Achondroplasia is a bone growth disorder that is a form of short-limbed dwarfism. Dwarfism is defined as a condition of short stature as adults and sometimes is referred as “little people.” People with achondroplasia are short in stature with a normal sized torso and short limbs. Their heads are usually larger than average with a bigger forehead. The average height for an adult with achondroplasia is a little over 122 cm.
Achondroplasia is the most common type of dwarfism. About three-quarters of all cases of short stature are caused by achondroplasia.
What causes achondroplasia?
Most of your skeleton is made up of cartilage during early fetal development. The cartilage converts to form your bones through a process called ossification. If you have achondroplasia, a lot of the cartilage are unable to convert to bones. It is suggested the cause is a mutation in the FGFR3 gene.
The FGFR3 gene instructs your body to make a protein necessary for bone growth and maintenance. Mutations in the FGFR3 gene cause the protein to be overactive. This impairs the normal bone development process.
About 20 percent of the mutations are inherited, which means that one parent passes down a defective FGFR3 gene. The other 80 percent of cases are not inherited and are caused by spontaneous mutations.
If one parent has the condition, the child has a 50 percent chance of getting it. If both parents have the condition, the child may have 50 percent chance of getting it with 25 percent chance of having 2 defective genes. This form of achondroplasia is called homozygous achondroplasia which is life-threatening. Infants born with homozygous achondroplasia are usually stillborn or have a very short life-span.
If there’s a history of achondroplasia in your family, you may want to consider genetic testing prior to becoming pregnant so that you fully understand your future child’s health risks.
What are the signs and symptoms of achondroplasia?
People with achondroplasia generally do not have any effects on their cognitive function. Signs and symptoms are instead physical.
An infant with achondroplasia will likely have:
- A short stature that’s significantly below average for age and sex;
- Short arms and legs, especially the upper arms and thighs, in comparison to body height;
- Short fingers in which the ring and middle fingers may also point away from each other;
- A disproportionately large head compared to the body;
- An abnormally large, prominent forehead;
- An underdeveloped area of the face between the forehead and upper jaw;
- Decreased muscle tone, which can cause delays in walking and other motor skills;
- Apnea, which involves brief periods of slowed breathing or breathing that stops;
- Hydrocephalus, or water on the brain;
- Spinal stenosis, which is a narrowing of the spinal canal that can compress the spinal cord.
Children and adults with achondroplasia may:
- Have difficulty bending their elbows;
- Be obese;
- Experience recurrent ear infections because of narrow passages in the ears;
- Develop bowed legs;
- Develop an abnormal curvature of the spine called kyphosis or lordosis;
- Develop new or more severe spinal stenosis.
If there are any concerns about your signs or symptoms, please contact your doctor for more information.
How is achondroplasia diagnosed?
Your doctor may diagnose your child with achondroplasia while you’re pregnant or after your baby is born.
During pregnancy, some characteristics of achondroplasia are detectable in your baby through an ultrasound. These include hydrocephalus or an abnormally large head. If your doctor suspects achondroplasia, genetic tests may be ordered. These tests look for the defective FGFR3 gene in a sample of amniotic fluid, which is the fluid that surrounds the fetus in the womb.
After birth, your doctor can diagnose your child by looking at his or her features. The doctor may also order X-rays to measure the length of your infant’s bones. This can help confirm a diagnosis. Blood tests may also be ordered to look for the defective FGFR3 gene.
What is the treatment for achondroplasia?
Currently, there is no specific treatment for achondroplasia. Children born with achondroplasia need to have their height, weight, and head circumference monitored using special growth curves standardized for achondroplasia. It is recommended to avoid obesity at an early age by maintaining a healthy diet and regular exercise.
A magnetic resonance imaging (MRI) or CT scan may be needed for further evaluation of severe muscle weakness (hypotonia) or signs of spinal cord compression. To help with breathing, surgical removal of the adenoids and tonsils, continuous positive airway pressure (CPAP) by nasal mask, or a surgical opening in the airway (tracheostomy) may be needed to correct obstructive sleep apnea.
When there are problems with the lower limbs, such as hyperreflexia, clonus or central hypopnea, then surgery called suboccipital decompression is performed to decrease pressure on the brain.
Children who have achondroplasia need careful monitoring and support for social adjustment.
Hello Health Group does not provide medical advice, diagnosis or treatment.
Review Date: September 6, 2016 | Last Modified: January 4, 2017
Learning About Achondroplasia. https://www.genome.gov/19517823. Accessed September 6, 2016.
Achondroplasia. https://ghr.nlm.nih.gov/condition/achondroplasia. Accessed September 6, 2016.
Achondroplasia. http://www.healthline.com/health/achondroplasia#Diagnosis6. Accessed September 6, 2016.