Mutations in B4GALNT1 have been identified, which lead to deficiency in GM2 synthesis and are associated with a hereditary spastic paraplegia.49 This suggests that targeted mutation of the porcine B4GALNT1 gene, to eliminate SDa antigen on GM2 gangliosides, may have deleterious effects on donor animals. The gene discussed is B4GALNT1; the disease is hereditary spastic paraplegia.