Table 1.

Assignment of predicted G6PD phenotype based on genotype

Predicted phenotype	Genotypea	Examples of G6PD genotypesb
Normal	A person with one X chromosome carrying a non-deficient (class IV) allele A person carrying two non-deficient (class IV) alleles	B, Sao Boria, IV B/B, B/Sao Boria, B/A, IV/IV
Deficient	A person with one X chromosome carrying a deficient (class II-III) allele A person carrying two deficient (class II-III) alleles OR one class I allele and one class II or III allele	A-, Orissa, Kalyan-Kerala, Mediterranean, Canton, Chatham, II, III A-/A-, A-/Orissa, Orissa/ Kalyan-Kerala, Mediterranean/ Mediterranean, Chatham /Mediterranean, Canton/ Viangchan, II/II, II/III, III/III, I/II, I/III
Deficient with CNSHA	A person with one X chromosome carrying a deficient (class I) allele A person carrying two deficient (class I) allelesd	Bangkok, Villeurbanne, I Bangkok/Bangkok, Bangkok/Villeurbanne, I/I
Variablec	A person carrying one non-deficient (class IV) allele and one deficient (class I-III) allele	B /Bangkok, B/Mediterranean, B/A-, IV/I, IV/II, IV/III

CNSHA, chronic non-spherocytic hemolytic anemia; G6PD, glucose-6-phosphate dehydrogenase; WHO, World Health Organization

^aWHO classifications from (8), other details from (14). Class I alleles are extremely rare; the distinction between Class II and III alleles is not clear. Almost all patients will carry class II, III, or IV alleles.

^bDue to the large number of G6PD alleles, other genotypes may be possible besides those given as examples here; see the G6PD Allele Definition Table (5, 6) for a more comprehensive list of alleles and G6PD Allele Functionality Table (5, 6) for their assigned function (WHO class). Note that some labs use the designation “B allele” to indicate an allele carrying no known class I-III variants. The G6PD Frequency Table (5, 6) can be referenced for the frequency of G6PD alleles across major biogeographical groups.

^cDue to X-linked mosaicism, persons heterozygous (generally females) for one non-deficient (class IV) and one deficient (class I-III alleles) allele may display a normal or a deficient phenotype. It is therefore difficult to predict the phenotype of these individuals (see Supplement, G6PD Heterozygotes).

^dSuch genotypes have never been seen and are presumably exceedingly rare.