Anemia, Nonspherocytic Hemolytic, Due To G6pd Deficiency

A number sign (#) is used with this entry because nonspherocytic hemolytic anemia can be caused by mutation in the G6PD gene (305900) on chromosome Xq28.

Description

G6PD deficiency is the most common genetic cause of chronic and drug-, food-, or infection-induced hemolytic anemia. G6PD catalyzes the first reaction in the pentose phosphate pathway, which is the only NADPH-generation process in mature red cells; therefore, defense against oxidative damage is dependent on G6PD. Most G6PD-deficient patients are asymptomatic throughout their life, but G6PD deficiency can be life-threatening. The most common clinical manifestations of G6PD deficiency are neonatal jaundice and acute hemolytic anemia, which in most patients is triggered by an exogenous agent, e.g., primaquine or fava beans. Acute hemolysis is characterized by fatigue, back pain, anemia, and jaundice. Increased unconjugated bilirubin, lactate dehydrogenase, and reticulocytosis are markers of the disorder. The striking similarity between the areas where G6PD deficiency is common and Plasmodium falciparum malaria (see 611162) is endemic provided evidence that G6PD deficiency confers resistance against malaria (summary by Cappellini and Fiorelli, 2008).

Clinical Features

In primaquine-sensitive patients with hemolytic anemia, Carson et al. (1956) demonstrated an abnormality in the direct oxidation of glucose in red blood cells and deficiency of glucose-6-phosphate dehydrogenase.

Cooper et al. (1972) and Gray et al. (1973) found that complete deficiency of G6PD produces not only nonspherocytic hemolytic anemia but also chronic granulomatous disease due to neutrophil dysfunction. The patient of Cooper et al. (1972) was a woman with complete leukocyte G6PD deficiency, partial deficiency in her red cells, and no family history of G6PD deficiency. Of the various possible explanations advanced by the authors, they preferred the suggestion that X-inactivation had affected the red cell and white cell series differently and that the patient indeed had G6PD deficiency. Gray et al. (1973) described 3 affected brothers. The mother showed an intermediate defect in leukocyte microbicidal and metabolic activity, as well as red and white blood cell mosaicism.

In Saudi Arabia, Mallouh and Abu-Osba (1987) reviewed the G6PD status of all children aged 1 month to 14 years who were treated for meningitis, septicemia, osteomyelitis, or typhoid fever during a 9-year period. The observed frequency of G6PD deficiency was significantly higher than expected for the entire group, for females with both catalase-positive and catalase-negative infection, and for males with catalase-positive infections.

Beutler (1994) pointed out that 35 years previously, William Demeshek, the first editor of the emerging journal 'Blood,' had invited him to write a review on 'The Hemolytic Effect of Primaquine and Related Compounds' (Beutler, 1959). Beutler (1994) attempted to put into perspective what had been learned in the 35-year interval and to touch upon what still needed to be learned. He provided a comprehensive tabulation of those G6PD variants that had been characterized at the DNA level as well as information on the population distribution of common G6PD mutations. He pointed out that the most dangerous consequence of G6PD deficiency is neonatal icterus. Kernicterus has been documented repeatedly in populations in which class 2 variants are common and is an important preventable form of mental retardation. Phototherapy has been used to reduce bilirubin levels and phenobarbital has been used prophylactically with some success. Exchange transfusion is required if the bilirubin exceeds 20 mg/dL.

Ninfali et al. (1995) studied muscle expression of G6PD in normal individuals and in persons with G6PD deficiency of 3 types. They were prompted to undertake these studies because of patients with symptoms such as myalgia, cramps, and muscle weakness under conditions of stress, particularly physical exertion. All 3 variants--Mediterranean (305900.0006), Seattle-like (305900.0010), and G6PD A- (305900.0002)--showed the enzyme defect in muscle. A statistically significant relationship was found in the activity of G6PD in erythrocytes and muscle of male subjects. The results suggested to the authors that, for a given variant, the extent of the enzyme defect in muscle can be determined from the G6PD activity of erythrocytes, using an equation that they derived.

