Title: Intrathecal Administration of scAAV9/JeT-GAN for the Treatment of Giant Axonal Neuropathy Background: \- The Gigaxonin gene lets the body make a protein chemical called Gigaxonin. Nerves need Gigaxonin to work properly. Giant Axonal Neuropathy (GAN) causes a shortage of functional Gigaxonin. Nerves stop working normally in people with GAN. This causes problems with walking and sometimes with eating, breathing, and many other activities. GAN has no cure. Over time, GAN can shorten a person s life. Researchers want to see if a gene transfer treatment may help people with GAN. Objectives: \- To see if a gene transfer is safe and shows potential to help people with GAN. Eligibility: \- People age 3 and older with GAN. Design: * For 1 month following gene transfer participants must live full-time within 100 miles of the NIH. * Participants will be screened by phone and in person. They will take many tests. Some are listed below. Their medical records will be reviewed. Their caregivers may be contacted. * Participants will have a total of about 27 visits, weekly, monthly, and then yearly over 15 years. They will include many of the tests below. * Physical and nervous system exams. * Blood, urine, and stool samples. * Nerve, lung, heart, and eye tests. * Questionnaires. * MRI scans, nerve biopsies, and spinal taps. Participants will be sedated for some tests. * Speech, memory, muscle, and mobility tests. * Skin biopsy (small sample removed). * Participants will take many medicines. Some require intravenous lines. * Participants will get the gene transfer through an injection by spinal tap into their cerebrospinal fluid, which flows around the brain and spinal cord. The genes are packed in a modified virus that carries the genes to cells in their body. Participants safety is not guaranteed.