Vitamin B12 deficiency anaemia due to selective vitamin B12 malabsorption with proteinuria (Q88870)

Imerslund-Gräsbeck syndrome or selective vitamin B12 (cobalamin) malabsorption with proteinuria is a rare autosomal recessive disorder characterised by vitamin B12 deficiency commonly resulting in megaloblastic anaemia, which is responsive to parenteral vitamin B12 therapy and appears in childhood. Other manifestations include failure to thrive and grow, infections and neurological damage. Mild proteinuria (with no signs of kidney disease) is present in about half of the patients. The cause is a defect in the receptor of the vitamin B12-intrinsic factor complex of the ileal enterocyte. In most cases, the molecular basis of the selective malabsorption and proteinuria involves a mutation in one of two genes, cubilin (CUBN) on chromosome 10 or amnionless (AMN) on chromosome 14. Both the proteins are components of the intestinal receptor for the vitamin B12-intrinsic factor complex and the receptor mediating the tubular reabsorption of protein from the primary urine.