GIANT AXONAL NEUROPATHY

Giant Axonal Neuropathy (GAN) is a rare inherited genetic disorder that affects both the central and peripheral nervous systems. GAN is caused by mutations in the GAN gene, the gene that provides instructions for making a protein called gigaxonin, an important protein in cellular development. The majority of children with GAN will begin to show symptoms of the disease sometime before five years of age. Signs of GAN usually begin in the peripheral nervous system, which controls movement and sensation in the arms, legs, and other parts of the body. The typical symptoms of GAN are clumsiness and muscle weakness that progresses from a “waddling gait” to a pronounced difficulty in walking. Additional symptoms include numbness or lack of feeling in the arms and legs, seizures, nystagmus (rapid back and forth movement of the eyes), and intellectual disability.  

Diagnostic testing: The diagnosis of GAN is established by clinical findings including:

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  Nerve conduction velocity (NCV);

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  Lumbar puncture;

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  Brain magnetic resonance imaging (MRI);

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  Peripheral nerve biopsy; and

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  EEG (electroencephalogram).

A definitive diagnosis of GAN using genetic testing is available on a research basis.

Physical findings: Physical examination of GAN may reveal:

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  Low muscle tone;

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  Muscle weakness;

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  Decreased reflexes;

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  Impaired muscle coordination;

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  Impaired sensation; and

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  Developmental delay.

ICD-9: 356.0

GAN usually appears in infancy or early childhood. GAN generally progresses slowly as neurons degenerate and die. Most children have problems with walking in the early stages of the disorder. Later they may lose sensation, coordination, strength, and reflexes in their arms and legs. As time goes on, the brain and spinal cord may become involved, causing a gradual decline in mental function, loss of control of body movement, and seizures. Most children become wheelchair dependent in the second decade of life. Some children may survive into early adulthood.

There is no cure for this disorder. Treatment for GAN is symptom specific and supportive. Children with GAN usually work with a medical team consisting of a pediatric neurologist, orthopedic surgeon, physiotherapist, psychologist, and speech and occupational therapists. The primary goal of treatment is to maximize intellectual and physical development and improve adaptive functioning. Many children with GAN have normal intellectual development and are able to attend regular school. As the disease progresses neurological deterioration may occur. School age children may need to be monitored at least once a year to assess their intellectual abilities and signs of neurological deterioration.

SUGGESTED PROGRAMMATIC ASSESSMENT*

Suggested MER for Evaluation:

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  Clinical history and examination that describes the diagnostic features of the impairment and laboratory findings are needed to confirm the diagnosis.

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  Developmental assessment or psychological assessment to address allegations of mental impairment may be warranted.

Suggested Listings for Evaluation:

REMARKS

Listing level neurological and/or cognitive findings must be documented; diagnosis of GAN or laboratory testing results alone does not meet listing severity.

Must satisfy listing-level severity.