Glycosylation is a highly regulated enzymatic process where carbohydrates are attached to the backbone of proteins and plays a critical role in protein processing, contributing to protein structure stability and function. It is critical for physiological and pathological cellular functions like cell adhesion, cell receptor activation and intermolecular interactions. Defects in glycosylation leads to a group of genetic metabolic disorders called CDGs (Congenital Disorders of Glycosylation). There are approximately 170 different types of CDG that have been discovered. PIGN-CDG is a disorder of GPI anchor biosynthesis where mutations in the PIGN gene (Phosphatidylinositol Glycan Anchor Biosynthesis Class N) results in reduction in GPI-anchor proteins on the cell surface. There are currently no approved treatments for PIGN-CDG, as well as no approved biomarkers for clinical diagnosis or evaluating new PIGN-CDG treatments, which are necessary to determine the functional efficacy of potential repurposed drug candidates for PIGN-CDG that have been recently identified. This poster outlines the initial steps taken to validate a flow cytometry assay for PIGN-CDG diagnosis that can be used as a biomarker in future PIGN-CDG repurposed drug studies.