What Your Test Results Mean:

Carriers typically show no symptoms of CDG-Ib; however, carriers are at an increased risk of having a child with CDG-Ib. Risk for the current or future pregnancies is dependent on your partner’s carrier status. Carrier testing of your partner is recommended in addition to consultation with a genetic counselor.

Disease Explained:

CDG-Ib is an inherited condition that is caused by abnormalities in mannose-6 phosphate isomerase. This enzyme is important in glycosylation, the process of adding carbohydrate chains to proteins used by the body to control protein folding, localization, activity, and stability. These carbohydrate structures cannot be formed properly without mannose-6 phosphate isomerase, leading to the development of chronic diarrhea, impaired ability of the intestines to absorb protein, and impaired blood clotting. Oral administration of mannose has been shown to be an effective treatment for this disorder.

How the Genetics Works:

The clinical features of CDG-Ib can be explained by pathogenic variants in the MPI gene. In general, individuals have two copies of the MPI gene. Carriers of CDG-Ib have a single variant in one copy of the MPI gene while individuals with CDG-Ib have variants in both copies of their genes, one inherited from each parent. Risk for two carriers to have a child with the disorder is 25%.