Association between cytomegalovirus seropositivity and Type 2 diabetes is explained by age and other demographic characteristics: the National Health and Nutrition Examination Survey.

AIMS: To assess the association between cytomegalovirus and Type 2 diabetes among 6664 participants from the National Health and Nutrition Examination Survey. METHODS: We used existing data from adults aged 20-49 years who participated in the National Health and Nutrition Examination Survey from 1999 to 2004. Cytomegalovirus status was determined using cytomegalovirus-specific immunoglobulin G antibodies. Prevalent Type 2 diabetes was assessed through self-report or a plasma fasting glucose of ≥7 mmol/l. Logistic regression models were used to evaluate the association between Type 2 diabetes and cytomegalovirus seropositivity after adjustment for age, gender, race/ethnicity, smoking status, education, BMI and physical activity. RESULTS: In a univariate model, the crude odds of Type 2 diabetes were 47% higher in those who were cytomegalovirus-seropositive vs cytomegalovirus-seronegative. The association was attenuated and no longer significant after adjustment for age and other covariates: the odds ratio for diabetes was 1.09 (95% CI 0.71 to 1.66) for cytomegalovirus-seropositive vs -seronegative individuals. CONCLUSIONS: Our study suggests that the association between cytomegalovirus and Type 2 diabetes is explained by age and other risk factors for diabetes.

Variants at the OCA2/HERC2 locus affect time to first cutaneous squamous cell carcinoma in solid organ transplant recipients collected using two different study designs.

BACKGROUND: Variants at the oculocutaneous albinism 2 (OCA2)/HECT and RLD domain containing E3 ubiquitin protein ligase 2 (HERC2) locus have been associated with pigmentation phenotypes and risk of developing several types of skin cancer. OBJECTIVES: To evaluate OCA2/HERC2 locus variants for their impact on time to develop cutaneous squamous cell carcinoma (cSCC) in organ transplant recipients (OTRs) who are at elevated risk of developing cSCC. METHODS: Participants were solid OTRs ascertained from two centres (n = 125 and 261) with an average of 13·1 years of follow-up post-transplant. DNA was available for genotyping for all participants, in addition to medical records and questionnaire data. The Ohio State University study had a case-control design with prospective follow-up, and the University of California San Francisco study was a national cross-sectional survey with retrospective chart review. RESULTS: OCA2 variants rs12913832 and rs916977 were significantly associated with time to first cSCC post-transplant. OTRs homozygous for the brown-eye alleles of rs916977 (GG) and rs12913832 (AA) had significant delays of time to first cSCC post-transplant compared with individuals homozygous for the blue-eye alleles (hazard ratio 0·34, P < 0·001 and hazard ratio 0·54, P = 0·012, respectively). Both variants were highly associated with eye colour in the combined studies (P < 0·001). CONCLUSIONS: This study is the first to show an association between OCA2/HERC2 variants and time to first cSCC post-transplant. This may impact dermatological screening recommendations for high-risk populations.

Occupational asphalt is not associated with head and neck cancer.

BACKGROUND: Epidemiologic studies that evaluate the relationship between occupational asphalt exposure and head and neck cancer have had a limited ability to control for known risk factors such as smoking, alcohol and human papillomavirus (HPV). AIMS: To better elucidate this relationship by including known risk factors in a large case-control study of head and neck squamous cell carcinoma (HNSCC) from the greater Boston area. METHODS: We analysed the relationship between occupational asphalt exposure and HNSCC among men in the Greater Boston area of Massachusetts. Analyses were conducted using unconditional multivariable logistic regression, performed with adjustments for age, race, education, smoking, alcohol consumption and HPV serology. RESULTS: There were 753 cases and 913 controls. No associations between HNSCC and occupational asphalt exposure (neither among ever-exposed nor by occupational duration) were observed for exposures in any occupation or those restricted to the construction industry. We also observed no associations in subgroup analyses of never-smokers and ever-smokers. Adjusting for known risk factors further reduced the estimated effect of asphalt exposure on HNSCC risk. CONCLUSIONS: We found no evidence for an association between occupational asphalt exposure and HNSCC. The null findings from this well-controlled analysis could suggest that the risk estimates stemming from occupational cohort studies may be overestimated due to uncontrolled confounding and enhance the literature available for weighing cancer risk from occupational exposure to bitumen.

