Genetic Epidemiological Studies Of Nasopharyngeal Cancer

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Nasopharyngeal carcinoma (NPC) occurs much more commonly in southern China and Taiwan than in other parts of the world. Epstein-Barr virus is suspected to play a role in disease etiology, but supporting data are quite limited. The disease exhibits clear familial aggregation, and our previously reported segregation analyses suggest that a recessively transmitted major gene may be involved. Our current studies are aimed at determining the basic causes of this disease using molecular epidemiological approaches. We have obtained questionnaire data regarding the family history of this disease and correlation with risk factors from a large number of subjects. To date, we have obtained DNA, serum, oral rinses, oral brushes and saliva for 1,449 subjects from 297 families identified with two or more members affected by NPC. We also obtained 1,645 risk factor questionnaires from our multiplex family members. Epstein Barr Virus (EBV) anitbody titres are being assessed on serum samples from all study subjects. A whole genome scan has been completed for approximately 767 DNA samples using highly informative Short Tandem Repeat (STR) markers of the Applied Biosystems Version 2.0 set. Laboratory assays of candidate gene SNPs including HLA variants are also ongoing, in collaboration with scientists at the NCI. We used fluorescently labeled oligonucleotide primers incorporated during PCR. Products were sized by denaturing PAGE on Applied Biosystems (Perkin Elmer) Model 373 and 377 automated DNA analyzers. GENESCAN and GENOTYPER computer programs (Applied Biosystems) were used to identify microsatellite alleles from the gel images. Statistical analyses of these data using methods thought to be most powerful and robust for complex diseases have identified several genes and chromosomal regions that are very promising candidates for having major influence on differences among individuals in susceptibility to NPC. Some analyses are general and are being applied to all complex diseases under study in the Branch. Other analyses involve novel approaches specific for NPC such as using EBV titres as covariates for predicting NPC risk. Transmission disequilibrium tests (TDTs) are being performed on the candidate genes being assayed including SNPs at HLA loci and CYP2E1 that have been previously suggested to be associated with the risk of NPC. Extensive questionnaire data collected for all participating subjects are being evaluated to identify the most important environmental risk factors for this disease. Statistical methods which account for relationships among family members will be used for these analyses. EBV antibody titres are being analyzed as a dependent variable of direct interest for understanding the genetic basis of host defense. Gene mapping studies of these immune response phenotypes have required minimal additional cost, since biospecimens and substantial numbers of genotypes are already available for these subjects. Sections from paraffin-embedded tumor tissue are being obtained from approximately half of these NPC cases for molecular analyses.