Deciphering the Neurological Puzzle in ALG13-CDG Through Cutting-Edge Brain Organoid Modeling.

Asparagine-linked glycosylation 13 (ALG13) is an X-linked congenital disorder of glycosylation (CDG). Our study addresses the urgent need for deeper insights into ALG13-CDG characterized by significant gaps in our understanding of its pathobiology and the absence of effective treatment options. Despite extensive research on various CDG, investigations into ALG13-CDG have been hindered by the lack of observable glycosylation defects in patient samples, particularly in blood and fibroblasts. However, the profound neurological symptoms associated with ALG13-CDG strongly suggest a primary impact on the brain. To test this hypothesis, we established a brain model of ALG13-CDG using induced pluripotent stem cells derived from fibroblasts, which were subsequently differentiated into human cortical cortical organoids(hCOs). Contrary to previous reports of random X-inactivation in individuals with ALG13-CDG, we observed X-inactivation skewing within ALG13-CDG cell lines. Our multi-omics approach, encompassing single-cell RNA-seq, proteomics, glycoproteomic, and metabolomics analyses, revealed significant reductions in glycosylation and expression of key proteins essential for axon growth, neuronal migration, and synaptic plasticity. Additionally, alterations in protein abundances associated with neuronal migration and nucleotide synthesis were also observed, along with distinctive changes in genes linked to epilepsy risk and lipid metabolism. Metabolomic analyses ALG13-CDG hCOs showed elevated GlcNAc levels and decreased nucleotide synthesis metabolites. Importantly, our study sheds light on the previously unrecognized protein glycosylation defect in ALG13-CDG, offering valuable insights into the brain-related disturbances underlying the disease pathology. Furthermore, our findings hold promise for guiding the clinical management of seizures in ALG13-CDG patients, addressing a critical unmet medical need.