Congenital Disorder of Glycosylation: Type Ib

Congenital disorder of glycosylation (CDG) is a group of inherited disorders caused by defects in glycosylation, the process of attaching sugars to proteins and lipids. CDG type Ib, which is also called MPI-CDG, is due to reduced activity of an enzyme called phosphomannose isomerase. CDG-Ib is distinct from most other CDGs in two ways. First, CDG-Ib does not significantly affect the central nervous system. Second, this potentially fatal disorder can be treated. CDG-Ib affects the liver and the gastrointestinal tract. Infants with CDG-Ib present with chronic diarrhea, recurring vomiting, liver problems, low blood sugar, and malnutrition. Severity is variable among affected individuals. CDG-Ib can be treated effectively by lifelong dietary supplements of a particular sugar known as mannose. CDG-Ib is caused by pathogenic variants in the gene MPI.

CDG-Ib is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

There are generally no signs or symptoms associated with being a carrier for CDG-Ib. However, the risk to have a child affected with CDG-Ib is increased. Testing of reproductive partners is recommended for carriers of CDG-Ib.

CDG-Ib is a rare disease with less than 50 cases reported. The worldwide incidence of disease is unknown and researchers suspect CDG-Ib is under diagnosed.

Genetic Alliance: Congenital Disorder of Glycosylation Type 1B (http://www.diseaseinfosearch.org/)

OMIM [CDG-Ib: 602579] (http://www.ncbi.nlm.nih.gov/omim)
Gene Reviews: Congenital Disorders of N-linked Glycosylation Pathway Overview (http://www.ncbi.nlm.nih.gov/books/NBK1116/)

• Full gene sequencing