What is Achondroplasia?
Achondroplasia is a bone growth disorder that causes
disproportionate dwarfism. Dwarfism is defined as a condition of short stature
as an adult. People with achondroplasia are short in stature with a normal sized
torso and short limbs. It’s the most common type of disproportionate dwarfism.
The disorder occurs in approximately 1 in 25,000 live births,
according to Columbia University Medical Center
(CUMC). It’s equally common in males as females.
What Causes Achondroplasia?
During early fetal development, much of your skeleton is made up
of cartilage. Normally, most cartilage converts to bone. However, if you have
achondroplasia, a lot of the cartilage doesn’t convert to bone. This is caused
by mutations 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 interferes with normal skeletal development.
Is Achondroplasia Inherited?
In more than 80 percent of cases, achondroplasia isn’t inherited,
according to the National Human
Genome Research Institute (NHGRI). These cases are caused by spontaneous
mutations in the FGFR3 gene.
About 20 percent of cases are inherited. The mutation follows an
autosomal dominant inheritance pattern. This means that only one parent needs
to pass down a defective FGFR3 gene for a child to have achondroplasia.
If one parent has the condition, the child has a 50 percent
chance of getting it.
If both parents have the condition, the child has:
- a 25 percent chance of normal stature
- a 50 percent chance of having one defective gene
that causes achondroplasia
- a 25 percent chance of inheriting two defective
genes, which would result in a fatal form of achondroplasia called homozygous achondroplasia
Infants born with homozygous achondroplasia are usually stillborn
or die within a few months of being born.
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 Symptoms of Achondroplasia?
People with achondroplasia generally have normal intelligence
levels. Their symptoms are instead physical.
At birth, a child with this condition 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
- an abnormally large, prominent forehead
- an underdeveloped area of the face between the
forehead and upper jaw
Health problems an infant may have include:
- 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
How Tall Will My Child Grow?
The average height for adults with achondroplasia is 4 feet, 4 inches
for males and 4 feet, 1 inch for females, according to The
Children's Hospital of Philadelphia (CHOP). It’s rare for an adult with
achondroplasia to reach a height of 5 feet.
How Is Achondroplasia Diagnosed?
Your doctor may diagnose your child with achondroplasia while
you’re pregnant or after your infant is born.
Diagnosis During Pregnancy
Some characteristics of achondroplasia are detectable during 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.
Diagnosis After Your Child Is Born
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.
How Is Achondroplasia Treated?
There’s no cure or specific treatment for achondroplasia. If any
complications arise, then your doctor will address those issues. For example,
antibiotics are given for ear infections and surgery may be performed in severe
cases of spinal stenosis.
Some doctors use growth hormones to increase the growth rate of a
child’s bones. However, their long-term effects on height haven’t been determined.
According to the NHGRI,
most people with achondroplasia have a normal life span. However, there’s a
slightly increased risk of death during the first year of life. There may also
be an increased risk of heart disease later in life.
If you have achondroplasia, you may need to make some physical
adaptations, such as avoiding impact sports that could damage the spine.
However, you can still live a full life.