Many building blocks of the body, such as proteins, fats and other molecules, need to have sugars attached to them to work properly. Individuals with congenital disorders of glycosylation (CDG) cannot attach these sugars or sugar chains properly. Children or adults with CDG may have problems with growth and learning, and the disorder may affect many parts of the body, including the brain, nerves, muscles, liver and immune system. Examples of CDGs include PMM2-CDG, ALG1-CDG, PIGT-CDG and MPI-CDG. Additionally, individuals may also have NGLY1-CDDG, a disorder where the body has trouble taking off sugar chains from some proteins.