Manhattan plot illustrating results of a GWAS with MTX clearance as the phenotype. The y-axis plots the inverse of the log of the association P value for each typed SNP (> 500 000 SNPs interrogated per patient) as it relates to MTX clearance; the x-axis sorts SNPs based on chromosomal position. The peak of P values corresponds to SNPs that localize to SLCO1B1, indicating that variation in this gene identified genetic variation associated with interpatient variability in MTX clearance among 1279 children with ALL.¹⁸