Perhaps a wee bit of sugar would help

Aberrant N-glycosylation is a therapeutic target in carriers of a common and highly pleiotropic mutation in the manganese transporter ZIP8

The treatment of defective glycosylation in clinical practice has been limited to patients with rare and severe phenotypes associated with congenital disorders of glycosylation (CDG). Carried by approximately 5% of the human population, the discovery of the highly pleiotropic, missense mutation in a manganese transporter ZIP8 has exposed under-appreciated roles for Mn homeostasis and aberrant Mn-dependent glycosyltransferases activity leading to defective N-glycosylation in complex human diseases. Here, we test the hypothesis that aberrant N-glycosylation contributes to disease pathogenesis of ZIP8 A391T-associated Crohn's disease. Analysis of N-glycan branching in intestinal biopsies demonstrates perturbation in active Crohn's disease and a genotype-dependent effect characterized by increased truncated N-glycans. A mouse model of ZIP8 391-Thr recapitulates the intestinal glycophenotype of patients carrying mutations in ZIP8. Borrowing from therapeutic strategies employed in the treatment of patients with CDGs, oral monosaccharide therapy with N-acetylglucosamine ameliorates the epithelial N-glycan defect, bile acid dyshomeostasis, intestinal permeability, and susceptibility to chemical-induced colitis in a mouse model of ZIP8 391-Thr. Together, these data support ZIP8 391-Thr alters N-glycosylation to contribute to disease pathogenesis, challenging the clinical paradigm that CDGs are limited to patients with rare diseases. Critically, the defect in glycosylation can be targeted with monosaccharide supplementation, providing an opportunity for genotype-driven, personalized medicine.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

DISCUSSION

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.

Oral D-galactose supplementation in PGM1-CDG

PurposePhosphoglucomutase-1 deficiency is a subtype of congenital disorders of glycosylation (PGM1-CDG). Previous casereports in PGM1-CDG patients receiving oral D-galactose (D-gal) showed clinical improvement. So far no systematic in vitro and clinical studies have assessed safety and benefits of D-gal supplementation. In a prospective pilot study, we evaluated the effects of oral D-gal in nine patients.MethodsD-gal supplementation was increased to 1.5 g/kg/day (maximum 50 g/day) in three increments over 18 weeks. Laboratory studies were performed before and during treatment to monitor safety and effect on serum transferrin-glycosylation, coagulation, and liver and endocrine function. Additionally, the effect of D-gal on cellular glycosylation was characterized in vitro.ResultsEight patients were compliant with D-gal supplementation. No adverse effects were reported. Abnormal baseline results (alanine transaminase, aspartate transaminase, activated partial thromboplastin time) improved or normalized already using 1 g/kg/day D-gal. Antithrombin-III levels and transferrin-glycosylation showed significant improvement, and increase in galactosylation and whole glycan content. In vitro studies before treatment showed N-glycan hyposialylation, altered O-linked glycans, abnormal lipid-linked oligosaccharide profile, and abnormal nucleotide sugars in patient fibroblasts. Most cellular abnormalities improved or normalized following D-gal treatment. D-gal increased both UDP-Glc and UDP-Gal levels and improved lipid-linked oligosaccharide fractions in concert with improved glycosylation in PGM1-CDG.ConclusionOral D-gal supplementation is a safe and effective treatment for PGM1-CDG in this pilot study. Transferrin glycosylation and ATIII levels were useful trial end points. Larger, longer-duration trials are ongoing.