Volume 2, Issue 1, March 2007
Dr Edmond S K Ma
MD (HK), FRCPath, FHKAM (Pathology)
Department of Pathology, Hong Kong Sanatorium & Hospital
G6PD catalyzes the conversion of glucose-6-phosphate (G6P) to 6-phosphogluconate concurrent with reduction of NADP to NADPH, which in turn acts through glutathione and catalase pathways to detoxify hydrogen peroxide, thus counteracting oxidative stress to the cell. In the body, red cells are most susceptible to oxidative damage because oxygen radicals are generated continuously as haemoglobin cycles from deoxygenated to oxygenated forms, as well as being readily exposed to exogenous oxidizing agents present in the blood. Hence G6PD deficiency is a prototype cause of haemolytic anaemia due to intrinsic red cell enzyme abnormality.
Deficiency of G6PD enzyme, an X-linked recessive disorder and the commonest inheritedenzymopathy in humans, is prevalent in Southern China. In Hong Kong, the prevalence of G6PD deficiency is 4.47% for males and 0.27% for females based on data generated from neonatal screening. Clinical manifestations of G6PD deficiency range from neonatal jaundice and episodic haem olysis precipitated by drugs, fava beans and infection, to the more severe cases of chronic non-spherocytic haemolytic anemia (CNSHA) associated with Class I G6PD variants. Occasionally, neonatal jaundice if severe enough may cause death or permanent neurological damage. Furthermore, patients with CNSHA may require intermittent blood transfusions. While more than 400 G6PD variants have been characterized using biochemical parameters, only around 129 variants have been deciphered at the molecular level . Similar to inherited globin disorders, the spectrum of G6PD mutations is different between ethnic groups. The common G6PD variants previously reported in the Chinese, such as G6PD Canton (nt 1376 G→T), Kaiping (nt 1388 G→A) and Gaohe (nt 95 A→G) are associated with mild to moderate clinical severity, and are categorized as Class II – III variants.