What is Friedreich ataxia?
is an inherited condition that affects the nervous system and causes movement problems. People with this condition develop impaired muscle coordination (ataxia) that worsens over time. Other features include the gradual loss of strength and sensation in the arms and legs, muscle stiffness (spasticity), and impaired speech. Many individuals often have a form of heart disease called hypertrophic cardiomyopathy
. Some people develop diabetes, impaired vision, hearing loss, or an abnormal curvature of the spine (scoliosis
). Most people with Friedreich ataxia begin to experience the signs and symptoms around puberty. This condition is caused by mutations in the FXN
gene and is inherited in an autosomal recessive
Last updated: 1/23/2012
What are the signs and symptoms of Friedreich ataxia?
Symptoms usually begin between the ages of 5 and 15 but can, on rare occasions, appear as early as 18 months or as late as 50 years of age. The first symptom to appear is usually difficulty in walking, or gait ataxia. 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 inward) may be early signs. Over time, muscles begin to weaken and waste away, especially in the feet, lower legs, and hands, and deformities develop. Other symptoms include loss of tendon reflexes, especially in the knees and ankles. There is often a gradual loss of sensation in the extremities, which may spread to other parts of the body. Dysarthria (slowness and slurring of speech) develops, and the person is easily fatigued. Rapid, rhythmic, involuntary movements of the eye (nystagmus) 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 that may occur include chest pain, shortness of breath, and heart palpitations. These symptoms are the result of various forms of heart disease that often accompany Friedreich ataxia, such as cardiomyopathy (enlargement of the heart), myocardial fibrosis (formation of fiber-like material in the muscles of the heart), and cardiac failure. Heart rhythm abnormalities such as tachycardia (fast heart rate) and heart block (impaired conduction of cardiac impulses within the heart) are also common. About 20 percent of people with Friedreich ataxia develop carbohydrate intolerance and 10 percent develop diabetes mellitus. Some people lose hearing or eyesight.
The rate of progression varies from person to person. Generally, within 10 to 20 years after the appearance of the first symptoms, the person is confined to a wheelchair, and in later stages of the disease individuals become completely incapacitated. Life expectancy may be affected, and many people with Friedreich ataxia die in adulthood from the associated heart disease, the most common cause of death. However, some people with less severe symptoms of Friedreich ataxia live much longer, sometimes into their sixties or seventies.
Last updated: 3/3/2010
What causes Friedreich ataxia?
Friedreich ataxia is caused by a defect in a gene called Frataxin (FXN)
, which provides instructions for making a protein called frataxin. 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.
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.
Last updated: 1/23/2012
How is Friedreich ataxia inherited?
Friedreich ataxia is inherited in an autosomal recessive
pattern, which means that both copies of the FXN gene
in each cell
. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene (and are referred to as carriers
); but they typically do not show signs and symptoms of the condition. When two people who are carriers of an autosomal recessive condition have a child, each time there is a 25% (1 in 4) chance that the child will have the condition, a 50% (1 in 2) chance that the child will be a carrier like each of the parents, and a 25% (1 in 4) chance that the child will not have the condition and not be a carrier.
Last updated: 1/23/2012