The ST6GAL1 gene encodes β-Galactosamide α-2,6-Sialyltransferase 1. It is a type II membrane protein and is localized to the trans-Golgi network. It catalyzes 2,6-sialylation of Galβ1,4-GlcNAc structures on N-glycans. ST6GAL1 is highly expressed in the liver and other tissues. ST6GAL1 deficiency causes abnormalities in B-cell immunoreactivity. The expression and activity of ST6GAL1 are associated with tumor metastasis in breast and colon cancers. The majority of ST6GAL1 in the liver is cleaved and secreted into the serum and may be used as a biomarker for hepatitis diseases.