Intrinsic factor is a protein that helps the body absorb vitamin B-12. When stomach secretions do not have enough intrinsic factor, vitamin B-12 is not absorbed well. This results in pernicious anemia and other problems related to low levels of vitamin B-12. Nerve and blood cells need vitamin B-12 to function properly, so deficiency can cause a wide variety of symptoms, including fatigue, shortness of breath, tingling sensations, difficulty walking, and diarrhea. Other causes of low levels of intrinsic factor (and thus of pernicious anemia) include atrophic gastric mucosa, autoimmunity against gastric parietal cells, and autoimmunity against intrinsic factor. Absence of intrinsic factor itself is the most common cause of vitamin B-12 deficiency. Intrinsic factor is produced by cells in the stomach. In adults, the inability to make intrinsic factor can be the result of chronic gastritis or the result of surgery to remove the stomach. The onset of the disease is slow and may take decades. Very rarely, infants and children are born lacking the ability to produce effective intrinsic factor. This form of congenital (born with) pernicious anemia is inherited as an autosomal recessive disorder (you need a defective gene from each parent to get it). Most often, however, pernicious anemia and other forms of megaloblastic anemia in children results from other causes of vitamin B-12 deficiency or other vitamin deficiencies. Although a form of the disease can occur in children, pernicious anemia usually does not appear before age 30. The average age at diagnosis is 60. In fact, one recent study revealed that nearly 2% of individuals over 60 have pernicious anemia. Slightly more women than men are affected. The disease occurs in all racial groups, but occurs most often in people of Scandinavian or Northern European descent. Risk factors include a family history of pernicious anemia, Scandinavian or Northern European descent, and a history of autoimmune endocrine disorders. Pernicious anemia is seen in association with some autoimmune endocrine diseases such as type 1 diabetes, hypoparathyroidism, Addison's disease, hypopituitarism, testicular dysfunction, Graves disease, chronic thyroiditis, myasthenia gravis, secondary amenorrhea, and vitiligo. In addition to pernicious anemia, other causes of vitamin B-12 deficiency include: - Nutrition (strict vegetarians without B-12 supplementation, poor diet in infant, or poor maternal nutrition during pregnancy)
- Infection (intestinal parasites, bacterial overgrowth)
- Gastrointestinal disease (stomach removal surgery, celiac disease [sprue], Crohn's disease)
- Drugs (colchicine, neomycin, tuberculosis treatment with para amino salicylic acid)
- Metabolic disorders (methylmalonic aciduria, homocystinuria)
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