Pernicious anemia is due to

Deficiency of Vitamin B12 also known as cobalamin causes a blood disorder called pernicious anemia, a disease in which not enough red blood cells are produced. The human body is unable to synthesis vitamin B12 and must be obtained from the diet. The absorption of vitamin B12 requires a protein called Gastric intrinsic factor or intrinsic factor for its absorption in the small intestine. The deficiency of Gastric intrinsic factor causes blockage of vitamin B12 absorption, which leads to pernicious anemia.