POMT2 and muscular dystrophy-dystroglycanopathy, type A: As POMT2 catalyzes the first step in O-mannosylation of α-DG, it is believed that POMT2 mutations would cause severe phenotypes, and the first case of POMT2-related α-DGP presented the most severe phenotype of WWS, as expected (van Reeuwijk et al., 2005).