Since glycans are created without the genetic template, alternative glycosylation creates an additional layer of protein complexity by combining genetic variability with past and present environmental factors. Individual variability in glycome composition is very large, but glycosylation of an individual protein seems to be under strong genetic influence, with heritability being up to 80% for some glycans. Structural details of the attached glycans are of great physiological significance and many pathological conditions are associated with various types of glycan changes. For example, glycans attached to the Fc part of immunoglobulin G are important modulators of IgG effector functions. Slight modifications in the composition of the IgG glycome significantly tune IgG towards binding to different Fc receptors and can convert IgG from a pro-inflammatory effector into an anti-inflammatory agent.
Since the onset of genome wide association studies, thousands of genetic loci have been associated with different diseases and traits. However, in the last few years it is becoming increasingly clear that variations in a DNA sequence are only a beginning of the understanding of complex human diseases. Genetic polymorphisms have to be put in the context of complex biology of life and a more elaborate approach that combines different ‘omics phenotypes is needed to understand disease mechanisms and perform patient stratification that transcends genomics. Glycomics, as by far the most complex epiproteomic modification, has an immense potential in this respect, which is only beginning to be investigated.