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      The fate of orally administered sialic acid: First insights from patients with N-acetylneuraminic acid synthase deficiency and control subjects


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          In NANS deficiency, biallelic mutations in the N-acetylneuraminic acid synthase ( NANS) gene impair the endogenous synthesis of sialic acid ( N-acetylneuraminic acid) leading to accumulation of the precursor, N-acetyl mannosamine (ManNAc), and to a multisystemic disorder with intellectual disability. The aim of this study was to determine whether sialic acid supplementation might be a therapeutic avenue for NANS-deficient patients.


          Four adults and two children with NANS deficiency and four adult controls received oral NeuNAc acid (150 mg/kg/d) over three days. Total NeuNAc, free NeuNAc and ManNAc were analyzed in plasma and urine at different time points.


          Upon NeuNAc administration, plasma free NeuNAc increased within hours ( P < 0.001) in control and in NANS-deficient individuals. Total and free NeuNAc concentrations also increased in the urine as soon as 6 h after beginning of oral administration in both groups. NeuNAc did not affect plasma and urinary ManNAc, that remained higher in NANS deficient subjects than in controls (day 1–3; all P < 0.01). Oral NeuNAc was well tolerated with no significant side effects.


          Orally administered free NeuNAc was rapidly absorbed but also rapidly excreted in the urine. It did not change ManNAc levels in either patients or controls, indicating that it may not achieve enough feedback inhibition to reduce ManNAc accumulation in NANS-deficient subjects. Within the limitations of this study these results do not support a potential for oral free NeuNAc in the treatment of NANS deficiency but they provide a basis for further therapeutic approaches in this condition.


          • NANS deficiency is a recessively inherited disorder.

          • Patients present with cognitive delay, bone dysplasia and dysmorphic features.

          • Endogenous synthesis of sialic acid is blocked with accumulation of the precursor, N-acetyl mannosamine (ManNAc)

          • Sialic acid supplementation in NANS deficiency was ineffective in reducing ManNAc.

          • Nutritional therapy for NANS deficiency requires further exploration.

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          Most cited references41

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          A new equation to estimate glomerular filtration rate.

          Equations to estimate glomerular filtration rate (GFR) are routinely used to assess kidney function. Current equations have limited precision and systematically underestimate measured GFR at higher values. To develop a new estimating equation for GFR: the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Cross-sectional analysis with separate pooled data sets for equation development and validation and a representative sample of the U.S. population for prevalence estimates. Research studies and clinical populations ("studies") with measured GFR and NHANES (National Health and Nutrition Examination Survey), 1999 to 2006. 8254 participants in 10 studies (equation development data set) and 3896 participants in 16 studies (validation data set). Prevalence estimates were based on 16,032 participants in NHANES. GFR, measured as the clearance of exogenous filtration markers (iothalamate in the development data set; iothalamate and other markers in the validation data set), and linear regression to estimate the logarithm of measured GFR from standardized creatinine levels, sex, race, and age. In the validation data set, the CKD-EPI equation performed better than the Modification of Diet in Renal Disease Study equation, especially at higher GFR (P < 0.001 for all subsequent comparisons), with less bias (median difference between measured and estimated GFR, 2.5 vs. 5.5 mL/min per 1.73 m(2)), improved precision (interquartile range [IQR] of the differences, 16.6 vs. 18.3 mL/min per 1.73 m(2)), and greater accuracy (percentage of estimated GFR within 30% of measured GFR, 84.1% vs. 80.6%). In NHANES, the median estimated GFR was 94.5 mL/min per 1.73 m(2) (IQR, 79.7 to 108.1) vs. 85.0 (IQR, 72.9 to 98.5) mL/min per 1.73 m(2), and the prevalence of chronic kidney disease was 11.5% (95% CI, 10.6% to 12.4%) versus 13.1% (CI, 12.1% to 14.0%). The sample contained a limited number of elderly people and racial and ethnic minorities with measured GFR. The CKD-EPI creatinine equation is more accurate than the Modification of Diet in Renal Disease Study equation and could replace it for routine clinical use. National Institute of Diabetes and Digestive and Kidney Diseases.
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            Sialic acids in the brain: gangliosides and polysialic acid in nervous system development, stability, disease, and regeneration.

