upper back with a marked lumbar lordosis. Abnormalities of the thoracolumbar vertebra may lead to kyphosis in infancy, which disappears once the child starts walking, but may cause spinal cord compression is adolescents. There may be bowing of the legs and feet are generally short and flat. Hands are short with stubby fingers and there may be a trident hand (separation between the middle and ring fingers).
Children with achondroplasia usually are slow to sit, stand & walk (delayed motor milestones). However, they are able to lead independent and productive lives.
Q: What are the complications of achondroplasia?
A: In infancy or early childhood, these children may die suddenly in sleep due to compression of the upper spinal cord. Narrowing of the foramen magnum and abnormalities of the upper cervical vertebra cause the compression.
These children may have frequent otitis media, leading to conductive deafness. These children may also develop symptomatic hydrocephalus. The most common complication in adults is lumbar spinal cord compression due to lumbar spinal stenosis. This complication is treatable with surgical decompression, if diagnosed early.
These children may also have airway obstruction due to large tonsils and small facial structure.
Q: How does Achondroplasia occur?
A: Achondroplasia is an autosomal dominant condition with the abnormal gene located on chromosome 4. However, 75% of cases are new mutations. The parents of children with achondroplasia resulting from a new mutation are usually of normal stature. Their chance of having a second affected child is extremely small. It has been observed that father above 40 years of age are more likely to have children with achondroplasia and other autosomal dominant conditions.
Q: How is achondroplasia diagnosed?
A: Based on clinical features and specific features on radiographs, the diagnosis of Achondroplasia is made. The radiography may show contracted base of the skull, a square shape of pelvis with small sacrosciatic notch, rhizomelic dwarfism, trident hands & proximal femoral radiolucency. Hypochondroplasia and thanatophoric dysplasia, though similar to achondroplasia, can be distinguished as hypochondroplasia is usually milder and than thanatophoric dysplasia is usually severe & lethal.
Q: How is the disease treated?
A: In the newborn, the condition can be diagnosed by radiographic studies. Special achondroplasia growth curves and infant development charts are available from which expected adult height could be estimated. Serial arm span, head circumference, total body length and upper to lower body segment ratio should be evaluated. Since, hydrocephalus may develop during the 1st 2 years, head circumference should be monitored every monthly for the first year and every 3 monthly in the second year. If the head circumference increases rapidly, a cranial ultrasound may be required at 2, 4 or 6 months of age to evaluate the ventricular size. After 6 months, neuroimaging may be required. The same may be required if the infant shows asymmetrical reflexes, extreme hypotonia or early hand preference. Then the patient should be referred to a pediatric neurosurgeon for shunting.
Development of thoracolumbar kyphosis has been found to be associated with unsupported sitting before there is adequate trunk muscle strength. Parents should be instructed to avoid carrying such a child in a curled-up position. They should provide back support for the first year of life. If kyphosis does not disappear even after the child starts walking (usually it disappears) then it can be corrected by a brace or with surgery.
Patients with achondroplasia have a small foramen magnum, which may rarely cause cord compression at the cervicomedullary junction leading to breathing difficulty and paralysis. Foremen magnum decompression may be required.
Bowing of the legs may occur due to fibular overgrowth at the ankles & knee. If the bowing leads to an inability to walk, surgical correction may be required.Speech should be evaluated latest by 2 years of age. If speech is abnormally delayed conductive hearing loss due to otitis media should be ruled out. Untreated, it can lead to conductive hearing loss.Patients with achondroplasia may also have obstructive sleep apnea due to flattened mid facial profile between 1 – 5 years. If upper airway obstruction is suspected, polysomnographic studies may be required.Dental crowding and malalignment of teeth may require orthodontic bracing and removal one or two teeth after 5 years of age.In mid to late childhood, children are prone to obesity and their eating habits should be evaluated. The child should avoid gymnastics and contact sports because of the potential for neck or back damage and cause spinal compression. To decrease the lumbar lordosis, the child should be encouraged correct posture. These children have another wise normal and productive life.
Q: How is achondroplasia detected antenatally ?
A: The diagnosis may be suspected by ultrasound on the basis of disproportionately short limbs in the fetus. Genetic testing can be done if both the parents have achondroplasia. Such homozygous infants are either stillborn or die shortly after birth. Such pregnancies should be followed by ultrasound at 14, 16, 18, 22 and 32 weeks of gestation to distinguish homozygosity from normal growth in the fetus.
Q: What precautions should a mother with achondroplasia take during pregnancy?
A: An expectant achondroplasic mother should undergo delivery by cesarean section due to a small pelvis. The mother should be given general anesthesia and not spinal/epidural anesthesia as the mother may develop complications due to spinal stenosis. A baseline pulmonary function study should also be done as the mother may develop respiratory compromise in the third trimester of pregnancy.
Q: How can achondroplasia be prevented ?
A: It cannot be prevented in majority of cases as 75 % of them occur as new mutations. However prenatal screening for achondroplasic parents can be offered.
|
|
|
Last created on 23-02-2001
Last updated on 28-04-2007 |
|
|
|
|
