What is favism?

By Chelsie Vandaveer

October 7, 2003

Suggested Reading: Click here.

Favism is anemia caused by hemolysis or the destruction of healthy erythrocytes (red blood cells, RBC). The victim, usually a male, feels tired, nauseous, dizzy, and has dark orange urine indicating the passage of blood. The anemia is usually transient (short-lived), but if severe enough, it is fatal. The anemia is caused by a deficiency in an enzyme, glucose-6-phosphate dehydrogenase (G6PD).

Glucose-6-phosphate dehydrogenase is present in every cell in the body. G6PD protects the cells from oxidants, chemicals that oxidize or break bonds between atoms in a molecule. Oxidation causes lysis; the cell membranes disintegrate allowing the contents to leak out.

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Dish of Broad Beans by Giovanni Garzoni

Most cells manufacture their own G6PD, but RBCs are short-lived cells geared entirely to carrying atmospheric oxygen (O₂) from the lungs to the rest of the body and carbon dioxide back to the lungs. Atmospheric oxygen is not the problem since it is bound to the hemoglobin molecules inside the RBC, but the hemoglobin can also be destroyed by the oxidants. (Chapter 108: Hemolytic Anemias and Acute Blood Loss, Harrison's Textbook of Medicine, National Parkinson Foundation, Inc.)

The oxidants that cause the damage are freely circulating in the blood stream. If they come into contact with the RBCs, the cells lyse and anemia ensues. The anemic person is tired and ill. Normal G6PD activity neutralizes the oxidants before they contact the red blood cells.

The gene (Gd) that codes for this enzyme is in the telomere (the end region) of the long arm of the X chromosome. Across the world's population, there are about three hundred alleles (variations) of the Gd gene. Because men inherit a single X chromosome, they are prone to problems should they inherit a gene that does not code for a normal copy of G6PD. In the Mediterranean, the allele is known as Gd^Med; in Africa, it is the Gd^A- allele.

Favism is caused when the Gd^Med or Gd^A- is inherited and the person should happen to eat fava beans or inhale pollen from the flowers. Vicine and covicine present in fava beans are metabolized into divicine and isouramil in the intestinal tract. Without normal G6PD, these metabolites in the blood stream are strong oxidants that attack the membranes of the red blood cells. ("Glucose-6-Phosphate Dehydrogenase and Malaria" Human Adaptability, ANT 475/575, Dr. J. Bindon, University of Alabama)

Wikipedia, the free encyclopedia, has a great close-up of the fava bean (Vicia faba Linnaeus). To view the photograph, click on the link:

http://en.wikipedia.org/wiki/Vicia_faba

Suggested Reading:

Why does favism exist? Plants that Changed History - October 14, 2003
What is favism? Plants that Changed History - October 7, 2003
Why did ladies use bean poultices? Herbal Folklore - September 8, 2003
What is L-dopa? Plants that Changed History - September 2, 2003
What is a fava bean? Weird Plants - September 4, 2003
How did we get so many varieties from the common bean? Weird Plants - September 20, 2001
How is a toxin found in the kidney bean useful? Herbal Folklore - September 17, 2001

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