Glycosylation is a common post-translational modification of proteins. Glycosylation is associated with a number of human diseases. Defining genetic factors altering glycosylation may provide a basis for novel approaches to diagnostic and pharmaceutical applications. Here we report a genome-wide association study of the human blood plasma N-glycome composition in up to 3811 people measured by Ultra Performance Liquid Chromatography (UPLC) technology. Starting with the 36 original traits measured by UPLC, we computed an additional 77 derived traits leading to a total of 113 glycan traits. We studied associations between these traits and genetic polymorphisms located on human autosomes. We discovered and replicated 12 loci. This allowed us to demonstrate an overlap in genetic control between total plasma protein and IgG glycosylation. The majority of revealed loci contained genes that encode enzymes directly involved in glycosylation (FUT3/FUT6, FUT8, B3GAT1, ST6GAL1, B4GALT1, ST3GAL4, MGAT3 and MGAT5) and a known regulator of plasma protein fucosylation (HNF1A). However, we also found loci that could possibly ref lect other more complex aspects of glycosylation process. Functional genomic annotation suggested the role of several genes including DERL3, CHCHD10, TMEM121, IGH and IKZF1. The hypotheses we generated may serve as a starting point for further functional studies in this research area.

45Glycosylation is a common post-translational modification of proteins. It is known, that glycans 46 are directly involved in the pathophysiology of every major disease. Defining genetic factors 47 altering glycosylation may provide a basis for novel approaches to diagnostic and pharmaceutical 48 applications. Here, we report a genome-wide association study of the human blood plasma N-49 glycome composition in up to 3811 people. We discovered and replicated twelve loci. This 50 allowed us to demonstrate a clear overlap in genetic control between total plasma and IgG 51 glycosylation. Majority of loci contained genes that encode enzymes directly involved in 52 glycosylation (FUT3/FUT6, FUT8, B3GAT1, ST6GAL1, B4GALT1, ST3GAL4, MGAT3, and 53 MGAT5). We, however, also found loci that are likely to reflect other, more complex, aspects of 54 plasma glycosylation process. Functional genomic annotation suggested the role of DERL3, which 55 potentially highlights the role of glycoprotein degradation pathway, and such transcription factor 56 as IKZF1. 57 58 59Glycosylation -addition of carbohydrates to a substrate -is a common cotranslational and 60 posttranslational modification of proteins. that affects the physical properties of proteins 61 (solubility, conformation, folding, stability, trafficking, etc.) [1-4] as well as their biological 62 functions -from protein-protein interactions, interaction of proteins with receptors, to cell-cell, 63 cell-matrix, and host-pathogen interactions [2,3,5,6]. It has been estimated that more than half of 64 all proteins are glycosylated [7][8][9]. Given the fact that glycans participate in many biological 65 processes, it is therefore not surprising that molecular defects in protein glycosylation pathways 66 are increasingly recognized as direct causes of diseases, such as rheumatoid arthritis, 67 cardiometabolic disorders, cancer, variety of autoimmune diseases, type 2 diabetes, inflammatory 68 bowel disease and others [10][11][12][13][14][15][16][17]. More specifically, a variety of N-glycan structures are now 69 considered as disease markers and represent diagnostic as well as therapeutic targets [5,12,[18][19][20][21][22][23][24][25]. 70Defining the genetic control of protein glycosylation expands our knowledge about the regulation 71 of this fundamental biological process, and it may also shed new light onto how alterations in 72 glycosylation can lead to the development of complex human diseases [11]. 73

To our knowledge, this is a first large clinical study on CLBP patients and plasma N-glycome providing a new glycomics perspective on potential disease pathology.