SV40 associated miRNAs are not detectable in mesotheliomas.

BACKGROUND: Simian virus-40 (SV40) is a DNA tumour virus that was introduced into the human population with contaminated poliovirus vaccine, and its role in mesothelioma is widely debated. PCR based testing has been called into question, as false positives can be because of cross-reactivity with related viruses, or to laboratory contamination. The Institute of Medicine has recommended the development of more sensitive and specific tests to resolve this controversy. METHODS: We have characterized highly sensitive RT-PCR based assays that are specific for SV40-encoded microRNAs (miRNAs), as an alternative to current testing methods. RESULTS: Using this sensitive and specific detection method, we were unable to identify SV40 miRNA expression in human malignant pleural mesothelioma (MM) samples. CONCLUSION: Our work indicates that SV40 miRNAs are not likely to contribute to mesothelioma tumourogenesis, but highlights the value of this approach when compared with the relatively unspecific current testing methods.

KRAS mutation, KRAS-LCS6 polymorphism, and non-small cell lung cancer.

The let-7 family of microRNAs are important regulatory molecules in lung cancer. One downstream target of let-7 is the RAS gene family, including KRAS, an important oncogene in the etiology and clinical outcome of lung adenocarcinoma. Recently, a SNP in the let-7 binding region of the KRAS 3' UTR was identified (termed LCS6). This functional polymorphism alters let-7 binding, resulting in both increased KRAS expression and decreased let-7 exposure. Further, this SNP has been reported as a risk trait for lung cancer among low-moderate smokers. Given the functionality of LCS6, we tested the hypothesis that this SNP is associated with the occurrence of KRAS mutation as well as patient survival. Here, we report there is no association between the LCS6 KRAS polymorphism and KRAS mutation. Further, we find no association between the LCS6 polymorphism and lung cancer survival. These unexpected findings imply that this newly reported KRAS-LCS6 polymorphism will have limited clinical utility for NSCLC.

Human papillomavirus 6 seropositivity is associated with risk of head and neck squamous cell carcinoma, independent of tobacco and alcohol use.

BACKGROUND: The risk of head and neck squamous cell carcinoma (HNSCC) associated with common human papillomavirus types has not been well defined. METHODS: We conducted a case-control study of 1034 individuals (486 incident cases diagnosed with HNSCC and 548 population-based controls matched to cases by age, gender, and town of residence) in Greater Boston, MA. Sera were tested for antibodies to human papillomavirus (HPV)6, HPV11, HPV16, and HPV18 L1. RESULTS: HPV6 antibodies were associated with an increased risk of pharyngeal cancer [odds ratio (OR)=1.6, 1.0-2.5], controlling for smoking, drinking, and HPV16 seropositivity. In HPV16-seronegative subjects, high HPV6 titer was associated with an increased risk of pharyngeal cancer (OR=2.3, 1.1-4.8) and oral cancer (OR=1.9, 1.0-3.6), suggesting that the cancer risk associated with HPV6 is independent of HPV16. There was no association between smoking and alcohol use and HPV6 serostatus. Further, the risk of pharyngeal cancer associated with heavy smoking was different among HPV6-seronegative (OR 3.1, 2.0-4.8) and HPV6-seropositive subjects (OR=1.6, 0.7-3.5), while heavy drinking also appears to confer differing risk among HPV6-negative (OR 2.3, 1.5-3.7) and -positive subjects (OR=1.3, 0.6-2.9). CONCLUSIONS: There may be interactions between positive serology and drinking and smoking, suggesting that the pathogenesis of human papillomavirus in HNSCC involves complex interactions with tobacco and alcohol exposure.

Interaction between the bone morphogenetic proteins and Ras/MAP-kinase signalling pathways in lung cancer.

