Single Nucleotide Polymorphisms within the 8Q24 Region are Not Associated with the Risk of Intraductal Papillary Mucinous Neoplasms of the Pancreas

Background & Aims: Intraductal papillary mucinous neoplasms (IPMNs) of the pancreas have been reported to be associated with an increased risk of developing extra-pancreatic malignancies. A common genetic background has been hypothesised to be responsible for such an association. Human chromosomal region 8q24 has been associated with many types of cancer. The majority of these associations lie at approximately 128 Mb on chromosome 8. We conducted a study in order to examine the association between IPMN and single nucleotide polymorphisms (SNPs) from the 8q24 region, namely rs10505477, rs6983267, rs7014346, rs6993464, previously reported to influence general cancer susceptibility. Methods. The study was performed on 117 IPMN cases and 231 controls. Cases were enrolled at the Digestive Endoscopy Unit, Policlinico Agostino Gemelli from January, 2010 to June, 2011, with either a prevalent or incident IPMN diagnosis. Status of SNPs was determined using a StepOne Real-time PCR system (Applied Biosystems) and TaqMan SNP Genotyping Assay™ 40X. Unconditional multiple logistic regression models were used to estimate odds ratios and 95% confidence intervals for the association of selected SNPs and IPMNs. Results. Cases were more likely to report a 1st degree family history of cancer (p<0.001), as well as heavy smoking (p=0.001) and heavy drinking habits (p<0.001). No significant association was observed between IPMN and selected SNPs. The results were confirmed also when stratified according to any 1st-degree family history of cancer. Conclusion. Patients with IPMN do not have a higher prevalence of SNPs in the human chromosomal region 8q24 in respect to the control population. Abbreviations: CASC8: cancer susceptibility candidate 8; CRC: colorectal cancer; ENPP2: ectonucleotide pyrophosphatase/phosphodiesterase 2; EPM: extra-pancreatic malignancy; eQTLs: expression quantitative trait loci; IPMN: intraductal papillary mucinous neoplasm; MYC: myelocytomatosis viral oncogene homolog gene; NOV: nephroblastoma over-expressed gene; PCR: polymerase chain reaction; POU5F1P1: POU class 5 homeobox 1 pseudogene 1 gene; S-MRCP: magnetic resonance cholangiopancreatography with secretin stimulation; SNP: single nucleotide polymorphism; TCF4: transcription factor 4.

Spectrum of Nonrandom Associations Between Microsatellite Loci on Human Chromosome 11p15

Most evidence about nonrandom association of alleles at different loci, or gametic disequilibrium, across extensive anonymous regions of the human genome is based on the analysis of overall disequilibrium between pairs of microsatellites. However, analysis of interallelic associations is also necessary for a more complete description of disequilibrium. Here, we report a study characterizing the frequency and strength of both overall and interallelic disequilibrium between pairs of 12 microsatellite loci (CA repeats) spanning 19 cM (14 Mb) on human chromosome 11p15, in a large sample (810 haplotypes deduced from 405 individuals) drawn from a single population. Characterization of disequilibrium was carried out, taking into account the sign of the observed disequilibria. This strategy facilitates detection of associations and gives more accurate estimates of their intensities. Our results demonstrate that the incidence of disequilibrium over an extensive human chromosomal region is much greater than is commonly considered for populations that have expanded in size. In total, 44% of the pairs of microsatellite loci and 18% of the pairs of alleles showed significant nonrandom association. All the loci were involved in disequilibrium, although both the frequency and strength of interallelic disequilibrium were distributed nonuniformly along 11p15. These findings are especially relevant since significant associations were detected between loci separated by as much as 17–19 cM (7 cM on average). It was also found that the overall disequilibrium masks complicated patterns of association between pairs of alleles, dependent on their frequency and size. We suggest that the complex mutational dynamics at microsatellite loci could explain the allele-dependent disequilibrium patterns. These observations are also relevant to evaluation of the usefulness of microsatellite markers for fine-scale localization of disease genes.