Achondroplasia is a birth defect that affects a baby’s bone growth.
Birth defects are health conditions that are present at birth. Birth defects change the shape or function of one or more parts of the body. They can cause problems in overall health, how the body develops, or in how the body works.
As a baby grows, a body tissue called cartilage normally becomes bone in most parts of the body. But if a baby has achondroplasia, cartilage in places like the arms and legs doesn’t turn into bone the way it should. Achondroplasia is a common cause of dwarfism (also called little people), a condition in which a person is very short (less than 4 feet 10 inches as an adult).
Achondroplasia affects about 1 in 15,000 to 1 in 40,000 babies. Most babies born with achondroplasia live a normal life span, but a few may have severe bone problems that can lead to death.
What causes achondroplasia?
A gene change (also called a mutation) causes achondroplasia. Genes are parts of your body’s cells that store instructions for the way your body grows and works. Genes are passed from parents to children. A gene change is a change to the instructions in a gene. These changes can cause birth defects and other health conditions.
Most babies with achondroplasia are born to parents who don’t have the condition. This happens when there’s a random gene change in either the egg or sperm that join together and create a baby.
If you or your partner has achondroplasia, you can pass it to your baby. If only one of you has the condition, there’s a 1 in 2 chance (50 percent) that your baby can have the condition. If both you and your partner have achondroplasia, there is:
- A 1 in 2 chance (50 percent) that your baby can have the condition
- A 1 in 4 chance (25 percent) that your baby won’t have the condition
- A 1 in 4 chance (25 percent) that your baby has the severe kind of achondroplasia that can lead to death
If you or your partner has achondroplasia or you’re the parent of a child with achondroplasia, talk to a genetic counselor about the condition. A genetic counselor is a person who is trained to help you understand about how genes, birth defects and other medical conditions run in families, and how they can affect your health and your baby's health. To find a genetic counselor, ask your provider or contact the National Society of Genetic Counselors.
How do you know if your baby has achondroplasia?
Before birth, your provider may think your baby has achondroplasia if an ultrasound shows your baby has bone problems, like shortened bones. An ultrasound uses sound waves and a computer screen to show a picture of your baby inside the womb.
If the ultrasound shows these bone problems, your provider may recommend a prenatal test called amniocentesis (also called amnio) to confirm that your baby has achondroplasia. In an amnio, your provider takes some amniotic fluid from around your baby in the uterus. The test checks for birth defects and genetic conditions in your baby.
After birth, your baby’s provider can use X-rays, a physical exam and a blood test to check your baby for achondroplasia.
What are some physical characteristics of someone with achondroplasia?
A person with achondroplasia often has:
- Short height
- Short upper arms and thighs (compared to the forearms and lower legs)
- Large head and forehead with a flat bridge of the nose
- Dental problems, including crowded or crooked teeth
- Broad, flat feet, short toes and short fingers
- Trident hand, a condition in which you have an extra space between the middle and ring fingers
- Weak muscle tone. Babies with weak muscle tone may have delays in meeting developmental milestones, like sitting, standing and walking.
- Bowed legs. This is when legs curve outward between the thighs and ankles. Bowed legs can cause pain and trouble with walking. If the bowing or pain is severe, surgery can fix bowed legs.
What health problems can achondroplasia cause and how are they treated?
People with achondroplasia can have a range of health problems, so it’s important to take your baby to see his health care provider for routine well-baby checkups.
At these checkups, your baby’s provider can compare your baby’s height, weight and head size to those of other babies with achondroplasia. This can help your baby’s provider spot and treat some problems early on.
People with achondroplasia often have these health problems:
- Apnea. This is when a baby stops breathing for 15 to 20 seconds or more. Babies with apnea and other breathing problems may need surgery to remove the tonsils and adenoids (lymph tissue near the throat).
- Repeat ear infections. Some babies with achondroplasia need ear tubes. These are small tubes placed in the ear that let air into the middle ear and help lower chances of ear infections. Without treatment, repeat ear infections can cause hearing loss.
- Obesity (being very overweight). Healthy eating and being active can help your child stay at a healthy weight as she grows.
- Compression of the upper end of the spinal cord. This is when the opening where the head and spine (backbone) connect is too small. The spinal cord gets squeezed (compressed), causing trouble with breathing. A small number of babies with achondroplasia die suddenly (often during sleep) from compression. If needed, surgery can widen the opening to ease pressure on the spinal cord.
- Spinal stenosis. Spinal stenosis causes the spine to narrow, putting pressure on the nerves and spinal cord. This can cause low back pain, problems with urination and weakness, tingling and pain in the legs. Symptoms usually appear when a person with achondroplasia is a teen or adult. Surgery can ease pressure on the spinal cord.
- Hydrocephalus (fluid buildup in the brain). Your baby’s provider measures your baby’s head at regular checkups to help catch hydrocephalus early. In some cases, a surgeon needs to drain the extra fluid from a baby’s brain.
- Kyphosis (a small hump in the upper back). A baby may have kyphosis due to poor muscle tone, but it usually goes away after she starts walking. Strollers or carriers that don’t give good back support can make kyphosis worse. If your child stills has kyphosis after she starts walking, she may need a back brace or surgery to correct it.
- Lordosis (inward curving of the lower back). This can develop after your child starts walking and can lead to waddling. Special exercises or physical therapy can help.
- Little People of America (LPA)
- Human Growth Foundation
- The Magic Foundation for Children’s Growth and Related Adult Disorders
Last reviewed: April, 2013