Mutations In Circadian Rhythm Genes Are Associated with Diffuse Large B-Cell Lymphoma In the Mexican Population

Abstract 2478

In Mexico, diffuse large B-cell lymphoma (DLBCL) is the most common histological non-Hodgkin's lymphoma (NHL) subtype and is observed in up to 48% of all diagnoses of lymphoma. It has recently been hypothesized that circadian disruption may have a connection with lymphomagenesis. The circadian clock maintains biological rhythms over a cycle of approximately 24 hours, and many physiological functions in the human body are regulated by this system. The disruption of the circadian cycle may negatively affect cellular function, potentially leading to increased susceptibility to certain malignancies. Evidence in support of this association has been provided by epidemiological studies that demonstrate that night-time work significantly increased the risk of NHL in men, the overall relative risk being 1.10 (95%CI = 1.03–1.19, p = 0.010)(Lahti et al., Int J Cancer 2008). The study was performed to determinate if functional single nucleotide polymorphisms (SNP) in circadian rhythm genes are associated with the presence of DLBCL in Mexican patients. A molecular mechanism to regulate the circadian rhythm has been identified, where nine genes have been involved: clock, npas2, bmal1, per1-3, cry1-2, and csnk1e. Recent studies have shown that approximately 10% of genes exhibit circadian patterns of expression in a given tissue, and 10% of these clock-controlled genes identified regulate either cell proliferation or apoptosis. For this current study, SNPs were evaluated in DNA samples isolated from histopathologically-confirmed DLBCL patients (N=30) and healthy volunteers (N=50) as a control population. Samples were provided by Hospital Regional de Especialidades IMSS No. 25 and Hospital Metropolitano, in Monterrey, Nuevo Leon, Mexico. The selection of functional SNPs was made using a bioinformatic tool called Function Analysis and Selection Tool for Single Nucleotide Polymorphisms (FASTSNP)(Yuan et al., Nucl. Acids Res 2006). Six genes that regulate the circadian rhythm were submitted to FASTSNP, and 13 high-risk SNPs were used for this study. The results provided were npas2 rs11541353, per1 rs3027189, rs3027180, and rs3027177; per2 rs2340885, and rs3739068; per3 rs228697, rs2640905, rs12078704, and rs57875989; tim rs2291739, and rs2638290; and cry2 rs2863712. Primers were designed for the 13 high-risk SNPs. The SNPs were amplified by PCR in a 96-well plate. Alleles were determined by presence of the resultant bands in an agarose gel electrophoresis. SNPs analysis showed that DLBCL patients were mutated in 93.3% (28/30), while the population of controls were only in 74.0% (37/50) who presented with mutations (p = 0.023). The rs2291739 variant of the tim gene was the most frequent homozygous mutant found in at least 50% of both controls and patients. Two SNPs were found to be statistically significant associated with DLBCL, these were per1 rs3027189 (p = 0.006) and cry2 rs2863712 (p = 0.002). The per1 gene plays an important role in regulating growth and DNA damage control and also interacts with proteins in the cell-cycle pathway. CRY2 has been shown to alter genes associated with immune response and hematological system development. These results suggest that these two genes might play an important role in influencing biological pathways relevant for lymphomagenesis. These findings contribute in part to the recent research that links the disruption of circadian rhythm with the processes of lymphomagenesis. Further studies are warranted. This study was supported by Catedra de Hematologia y Cancer from Tecnologico de Monterrey.