Polyprenal reductase is an enzyme encoded by the SRD5A3 gene, which is involved in the synthesis of dolichol from polyprenol. Dolichol serves as a carrier for glycan precursors or monosaccharides in N-linked glycosylation. Pathogenic variants in SRD5A3 can result in a congenital disorder of glycosylation (CDG), SRD5A3-CDG, which is inherited in an autosomal recessive manner. Most plasma proteins are glycosylated and changes in the glycosylation of several glycoproteins are associated with pathological consequences. Despite the critical role of SRD5A3 in glycosylation, the impact of its deficiency on the glycosylation of serum proteins remains largely unexplored. In this study, we used tandem mass tag-based multiplexed quantitative approach to analyze serum N-glycoproteomics and proteomics in SRD5A3-CDG patients and controls. We quantified 2200 serum N-glycopeptides from 359 N-glycosites from 204 serum proteins. Extensive hypoglycosylation of serum proteins was observed in patients, with 245 of 291 altered glycopeptides decreased in SRD5A3-CDG. Altered glycopeptides included those derived from haptoglobin, plasma serine protease inhibitor, alpha-1-B glycoprotein, alpha-2-macroglobulin, and ceruloplasmin. Some of these proteins have previously been reported to be associated with liver dysfunction, anemia, and coagulopathy, which could underlie similar clinical features observed in SRD5A3-CDG patients. Overall, our study provides novel insights into alterations in the glycosylation status of specific serum proteins in SRD5A3-CDG. Some of these alterations could be further pursued to develop glycopeptide-based biomarkers as the current diagnosis of SRD5A3-CDG by screening assays remains challenging. In addition, knowledge of altered glycoproteins could enhance our understanding of the disease spectrum and potentially unveil additional therapeutic avenues.

We report a very rare autosomal recessive metabolic disorder in monozygotic twin sisters caused by the steroid 5a-reductase type 3 (SRD5A3) gene defect, a subtype of congenital disorder of glycosylation (CDG). SRD5A3 activity is required for N-glycosylation of proteins. This step is important for the protein to gain its function. The condition is characterized by severe neurodevelopmental delay, cerebellar atrophy or hypoplasia, ocular abnormalities, and ichthyotic skin changes. We describe 20-month-old female monozygotic twins born to non-consanguineous South Asian parents. Notably, both twins exhibited generalized tonic-clonic seizures starting in early infancy - a feature less commonly reported in SRD5A3-CDG. Physical examination of both children showed central hypotonia and bilateral horizontal nystagmus. Fundoscopy of the twins showed optic disc pallor suggestive of optic atrophy. Other features, such as ichthyosis and joint laxity, were absent. Crucially, despite prominent neurological symptoms, brain MRIs at 20 months were entirely normal, showing no evidence of cerebellar hypoplasia or atrophy typically associated with this condition. Whole-exome sequencing identified a homozygous nonsense mutation at exon 1 c.57G>A (p.Trp19Ter), in the SRD5A3 gene, classified as a pathogenic variant as per the American College of Medical Genetics and Genomics (ACMG), helping in establishing the diagnosis. SRD5A3-CDG should be one of the differentials in infants with unexplained seizures, hypotonia, and early ocular signs. This case highlights the phenotypic diversity of SRD5A3-CDG and demonstrates that structural brain anomalies may be absent in the early years of life. It underscores the importance of considering CDG as a differential in infants with unexplained hypotonia and ocular signs, even in the setting of normal neuroimaging.

Congenital disorders of glycosylation (CDG) are rare inherited disorders resulting from defects in cellular glycosylation machinery. Albumin has recently been shown to be N-glycosylated at two non-canonical glycosylation sites. We applied multiplexed mass spectrometry-based glycoproteomics to identify site-specific N-glycosylation alterations in albumin from patients with PMM2-CDG, MPI-CDG, SRD5A3-CDG, MAN1B1-CDG and PGM1-CDG. Our findings demonstrate that the glycosylation of albumin is indeed affected in CDG and indicate a potential role for albumin-derived glycopeptides as diagnostic biomarkers.

SRD5A3-CDG is a rare autosomal recessive congenital disorder of glycosylation characterized by multisystemic dysfunction, including neurological, psychomotor, cognitive, and visual impairments. Approximately 60 cases have been reported, with treatment limited to symptomatic management. SRD5A3 encodes a polyprenal reductase enzyme essential for synthesizing dolichol, a lipid carrier of the oligosaccharide precursor in N-glycosylation. To address the lack of effective treatments and disease models suitable for high-throughput screening, we developed the first C. elegans model of SRD5A3-CDG, harboring the homozygous W19X nonsense mutation commonly observed in patients. This model recapitulates disease-relevant phenotypes, including developmental delays, neurological dysfunction, and mevalonate pathway dysregulation. Using this model, we conducted a high-throughput motility-based drug repurposing screen and identified atorvastatin, an FDA-approved HMG-CoA reductase inhibitor, as a repurposing candidate. Atorvastatin rescued disease-relevant phenotypes in the worm model and restored polyprenol-to-dolichol ratios in patient fibroblasts. These findings highlight atorvastatin as a promising drug repurposing candidate for SRD5A3-CDG.

Congenital Disorders of Glycosylation (CDG) are a rapidly expanding group of inherited metabolic diseases caused by defects in glycosylation. Although over 190 genetic defects have been identified, effective treatments remain available for only a few. We hypothesized that integrative analysis of multi-omics datasets from individuals with various CDG could uncover common molecular signatures and highlight shared therapeutic targets. We compiled all publicly available RNA sequencing, proteomics and glycoproteomics datasets from patients with PMM2-CDG, ALG1-CDG, SRD5A3-CDG, NGLY1-CDDG, ALG13-CDG and PGM1-CDG, spanning different tissues, including induced cardiomyocytes, human cortical organoids, fibroblasts, and lymphoblasts. Differential expression and glycosylation analyses were performed, followed by Gene Set Enrichment Analysis (GSEA) to identify commonly dysregulated pathways. We then applied the EMUDRA drug prediction algorithm to prioritize candidate compounds capable of reversing these shared molecular signatures. We identified four glycoproteins with consistent differential glycosylation across all eight glycoproteomics datasets. Six glycosylation sites and glycan structures were recurrently altered across CDG and showed partial correction with treatment. Pathway analysis revealed shared disruptions in autophagy, vesicle trafficking, and mitochondrial function. EMUDRA predicted several repurposable drug classes, including muscle relaxants, antioxidants, beta-adrenergic agonists, antibiotics, and NSAIDs, that could reverse key pathway abnormalities, particularly those involving autophagy and N-glycosylation. Most dysregulated pathways were shared across CDG, suggesting the potential for common therapeutic strategies. Several candidate drugs targeting these shared abnormalities emerged from integrative analysis and warrant validation in future in vitro studies.