Glucose 6-phosphate dehydrogenase (G6PD) deficiency is 1 of the commonest human enzymopathies, caused by inherited mutations of the X-linked gene G6PD. G6PD deficiency makes red cells highly vulnerable to oxidative damage, and therefore susceptible to hemolysis. Over 200 G6PD mutations are known: approximately one-half are polymorphic and therefore common in various populations. Some 500 million persons with any of these mutations are mostly asymptomatic throughout their lifetime; however, any of them may develop acute and sometimes very severe hemolytic anemia when triggered by ingestion of fava beans, by any of a number of drugs (for example, primaquine, rasburicase), or, more rarely, by infection. Approximately one-half of the G6PD mutations are instead sporadic: rare patients with these mutations present with chronic nonspherocytic hemolytic anemia. Almost all G6PD mutations are missense mutations, causing amino acid replacements that entail deficiency of G6PD enzyme activity: they compromise the stability of the protein, the catalytic activity is decreased, or a combination of both mechanisms occurs. Thus, genotype-phenotype correlations have been reasonably well clarified in many cases. G6PD deficiency correlates remarkably, in its geographic distribution, with past/present malaria endemicity: indeed, it is a unique example of an X-linked human polymorphism balanced through protection of heterozygotes from malaria mortality. Acute hemolytic anemia can be managed effectively provided it is promptly diagnosed. Reliable diagnostic procedures are available, with point-of-care tests becoming increasingly important where primaquine and its recently introduced analog tafenoquine are required for the elimination of malaria.

When persons with G6PD deficiency eat fava beans, acute hemolytic anemia may develop. It is caused by the generation of free radicals from the metabolism of glucosides in the beans. The free radicals damage red cells, resulting in intravascular and extravascular lysis.

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 (F1) 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 F1 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.

COVID-19, which is caused by the SARS-CoV-2, has ravaged the world for the past 2 years. Here, we review the current state of research into the disease with focus on its history, human genetics and genomics and the transition from the pandemic to the endemic phase. We are particularly concerned by the lack of solid information from the initial phases of the pandemic that highlighted the necessity for better preparation to face similar future threats. On the other hand, we are gratified by the progress into human genetic susceptibility investigations and we believe now is the time to explore the transition from the pandemic to the endemic phase. The latter will require worldwide vigilance and cooperation, especially in emerging countries. In the transition to the endemic phase, vaccination rates have lagged and developed countries should assist, as warranted, in bolstering vaccination rates worldwide. We also discuss the current status of vaccines and the outlook for COVID-19.