Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a genetic metabolic abnormality caused by deficiency of the enzyme G6PD. This enzyme is critical for the proper function of red blood cells: when the level of this enzyme is too low, red blood cells can break down prematurely (hemolysis). When the body cannot compensate for accelerated loss, anemia develops. However, deficiency of this enzyme is not sufficient to cause hemolysis on its own; additional factors are required to “trigger” the onset of symptoms. Triggers of hemolysis in G6PD-deficient persons include certain infectious diseases, certain drugs, and eating fava beans: this can cause a potentially serious acute hemolytic anemia known as favism. Symptoms can include fatigue, pale color, jaundice or yellow skin color, shortness of breath, rapid heartbeat, dark urine and enlarged spleen (splenomegaly).

Most important, in the absence of triggering factors, the majority of people with G6PD deficiency are normal, and they sail through life without any knowledge or any noticeable symptoms of the disorder. G6PD deficiency is caused by alterations (mutations) in the G6PD gene, and it maps to the X chromosome.

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