Mutations in the Glycosyltransferase Domain of GLT8D1 Cause Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disorder without effective neuroprotective therapy. Known genetic variants impair pathways including RNA processing, axonal transport and protein homeostasis. Here we report mutations in a new ALS gene encoding the glycosyltransferase GLT8D1; this class of proteins has not previously been associated with neurodegeneration. Exome sequencing in an autosomal dominant ALS pedigree identified p.R92C mutations in GLT8D1 which co-segregate with disease. Sequencing of local and international cohorts demonstrated significant ALS-association in the same exon, including additional rare deleterious mutations in conserved amino acids. Mutations are associated with the substrate binding site and R92C reduces GLT8D1 enzyme activity ~2-fold. Mutated GLT8D1 exhibits in vitro cytotoxicity and induces motor deficits in zebrafish consistent with ALS. Relative toxicity of mutations in model systems mirrors clinical severity. In conclusion, we have discovered a previously uncharacterised pathophysiological pathway for ALS caused by inherited mutations within a glycosyltransferase enzyme.