Friedreich's ataxia

Alternative names

Spinocerebellar degeneration

Definition

Friedreich's ataxia is an inherited form of progressive dysfunction of the cerebellum (the part of the brain responsible for movement and complex behavior), spinal cord, and peripheral nerves.

Causes, incidence, and risk factors

Friedreich's ataxia is an autosomal recessive condition, which means that a person must inherit the defective gene from both parents in order to be affected. It is a polyneuropathy, which means that there is damage to multiple nerves

The condition affects 1 in 50,000 people. Symptoms are caused by degeneration of structures in the cerebellum and spinal cord responsible for coordination, muscle movement, and some sensory functions. Vision, particularly color vision, is often mildly affected. Hearing loss occurs in about 10% of patients.

Symptoms generally begin in childhood before puberty. Early symptoms include an unsteady gait, changes in speech, loss of reflexes, and jerky eye movements.

Abnormal muscle control and tone lead to spinal changes and scoliosis, or kyphoscoliosis may develop. Individuals with Friedreich's ataxia may also have hammer toe and high arches.

Heart disease usually develops and may progress into heart failure. Death may result from heart failure or dysrhythmias that will not respond to treatment. Diabetes may develop in later stages of the disease in up to one third of patients.

Friedreich's ataxia results from lack of a specific protein (frataxin) in cells of the brain, nerves, heart, and pancreas. The gene encoding this protein is susceptible to a particular kind of DNA mutation called triplet repeat expansion. What happens is that a sequence of three DNA "letters" is copied more times than is needed, and typically each time the disease is passed on, the number of repeats increases and the symptoms start earlier and become more severe. It is easily and reliably tested for in patient DNA from a blood sample.

Symptoms

• Unsteady gait and uncoordinated movements (ataxia) that gets progressively worse
  
• Loss of coordination and balance; frequent falls or falling more than usual
  
• Jerky eye movements
  
• Abnormal speech
  
• Clumsiness, difficulty controlling the hands
  
• Muscle weakness (decreased muscle strength, independent of exercise)
  o Legs, arms, or other parts of the body
  o May progress to paralysis
  
• Difficulty getting out of a chair or climbing stairs (hip or pelvis weakness)