Abstract
FUT8-CDG is a severe multisystem disorder caused by mutations in FUT8, encoding the α-1,6-fucosyltransferase. We report on dizygotic twins with FUT8-CDG presenting with dysmorphisms, failure to thrive, and respiratory abnormalities. Due to the severe phenotype, oral L-fucose supplementation was started. Glycosylation analysis using mass spectrometry indicated a limited response to fucose therapy while the clinical presentation stabilized. Further research is needed to assess the concept of substrate supplementation in FUT8-CDG.