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).