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Friedreich's Ataxia

Friedreich's ataxia is an inherited disease that causes progressive damage to the nervous system resulting in symptoms ranging from muscle weakness and speech problems to heart disease. Ataxia results from the degeneration of nerve tissue in the spinal cord and of nerves that control muscle movement in the arms and legs.

Friedreich's ataxia, although rare, is the most prevalent inherited ataxia, affecting about 1 in every 50,000 people in the United States. Males and females are affected equally.

Symptoms

Symptoms usually begin between the ages of 5 and 15 but can appear as early as 18 months or as late as 30 years of age. The first symptom is usually difficulty in walking. The ataxia gradually worsens and slowly spreads to the arms and then the trunk. Foot deformities such as clubfoot, flexion (involuntary bending) of the toes, hammer toes, or foot inversion (turning in) may be early signs. Rapid, rhythmic, involuntary movements of the eyeball are common. Most people with Friedreich's ataxia develop scoliosis (a curving of the spine to one side), which, if severe, may impair breathing. Other symptoms include chest pain, shortness of breath, and heart palpitations. Doctors diagnose Friedreich's ataxia by performing a careful clinical examination, which includes a medical history and a thorough physical examination. Several tests may be performed, including electromyogram (EMG) and genetic testing.

Causes

Mutations in the FXN gene cause Friedreich ataxia. This gene provides instructions for making a protein called frataxin. Although its role is not fully understood, frataxin appears to be important for the normal function of mitochondria, the energy-producing centers within cells. One region of the FXN gene contains a segment of DNA known as a GAA trinucleotide repeat. This segment is made up of a series of three DNA building blocks (one guanine and two adenines) that appear multiple times in a row. Normally, this segment is repeated 5 to 33 times within the FXN gene.

In people with Friedreich ataxia, the GAA segment is repeated 66 to more than 1,000 times. The length of the GAA trinucleotide repeat appears to be related to the age at which the symptoms of Friedreich ataxia appear. People with GAA segments repeated fewer than 300 times tend to have a later appearance of symptoms (after age 25) than those with larger GAA trinucleotide repeats. The abnormally long GAA trinucleotide repeat disrupts the production of frataxin, which severely reduces the amount of this protein in cells. Certain nerve and muscle cells cannot function properly with a shortage of frataxin, leading to the characteristic signs and symptoms of Friedreich ataxia.

This condition is inherited in an autosomal recessive pattern.

Treatment

As with many degenerative diseases of the nervous system, there is currently no cure or effective treatment for Friedreich's ataxia. However, many of the symptoms and accompanying complications can be treated to help patients maintain optimal functioning as long as possible. Diabetes, if present, can be treated with diet and medications such as insulin, and some of the heart problems can be treated with medication as well. Orthopedic problems such as foot deformities and scoliosis can be treated with braces or surgery. Physical therapy may prolong use of the arms and legs. Scientists hope that recent advances in understanding the genetics of Friedreich's ataxia may lead to breakthroughs in treatment.

 

Sources

National Institute of Neurological Disorders and Stroke, USA

Genetics Home Reference, U. S. National Library of Medicine