"COMPLETE" ERYTHROCYTE GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY

Maternally transmitted severe glucose 6-phosphate dehydrogenase deficiency is an embryonic lethal

Mouse chimeras from embryonic stem cells in which the X-linked glucose 6-phosphate dehydrogenase (G6PD) gene had been targeted were crossed with normal females. First-generation (F(1)) G6PD(+/-) heterozygotes born from this cross were essentially normal; analysis of their tissues demonstrated strong selection for cells with the targeted G6PD allele on the inactive X chromosome. When these F(1) G6PD(+/-) females were bred to normal males, only normal G6PD mice were born, because: (i) hemizygous G6PD(-) male embryos died by E10.5 and their development was arrested from E7.5, the time of onset of blood circulation; (ii) heterozygous G6PD(+/-) females showed abnormalities from E8.5, and died by E11.5; and (iii) severe pathological changes were present in the placenta of both G6PD(-) and G6PD(+/-) embryos. Thus, G6PD is not indispensable for early embryo 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.

Genetic heterogeneity of glucose 6-phosphate dehydrogenase deficiency in Sardinia

Glucose 6-phosphate dehydrogenase (G6PD) activity was assayed quantitatively in red cells from 100 consecutive G6PD-deficient newborn male babies born in a city hospital in Sassari, Sardinia. In four cases G6PD activity was between 30% and 45% of normal: these appeared on electrophoresis to be identical with G6PD Seattle-like. In 65 cases G6PD activity ranged from 2% to 14% of normal, while in the remaining 31 samples no activity could be detected in crude hemolysates. G6PD was partiall purified from 39 samples having activity below 14% of normal (including 20 with zero activity). G6PD activity could now be determined in all, and it was fully characterized in nine samples. These were shown to belong to two distinct classes on grounds of the Michaelis constant for glucose 6-phosphate and the elution profile from DEAE-Sephadex columns. These properties were compared with those of G6PD-deficient samples from Greece and from Israel. We conclude that there are at least three polymorphic G6PD-deficient variants in Northern Sardinia: G6PD Seattle-like, G6PD Mediterranean, and a new variant, which we designate G6PD Sassari. The GdMediterranean and GdSassari genes have been shown to breed true in family studies. We also produce evidence that the definition of G6PD Mediterranean must be carefully reassessed.

Absence of glucose-6-phosphate dehydrogenase in red cells of an African

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Enzymic properties of different types of human erythrocyte glucose-6-phosphate dehydrogenase, with characterization of two new genetic variants

Enzymic properties have been compared in the following five genetic variants of glucose-6-phosphate dehydrogenase from human erythrocytes: the two common variants with normal activity, A and B; the common variant associated with enzyme deficiency, A-; and two new rare variants, "Ijebu-Ode" and "Ita-Bale."The maximal velocity of the enzyme reaction (V(max)) increases steadily with pH over the entire range explored (from pH 5.5 to 9.5) for all enzyme variants when buffers are used that show no specific ion effects on enzyme activity. Small differences are found among the variants in the pH range 7.5-8.2, where A and B show a "peak and trough," while A-, "Ijebu-Ode," and "Ita-Bale" exhibit a plateau. When the effects of reagents that bind to sulphydryl groups are compared, iodoacetate, bromoacetate, and iodoacetamide are weak inhibitors, while N-ethylmaleimide (NEM) and hydroxymercuribenzoate (HMB) are potent inhibitors. The last two reagents have differential inhibitory action on different variants; one of these, "Ijebu-Ode," is strikingly resistant to HMB and totally resistant to NEM (up to 3 mmoles/liter). The enzyme inactivation as a function of temperature exhibits distinctive profiles for all variants examined. BOTH OF THE NEW VARIANTS DESCRIBED DIFFER SIGNIFICANTLY FROM THE NORMAL B TYPE IN SEVERAL RESPECTS: "Ijebu-Ode" in electrophoretic mobility, thermostability, dependence of V(max) on pH, and resistance to sulphydryl group reagents; "Ita-Bale" in electrophoretic mobility, Michaelis constant (K(m)) for glucose-6-phosphate, and dependence of V(max) on pH. When these data are compared with those available in the literature, both variants are different from all those previously described. The estimated frequencies of the corresponding genes in western Nigeria are between 0.0005 and 0.0025 for "Ijebu-Ode" and less than 0.0005 for "Ita-Bale". The A- variant, compared to A, has a distinctly higher K(m) for 2-deoxyglucose-6-phosphate and is more inhibited by very low concentrations of HMB. These are the first observed differences in kinetic properties between A and A-.