– Protein O-Linked-Mannose β-1 2-N-Acetylglucosaminyltransferase 1 (POMGNT1) belongs to the Glycosyltransferase 13 family. Amino acid residues between 299-311 are important for both protein expression and enzymatic activity. The minimal catalytic domain is located between positions 299-651. It is suggested that the stem domain of the soluble form is unnecessary for activity, but that some amino acids play a crucial role in the membrane-bound form. Defects in POMGNT1 are the cause of muscular dystrophy-dystroglycanopathy congenital with brain and eye anomalies type A3 (MDDGA3).