Is There a Need for Neonatal Screening of Glucose-6-Phosphate Dehydrogenase Deficiency in Canada?

BIOCHEMISTRY AND NATURAL HISTORY OF G6PD DEFICIENCY G6PD is an enzyme in the pentose phosphate pathway, a metabolic pathway that supplies reducing energy to cells, in particular erythrocytes, by maintaining the level of nicotinamide adenine dinucleotide phosphate (NADPH). NADPH in turn maintains the level of glutathione that helps protect erythrocytes against oxidative damage. In states of oxidative stress, glutathione is rapidly consumed and the build up of oxidants can cause the red cell to lyse. Hence, G6PD deficiency most commonly manifests as either prolonged neonatal jaundice or acute hemolytic anemia. Patients of G6PD deficiency are almost exclusively male, due to the X-linked pattern of inheritance, but female carriers can be clinically affected due to lyonization. Lyonization is the random inactivation of an X-chromosome in certain cells, which creates a population of G6PD deficient erythrocytes coexisting with normal cells. The peak incidence of neonatal jaundice occurs during the second or third day of life. The severity of the jaundice ranges from subclinical to levels compatible with kernicterus, a condition in infants characterized by damage to brain centers due to high levels of bilirubin. Acute hemolytic anemia usually begins within hours of an oxidative stress and ends when G6PD deficient erythrocytes have hemolyzed; therefore, the severity of the anemia associated with these acute hemolytic episodes is proportionate to the deficiency of G6PD and oxidative stress. Viral and bacterial infections are the most common triggers, but many drugs and toxins can also precipitate hemolysis (3). The disorder, favism, in a G6PD deficient patient results from hemolysis secondary to the ingestion of fava beans, which contain beta-glycosides and naturally occurring oxidants. One such peroxidative component of fava beans is divicine, which reduces catalase activity in G6PD-deficient erythrocytes (14). Interestingly, G6PD deficiency also increases the risk for certain unrelated diseases. For example, it has been shown that there is an increased clinical incidence of G6PD deficiency in female patients with multi-lineage clonal marrow disorders (15). Likewise, G6PD deficiency has been implicated in the pathogenesis of a number of common diseases. It has 31 Copyright © 2007 by MJM MJM 2007 10(1):31-34