Twelve Years of Genome-Wide Association Studies of Human Protein N-Glycosylation

Abstract

Most human-secreted and membrane-bound proteins have covalently attached oligosaccharide chains or glycans. Glycosylation influences the physical and chemical properties of proteins, as well as their biological functions. Unsurprisingly, alterations in protein glycosylation have been implicated in a growing number of human diseases, and glycans are increasingly being considered as potential therapeutic targets, an essential part of therapeutics, and biomarkers. Although glycosylation pathways are biochemically well-studied, little is known about the networks of genes that guide the cell- and tissue-specific regulation of these biochemical reactions in humans in vivo. The lack of a detailed understanding of the mechanisms regulating glycome variation and linking the glycome to human health and disease is slowing progress in clinical applications of human glycobiology. Two of the tools that can provide much sought-after knowledge of human in vivo glycobiology are human genetics and genomics, which offer a powerful data-driven agnostic approach for dissecting the biology of complex traits. This review summarizes the current state of human populational glycogenomics. In Section 1, we provide a brief overview of the N-glycan’s structural organization, and in Section 2, we give a description of the major blood plasma glycoproteins. Next, in Section 3, we summarize, systemize, and generalize the results from current N-glycosylation genome-wide association studies (GWASs) that provide novel knowledge of the genetic regulation of the populational variation of glycosylation. Until now, such studies have been limited to an analysis of the human blood plasma N-glycome and the N-glycosylation of immunoglobulin G and transferrin. While these three glycomes make up a rather limited set compared with the enormous multitude of glycomes of different tissues and glycoproteins, the study of these three does allow for powerful analysis and generalization. Finally, in Section 4, we turn to genes in the established loci, paying particular attention to genes with strong support in Section 5. At the end of the review, in Sections 6 and 7, we describe special cases of interest in light of new discoveries, focusing on possible mechanisms of action and biological targets of genetic variation that have been implicated in human protein N-glycosylation.