Metabolic manipulation of glycosylation disorders in humans and animal models

In the last decade, over 40 inherited human glycosylation disorders were identified. Most patients have hypomorphic, rather than null alleles. The phenotypic spectrum is broad and most of the disorders affect embryonic and early post-natal development; a few appear in adult life. Some deficiencies can be treated with simple dietary sugar (monosaccharide) supplements. Here we focus on four glycosylation disorders that have been treated with supplements in patients or in model systems, primarily the mouse. Surprisingly, small differences in the amount of exogenous sugar have a major impact on the diseases in specific cells or organs while others are unaffected. The underlying mechanisms are mostly unknown, but changes in the contributions of the de novo, salvage and dietary pathways may contribute to the beneficial outcome. Clearly, the metabolic chart is not flat; all arrows are not equally robust at all points of time and space. This metabolic perspective may help explain some of these observations and guide the development of other vertebrate models of glycosylation disorders that can respond to dietary manipulation.