Three known non-synonymous polymorphisms (Ala394Thr, Ser471Leu and Pro690Ala) in the largest circadian gene, Neuronal PAS domain protein 2 (NPAS2), were genotyped in a breast cancer case-control study conducted in Connecticut, USA (431 cases and 476 controls). We found that women with the heterozygous Ala394Thr genotype were significantly associated with breast cancer risk compared to those with the common homozygous Ala394Ala (OR = 0.61, 0.46-0.81, P = 0.001). This is the first evidence demonstrating a role of the circadian gene NPAS2 in human breast cancer, suggesting that genetic variations in circadian genes might be a novel panel of biomarkers for breast cancer risk.

Circadian disruption is theorized to cause immune dysregulation, which is the only established risk factor for non-Hodgkin's lymphoma (NHL). Genes responsible for circadian rhythm are also involved in cancer-related biological pathways as potential tumor suppressors. However, no previous studies have examined associations between circadian genes and NHL risk. In this populationbased case control study (n 5 455 cases; 527 controls), we examined the only identified nonsynonymous polymorphism (Ala394Thr; rs2305160) in the largest circadian gene, neuronal PAS domain protein 2 (NPAS2), in order to examine its impact on NHL risk. Our results demonstrate a robust association of the variant Thr genotypes (Ala/Thr and Thr/Thr) with reduced risk of NHL (OR 5 0.66, 95% CI: 0.51-0.85, p 5 0.001), especially B-cell lymphoma (OR 5 0.61, 95% CI: 0.47-0.80, p 0.0001). These findings provide the first molecular epidemiologic evidence supporting a role of circadian genes in lymphomagenesis, which suggests that genetic variations in circadian genes might be a novel panel of promising biomarkers for NHL and warrants further investigation. ' 2006 Wiley-Liss, Inc.

Introduction MBD2, the gene encoding methyl-CpG-binding domain (MBD)2, is a major methylation related gene and functions as a transcriptional repressor that can specifically bind to the methylated regions of other genes. MBD2 may also mediate gene activation because of its potential DNA demethylase activity. The present case-control study investigated associations between two single nucleotide polymorphisms (SNPs) in the MBD2 gene and breast cancer risk.

Circadian disruption has been indicated as a risk factor for breast cancer in recent epidemiologic studies. A novel finding in circadian biology is that genes responsible for circadian rhythm also regulate many other biological pathways, including cell proliferation, cell cycle regulation, and apoptosis. Therefore, mutations in circadian genes could conceivably result in deregulation of these processes and contribute to tumor development, and be markers for susceptibility to human cancer. In this study, we investigated the association between an exonic length variation in a circadian gene, Period3 (Per3), and breast cancer risk using blood samples collected from a recently completed breast cancer case-control study in Connecticut. There were 389 Caucasian cases and 432 Caucasian controls included in our analysis. We found that the variant Per3 genotype (heterozygous + homozygous 5-repeat alleles) was associated with an increased risk of breast cancer among premenopausal women (odds ratio, 1.7; 95% confidence interval, 1.0-3.0). Our finding suggests that the circadian genes might be a novel panel of potential biomarkers for breast cancer and worth further investigation.