Causes of Dwarfism
Achondroplasia is a bone growth disorder and the most common form of dwarfism. It is congenital in nature and results when the FGFR3 gene contains a mutation that causes abnormal cartilage development, leading to short bones.
Inheritance Patterns
People stricken with this disorder have one normal gene, but also a mutant one. If two mutant genes are present, death often occurs before or immediately after birth. People with this particular disorder have a 50% chance of passing the gene to their offspring, which means that each child born to them will stand a 50% chance of having the disorder. When both parents carry the disorder, the risk percentage raises to nearly 100%. In most cases, however, people having achondroplasia are born to parents who do not have the disorder themselves.
New Mutations
The paternal parent is predominately responsible for passing on new gene mutations. More than 99% of achondroplasia cases are caused by these new mutations.
Detecting Achondroplasia
Prenatal ultrasound is used to detect achondroplasia before birth. If the condition is present, the ultrasound normally shows an excessive amount of amniotic fluid surrounding the infant. DNA testing can also be conducted before birth to detect homozygosity (when two copies of the mutant gene are inherited). This condition causes stillbirth and is almost always fatal.
Other indicators of achondroplasia (those detected after birth) are slow motor movement, hypotonia (low muscle tone), obesity, otitis media (middle ear infections), bowed legs, spine curvatures, spinal stenosis, short stature, short arms and legs, large foreheads, abnormal hand structure, large head-to-body ratio, abnormal head size (measuring from front to back), and dental abnormalities. There may be signs of “water on the brain,” or hydrocephalus.
Additional detection tools include skeletal surveys and fetal ultrasounds.
Treatments
No treatment is yet available for achondroplasia. Spinal stenosis and spinal cord compression, two related abnormalities, should be treated if they cause medical problems.
Prognosis
People with this disorder rarely reach a height of 5 feet, although their intelligence usually falls within the normal range. Infants receiving the abnormal gene from both parents normally do not live more than a few months.
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