2.2 G6PD phenotype assigned based on genotype
G6PD genotyping was performed for patients enrolled on our
preemptive pharmacogenetic testing protocol
(PG4KDS-www.stjude.org/pg4kds)15from September 2017 to June 2020. The primary objective of PG4KDS is to
preemptively genotype all eligible patients receiving treatment for
active disease at St. Jude Children’s Research Hospital to guide
medication prescribing. Genotyping was performed using the
PharmacoScanTM assay (Thermo Fisher Scientific,
Waltham, MA) which interrogates 164 G6PD variants, including the
A-(202A_376G) variant.
Phenotype assignment from genotype differed for male and female
patients16 and was consistent with the phenotype
assignment outlined in the Clinical Pharmacogenetics Implementation
Consortium (CPIC®) guideline for rasburicase andG6PD. 5 G6PD alleles were categorized
using the World Health Organization (WHO) classification method
according to enzyme activity17 with class I, II, and
III alleles (e.g., A-(202A_376G), A-(968C_376G), Asahi, and Kalyan-
Kerala variants) consistent with deficient G6PD enzyme activity and
class IV alleles (e.g., A18 and Mira d’Aire variants
and the wildtype B allele) consistent with normal G6PD enzyme activity.
Males with one deficient G6PD allele (class I-III) and females
with two deficient alleles were assigned a G6PD deficient phenotype.
Heterozygous females, with one deficient allele (class I-III) and one
normal allele (class IV), were assigned a variable G6PD phenotype.
Patients with only normal alleles (class IV) were assigned a normal G6PD
phenotype.5 G6PD phenotype was assigned from genotype
alone for patients who did not have a G6PD activity result available in
the medical record; however, for females with a predicted variable
phenotype, a recommendation was made to obtain an activity test before a
high-risk medication was prescribed (Fig. 2).