The First Metabolome Analysis in Children with Epilepsy and ALG13-CDG Resulting from c.320A>G Variant

Case Report: Identification of Two Variants of ALG13 in Families With or Without Seizure and Binocular Strabismus: Phenotypic Spectrum Analysis

Background: Genetic causes in most affected children with intellectual disability and/or development delay remain unknown. Methods: To identify potential variants responsible for these disorders, we recruited 161 affected families and performed whole-exome sequencing and associated bioinformatics analysis. Results: In the present study, we report the identification of variants in the ALG13 gene in two of the families. In family 1, a known pathogenic missense variant (c.23T > C; p.V8A) of ALG13 was identified in a boy and his mother. In family 2, a novel missense variant (c.862C > G; p.L288V) of the same gene was identified in the affected boy and his phenotypically normal mother. Genotype-phenotype correlation analysis by comparing reported 28 different variants (HGMD) showed that three major phenotypes, including various seizures/epilepsy, intellectual disability, and development delay (such as growth, speech, motor, etc.), are present in most affected individuals. However, other phenotypes, such as strabismus and absence of seizure in our second patient, are not reported if any, which may represent a unique case of X-linked recessive nonsyndromic disorder caused by a mutation in ALG13. Conclusion: We identified two missense variants in ALG13 in a cohort of 161 families with affected individuals diagnosed as intellectual disability and/or development delay. A novel c.862C > G mutation may represent a case of X-linked recessive.

Structural Analysis of the Effect of Asn107Ser Mutation on Alg13 Activity and Alg13-Alg14 Complex Formation and Expanding the Phenotypic Variability of ALG13-CDG

Congenital Disorders of Glycosylation (CDG) are multisystemic metabolic disorders showing highly heterogeneous clinical presentation, molecular etiology, and laboratory results. Here, we present different transferrin isoform patterns (obtained by isoelectric focusing) from three female patients harboring the ALG13 c.320A>G mutation. Contrary to other known variants of type I CDGs, where transferrin isoelectric focusing revealed notably increased asialo- and disialotransferrin fractions, a normal glycosylation pattern was observed in the probands. To verify this data and give novel insight into this variant, we modeled the human Alg13 protein and analyzed the dynamics of the apo structure and the complex with the UDP-GlcNAc substrate. We also modeled the Alg13-Alg14 heterodimer and ran multiple simulations of the complex in the presence of the substrate. Finally, we proposed a plausible complex formation mechanism.

Congenital Disorders of Glycosylation: What Clinicians Need to Know?

Congenital disorders of glycosylation (CDG) are a group of clinically heterogeneous disorders characterized by defects in the synthesis of glycans and their attachment to proteins and lipids. This manuscript aims to provide a classification of the clinical presentation, diagnostic methods, and treatment of CDG based on the literature review and our own experience (referral center in Poland). A diagnostic algorithm for CDG was also proposed. Isoelectric focusing (IEF) of serum transferrin (Tf) is still the method of choice for diagnosing N-glycosylation disorders associated with sialic acid deficiency. Nowadays, high-performance liquid chromatography, capillary zone electrophoresis, and mass spectrometry techniques are used, although they are not routinely available. Since next-generation sequencing became more widely available, an improvement in diagnostics has been observed, with more patients and novel CDG subtypes being reported. Early and accurate diagnosis of CDG is crucial for timely implementation of appropriate therapies and improving clinical outcomes. However, causative treatment is available only for few CDG types.