Phosphomannomutase deficiency (PMM2-CDG) is the most common congenital disorder of glycosylation, characterized by variable early-onset neurological (hypotonia, cerebellar syndrome, developmental delay) and multi-organ manifestations. Although several clinical trials are ongoing, current biomarkers lack prognostic or monitoring utility. Emerging transcriptomic studies suggest dysregulated pathways in PMM2-CDG, but miRNAs, key gene expression regulators, remain unexplored. This cross-sectional study aims to investigate a circulating miRNA signature that may distinguish PMM2-CDG patients from unaffected controls, providing an initial framework for future studies on potential predictive and monitoring tools