PGM1-CDG is caused by changes in DNA specifically responsible for PGM1 enzyme. These changes result in a defective PGM1 enzyme, which cannot function properly. PGM1 is involved in many processes in the cell, that helps it function properly and a PGM1 deficiency result in a disorder. Patients with PGM1-CDG specifically have a problem with glycosylation, a biochemical process that is responsible for production of glycans- sugar chains. These sugar chains are important as they are involved in many cellular processes and help maintain homeostasis.