MGAT4C is a glycosyltransferase that catalyzes the transfer of N-acetylglucosamine (GlcNAc) to core mannose residues of N-linked glycans, specifically forming GlcNAcβ1-4 branches on the GlcNAcβ1-2Manα1-3 arm [UniProt]. This enzyme is essential for producing tri- and tetra-antennary N-linked sugar chains and is a positive regulator of cell surface AC133 expression on CD133 glycoproteins 1. MGAT4C functions in the Golgi membrane and participates in viral protein processing through N-linked glycosylation [GO Annotations]. Mechanistically, pro-inflammatory cytokines alter MGAT4C expression, impacting glycosylation patterns on extracellular proteins like fibronectin and aggrecan 2. Disease relevance includes associations with osteoarthritis (altered N-glycan patterns), neurocognitive disorders (rare CNV deletion) 3, schizophrenia (somatic copy number losses at 12q21.31) 4, and autism spectrum disorder (identified as a key discriminatory biomarker, AUC=0.730) 5. Clinically, MGAT4C CNVs significantly modulate prostate cancer cell proliferation and migration, with overexpression in metastatic versus localized disease 6. Gene duplication in birds (Neoaves) suggests evolutionary importance for oxidative stress mitigation 7.