Human glycosylation disorders.

Over the past 20 years, clinical disorders of glycosylation have expanded to include over 50 recognized defects in the network of glycobiologic pathways. In parallel, more cases have been recognized by astute clinicians increasing both the number of known affected individuals as well as the breadth of clinical features attributed to these disorders. The descriptions of affected individuals may include a functional adult with cognitive impairments, a developmentally normal child with significant gastrointestinal symptoms, a severely ill infant or a fetus with hydrops fetalis. These clinical cases have led to the recognition of gene mutations affecting different enzymes and transporters active in the interconnected synthetic pathways of the myriad of oligosaccharides with essential roles in human development and biology.