Bone morphogenetic proteins (BMPs) are an integral component of the TGFbeta superfamily, responsible for regulation of cell proliferation, differentiation, migration and programmed cell death in a variety of cell types. The BMPs transduce their signals directly through the SMAD family of proteins but they also have been reported to interact with the MAPK and Erk pathways. Inactivation of the BMP pathway genes has been implicated as important in several cancers. Recent work has shown that BMP3b is epigenetically inactivated in cancer and suggests that BMP6 can be epigenetically inactivated. We investigated whether BMP6 is epigenetically inactivated in cell lines and whether BMP3b and BMP6 are epigenetically inactivated in non-small-cell lung cancer (NSCLC). We also studied the relationship between BMP methylation and k-ras mutation. Here, we demonstrate that the BMP3b and BMP6 genes are common targets of epigenetic inactivation in NSCLC, and that they are significantly more likely to be concurrently inactivated (P=0.009). Furthermore, this coinactivation of BMP3b and BMP6 is significantly associated with mutation of k-ras codon 12 in lung cancer (P=0.003); those with a k-ras mutation were six times more likely to have concurrent methylation of these BMP loci. Hence, these data suggest that concurrent inactivation of the BMP and activation of the Ras signalling pathways are important in lung carcinogenesis.

A population-based study of immunohistochemical detection of p53 alteration in bladder cancer.

The molecular pathology of bladder cancer has been the subject of considerable interest and mutation of the p53 gene, which has been associated with more invasive bladder cancer, has been widely studied. Further, there is evidence that p53 inactivation (either mutation or protein dysregulation), independent of stage, may be predictive of bladder cancer progression. In an effort to avoid possible biases associated with selection of more advanced cases, we examined p53 inactivation in a population-based study of bladder cancer in New Hampshire, using both mutation and immunohistochemical methods. We found the overall prevalence of mutation to be approximately 10%, while immunohistochemical analysis suggests that approximately 66% of the tumours have dysregulated p53 at the protein level. There was a significant association of mutation with persistent p53 staining, but there remained a marked number of tumours discordant for mutation and aberrant p53 immunohistochemistry. Based upon immunohistochemical staining alone, intensity rather than extent of p53 staining was more strongly related to tumour invasiveness. Additionally, all tumours with a mutation in exon 8 stained intensely. Taken together, this suggests that intense staining represents a distinct phenotype of dysfunctional protein. Our data indicate that population-based approaches to somatic alteration of p53 in bladder cancer are crucial to understanding the relationship of p53 changes to aetiology and the outcome of this disease, and further suggest that the pattern of immunohistochemical staining may represent distinct, discernible phenotypes. British Journal of Cancer (2004) 90, 1572-1576. doi:10.1038/sj.bjc.6601748 www.bjcancer.com Published online 6 April 2004

Scanning ultraviolet two-step laser mass spectroscopy of polycyclic aromatic hydrocarbon distributions on creosote-contaminated soil particles.

The distribution of polycyclic aromatic hydrocarbons (PAHs) on creosote-contaminated soil has been examined with scanning ultraviolet two-step laser desorption/laser ionization mass spectroscopy (UV-L2MS). The instrument has been constructed in-house by modifying a reflectron time-of-flight mass spectrometer. Two-dimensional chemical maps were accurately generated from model patterned PAH distributions. From examination of three-dimensional substrates, the depth of field of the experiment allows surfaces with roughness of up to 120 microm to be treated as a two-dimensional system and still achieve an accurate representation of the surface deposits. Soil was obtained from a former wood treatment facility. Individual particles of 100-1000 microm were mounted on indexed sample plates and examined by reflectance infrared microscopy, optical microscopy, and imaging UV-L2MS. The most intense PAH signals were associated with regions on the particles where clay/organic carbon deposits were found.

Promoter methylation of DAP-kinase: association with advanced stage in non-small cell lung cancer.

Death associated protein (DAP)-kinase is a 16 kDa calmodulin-dependent serine/threonine kinase that carries a death domain at its C-terminus. DAP-kinase functions as a positive mediator of apoptosis that is induced by interferon-gamma. Recent studies suggest that DAP-kinase is involved in tumor metastasis and that it can be inactivated by methylation of CpG islands in the promoter region of the gene in some human tumors. However, little is known about the factors that are associated with the occurrence of DAP-kinase promoter methylation. We investigated both the possible associations of tobacco carcinogen and asbestos exposure with DAP-kinase promoter methylation, and the demographic and clinical factors associated with DAP-kinase promoter methylation in non-small cell lung cancer (NSCLC). One hundred and eighty-five patients diagnosed with NSCLC undergoing surgical resection from June, 1992 through December, 1996 at Massachusetts General Hospital participated in this study. Methylation-Specific PCR (MSP), performed using fresh-frozen tissue, was used to determine the methylation status of the promoter region of the DAP-kinase gene. Forty-seven (25%) of 185 tumors showed DAP-kinase promoter methylation. There was a significant association between methylation and an advanced pathologic stage (P=0.003, Fisher's exact test). Methylation of the DAP-kinase promoter was also associated with an increase in tumor size (P=0.009, Fisher's exact test) and lymph node involvement (P=0.04). No association was found between promoter methylation of DAP-kinase and k-ras or p53 mutation. In addition there was no association with a history of exposure to tobacco or asbestos. Controlling for age, sex, and histology, the odds ratios describing the association of DAP-kinase hypermethylation with stage were 2.70 (1.13--6.45), 3.11 (1.37--7.08) and 7.77 (1.21--50.03) in stages II, III and IV, respectively. Stage I cases with DAP-kinase promoter methylation had worse overall survival, but with the small sample size and limited follow-up this did not reach statistical significance. Our findings suggest that methylation of the promoter region of the DAP-kinase gene is not associated with exposure to tobacco or asbestos. However, they strongly suggest that DAP-kinase may be important in the progression of non-small cell lung cancer from early to late stage disease.

