Imerslunf-Gräsbeck Syndrome (IGS) is a genetic disorder in which cobalamin (Vitamin B12) is not absorbed from food in the intestine, resulting in a cobalamin deficiency. Lack of cobalamin leads to changes in the hematopoietic system, such as megaloblastic anemia (fewer red blood cells). Left untreated a chronic deficiency of cobalamin can lead to neurological symptoms due to irreversible damage of the brain and nervous system. Symptoms include anorexia, lethargy and failure to gain weight. Cobalamin malabsorption can be managed by supplementation with regular doses of cobalamin.