Diagnosis of Friedreich’s Ataxia

Diagnosis of Friedreich’s ataxia (FA) can be carefully done by reviewing the symptoms, medical history, and any history of neuromuscular disorders in a family.

A doctor will perform a thorough physical and neurological examination, and will look for problems like difficulty balancing and irregular reflexes, which are indicative of the type of nerve damage that occurs in FA.

Tests that may help diagnose FA include nerve conduction studies, tests of heart function, magnetic resonance imaging, and blood tests. However, a conclusive diagnosis of Friedreich’s ataxia can only be made through genetic testing.

Physical examination

The first step in diagnosing FA is a physical examination, where the neurologist will look for signs of muscle weakness, particularly in the arms and legs. A doctor will also look for skeletal problems, including high-arched feet and scoliosis (curvature of the spine), or involuntary eye movements that can be an indication of FA.

Nerve conduction tests

The nerve conduction velocity (NCV) test measures the speed at which nerve cells transmit impulses (electrical signals). These tests determine whether the speed of nerve impulses is reduced due to nerve cell damage.

The NCV test is performed by placing electrodes on the surface of the skin at various points over a nerve. One electrode delivers small electrical shocks to the nerve, and the other records the nerve’s responses. In people with FA, the responses are typically slower than normal due to nerve damage.

Tests of heart function

Heart-related health problems are common in people with FA. Hypertrophic cardiomyopathy, where the heart muscles become enlarged and weakened, is particularly frequent. Several different tests, including electromyogram, electrocardiogram, and echocardiogram, can be used individually or together to identify hypertrophic cardiomyopathy and other heart-related abnormalities in people with FA.

An electromyogram is a test that checks the health of the muscles and the nerves that control them. It measures the electrical activity of muscle cells and looks for any muscle damage. It is performed by inserting a needle-like electrode into a muscle and recording the electrical signals generated during muscle contraction.

An electrocardiogram (ECG) is a test that gives a graphic representation of the electrical activity or beat pattern of the heart. It checks for abnormalities in the heartbeat. Sometimes, ECG is done using a Holter monitor, which is a portable device that measures the activity of the heart continuously for 24 to 48 hours.

An echocardiogram uses sound waves to produce images of the heart. It assesses heart function, measures the thickness of the heart muscle, and determines the size of the heart chambers. It also records the position and motion of heart muscle.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) is an imaging test that uses powerful magnetic waves and radio waves to scan the brain and spinal cord to look for signs of deterioration. In Friedreich’s ataxia, it is common for certain parts of the brain and spine to be atrophied (smaller), particularly the neck region of the spinal cord and the cerebellum, a part of the brain that is important for coordinating voluntary movement.

MRI images are useful for ruling out other neurological conditions that can cause symptoms similar to FA. For example, a tumor or blood clot in the brain can cause ataxia-like symptoms, and these abnormalities are usually visible on an MRI.

Blood tests and urine analysis

Blood and urine tests check for high blood sugar (glucose) to determine if the individual has diabetes or glucose intolerance. These tests can also rule out other illnesses that may cause similar symptoms, like certain infections.

Genetic testing

Genetic testing analyzes the FXN gene sequence to look for mutations that cause the disease; the most common type of FA-causing mutation is an expanded GAA repeat. FA occurs when both copies of the FXN gene (one inherited from each biological parent) are mutated.

Genetic testing is highly reliable and can confirm the genetic abnormality that causes FA, which allows for a definitive diagnosis of the disease. The DNA used for genetic testing is usually taken from blood cells acquired from a blood sample.

Genetic testing can be done before birth to see if a developing baby is affected by the disease.

It also can determine whether a person has one mutated copy and one normal copy of FXN. Such individuals are said to be “carriers” of the disease, because they will not develop FA themselves, but may pass disease-causing genes to their children. Two people who are both carriers have a 25% chance of having a biological child with FA.

 

Last updated: April 9, 2021

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