GALNT3 (Polypeptide N-Acetylgalactosaminyltransferase 3): GALNT3 is a gene that encodes a protein involved in O-linked glycosylation, which adds N-acetylgalactosamine to proteins. This modification is crucial for proper protein function and cell signalling. Mutations in GALNT3 can disrupt calcium and phosphate balance, resulting in disorders such as familial tumoral calcinosis.