Sickle cell trait is not associated with endemic Burkitt lymphoma: An ethnicity and malaria endemicity‐matched case–control study suggests factors controlling EBV may serve as a predictive biomarker for this pediatric cancer

Abstract

Endemic Burkitt lymphoma (eBL) is associated with Epstein–Barr virus (EBV) and Plasmodium falciparum coinfections. Malaria appears to dysregulate immunity that would otherwise control EBV, thereby contributing to eBL etiology. Juxtaposed to human genetic variants associated with protection from malaria, it has been hypothesized that such variants could decrease eBL susceptibility, historically referred to as “the protective hypothesis.” Past studies attempting to link sickle cell trait (HbAS), which is known to be protective against malaria, with protection from eBL were contradictory and underpowered. Therefore, using a case–control study design, we examined HbAS frequency in 306 Kenyan children diagnosed with eBL compared to 537 geographically defined and ethnically matched controls. We found 23.8% HbAS for eBL patients, which was not significantly different compared to 27.0% HbAS for controls [odds ratio (OR) = 0.85; 95% confidence interval (CI) 0.61–1.17; p-value = 0.33]. Even though cellular EBV titers, indicative of the number of latently infected B cells, were significantly higher (p-value < 0.0003) in children residing in malaria holoendemic compared to hypoendemic areas, levels were not associated with HbAS genotype. Combined, this suggests that although HbAS protects against severe malaria and hyperparasitemia, it is not associated with viral control or eBL protection. However, based on receiver operating characteristic curves factors that enable the establishment of EBV persistence, in contrast to those involved in EBV lytic reactivation, may have utility as an eBL precursor biomarker. This has implications for future human genetic association studies to consider variants influencing control over EBV in addition to malaria as risk factors for eBL.What's new?Although the hypothesis dates back to 1970, studies of the “protective effect” of sickle cell trait (HbAS) on the development of endemic Burkitt lymphoma (eBL) have led to contradictory conclusions. This new study analyzed an unprecedented number of eBL cases and highlighted the importance of matching controls on ethnicity as well as malaria endemicity. The findings contribute to resolving the controversy by showing that HbAS frequency does not differ between children diagnosed with eBL and healthy children. The study also examined cellular Epstein-Barr Virus (EBV) titers, which in contrast to plasma EBV levels may serve as an informative eBL biomarker.

Burkitt’s lymphoma patients in Northwest Cameroon have a lower incidence of sickle cell trait (Hb AS) than healthy controls

“…It is not clear whether controls in the Kenyan study [5] were carefully matched for age and if they were indeed nearest-neighbour controls. This is of critical importance because of large differences in the distribution of the AS gene.…”

“…No difference in frequency of AS was, however, subsequently observed between 306 Kenyan children with BL and age-, ethnically and geographically matched controls. [4,5] We observed an AS incidence of 7% in 167 BL patients treated in Cameroon, [6] and subsequently conducted a prospective study in surviving BL patients resident in the Northwest region.…”

Interleukin-6 and Interleukin-10 Gene Promoter Polymorphisms and Risk of Endemic Burkitt Lymphoma

“…39 However, in the Brazilian study, 39 only 54.1% of the BL patients were EBV-positive (defined as intermediate BL), whereas in our study, all cases were EBV-positive. 31 In addition, they had a smaller sample size, and their controls were from different genetic backgrounds, which could have contributed to the discrepancies between the two studies. Furthermore, the previous study did not select age-matched controls, and instead, they included adults with a median age of 36 years old.…”

“…Viral quantification was performed as previously described for EBV BALF5. 31 The quantitative PCR (qPCR) cycle was 3 minutes at 95 C, 10 seconds at 95 C, and 30 seconds at 62.5 C repeated for 40 cycles and read by a Bio-Rad CFX96 Real-Time System C1000 Thermal Cycler Base (BioRad Laboratories, Hercules, CA), and it was performed for all the reactions. Standard curves were generated using EBV-positive Namalwa and EBV-negative BL41 cell lines (ATCC, Manassas, VA).…”

“…Cellassociated viral loads were normalized based on EBV genome copies per microgram human β-actin DNA multiplexed in the qPCR assay as previously described. 31 Statistical analysis. All statistical tests were carried out using SPSS Statistical Software Package, version 20.0 (IBM SPSS, Inc., Chicago, IL).…”