Cocco et al. (1998) reported a mortality study of a cohort of 1,756 men with G6PD deficiency identified during a 1981 population screening in Sardinia and followed during the period January 1, 1982 through December 31, 1992. Outcome measures were cause-specific standardized mortality ratios (SMRs), which were computed as 100 times the observed/expected ratio, with the general Sardinian male population as the reference. Deaths from all causes were significantly less than expected due to decreased SMRs for ischemic heart disease, cerebrovascular disease, and liver cirrhosis, which explained 95.6% of the deficit in total mortality. All cancer mortality was close to the expectation, with a significant increase in the SMR for non-Hodgkin lymphoma. Increased mortality from non-Hodgkin lymphoma and decrease in mortality from liver cirrhosis were new observations. Decrease in mortality from cardiovascular disease may have been based on selection bias because the population screening was not random but was based on volunteers, who may have been more concerned than the average about their health.

In comparison with normal neonates, G6PD-deficient neonates experience a 2-fold increase in the prevalence of significant hyperbilirubinemia requiring phototherapy. Kappas et al. (2001) tested the efficacy of a single dose of intramuscular SN-mesoporphyrin, a potent inhibitor of heme oxygenase activity, in ameliorating jaundice in G6PD-deficient newborns in Greece. When compared with an untreated control group and a group of G6PD-normal newborns, a single dose of SN-mesoporphyrin shifted the peak plasma bilirubin concentration distribution to lower values, even in relation to normal neonates, and entirely eliminated the need for phototherapy.

Susceptibility to Favism

The most common trigger for acute hemolytic anemia in G6PD-deficient individuals is favism, caused by ingestion of fava beans (Vicia faba). V. faba contains high concentrations of 2 beta-glucosides: vicine and convicine. On ingestion of fava beans, these glucosides undergo hydrolysis by glucosidases present both in the beans and in the gastrointestinal tract, releasing the respective aglycones divicine and isouramil, which are capable of triggering a favism attack. Favism occurs commonly only where the frequency of G6PD deficiency is relatively high and where fava beans are a popular food item, i.e., in southern Europe, the Middle East, and Southeast Asia. Favism may be life-threatening, especially in children (summary by Luzzatto and Arese, 2018).

Resistance to Malaria

That resistance to severe malaria (see 611162) is the basis of the high frequency of G6PD deficiency and that both hemizygotes and heterozygotes enjoy an advantage was established by Ruwando et al. (1995) in 2 large case-control studies of more than 2,000 African children. They found that the common African form of G6PD deficiency (G6PD A-; 305900.0002) was associated with a 46 to 58% reduction in risk of severe malaria for both female heterozygotes and male hemizygotes. A mathematical model incorporating the measured selective advantage against malaria suggested that a counterbalancing selective disadvantage, associated with this enzyme deficiency, has retarded its rise in frequency in malaria-endemic regions.

Inheritance

G6PD deficiency is an X-linked dominant disorder (Luzzatto and Arese, 2018).

X-chromosome Inactivation

Puck and Willard (1998) reviewed the mechanism for a skewed pattern of X-chromosome inactivation in females heterozygous for X-linked traits. Their Figure 1 diagrammed 3 different mechanisms for an extremely unbalanced pattern of somatic cell mosaicism in women after X inactivation. Luzzatto and Martini (1998) noted that at least one possible example of each of the 3 mechanisms at work in different women with G6PD deficiency can be pointed to. The first mechanism (the extreme end of a normal distribution curve after random X inactivation) was deemed the simplest explanation for the G6PD values in the fully deficient range reported by Rinaldi et al. (1976) in about 1% of genetically confirmed heterozygotes for the Mediterranean variant of G6PD deficiency (305900.0006). The second mechanism could be called 'somatic selection after X inactivation.' Luzzatto and Martini (1998) preferred this term to 'nonrandom X inactivation' because, in fact, X inactivation itself is still random. This mechanism has been well characterized (Filosa et al., 1996) in many heterozygous mothers of patients with chronic nonspherocytic hemolytic anemia due to G6PD deficiency. Here, the selection affects hematopoietic cells in a way that is analogous to what happens to lymphoid cells in immunodeficiency syndromes. As for the third mechanism, G6PD Ilesha (305900.0004) was observed by Luzzatto et al. (1979) in a family in which every heterozygous woman had an extremely unbalanced X-inactivation pattern, which could not have resulted from selection against the cells with G6PD Ilesha, because in some members of the family, the imbalance favored the X chromosome with a normal G6PD allele, whereas in other members, it favored the X chromosome with the G6PD Ilesha allele. Although at the time of report the explanation favored was selection for cells expressing a selectable allele of some other X-linked gene, there may have been a defect in the X-inactivation process in this family. Since the X-inactivation-specific transcript (XIST; 314670) gene maps to Xq13 and G6PD maps to Xq28, one would predict an even chance of recombination, in keeping with what was observed in the family with the G6PD Ilesha mutation.

