The lack of this substance produced by the stomach lining can cause pernicious anemia?

The substance that, when lacking, can cause pernicious anemia is intrinsic factor. Intrinsic factor is a glycoprotein produced by the stomach lining, essential for the absorption of vitamin B12 in the intestines. Without sufficient intrinsic factor, the body cannot properly absorb vitamin B12, leading to a deficiency that results in pernicious anemia, characterized by fatigue, weakness, and neurological issues. Treatment typically involves vitamin B12 injections or high-dose oral supplements.