            Every cell in nature carries a rich surface coat of glycans, its glycocalyx, which constitutes the cell's interface with its environment. In eukaryotes, the glycocalyx is composed of glycolipids, glycoproteins, and proteoglycans, the compositions of which vary among different tissues and cell types. Many of the linear and branched glycans on cell surface glycoproteins and glycolipids of vertebrates are terminated with sialic acids, nine-carbon sugars with a carboxylic acid, a glycerol side-chain, and an N-acyl group that, along with their display at the outmost end of cell surface glycans, provide for varied molecular interactions. Among their functions, sialic acids regulate cell-cell interactions, modulate the activities of their glycoprotein and glycolipid scaffolds as well as other cell surface molecules, and are receptors for pathogens and toxins. In the brain, two families of sialoglycans are of particular interest: gangliosides and polysialic acid. Gangliosides, sialylated glycosphingolipids, are the most abundant sialoglycans of nerve cells. Mouse genetic studies and human disorders of ganglioside metabolism implicate gangliosides in axon-myelin interactions, axon stability, axon regeneration, and the modulation of nerve cell excitability. Polysialic acid is a unique homopolymer that reaches >90 sialic acid residues attached to select glycoproteins, especially the neural cell adhesion molecule in the brain. Molecular, cellular, and genetic studies implicate polysialic acid in the control of cell-cell and cell-matrix interactions, intermolecular interactions at cell surfaces, and interactions with other molecules in the cellular environment. Polysialic acid is essential for appropriate brain development, and polymorphisms in the human genes responsible for polysialic acid biosynthesis are associated with psychiatric disorders including schizophrenia, autism, and bipolar disorder. Polysialic acid also appears to play a role in adult brain plasticity, including regeneration. Together, vertebrate brain sialoglycans are key regulatory components that contribute to proper development, maintenance, and health of the nervous system.
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              Sialic acids: fascinating sugars in higher animals and man.

              Sialic acids are acidic monosaccharides, which are among the most important molecules of higher animals, and occur in some microorganisms. They are bound to complex carbohydrates and occupy prominent positions, especially in cell membranes. Their structural diversity is high and, correspondingly, the mechanisms for their biosynthesis are complex. Sialic acid substituents strongly influence the activity of catabolic enzymes, in particular the sialidases, and thus the turnover rate of glycoconjugates. These sugars are involved in manifold cell functions. Due to the surface location of the acidic molecules they shield macromolecules and cells from enzymatic and immunological attacks. But they also represent recognition sites for various physiological receptors as well as for toxins and microorganisms, and thus allow their colonization. Many viruses use sialic acids for the infection of cells. As sialic acids also play a decisive role in tumor biology they prove to be rather versatile molecules that modulate cell biological events in a sensitive way. It is discussed that their evolvement may have stimulated evolution and rendered organisms less vulnerable to environmental attacks. However, disturbance of their metabolism may cause diseases.

                Author and article information

                Mol Genet Metab Rep
                Mol Genet Metab Rep
                Molecular Genetics and Metabolism Reports
                26 June 2021
                September 2021
                26 June 2021
                : 28
                [a ]Center for Molecular Diseases, Division of Genetic Medicine, University of Lausanne and University Hospital of Lausanne, Switzerland
                [b ]Medical Genetics Unit, Azienda ULSS 2, Treviso, Italy
                [c ]Pediatric Metabolic Unit, Pediatrics, Woman-Mother-Child Department, University of Lausanne and University Hospital of Lausanne, Switzerland
                [d ]Department of Paediatrics, Neuropediatrics, Bern University Hospital, Switzerland
                [e ]Metabolomics Platform, Faculty of Biology and Medicine, University of Lausanne, Switzerland
                [f ]Division of Biostatistics, Center for Primary Care and Public Health (Unisanté), University of Lausanne, Switzerland
                [g ]Translational Metabolic Laboratory, Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, the Netherlands
                [h ]Medical Genetics Unit, Maternal and Child Health Department, Azienda USL-IRCCS di Reggio Emilia, Reggio Emilia, Italy
                [i ]Institute of Medical Genetics, University of Zurich, Switzerland
                Author notes
                [* ]Corresponding author at: Center for Molecular Diseases, Lausanne University Hospital, Division of Genetic Medicine, Beaumont-02/248, CH-1011, Lausanne 1011, Switzerland. christel.tran@ 123456chuv.ch
                S2214-4269(21)00071-9 100777
                © 2021 The Authors

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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