Giant axonal neuropathy.
Giant axonal neuropathy (GAN) is a rare autosomal recessive disorder affecting both the central and peripheral nervous systems. Cytopathologically, the disorder is characterized by giant axons with derangements of cytoskeletal components. Geneticists refined the chromosomal interval containing the locus, culminating in the cloning of the defective gene, GAN. To date, many distinct mutations scattered throughout the coding region of the locus have been reported by researchers from different groups around the world. GAN encodes the protein, gigaxonin. Recently, a genetic mouse model of the disease was generated by targeted disruption of the locus. Over the years, the molecular mechanisms underlying GAN have attracted much interest. Studies have revealed that gigaxonin appears to play an important role in cytoskeletal functions and dynamics by directing ubiquitin-mediated degradations of cytoskeletal proteins. Aberrant accumulations of cytoskeletal-associated proteins caused by a defect in the ubiquitin-proteasome system (UPS) have been shown to be responsible for neurodegeneration occurring in GAN-null neurons, providing strong support for the notion that UPS plays crucial roles in cytoskeletal functions and dynamics. However, many key questions about the disease remain unanswered.