Genetics of Achondroplastic Dwarfism

In learning about the genetics of achondroplastic dwarfism we know that it is a very common type of dwarfism. This bone growth disorder is characterized by cartilage having trouble turning into bone. This is especially true for the long bones in the patients legs and arms. As the most common short-limbed dwarfism, it is seen in about one in 15,000 to 40,000 newborn babies.

Genetics

In understanding the genetics of achondroplastic dwarfism, we know that an FGFR3 gene mutation is the cause. This gene is necessary for the maintenance and development of brain and bone tissue. This condition is inherited in an autosomal dominant pattern. However, not every case is genetically inherited.

Signs and Symptoms

The characteristic appearance of this type of dwarfism is present at birth. Symptoms may include:

• Bowed legs
• Large head to body size is disproportionately different
• Shortened legs and arms
• Spinal stenosis
• Hands appear abnormal with persistent space between ring and long fingers
• Decreased muscle tone
• Prominent forehead
• Short stature
• Lordosis and kyphosis

Spinal stenosis is a condition in which the spinal column is narrowed putting pressure on the spinal cord.

Lordosis is a curving of the lower spine where it curves inward. Kyphosis is a curving of the midspine where it curves outward.

People with this condition can also have clubbed feet and hydrocephalus. Hydrocephalus is a buildup of fluid on the brain. This can lead to brain swelling and a variety of complications if not promptly treated.

Diagnosis

When a woman is pregnant, she can have a prenatal ultrasound. If this shows excessive amniotic fluid around her unborn infant, this condition is possible.

After the baby is born, an examination may show a front-to-back head size increase. The signs of hydrocephalus may be present. These may include irritability, sleepiness, eyes seem to gaze downward, seizures and vomiting.

In newborns, achondroplasia may be revealed in the long bones by X-rays.

Treatment

There is no set course of treatment for this condition. As the related abnormalities cause problems, they should be treated. People with hydrocephalus are treated by having their flow of CSF improved. This may be done by surgically removing the blockage or placing a shunt.

Spinal stenosis can often be managed with medications. If the patient is experiencing pain, nonsteroidal anti-inflammatory drugs can help to reduce it. Physical therapy and lifestyle changes can also be helpful. For acute episodes of increased pain, the patient may benefit from short-term stronger pain medications and/or steroid injections. Other medications the patient may benefit from include phenytoin, tricyclic antidepressants and carbamazepine. If the compression is severe, surgery may be necessary.

Lordosis and kyphosis are usually treated with the “wait and see” approach, where the condition is monitored until such time as treatment is necessary. Other issues will be treated if they arise.

Resources

Genetics Home Reference. (2006). Achondroplasia. Retrieved on April 14, 2011 from Genetics Home Reference: https://ghr.nlm.nih.gov/condition/achondroplasia

Cedars Sinai Medical Center. (2011). Achondroplastic Dwarfism. Retrieved on April 14, 2011 from Cedars Sinai Medical Center: https://www.cedars-sinai.edu/Patients/Health-Conditions/Achondroplastic-Dwarfism.aspx

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