Predictive models for human glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase deficiency: a historical perspective

Glucose-6-phosphate dehydrogenase deficiency serves as a prototype of the many human enzyme deficiencies that are now known. Since its discovery more than 50 years ago, the high prevalence of the defect and the easy accessibility of the cells that manifest it have made it a favorite tool of biochemists, epidemiologists, geneticists, and molecular biologists as well as clinicians. In this brief historical review, we trace the discovery of this defect, its clinical manifestations, detection, population genetics, and molecular biology.

The interactive effect of chlorine, copper and nitrite on methaemoglobin formation in red blood cells of Dorset sheep

Simultaneous exposure to chemicals which can oxidize the haemoglobin of the red blood cell to methaemoglobin is common. Although the effects of some of these agents have been documented individually, little research considers the interactive effects. In-vitro experiments on the treated blood of female Dorset sheep assessed the interactive capacity of chlorite, copper and nitrite to affect methaemoglobin formation. All combinations of doses which produced 2.5, 5, 10% methaemoglobin were tested in all possible combinations (a total of 80), as were the controls. This included data on each chemical alone, each two-way combination and the three-way combination. The response is largely additive (the sum of the individual effects) except for one of the two-way interactions, chlorite/nitrite (P less than .01), which showed antagonism. Chlorite may oxidize nitrite which could explain the less-than-additive response. Overall, the result of combining these agents on methaemoglobin was additive.

Glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzymopathy. Because its gene locus is on the X-chromosome it is more common in males than females in all populations. Prevalence rates vary from 62% among Kurdish Jews to the very low rates (0.1% or less in Japan, for example), which are compatible with sporadic cases arising from spontaneous mutations. However, there is at least one population in which G6PD deficiency has not been found, namely the indigenous (Amerindian) population of America. Approximately 400 variants have been described. Despite the clinical burden imposed by this enzymopathy, polymorphic frequencies have been reached in many populations. There is abundant epidemiological evidence that this has happened because of a biological advantage conferred on heterozygotes in falciparum malaria endemic areas. This advantage may apply to quartan malaria as well. Clinical severity varies, from the rare chronic nonspherocytic haemolytic anaemia to progressively milder forms like the Mediterranean and A- types. The other clinical syndromes, i.e. neonatal jaundice and haemolysis caused by infections, foods, drugs and chemicals, are not always predictable. This is because only a fraction of such enzymopathic persons develop these syndromes after exposure to the relevant stimulus. Modern techniques of molecular biology may elucidate why this is so. There is some emerging evidence that the genetic burden or survival value associated with G6PD deficiency may be relevant not only in tropical and infectious diseases, but also in their chemotherapy (e.g. malaria) as well as in the control of a long-recognized environmental pollutant such as lead.