B4GALNT1 and Cognitive impairment: Pathogenic variants in the human B4GALNT1 gene cause SPG26, an autosomal recessive (OMIM #609195), complicated HSP, characterized not only by lower limb weakness, but also by cognitive impairment, developmental delay, cerebellar ataxia, dysarthria, and peripheral neuropathy, and these clinical phenotypes are similar to those of B4galnt1 KO mice (Boukhris et al., 2013; Harlalka et al., 2013; Bhuiyan et al., 2019).