POMT1 and muscular dystrophy-dystroglycanopathy, type A: Our present findings indicate that POMT1 is a key O-mannosyltransferase relevant for the formation and function of synapses between photoreceptors and their postsynaptic bipolar cells, its mutational loss thereby mimicking a good part of the retinal pathology found in WWS and other POMT1-associated MDDGs.