Giant axonal neuropathy
Overview
Giant axonal neuropathy is a rare, autosomal recessive neurological disorder that causes disorganization of neurofilaments. Neurofilaments form a structural framework that helps to define the shape and size of neurons and are essential for normal nerve function.
Symptoms
* Kinky hair * Unusual leg posture * Poor vision * Impaired muscle coordination * Muscle weakness
Causes
Giant axonal neuropathy results from mutations in the GAN gene, which codes for the protein gigaxonin. This alters the shape of the protein, changing how it interacts with other proteins when organizing the structure of the neuron. Neurons affected by the altered protein accumulate excess neurofilaments in the axon, the long extension from the nerve cell that transmits its signal to other nerve cells and to muscles. These enlarged or 'giant' axons cannot transmit signals properly, and eventually deteriorate, resulting in the range of neurological anomalies associated with the disorder.
Diagnosis
Giant axonal neuropathy usually appears in infancy or early childhood, and is progressive. Early signs of the disorder often present in the peripheral nervous system, causing individuals with this disorder to have problems walking. Later, normal sensation, coordination, strength, and reflexes become affected. Hearing or vision problems may also occur. Abnormally kinky hair is characteristic of giant axonal neuropathy, appearing in almost all cases. As the disorder progresses, central nervous system becomes involved, which may cause a gradual decline in mental function, loss of control of body movement, and seizures.
Prognosis
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.
Treatment
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.