GBGT1 encodes globoside alpha-1,3-N-acetylgalactosaminyltransferase 1, a glycosyltransferase involved in glycosphingolipid metabolism. In most humans, GBGT1 is functionally inactive due to two conserved inactivating missense mutations (c.688G>A [p.Gly230Ser] and c.887A>G [p.Gln296Arg]) that prevent synthesis of the Forssman (FORS1) glycosphingolipid antigen 1. However, reversion of these mutations restores enzymatic activity to synthesize FORS1 on red blood cells and other tissues 1. Rare individuals carrying the c.887G>A mutation express functional GBGT1 and display the FORS1+ blood group phenotype 2. GBGT1 expression is epigenetically regulated by DNA methylation in various tissues, with particularly high expression in normal ovary tissue but silenced expression in most ovarian cancer cell lines through promoter hypermethylation 3. Most humans naturally produce anti-FORS1 antibodies, with notably no anti-FORS1 detected in ABO A1 or A1B blood groups 2. GBGT1 is evolutionarily conserved despite its pseudogene status in humans, suggesting continued selective pressure 4. Clinically, while GBGT1 is dispensable in humans, FORS1 serves as a receptor for various pathogens and has been detected in cancer tissues 5, and elevated GBGT1 protein levels show promise as a biomarker for unstable angina 6.