A severe disorder of blood, found mostly in older adults, that results from the body's inability to absorb vitamin B12 which is essential for normal red blood cell production in the bone marrow: Symptoms of pernicious anemia include weakness, breathing difficulties, and weight loss and those who have the illness do not produce the substance called "intrinsic factor" in the stomach, which allows the body to absorb the vitamin which is also essential for normal nerve cell development.