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, causing disorders such as familial tumoral calcinosis.