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Nucleotide sugars (NS) are fundamental molecules in life and play a key role in glycosylation reactions and signal conduction. Several pathways are involved in the synthesis of NS. The Leloir pathway, the main pathway for galactose metabolism, is crucial for production of uridine diphosphate (UDP)-glucose and UDP-galactose. The most common metabolic disease affecting this pathway is galactose-1-phosphate uridylyltransferase (GALT) deficiency, that despite a lifelong galactose-restricted diet, often results in chronically debilitating complications. Alterations in the levels of UDP-sugars leading to galactosylation abnormalities have been hypothesized as a key pathogenic factor. However, UDP-sugar levels measured in patient cell lines have shown contradictory results. Other NS that might be affected, differences throughout development, as well as tissue specific profiles have not been investigated. Using recently established UHPLC-MS/MS technology, we studied the complete NS profiles in wildtype and galt knockout zebrafish (Danio rerio). Analyses of UDP-hexoses, UDP-hexosamines, CMP-sialic acids, GDP-fucose, UDP-glucuronic acid, UDP-xylose, CDP-ribitol, and ADP-ribose profiles at four developmental stages and in tissues (brain and gonads) in wildtype zebrafish revealed variation in NS levels throughout development and differences between examined tissues. More specifically, we found higher levels of CMP-N-acetylneuraminic acid, GDP-fucose, UDP-glucuronic acid, and UDP-xylose in brain and of CMP-N-glycolylneuraminic acid in gonads. Analysis of the same NS profiles in galt knockout zebrafish revealed no significant differences from wildtype. Our findings in galt knockout zebrafish, even when challenged with galactose, do not support a role for abnormalities in UDP-glucose or UDP-galactose as a key pathogenic factor in GALT deficiency, under the tested conditions., (© 2020 The Authors. Journal of Inherited Metabolic Disease published by John Wiley & Sons Ltd on behalf of SSIEM.)

Whole-blood galactose-1-phosphate uridyl transferase (Gal-PUT) (EC 2.7.7.12) activity was absent in a newborn boy with galactosaemic symptoms. The symptoms disappeared on a galactose free diet. In the next pregnancy prenatal diagnosis was performed. Gal-PUT activity was measured by isotope technique and Gal-PUT genotype was determined by gel electrophoresis. The mother was shown to be heterozygous Duarte/heterozygous Los Angeles, the father heterozygous Duarte/heterozygous galactosaemia. The fetus had the same genotype as the father. A normal girl without galactosaemic symptoms was born. Reinvestigation of the index case showed that he was also heterozygous Duarte/heterozygous galactosaemia. It is concluded that the activity of Gal-PUT should always be measured by isotope technique to prove the diagnosis of heteditary galactosaemia. Furthermore, Gal-PUT-genotyping in families with rare alleles is essential for safe prenatal diagnosis.