PIGX (phosphatidylinositol glycan anchor biosynthesis class X) encodes a regulatory subunit of the glycosylphosphatidylinositol (GPI)-mannosyltransferase I complex 1. As a stabilizing subunit, PIGX facilitates the transfer of the first mannose residue to GPI core structures, a critical early step in GPI-anchor biosynthesis that enables attachment of diverse proteins to cell membranes 1. These GPI-anchored proteins localize to lipid rafts and function as cell co-receptors, enzymes, and adhesion molecules 1. Beyond its canonical GPI-biosynthetic role, PIGX participates in cancer biology through interaction with reticulocalbin proteins (RCN1/RCN2), where the RCN1/PIGX/RCN2 complex negatively regulates tumor suppressors ZIC1 and EHD2, promoting breast cancer cell proliferation 2. PIGX upregulation is frequently observed in breast cancer, suggesting oncogenic potential 2. Additionally, PIGX appears in gene fusion events associated with therapeutic responses; PAK2::PIGX fusions were identified in patients with PDGFRA/B-negative hypereosinophilic syndrome responding to imatinib treatment 34. Germline PIGX mutations have been identified as potentially pathogenic variants in young never-smokers with lung adenocarcinoma, suggesting involvement in cancer predisposition 5. The protein's complex regulatory interactions indicate broader roles in cellular homeostasis beyond GPI biosynthesis.