Together with the lysosomal storage diseases, N-glycanase 1 deficiency is a congenital disorder of deglycosylation, which has been diagnosed in 27 patients, including two of them from Poland. The pathogenesis remains unknown, however, the main role is attributed to the disturbed endoplasmic reticulum-associated protein degradation process. The most characteristic symptoms include global developmental disability, hyperkinetic movement disorder, hypo-/alacrimia, and elevated serum transaminases. Identification of pathogenic variants in the NGLY1 gene is required to confirm the diagnosis.