Achondroplasia is caused by a gene alteration mutation in the FGFR3 gene. The FGFR3 gene makes a protein called fibroblast growth factor receptor 3 that is involved in converting cartilage to bone. FGFR3 is the only gene known to be associated with achondroplasia. Most people who have achondroplasia have average-size parents. In this situation, the FGFR3 gene mutation occurs in one parent's egg or sperm cell before conception.
Other people with achondroplasia inherit the condition from a parent who has achondroplasia. People who have achondroplasia have abnormal bone growth that causes the following clinical symptoms: short stature with disproportionately short arms and legs, short fingers, a large head macrocephaly and specific facial features with a prominent forehead frontal bossing and mid-face hypoplasia.
Infants born with achondroplasia typically have weak muscle tone hypotonia. Because of the hypotonia, there may be delays in walking and other motor skills. People with achondroplasia commonly have breathing problems in which breathing stops or slows down for short periods apnea.
Other health issues include obesity and recurrent ear infections. Adults with achondroplasia may develop a pronounced and permanent sway of the lower back lordosis and bowed legs. The problems with the lower back can cause back pain leading to difficulty with walking. Achondroplasia is diagnosed by characteristic clinical and X-ray findings in most affected individuals. By far the most common skeletal dysplasia is achondroplasia.
This short-limb dwarfism happens in about 1 of every 25, babies born of all races and ethnic groups. People with achondroplasia have a relatively long trunk and shortened arms and legs. This is most noticeable in the upper parts of their arms and legs called rhizomelic shortening. Diastrophic dysplasia is another short-limb dwarfism.
It happens in about 1 in , births. People who have this type tend to have shortened forearms and calves called mesomelic shortening. They might also have:. Most people with diastrophic dysplasia have joint changes that limit movement. People with diastrophic dysplasia often benefit from mobility aids , such as crutches, a scooter, or a wheelchair to get around.
Spondyloepiphyseal dysplasias SED are short-trunk skeletal dysplasias that involve the spine and the end of the bones that make up the joints epiphyses. Along with achondroplasia and diastrophic dysplasia, they're one of the more common types of dwarfism. In one type of SED, the short trunk may not be noticed until the child is school age. Other types are seen at birth. Most pregnant women have a prenatal ultrasound to measure the baby's growth at around 20 weeks. At that stage, features of achondroplasia aren't yet noticeable.
Doctors sometimes suspect achondroplasia before birth if an ultrasound late in a pregnancy shows that a baby's arms and legs are shorter than average and the head is larger. But many children with achondroplasia aren't diagnosed until after birth. Doctors can recognize some other types of skeletal dysplasia earlier in pregnancy. Others aren't noticed until the first few months or years of life, when a child's growth slows. A health care provider may take X-rays after birth to check for bone changes.
Doctors also may use genetic testing before or after birth to confirm the diagnosis. Each condition that causes dwarfism has its own possible medical complications, which can change over time. But doctors can treat many of these. Children with dwarfism are cared for by doctors who specialize in orthopedics, neurosurgery, ENT, and pulmonology.
Some medical concerns are treated with surgery. These are done with anesthesia, which can be more of a risk for little people because of their smaller body size and airways. Because of their shorter stature and differences in bone growth, children with dwarfism often learn to roll over, sit up, and walk at different ages than average-height children. These are not considered delays, but developmental differences.
Children with dwarfism figure out how to do it in their own time and in their own way. However, in about 80 percent of cases, achondroplasia results from a spontaneous mutation a sudden genetic defect that occurs in the developing embryo.
The following are the most common symptoms of achondroplasia; however, each child may experience the condition differently:. The symptoms of achondroplasia may resemble other problems or medical conditions. Always consult a physician for a diagnosis. Achondroplasia can be diagnosed before birth by fetal ultrasound or after birth by complete medical history and physical examination. DNA testing is now available before birth to confirm fetal ultrasound findings for parents who are at increased risk of having a child with achondroplasia.
Neurological impairment is caused by compression created as children grow faster than their bones. Arrested bone growth at the base of the skull and the spine can cause the spinal cord and brain stem to become compressed. This can compress key nervous system structures, like the brain stem, spinal cord, spinal nerve roots and cerebrospinal fluid CSF spaces. Eventually, this may lead to neurological deficits, including:.
Brainstem compression can ultimately lead to death if it is left untreated, so parents and physicians of children with achondroplasia should watch for these symptoms.
When the narrowing near the base of the spine prevents CSF from flowing freely around the brainstem or in and out of the skull, the CSF collects in ventricles spaces in the brain.
The resulting condition is hydrocephalus. In babies, the most evident symptom of hydrocephalus is a quickly enlarging head circumference. Additional symptoms include:. Because an enlarged head is normal in children with achondroplasia, pediatricians can use a special head circumference growth chart to distinguish between normal growth and possible hydrocephalus. Sometimes the vertebrae of children with achondroplasia do not grow enough to allow sufficient space for nerves exiting and entering the spinal cord to pass in and out of the bony spinal column.
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