Loss-of-function mutations in the B4GALNT1 gene cause a block of ganglioside biosynthesis downstream of GM3 and GD3 (Bhuiyan et al., 2019) and increased GM3 levels (Harlalka et al., 2013), resulting in a complicated form of hereditary spastic paraplegia (HSP26). The gene discussed is B4GALNT1; the disease is hereditary spastic paraplegia.