Sickle cell allele HBB-rs334(T) is associated with decreased risk of childhood Burkitt lymphoma in East Africa

Abstract

Burkitt lymphoma (BL) is an aggressive B-cell lymphoma that significantly contributes to childhood cancer burden in sub-Saharan Africa. Plasmodium falciparum, which causes malaria, is geographically associated with BL, but the evidence remains insufficient for causal inference. Inference could be strengthened by demonstrating that mendelian genes known to protect against malaria-such as the sickle cell trait variant, HBB-rs334(T)-also protect against BL. We investigated this hypothesis among 800 BL cases and 3845 controls in four East African countries using genome-scan data to detect polymorphisms in 22 genes known to affect malaria risk. We fit generalized linear mixed models to estimate odds ratios (OR) and 95% confidence intervals (95% CI), controlling for age, sex, country, and ancestry. The ORs of the loci with BL and P. falciparum infection among controls were correlated (Spearman's ρ = 0.37, p = .039). HBB-rs334(T) was associated with lower P. falciparum infection risk among controls (OR = 0.752, 95% CI 0.628-0.9; p = .00189) and BL risk (OR = 0.687, 95% CI 0.533-0.885; p = .0037). ABO-rs8176703(T) was associated with decreased risk of BL (OR = 0.591, 95% CI 0.379-0.992; p = .00271), but not of P. falciparum infection. Our results increase support for the etiological correlation between P. falciparum and BL risk.

Figure 1.. a) Map of the study sites: a locator map for Africa and a zoom out of EMBLEM study sites in Uganda, Kenya, and Tanzania and the Infections and Childhood Cancer Study site in Malawi.

Red crosses mark location of hospitals where cases were enrolled, and a green shade marks the 6 regions where cases and controls were enrolled in EMBLEM. Stars mark location of country capitals to show the relative distance between the participating hospitals versus enrollment hospitals. b) Flow chart showing participants enrolled and reasons for exclusion from the final set included in case-control analysis. c) Flow chart showing the process followed to identify polymorphisms associated with protection from or risk of severe malaria in epidemiological studies. Significantly associated polymorphisms were considered “malaria index” and the identified genes labeled “malaria index genes”. The genotypes are analyzed are based on genotype results from the Omni 5M array or from imputed results. Non-index polymorphisms were extracted and analyzed for hypothesis generation. Genotypes for HBA1 and HBA2 were determined using droplet digital PCR were included in the analysis. The 3.7 kb deletion (-α^3.7/), which has been reported to interact with the sickle cell trait, is the most prevalent in our population (details in Supplementary data).

Figure 2.. Forest plots showing associations between 32 malaria-risk index SNPs and endemic Burkitt lymphoma (left) or P. falciparum infection (right).

Forest plots show OR values (95% confidence intervals) and p-values from the mixed-effects logistic regression model analyses for association with BL among 4 581 BL cases and controls using model: BL case status~ SNP_ij+factor(P. falciparum)+ age+sex+pop-specific PC1+ pop-specific PC2+ pop-specific PC3+ factor(country)+[genetic relation matrix, random effect], and for association with P. falciparum infection among 3800 controls using model P. falciparum ~ SNP_ij+ age+sex+pop-specific PC1+ pop-specific PC2+ pop-specific PC3+ factor(country)+[genetic relation matrix, random effect]. p < 0.05 was considered statistically significant, * effect of SNP on BL concordant with effects against malaria in the literature and infection among the controls (see methods). The area of the squares/circles is proportional to the frequency (freq) of the variant in the population. The minor alleles are reported based on the sequence on the plus strand as reported in dbGAP, however results for HBB-rs334 are reported in the test based on the minus strand to be consistent with conventional usage across scientific literature on sickle cell disease.