B4GAT1 and muscular dystrophy-dystroglycanopathy, type A: To test how reported B4GAT1 missense mutations affect the intracellular localization of B4GAT1 and its enzymatic activity, we cloned three mutant B4GAT1-Myc expression constructs (Figure 5A): Mut1 (N390D) represents a mutation identified in a patient with Walker-Warburg syndrome (Buysse et al., 2013); Mut2 (D227N/D229N) is a mutation in the glycosyltransferase signature DXD motif (Wiggins and Munro, 1998; Bao et al., 2009); and Mut3 (M155T) mimics a mutant allele identified in a B4gat1-deficient mouse model with axon guidance defects (Wright et al., 2012).