Achondroplasia is a common form of dwarfism that causes shorter limbs. In babies, some potential signs include a head that is large compared to the body, a prominent forehead, and increased space between the middle and ring fingers.

Achondroplasia is the most common condition linked with short stature, and it affects 1 in 10,000–30,000 children. About 75–80% of people with achondroplasia are born to parents of average stature, due to how the condition passes down through genes.

This article looks at what achondroplasia is, the signs and symptoms in babies, and how soon doctors can tell if a child has the condition.

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Achondroplasia is an inherited condition that affects how bones grow. The word “achondroplasia” translates to “without cartilage formation.”

Cartilage is a flexible, tough tissue that makes up the majority of the skeleton in early development. In those with achondroplasia, the body can form cartilage but struggles to convert it into bone. This results in differences in growth, especially in the limbs.

All people with the condition have short stature. The average height of adults with achondroplasia is 4 feet 1 inch (124 centimeters) for females and 4 feet 4 inches (131 centimeters) for males.

Achondroplasia is not a condition that requires treatment or a cure. Many people with the condition lead healthy and fulfilling lives.

Changes to the FGFR3 gene cause achondroplasia. This gene is responsible for communicating how to make a protein that is part of the development and maintenance of bone and brain tissue. Two specific changes to the FGFR3 gene cause almost all cases of achondroplasia.

Researchers believe that these differences in the gene cause the FGFR3 protein to be overly active, which affects skeletal development and leads to the changes in bone growth associated with achondroplasia.

Achondroplasia may be inherited as an autosomal dominant trait. This means if a child inherits the affected gene from one parent, the child will have the condition.

If one parent has achondroplasia, the baby has a 50% chance of inheriting the condition. If both parents have achondroplasia, the baby has a 50% chance of inheriting it. However, they also have a 25% chance of inheriting a gene mutation that causes homozygous achondroplasia — a fatal form of the condition. In most cases, two parents without achondroplasia pass on a specific gene that has changed spontaneously.

The characteristic features of achondroplasia include short arms and legs, with especially short upper arms and thighs, and an average-sized trunk. However, these signs might be more challenging to see in a young baby.

Other signs and symptoms can include:

  • limited range of motion at the elbows
  • a head that is disproportionally large compared to the body
  • a prominent forehead
  • increased space between the middle and ring fingers
  • shorter fingers
  • decreased muscle tone
  • bowed legs
  • a curved spine

A doctor may diagnose achondroplasia during pregnancy if they notice shortened bones on an ultrasound scan. They can use the ultrasound to show excessive amniotic fluid around the baby, which can indicate achondroplasia.

Doctors can also diagnose achondroplasia right after birth. They may look for:

  • increased front-to-back head size
  • signs of hydrocephalus, which refers to excess fluid on the brain
  • shortened long bones in the arms and legs, particularly on X-rays

Doctors can perform genetic testing to confirm the diagnosis, but it is not always necessary.

Achondroplasia can increase the risk of certain health conditions. However, with appropriate medical care and support, doctors can treat, manage, or reduce the impact of complications.

Some conditions a person with achondroplasia may be more susceptible to include:

  • Recurring ear infections: Having small ear passages can mean a person is more likely to have frequent ear infections.
  • Curved spine: People with achondroplasia sometimes also develop a curved spine. This does not always cause health problems, but it can change someone’s posture. Occasionally, it may cause pain or put pressure on internal organs.
  • Apnea: Apnea occurs when breathing temporarily stops and then restarts. Over time, it can cause other symptoms and raise the risk of other conditions.
  • Spinal stenosis: This potentially severe complication causes the spinal column to narrow, placing pressure on the spinal cord. Spinal stenosis can cause numbness, tingling, pain, or difficulty walking.
  • Hydrocephalus: This is a less common complication, but it is also potentially serious. Hydrocephalus causes a buildup of fluid on the brain, increasing head size and potentially affecting the brain itself.

Children with achondroplasia often grow into healthy, independent adults. However, the way others perceive the condition can be harmful. This is a product of ableism.

It is important for parents and caregivers to be advocates for their child’s health and happiness as they get older. This may involve:

Encouraging self-esteem and independence

Self-worth and confidence are important aspects of any child’s development. Some ways caregivers can help foster self-esteem in a child with achondroplasia include:

  • treating them according to their age and level of development, not their size
  • treating achondroplasia as a difference, not a problem
  • asking the child how they would like to refer to themselves (e.g., a person of short stature, little person, or similar)
  • enabling the child to do things themselves, instead of doing things for them
  • adapting family activities so they can join in
  • asking family and friends to adopt these approaches too

People can find resources on dwarfism, either to read or share with others, at Little People of America and Understanding Dwarfism.

Looking after spine health

As a child with achondroplasia grows, they may develop spine curvatures, such as kyphosis or lordosis. Parents and caregivers can reduce the chance of this by:

  • positioning the baby with a straight back and head when feeding, with support from a firm pillow or feeding seat
  • avoiding unsupported sitting devices that cause curved sitting during the first year of life
  • seeking pediatric orthopedic care if the spine begins to curve

Promoting nutrition and exercise

Balanced nutrition and exercise can help anyone look after their bones and joints, but it is especially important for those with achondroplasia. It can also reduce the possibility of obesity, sleep apnea, and other complications.

Learn more about what makes up a healthy diet.

Anyone who believes their child may have achondroplasia should speak with a pediatrician for a diagnosis. Knowing a child has the condition can allow parents and caregivers to adapt their approach to parenting and prepare for future challenges that may arise. It also means doctors will know to monitor for any potential complications.

It is also important to attend routine appointments to monitor growth and development in children with achondroplasia.

Achondroplasia is the most common cause of dwarfism. Changes to the FGFR3 gene, which influences how the body produces bone, cause achondroplasia. People can pass on the gene even if they do not have achondroplasia themselves.

In a baby, the signs of achondroplasia may include shorter limbs, a larger head than is typical, and space between the middle and ring fingers. A doctor can provide a diagnosis through a physical examination and medical imaging. Sometimes, they may perform tests to detect the genetic change.

Achondroplasia does not require treatment, but some people may benefit from support so they can lead full and healthy lives. Every child is different, so it is important to base this support on their wants and needs and encourage independence.