Pernicious anemia.
Explanation:
Pernicious anemia is usually caused due to the deficiency of Vitamin B-12 in the body or absence of Intrinsic factor in the digestive system that lowers the uptake of vitamin B-12.
Due to lack of Vitamin B-12 in the body the nucleated megaloblasts do not mature into non-nucleated RBCs and flow into the blood vessels.
This results in low hemoglobin levels , fatigue, weight loss etc as common symptoms.