Achondroplasia is a genetic condition that affects the body’s ability to convert cartilage into bone, resulting in short limbs. The condition is caused by changes to the FGFR3 gene, which can pass from parents to children.
Achondroplasia causes a person to have short legs and arms, an enlarged head, and short fingers. A person’s ring and middle fingers may diverge, and this might give each hand a three-pronged appearance.
In this article, we look at achondroplasia and genetics, including how the condition occurs, how common it is, and how people can tell if they carry the gene that causes it.
We also describe the signs of achondroplasia, and how this form of dwarfism can affect a person’s life.
Achondroplasia can pass from parent to child as an autosomal dominant trait. This means that if only one parent passes down the altered gene, the child will have the condition.
Two specific changes to the FGFR3 gene cause almost all cases of achondroplasia. This gene is responsible for communicating to the body how to make a certain protein. This protein helps develop and maintain bone tissue.
In most cases, the FGFR3 gene changes spontaneously in a person who does not have achondroplasia. Around 80% of people born with the condition have parents who are of average stature. A person can have this altered gene without knowing it.
If one or both parents do have this form of dwarfism, there is a high chance that their child will inherit the changed gene, too. Sometimes, children who inherit two copies of the gene — one from each parent — have a severe form of achondroplasia.
Achondroplasia typically causes a person to have:
- short stature
- bowed legs
- a head that is large, compared with their body
- short arms and legs, especially the upper arms and thighs
- short fingers, with middle and ring fingers that may diverge
- joint laxity, which means that their joints are very mobile
- a prominent forehead
Achondroplasia is the most common form of short-limbed dwarfism, but overall, it is rare. The condition affects 1 in 10,000–30,000 people.
Most people with gene that causes achondroplasia do not know that they carry it. This is because, in most cases, the gene spontaneously changes before it passes from parent to child.
So unless people have DNA testing before they conceive, they may not be aware of their gene status.
If a person has achondroplasia, a doctor can usually recognize it by the visible signs. If a person has more than one genetic condition, or they do not have the typical signs of the condition, DNA testing can confirm the diagnosis.
Genetic testing can identify alterations in the FGFR3 gene in
A person might opt for genetic testing if they:
- want to conceive and want to be aware of any traits that they may pass on
- are pregnant and want to screen for genetic conditions before delivery
- have a child with possible signs of achondroplasia
Testing in adults
Any adult can ask for genetic testing to see if they carry an altered FGFR3 gene. For the test, a doctor or technician collects a sample of hair, blood, or saliva.
Next, they send the sample to a laboratory, where technicians look for specific changes to proteins, DNA, or chromosomes. To detect achondroplasia, they check for characteristic changes to the FGFR3 gene.
Testing during pregnancy
During pregnancy, a doctor may be able to diagnose achondroplasia in a fetus using an ultrasound scan. This may show characteristics of the condition, such as shortened humerus and femur bones.
To confirm the diagnosis, the doctor may suggest genetic testing. This involves a technique called percutaneous umbilical blood sampling — collecting a sample of blood from the umbilical cord.
This sampling carries a small risk for the fetus and the pregnant person. Rarely, the procedure causes bleeding around the puncture site or a sustained low heart rate in the fetus, either of which can be serious.
Testing in children
Doctors can often diagnose achondroplasia based on physical signs, but if a child is very young or the characteristics are not typical, a doctor may recommend genetic testing.
An early diagnosis can help doctors monitor for any related complications, such as a spinal curve, when the child is still very young. This ensures that they receive treatment and management as soon as possible.
A doctor may also use an X-ray to see if the “long bones,” such as the femur and humerus, are shortened.
Achondroplasia in itself is not typically life threatening and does not require a cure. With appropriate care, people with achondroplasia can lead full, satisfying lives.
Achondroplasia does not affect a person’s intelligence or necessarily prevent someone from doing typical things, such as going to school, working, or having a family.
Many of the day-to-day challenges that people associate with dwarfism are the result of ableism, rather than the condition itself.
Ableism is prejudice or discrimination against people with disabilities or people perceived as having disabilities. It is widespread and can make everyday life harder.
For example, many public spaces are not designed with accessibility in mind. This makes it more difficult for people with different physical needs to navigate and use these spaces. Because this is preventable, it is a form of inequity.
For people with achondroplasia, a lack of inclusivity in design can result in difficulty:
- reaching things
- finding accessible bathrooms
People with dwarfism can also face discrimination, which can impact mental health.
However, every person is different, and experiences of achondroplasia differ, too. People can find information about adapting the home, resources for caregivers and teachers, and first-person accounts of what it is like to have dwarfism on the Little People of America website.
People with achondroplasia have a higher risk of certain health complications. Doctors can treat or manage many of these.
Some of the most common are orthopedic, and may include:
- a curved spine, such as scoliosis or kyphosis
- narrowing of the spinal column, or spinal stenosis
- compression of the bones at the base of the skull
- a small ribcage, which may cause problems with the lungs or airways
- obstructive sleep apnea
- chronic pain
Also, many people with achondroplasia have some degree of hydrocephalus, which refers to fluid on the brain. A small amount usually is not harmful, but the condition can be serious. In this case, doctors can install a shunt to drain the excess fluid.
Achondroplasia is a form of short-limbed dwarfism. It results from inheriting an altered FGFR3 gene from one or both parents. In most cases, the parents do not have the condition.
Many people with the altered FGFR3 gene do not know that they have it. A doctor can identify it by performing genetic testing during childhood or adulthood, including during pregnancy. X-ray and ultrasound scans can also help with the diagnosis.
People with achondroplasia have a higher risk of certain complications, doctors can treat these or reduce their impact.