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Peripheral Nerve:

FRIEDREICH'S ATAXIA



What is Friedreich's Ataxia?

Friedreich's ataxia is an inherited condition 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.

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 changes 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, a thorough physical examination, and several tests.

What other conditions are associated with Friedreich's Ataxia?

There are conditions associated with Friedreich's Ataxia that do not result from the degeneration of nerves. Heart disease, sometimes in forms severe enough to be fatal, is one of the more common and threatening of these conditions. Abnormalities in heartbeat rhythm and diminished strength of the heart muscle have been noted in a large percentage of Friedreich's Ataxia patients, with palpitations and dyspnea (shortness of breath) the most common found symptoms.

Diabetes mellitus, characterised by abnormally high blood and urinary sugar levels, is another condition that may attend Friedreich's Ataxia. Most Friedreich's Ataxia patients who becomes diabetic will do so late in the course of the disease. The nature of the relationship between Friedreich's Ataxia and diabetes has not yet been determined.

What is the age of onset?

Friedreich's Ataxia symptoms may first appear any time between the age of five and fifteen.

What are the early symptoms?

Weakness in legs, unsteadiness in standing, and difficulties in walking are usually among the first symptoms. Typically people with Friedreich's Ataxia may over-or underextend the leg when it is brought forward in walking, and feet may be lifted higher than necessary and brought down too hard.

How disabling is the disease?

Friedreich's Ataxia usually results, within eight to ten years following the onset of symptoms, in an inability to walk. Occasionally, the disease goes into spontaneous remission, which sometimes lasts five to ten years or longer. Remissions, however, are uncommon.

How rapidly does Friedreich's Ataxia progress?

In most cases, the disease is slowly progressive. Scientists have described the progression of Friedreich's Ataxia in terms of two stages: ambulatory, when the patient is able to walk, and nonambulatory, when the patient requires a wheelchair.

The early ambulatory period is characterised by a decrease in or absence of muscle reflexes in addition to an unsteady gait. Elevated heels and flexed toes produce a foot deformity referred to as Friedreich's foot. Mild scoliosis (curvature of the spine) also develops during the period. A diminished sense of touch in arms and legs may occur. In the late ambulatory period, there is great difficulty in walking and a tendency to trip or fall. Use of a cane or other orthopedic aid is usually required. The hands and arms become affected, making writing and other manipulatory tasks difficult. Breakdowns in vocal articulation, irregularities in pitch and loudness, and other changes in voice quality such as speech muscle control. Scoliosis, if severe may cause respiratory problems. There may also be a mild horizontal oscillation of the eyeball, as eye muscles weaken.

The nonambulatory stage begins when the loss of muscle control in the legs has advanced to such a point as to require the constant use of a wheelchair. This usually happens in the third decade of life. The ataxia in the arms, head, and neck continue to worsen during the non ambulatory stage and it becomes increasingly difficult to sit upright. There is little if any movement in lower limbs by the late period of this stage, and upper limbs become very ataxic.

How is Friedreich's Ataxia transmitted?

As with all inherited diseases, Friedreich's Ataxia is caused by a genetic defect. It affects male and female children alike and is passed down as a recessive trait. This means that the disease will develop in offspring only when both mother and father transmit the recessive Friedreich's Ataxia gene. A child who receives the defective gene from one parent and a normal gene from the other becomes a "carrier" and never develops the disease. For this reason, there may be carriers of Friedreich's Ataxia in a family that has no known history of the disorder. When both parents are carriers, the chances of a child inheriting Friedreich's Ataxia are one in four.

How is Friedreich's Ataxia diagnosed?

Diagnosis is made through a thorough physical examination that may include tests for reflex and sensory responses. Laboratory tests such as the electromyogram, which measures the electrical activity of muscle cells, and nerve and muscle biopsies may also be used to confirm the diagnosis. In addition, the physician may take an electrocardiogram to determine if abnormalities in the heartbeat exist, and blood and urine analyses may be made to check for diabetes.

Is there any cure or treatment?

Although there is no known cure for Friedreich's Ataxia, many of the problems imposed by the disease can be treated. Orthopedic intervention, which may include surgery, can alleviate scoliosis, and orthopedic appliances and physical therapy can help prolong ambulation. Heart problems can also be successfully treated for many years with medication. Insulin therapy is effective in controlling diabetes mellitus.

Genetic counseling is also available to discuss pregnancy options.

What research is being done?

Scientists are conducting research into the biochemistry, neurobiology, and biophysics of central and peripheral nerves, heart and skeletal muscle, and the interactions between muscle and nerve to uncover the pathological process of Friedreich's Ataxia. In addition, in-depth studies of diabetes and heart disease are being conducted to determine their relationship with this neurological disorder.

Many investigators have also been focussing their efforts on the possibility that an abnormal enzyme initiates the disease process. One MDA-sponsored scientist has identified a deficiency of mitochondrial malic enzyme in Friedreich's Ataxia patients as a possible cause of the disease. This enzyme is involved in the breakdown of carbohydrates and proteins necessary for the production of cellular energy. In healthy people, mitochondrial malic enzyme activity is highest in the nervous system and heart. Although further studies are needed to substantiate current findings, mitochondrial malic enzyme deficiency could explain the major involvement of the nervous system and heart in Friedreich's Ataxia.


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