Population Genetics

Miwa and Fujii (1996) stated that an estimated 400 million people worldwide have G6PD deficiency associated with chronic hemolytic anemia and/or drug- or infection-induced acute hemolytic attacks.

The highest prevalence of G6PD deficiency is found in Africa, southern Europe, the Middle East, Southeast Asia, and the central and southern Pacific islands (summary by Cappellini and Fiorelli, 2008).

Luzzatto and Arese (2018) stated that favism had been reported in 35 countries and that more than 3,000 cases, mostly involving children, had been reported between 1988 and 2018.

Molecular Genetics

All G6PD mutations known, except G6PD A (305900.0001), are associated with more or less severe enzyme deficiency but never with complete loss of activity; complete loss would be lethal (summary by Luzzatto et al., 2016).

Variants of G6PD deficiency have been divided into 5 classes according to the level of enzyme activity: class 1--severe enzyme deficiency associated with chronic nonspherocytic hemolytic anemia; class 2--severe enzyme deficiency (less than 10%) associated with acute hemolytic anemia; class 3--moderate to mild enzyme deficiency (10-60%); class 4--very mild or no enzyme deficiency (60%); class 5--increased enzyme activity. Mutations causing nonspherocytic hemolytic anemia are clustered near the carboxy end of the enzyme, in the region between amino acids 362 and 446, whereas most of the clinically mild mutations are located at the amino terminal end of the molecule. As the intragenic defects have been identified, many variants that were thought to be unique have been found to be identical on sequence analysis (Beutler et al., 1991).

In patients with nonspherocytic hemolytic anemia, Beutler et al. (1992) identified missense mutations in the G6PD gene (see, e.g., 305900.0034; 305900.0037-305900.0040).

Filosa et al. (1996) analyzed fractionated blood cells in 4 heterozygotes for the class 1 G6PD mutations G6PD Portici (305900.0008) and G6PD Bari (1187G-T). In erythroid, myeloid, and lymphoid cell lineages there was a significant excess of G6PD-normal cells, suggesting that a selective mechanism operates at the level of pluripotent blood stem cells. They concluded that their studies provided evidence that severe G6PD deficiency adversely affects the proliferation or survival of nucleated blood cells.

Vulliamy et al. (1998) determined the causative mutation in 12 cases of G6PD deficiency associated with chronic nonspherocytic hemolytic anemia. In 11 cases, the mutation they found had previously been reported in unrelated individuals. These mutations comprised 7 different missense mutations and a 24-bp deletion, G6PD Nara (305900.0052), previously found in a Japanese boy. Repeated findings of the same mutations suggest that a limited number of amino acid changes can produce the chronic nonspherocytic hemolytic anemia phenotype and be compatible with normal development. They found 1 new mutation, G6PD Serres (305900.0051).

Genotype/Phenotype Correlations

Miwa and Fujii (1996) listed the mutations responsible for about 78 G6PD variants. Molecular studies disclosed that most of the class 1 G6PD variants associated with chronic hemolysis have the mutations surrounding either the substrate- or NADP-binding site.

