MONDO_0009853 (Imerslund-Grasbeck syndrome) (IGS) or selective vitamin B12 (cobalamin) malabsorption with proteinuria is a rare autosomal recessive disorder characterized by vitamin B12 deficiency commonly resulting in megaloblastic anemia, which is responsive to parenteral vitamin B12 therapy and appears in childhood. Also known as: Imerslund-Gräsbeck syndrome, familial megaloblastic anaemia, familial megaloblastic anemia, juvenile megaloblastic Anaemia, juvenile megaloblastic Anemia, selective cobalamin malabsorption with proteinuria.