Definition

Achondroplasia is a bone growth disorder caused by a genetic mutation that affects the arms and legs, leading to dwarfism. This condition is rare, occurring in about 1 in 15,000 to 40,000 births worldwide. Despite its rarity, achondroplasia is the most common form of growth disorder in children.

About 80% of people with achondroplasia have parents of average height and are born with a genetic mutation. Achondroplasia is an autosomal dominant condition, meaning only one parent needs to have the disorder for it to be passed on to their child. Babies born with achondroplasia typically have weak muscles and delayed motor development. Respiratory problems, ear infections, and obesity can also occur in individuals with achondroplasia.

Causes

Achondroplasia is caused by a genetic mutation that occurs during the early stages of fetal development. In achondroplasia, soft tissues that normally turn into bone do not develop properly. The mutation affects the FGFR3 gene, or Fibroblast Growth Factor Receptor 3.

This mutation leads to shorter bones with abnormal shapes, primarily affecting the bones of the arms and legs.

Most cases of achondroplasia result from spontaneous genetic mutations, meaning the genetic change is not inherited from the parents. The exact cause of these spontaneous mutations remains unknown.

Risk Factor

Heredity is a significant risk factor for achondroplasia. If one parent has achondroplasia, there is a 50% chance that the child will have the condition. If both parents have achondroplasia, the risks for the child are as follows:

• A 50% chance of inheriting a single gene causing achondroplasia.
• A 25% chance of either having a normal stature or inheriting two copies of the gene, leading to a fatal form of achondroplasia known as homozygous achondroplasia. In this case, the child may die in utero or within a few months after birth.

Symptoms

The most common symptom of achondroplasia is shorter-than-average bone length. The average adult height for individuals with achondroplasia is about 131 cm (4 feet 3 inches) for males and 124 cm (4 feet) for females. Other symptoms of achondroplasia include:

• Short limbs, hands, feet, and fingers
• A large gap between the third and fourth fingers
• A larger head size with a prominent forehead
• A flattened nose bridge
• Abnormal spine curvature, such as lordosis (inward curvature) or kyphosis (outward curvature)
• Bowed legs (O-shaped legs)
• Weak muscle tone

Despite having different physical characteristics, individuals with achondroplasia typically have normal intelligence.

Diagnosis

Achondroplasia can be detected before birth or soon after the baby is born. During pregnancy, achondroplasia can be identified through an ultrasound. In addition to ultrasound, FGFR3 gene mutation screening can be conducted during pregnancy.

After birth, achondroplasia can be diagnosed through various examinations, such as physical assessments, X-rays, genetic testing, or MRI scans. Physical examinations may reveal disproportionate short stature indicative of achondroplasia.

Genetic testing involves taking blood samples from the child and both parents to detect possible genetic abnormalities in a laboratory setting.

Management

There is no specific cure for achondroplasia; treatment focuses on managing symptoms. For example, parents can monitor their baby's height, weight, and head circumference upon an initial diagnosis of achondroplasia. Treatment aims to manage potential complications, such as:

• Maintaining a healthy weight to prevent obesity
• Surgery (ventriculoperitoneal shunt) to relieve brain fluid pressure or life-threatening complications like craniocervical junction compression
• Surgery to remove adenoids and tonsils
• Growth hormone therapy
• Dental care
• Continuous Positive Airway Pressure (CPAP) therapy for sleep apnea
• Ear tubes or antibiotics to prevent infections

Beyond medical management, it is also important to support the social integration of individuals with achondroplasia to ensure they maintain a healthy social life.

Complications

Some complications of achondroplasia in infants include:

• Reduced muscle mass, leading to delayed motor development, such as walking
• Apnea, which causes breathing problems, such as slow breathing
• Hydrocephalus, or fluid accumulation in the brain
• Narrowing of the spinal cord fibers

In children and adults, achondroplasia complications may include:

• Difficulty bending the elbows
• Obesity
• Recurrent ear infections
• Bowed legs, typically in an O-shape
• Severe spinal stenosis, or narrowing of the spinal canal

Prevention

Achondroplasia results from genetic mutations that may occur spontaneously or not be inherited. Therefore, there is no specific prevention for achondroplasia. If one parent has achondroplasia or has a family history of the condition, it is advisable to consult a doctor.

When to See a Doctor?

During pregnancy, it is important to have regular checkups with a doctor. This way, any fetal developmental disorders, including achondroplasia or other abnormalities, can be detected early.

Additionally, consult a doctor if your child does not meet the height criteria for their age or shows delayed motor development, such as sitting, crawling, or walking. If your child has breathing problems, recurrent ear infections, leg or back pain, or obesity, further consultation with a doctor is recommended.

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