Friedreich ataxia

Friedreich ataxia is a genetic condition that damages nerve tissue, causing a loss of muscle coordination (ataxia) that worsens over time. Other characteristics of this condition include the gradual loss of strength and sensation in the arms and legs, muscle stiffness (spasticity) in the limbs, and impaired speech. Friedreich ataxia may also affect heart function.

Typically, signs and symptoms of Friedreich ataxia first appear in childhood or the early teens. Poor balance when walking and slurred speech are often the initial symptoms. About 25 percent of cases, however, occur after age 25. These cases are classified as late-onset Friedreich ataxia (LOFA), with onset between 26 and 39 years, or very late-onset Friedreich ataxia (VLOFA), which begins at age 40 or older.

Friedreich ataxia is estimated to affect 1 in 40,000 people.

Mutations in the FXN gene cause Friedreich ataxia.

The FXN 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 energy-producing centers (mitochondria) within cells. Friedreich ataxia is caused by a mutation in which a DNA segment, known as the GAA triplet repeat, is abnormally expanded within the FXN gene. Normally, this segment is repeated 5 to 33 times within the FXN gene. In people with Friedreich ataxia, however, the GAA segment is repeated 66 to more than 1,000 times. The abnormally expanded GAA segment 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 signs and symptoms of Friedreich ataxia.

Read more about the FXN gene.

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.