Abstract

Background: Type 1 diabetes mellitus (T1DM) results from T cell-mediated pancreatic β-cell destruction, with Protein tyrosine phosphatase non-receptor type 22 (PTPN22) and cytotoxic T-lymphocyte–associated protein 4 (CTLA4) linked to T1DM susceptibility; their diagnostic value in established T1DM is unclear. Aim: This case–control study aimed to evaluate serum PTPN22 and CTLA4 as candidate diagnostic biomarkers for T1DM, following bioinformatics-based target prioritization.  Methods: Fifty T1DM patients and 50 healthy controls from Babylon City were studied between December 2024 and March 2025. PTPN22 and CTLA4 were identified as differentially expressed genes (|logFC| > 1, adjusted p < 0.01) via RNA-seq analysis. ELISA measured their serum levels, and data were analysed using t-tests and receiver operating characteristic (ROC) curves (significance threshold: p < 0.05). Results: Serum PTPN22 and CTLA4 levels were significantly higher in T1DM patients than in controls (PTPN22: 8.4 ± 1.2 vs. 2.1 ± 0.6 ng/mL, p < 0.001; CTLA4: 15.3 ± 2.8 vs. 3.7 ± 1.1 ng/mL, p < 0.001). ROC analysis demonstrated excellent diagnostic performance, with areas under the curve of 0.94 for PTPN22 and 0.96 for CTLA4, indicating strong discrimination between T1DM and healthy status. Conclusion: CTLA4 and PTPN22, identified through bioinformatics screening as high-impact immune regulators, show robust elevation in serum protein levels in T1DM and exhibit strong diagnostic accuracy, supporting their potential use as predictive and diagnostic biomarkers in autoimmune diabetes and illustrating the value of a bioinformatics-guided strategy for biomarker discovery.