MGAT5B encodes a glycosyltransferase that catalyzes the transfer of N-acetylglucosamine (GlcNAc) to mannose residues in both N-glycans and O-mannosyl glycans, creating β(1,6)-branched oligosaccharide structures 1. The enzyme acts on the core structure of N-glycans by adding GlcNAc to β1-6 linkage positions on both α1,3- and α1,6-linked mannose arms, and also modifies brain O-mannosyl glycans to form 2,6-branched structures 1. MGAT5B plays a crucial role in regulating integrin and laminin-dependent neuronal cell adhesion and migration through its O-mannosyl glycan pathway activity. The enzyme is significantly upregulated in metastatic prostate cancer, where its β(1,6)-branched oligosaccharide products serve as markers of tumor progression and correlate with poor disease-free survival 2. MGAT5B expression has been identified as a predictive biomarker in various cancers, including hepatocellular carcinoma metastasis 3 and non-small cell lung cancer, where baseline expression predicts pathological response to neoadjuvant chemo-immunotherapy and associates with shorter survival 4. The gene is also implicated in heart failure 5 and Moyamoya disease 6, highlighting its broader role in pathological processes beyond cancer.