What are the genetic changes related to ALG12-congenital disorder of glycosylation ?
Mutations in the ALG12 gene cause ALG12-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 ALG12 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.  ALG12 gene mutations lead to the production of an abnormal enzyme with reduced activity. Without a properly functioning enzyme, mannose cannot be added to the chain 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. As a result, glycosylation is reduced. The wide variety of signs and symptoms in ALG12-CDG are likely due to impaired glycosylation of proteins and lipids that are needed for normal function of many organs and tissues, including the brain.