What are the genetic changes related to ALG1-congenital disorder of glycosylation ?
Mutations in the ALG1 gene cause ALG1-CDG. This gene provides instructions for making an enzyme that is involved in a process called glycosylation. During this process, complex chains of sugar molecules (oligosaccharides) are added to proteins and fats (lipids). Glycosylation modifies proteins and lipids so they can fully perform their functions. The enzyme produced from the ALG1 gene transfers a simple sugar called mannose to growing oligosaccharides at a particular step in the formation of the sugar chain. Once the correct number of sugar molecules are linked together, the oligosaccharide is attached to a protein or lipid.  ALG1 gene mutations lead to the production of an abnormal enzyme with reduced activity. The poorly functioning enzyme cannot add mannose to sugar chains efficiently, and the resulting oligosaccharides are often incomplete. Although the short oligosaccharides can be transferred to proteins and fats, the process is not as efficient as with the full-length oligosaccharide. The wide variety of signs and symptoms in ALG1-CDG are likely due to impaired glycosylation of proteins and lipids that are needed for normal function of many organs and tissues.