Glycosylation is the enzyme-mediated process by which sugars are attached to nascent proteins as a form of post-translational modification. To study PMM2-CDG, a congenital disorder affecting glycosylation, mouse neuroblast cells were genetically modified using CRISPR to try and remove their phosphomannomutase activity, reminiscient of cells with PMM2-CDG. They were then screened using various proteomic methods to determine if the gene modification was successful. Cell lines were produced with reduced PMM activity that will be suitable for study of the PMM2-CDG disease.