Diagnosing Achondroplasia in Children

Doctors at Hassenfeld Children’s Hospital at NYU Langone are experienced in diagnosing achondroplasia, the most common cause of dwarfism, or short stature, in children. The condition is caused by mutations in a gene that affects a child’s growth plates—islands of soft tissue at the ends of bones where new bone grows—preventing them from turning into bone.

Adults with achondroplasia reach a height of no more than 4 feet and 4 inches. Characteristics that distinguish achondroplasia from other causes of dwarfism include a disproportionately large head and forehead, short limbs and fingers, and a flattened nose.

The mutations occur in the fibroblast growth factor receptor 3 gene, or the FGFR3 gene. A child who has a parent with the FGFR3 gene mutation has a 50 percent chance of inheriting it. But most FGFR3 mutations occur spontaneously, meaning that the gene mutation is not inherited. In fact, most children with achondroplasia have average-size parents.

Because the bones in the head and spine don’t form correctly, children with achondroplasia can face a number of health challenges and may develop certain orthopedic conditions.

Some babies and children develop hydrocephalus, a buildup of fluid in the brain that can cause brain damage. In addition, abnormally shaped bones in the middle ear can cause frequent ear infections, which can lead to speech delays and hearing loss over time.

Children with achondroplasia may also develop bowed, or curved, legs. Usually, growth plates in the knee fuel growth in the inner and outer portions of the lower leg bones at the same rate. In children with achondroplasia, the growth plates may not always work properly. As a result, one side of the leg bone grows faster than another, causing bowing.

Spinal curvature in the middle of the back, known as kyphosis, can develop in infants, children, and adults with achondroplasia. This condition may worsen over time, causing severe spinal deformity. Compression of the spinal cord or nerves branching off from the spinal cord, which can occur if the spinal canal that houses these nerves becomes narrowed, is another common problem in children and adults with achondroplasia. Left untreated, spinal cord compression may lead to weakness or paralysis.

Infants and children with achondroplasia may have either obstructive or central sleep apnea. Children with obstructive sleep apnea frequently snore and gasp for breath at night. This may be caused by small nasal passages or extra tissue that relaxes during sleep, blocking the airways. Children with central sleep apnea may stop breathing or breathe very shallowly while asleep because of a disruption in the brain’s signals. This may occur if your child’s spinal cord is compressed as it exits the base of the skull.

During Pregnancy

An initial diagnosis of achondroplasia may be made during pregnancy, while a child is in the womb. If you have a family history of achondroplasia, you may want to seek genetic counseling to determine your risk of having a child with this condition.

Our doctors may use information from prenatal imaging and genetic tests to make an initial diagnosis. Our experts can offer information about achondroplasia and refer you to our genetics experts and other specialists who may be involved in your child’s care.

Prenatal Ultrasound

A routine prenatal ultrasound, which uses sound waves to create an image of the baby in the womb, can often detect common characteristics of achondroplasia. For instance, the ultrasound may reveal shortened limbs or hydrocephalus, which causes a buildup of fluid in cavities within the brain and makes the head appear unusually large.

If the ultrasound reveals any of these features, the doctor may recommend testing the mother’s amniotic fluid for the presence of a mutation in the FGFR3 gene.

Amniocentesis

In amniocentesis, the doctor inserts a hollow needle through a pregnant woman’s abdomen and into the uterus, removing a small amount of amniotic fluid, which surrounds the baby in the womb. A specialized laboratory examines the fluid to look for the FGFR3 mutation.

Chorionic Villus Sampling

A chorionic villus sampling test involves analyzing a small tissue sample from the placenta, which carries oxygen and nutrients from a mother to the baby in her womb. The doctor threads a thin tube through the vagina and cervix and into the placenta to remove placental tissue, which is tested to see if it contains an altered FGFR3 gene.

After Delivery

To help confirm a diagnosis, our doctors perform a physical exam and other tests to look for signs of achondroplasia in babies and children.

Physical Exam

During a physical exam, your child’s pediatrician, geneticist, or orthopedic specialist may look for other signs of achondroplasia that may be more difficult to detect with prenatal ultrasound, such as the following:

• unusually short thighs and arms
• prominent forehead with a small, upturned nose
• small chest
• broad, flat feet, short toes, and short fingers
• extra space between the middle and ring fingers, called a trident hand
• weak muscle tone
• bowed legs

Blood Test

A routine blood test may be recommended to look for an altered FGFR3 gene if prenatal genetic tests have not been performed.

Imaging Tests

Doctors at Hassenfeld Children’s Hospital may use one or more imaging tests, either to help diagnose achondroplasia or to identify spinal cord compression, a common complication of achondroplasia that can cause pain and weakness in newborns and young children.

In X-rays, ionizing radiation beams are used to produce images of bones, which may be used to measure the length of the bones in your baby’s arms and legs. They can also be used to help detect spinal stenosis and curvature in the legs and back.

In CT scans, many X-rays are used to create cross-sectional, three-dimensional pictures of vertebrae—tiny bones in the spine.

MRI uses magnetic fields to create detailed, three-dimensional images of areas that are more difficult to see on an X-ray, such as the spinal cord.

Neurological Exam

Our pediatric neurologists perform a comprehensive neurological exam to look for signs of spinal cord compression, hydrocephalus, and other neurological problems that are common in babies and children with achondroplasia. A neurological exam is performed during each visit.

During this exam, the doctor usually tests the function of the cranial nerves—12 pairs of nerves that relay sensory information to the brain and help to control facial movement and other functions. The doctor may observe your child’s ability to make certain facial expressions, swallow water, and move the tongue from side to side. The doctor may also perform a vision test and determine how your child’s pupils—the circular black areas in the middle of the eyes that allow light in—respond to light. In addition, the doctor examines your child’s ability to move, which may be affected by spinal cord compression.

Sleep Study

The doctor may suggest that you use a home monitoring device to check if your child has signs of sleep apnea during the first few months of life. If your child wakes up repeatedly during the night, the doctor may recommend an overnight sleep study, or polysomnogram, in NYU Langone’s Pediatric Sleep Disorders Program.

The sleep study can help to determine whether your child has a breathing disorder, such as obstructive or central sleep apnea, that interferes with sleep. Either type of apnea wakes a child, and these sleep interruptions can cause excessive daytime sleepiness. Disturbances in a child’s sleep–wake cycle can also lead to frequent awakenings to use the bathroom, bed-wetting, or sleepwalking.

The doctor can recommend the best treatment for your child, based on the cause of the condition and the severity or frequency of your child’s symptoms.

Hearing Exam

If your child has repeated ear infections or a delay in speaking, the doctor may refer you to a pediatric otolaryngologist, a doctor who specializes in conditions that affect the ears, nose, and throat. During a visit with this specialist, your child has a comprehensive hearing exam—a test that is repeated as your child develops.

After diagnosis, your doctor can develop a care plan that addresses your child’s most prominent symptoms, with the goal of improving his or her overall health. Our specialists are available throughout diagnosis and treatment to offer the support you need.