Congenital disorders of glycosylation (CDG) constitutes a rapidly growing group of genetic disorders affecting mostly the nervous system and characterized by defective glycosylation of glycoproteins. Most disorders are caused by defects of N-glycans biosynthesis.
Two main groups of CDG are delineated on the basis of intracellular localisation of defects on the multistep biosynthesis pathway of N-glycans. Type I with twelve subtypes, denoted alphabetically from Ia to l, concerns defects of lipid-linked oligosaccharide (LLO) assembly on early steps of N-glycosylation, localised in cytoplasm and endoplasmic reticulum. Type II comprise six defects of N-glycan processing localised in the Golgi compartment. Patients with unrecognised primary defects are classified as CDG-Ix or CDG-IIx respectively.
The most common form is phosphomannomutase (PMM) deficiency or CDG-Ia with an autosomal recessive inheritance and incidence estimated at 1/20 000 – 1/50 000 live births. CDG Ia can manifest as severe multi-systemic disease of infancy or milder disorder with only neurological problems including ataxia, hypotonia and psychomotor retardation.
The aim of the study was to describe the clinical picture, molecular study and pathological findings in three children diagnosed with CDG (CDG-Ia, CDG-x).