Achondroplasia
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Achondroplasia is an inherited bone disorder that results in dwarfism characterized by short limbs, an average-sized trunk, and a large head. At Columbia University Irving Medical Center/NewYork-Presbyterian Hospital, we specialize in surgically treating brain- and spine-related conditions that may arise with achondroplasia, such as hydrocephalus, kyphosis, spinal stenosis, or an abnormal craniocervical junction.
Achondroplasia is the most common form of dwarfism, accounting for approximately 70% of cases. It occurs in approximately one in 25,000 live births. Average height for men with achondroplasia is 4 feet, 4 inches (131 cm), and average height for women is 4 feet, 1 inch (124 cm).
Symptoms
Most symptoms of achondroplasia are linked to improper bone growth in the spine, skull, and extremities. Classic symptoms may include the following:
- Short stature
- Shortened arms and legs, particularly the upper arms and thighs; short, broad hands, and feet
- Facial features such as macrocephaly, frontal bossing, flattened nasal bridge, and midface hypoplasia
- Difficulty straightening or rotating the elbows
- Trident hand
- Bowed legs
- Curvature in the spine—kyphosis and lordosis
- Hypotonia—infants with achondroplasia often have weak muscles. They tend to take longer to walk and perform other motor skills than infants without the condition.
- Apnea
- Recurrent ear infections, which can lead to hearing loss
- Misaligned or overcrowded teeth
The following symptoms can involve serious health problems related to the brain and spine:
Diagnosis
Achondroplasia can be diagnosed before or after birth.
Before birth, ultrasound imaging may detect certain physical characteristics like macrocephaly. A sample of the amniotic fluid, the fluid surrounding the baby in the womb, can be taken for genetic testing to determine whether the baby has a mutated FGFR3 gene.
Once a child is born, a physical examination and X-ray can provide a diagnosis. When symptoms are atypical, genetic testing can identify a mutation in FGFR3 and confirm a diagnosis.
Risk Factors
For bones in the arms and legs to lengthen, cartilage must convert to bone. In achondroplasia, cartilage is not converted to bone because a protein that plays a role in this process is mutated. The protein is called fibroblast growth factor receptor 3 (FGFR3). It is produced by the gene FGFR3.
FGFR3 is passed down from parent to child in what is called an autosomal dominant manner. Autosomal inheritance means that the gene is located on one of the autosomes (chromosome pairs 1 through 22), which do not differ between the sexes. Therefore, males and females are equally affected by autosomal genes. Dominant means that only one gene is necessary to express the trait. Therefore, a person needs to receive only one copy–rom either parent–of the altered gene to develop achondroplasia.
About 20% of people with achondroplasia receive the altered FGFR3 gene from a parent with the condition. If one parent has achondroplasia and the other doesn’t, there’s a 50% chance with each pregnancy of having a child with achondroplasia. If both parents have achondroplasia, possible outcomes for each pregnancy are the following:
Treatments
Currently, no “cure” is available for achondroplasia. Instead, most treatments aim to relieve complications caused by the conditions. Our neurosurgeons specialize in surgically treating the complications related to the brain and spine.
Kyphosis, a hunched upper back or neck, presents during infancy. Observation is the first-line approach because the condition often goes away by the age of 3. If kyphosis persists, then surgery is considered to correct the forward-curving spine.
A narrowing spinal canal can be surgically treated to relieve the pressure on the spinal cord. Similarly, for brainstem compression, surgery can relieve pressure on the brainstem and upper part of the spinal cord. Several surgical procedures exist, and our neurosurgeons’ choice of procedure depends on a patient’s needs.