Costa et al. (2000) pointed out that G6PD mutants causing class 1 variants (the most severe forms of the disease) cluster within exon 10, in a region that, at the protein level, is believed to be involved in dimerization. They identified a class 1 variant (G6PD Aveiro) mapping to exon 8 (305900.0053).

History

Beaconsfield et al. (1965) advanced the hypothesis that the incidence of cancer is inversely related to the frequency of G6PD deficiency in blacks.

Vicia faba apparently produces a substance that induces hemolysis of enzyme-deficient red cells (Mager et al., 1965).

Stamatoyannopoulos et al. (1966) stated that hemolytic anemia following ingestion of the bean of Vicia faba is conditioned primarily by a deficiency of erythrocyte glucose-6-phosphate dehydrogenase. They noted that in areas where G6PD deficiency is frequent, favism shows familial aggregation probably not accounted for by the familial occurrence of the enzyme deficiency alone. They interpreted studies in Greece as indicating the presence of an autosomal gene that in heterozygous state enhances the susceptibility to favism of G6PD-deficient persons.

Beutler (1970) suggested that DOPA-quinone is the active hemolytic principal in fava beans. (Fava beans are the main commercial source of L-DOPA.) Differences in susceptibility to favism by G6PD-deficient persons may be related to differences in the enzymatic system that converts L-DOPA to DOPA-quinone.

A genetic mechanism for susceptibility to favism on the part of G6PD-deficient persons was suggested by the finding of Bottini et al. (1971) that persons with favism are more often of a particular red cell acid phosphatase type than would be expected on the basis of population frequencies.

Since the metabolism of xylitol remains intact in G6PD-deficient red cells, Wang et al. (1971) suggested use of xylitol in the treatment of hemolytic crisis.

Zinkham (1961) found that individuals with primaquine-sensitive erythrocytes had deficiency of G6PD activity in the lens. Orzalesi et al. (1981) found that G6PD deficiency was significantly more frequent among 210 male cataract patients in Sardinia than in 672 control subjects. This was particularly the case with presenile cataracts. Also in Sardinia, however, Meloni et al. (1990) found that patients with cataract had frequencies of G6PD deficiency no different from those in the general population.

Ferraris et al. (1988) examined the hypothesis that there is a negative correlation between G6PD deficiency and hematologic malignancy. The frequency of G6PD deficiency in 481 Sardinian males with hematologic malignancies was not significantly different from that in a group of 16,219 controls. Similarly, no differences were found in the frequency of expression of the Gd(B) gene in women with clonal hematologic disorders and healthy heterozygotes. There was no evidence that G6PD provides a protective effect against the development of hematologic malignancy.

Animal Model

Lee et al. (1981) observed G6PD heterozygosity in female hares. Pretsch et al. (1988) recovered a mouse with X-linked G6PD deficiency from the offspring of 1-ethyl-1-nitrosourea-treated male mice.

Stockham et al. (1994) observed G6PD deficiency causing persistent hemolytic anemia and hyperbilirubinemia in a male American Saddlebred horse. The dam had abnormalities consistent with heterozygosity.

Longo et al. (2002) crossed mouse chimeras from embryonic stem cells in which the G6pd gene had been targeted with normal females. First-generation G6pd heterozygotes born from this cross were essentially normal; their tissues demonstrated strong selection for cells with the targeted G6pd allele on the inactive X chromosome. When these first-generation heterozygous females were bred to normal males, only normal G6pd mice were born. There were 3 reasons for this: hemizygous G6pd male embryos' development was arrested from embryonic day 7.5, the time of onset of blood circulation, and they died by embryonic day 10.5; heterozygous G6pd females showed abnormalities from embryonic day 8.5, and died by embryonic day 11.5; and severe pathologic changes were present in the placenta of both G6pd hemizygous and heterozygous embryos. Thus, G6PD is not indispensable for early embryonic development; however, severe G6PD deficiency in the extraembryonic tissues (consequent on selective inactivation of the normal paternal G6PD allele) impairs the development of the placenta and causes death of the embryo. Most importantly, G6PD is indispensable for survival when the embryo is exposed to oxygen through its blood supply.