Giant axonal neuropathy (GAN) is an inherited condition involving dysfunction of a specific type of protein in nerve cells (neurons). The protein is essential for normal nerve function because it forms neurofilaments. Neurofilaments make up a structural framework that helps to define the shape and size of the neurons.
This condition is characterized by abnormally large and dysfunctional axons, which are the specialized extensions of nerve cells that are required for the transmission of nerve impulses.
Giant axonal neuropathy is a very rare disorder; the incidence is unknown. It generally appears in infancy or early childhood and progresses slowly as neuronal injury becomes more severe.
Giant axonal neuropathy is caused by mutations in the GAN gene, which provides instructions for making a protein called gigaxonin. Gigaxonin is involved in a cellular function that destroys and gets rid of excess or damaged proteins. Neurons without functional gigaxonin accumulate excess neurofilaments in the axon, causing the axons to become distended. These giant axons do not transmit signals properly and eventually deteriorate, resulting in problems with movement and other nervous system dysfunction.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Signs of giant axonal neuropathy usually begin in the peripheral nervous system, which governs movement and sensation in the arms, legs, and other parts of the body. Most individuals with this disorder first have problems with walking. Later they may lose sensation, coordination, strength, and reflexes in their limbs. Hearing and visual problems may also occur. Extremely kinky hair (as compared to others in the family) is characteristic of giant axonal neuropathy, occurring in almost all affected people.
As the disorder progresses, 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.
Treatment is symptomatic. Children with GAN and their families usually work with a medical team that includes a pediatric neurologist, orthopedic surgeon, physiotherapist, psychologist, and speech and occupational therapists. The major goals of treatment are to maximize intellectual and physical development and minimize their deterioration as time passes. Many children with GAN begin with normal intellectual development and are able to attend a regular school program. Children should be monitored at least once a year to assess their intellectual abilities and to look for the presence of neurological deterioration.