p16(INK4a) and histology-specific methylation of CpG islands by exposure to tobacco smoke in non-small cell lung cancer.

The p16(INK4a) protein inhibits cyclin-dependent kinase 4, a key regulator of progression through the G(1) phase of the cell cycle. Methylation of CpG islands in the promoter region is an important avenue for inactivation of p16. The mechanism of methylation of the p16 promoter region, however, has not been elucidated. Recent reports investigating p16 methylation in non-small cell lung cancer (NSCLC) suggest that carcinogens in tobacco smoke induce the DNA methylation process. We investigated the association between methylation of the p16 promoter region and exposure to tobacco smoke in 185 primary NSCLCS: We also studied the relationship of p16 methylation with mutation of the K-ras and p53 genes, as well as with methylation at the DAP-kinase and p14(ARF) loci. Finally, we evaluated the prognostic significance of p16 methylation in NSCLC. The prevalence of p16 methylation was greater in squamous cell carcinoma (41%) compared with adenocarcinoma (22%; P = 0.03; Fisher's exact test). Methylation of p16 was significantly associated with pack-years smoked (P = 0.007; Wilcoxon rank sum test), duration of smoking (P = 0.0009; Wilcoxon rank sum test), and negatively with the time since quitting smoking (P = 0.03; Wilcoxon rank sum test). No methylation of the nearby p14(ARF) locus was detected, and methylation of the DAP-kinase locus was not associated with either p16 methylation or with exposure to tobacco smoke. In patients with stage 1 adenocarcinoma, p16 methylation was an independent risk factor predicting significantly shorter postsurgery survival (P = 0.03), controlling for the significant effects of other factors, including K-ras mutation. These findings suggest that methylation of CpG islands in tobacco-associated cancers occurs in a gene- and tissue-specific manner and is induced directly or indirectly by exposure to tobacco smoke in NSCLC.

Tobacco smoke-induced DNA damage and an early age of smoking initiation induce chromosome loss at 3p21 in lung cancer.

The short arm of chromosome 3 is thought to harbor a novel oncogenic locus that is important in the genesis of lung cancer. The region at 3p21 is believed to contain a distinct locus that is sensitive to loss from the action of tobacco smoke carcinogens and has been reported to be specifically targeted for deletion in lung cancer. To investigate whether 3p21 alteration in lung cancer is associated with carcinogen exposure, PCR-based analysis was performed to detect loss of heterozygosity (LOH) on chromosome 3 at 3p21 in non-small cell lung carcinoma (NSCLC). We also measured instability at the BAT-26 locus, because the mismatch DNA repair gene, hMLH1, is found at 3p21. LOH at 3p21 was analyzed for association with the clinical features of NSCLC, p53 mutation status, polynuclear aromatic hydrocarbon-DNA adduct levels (measured using 32P-postlabeling) and carcinogen exposure information including cigarette smoking and asbestos exposure. Of 219 lung cancers, 150 cases (68.5%) were informative at the D3S1478 locus, and 44.2% of squamous cell carcinoma cases and 30.2% of adenocarcinoma cases showed 3p21 LOH. None of the cancers showed BAT-26 instability. The prevalence of 3p21 LOH was higher in both current and former smokers compared with never smokers and was higher in p53 mutated cases. Among squamous cell carcinoma cases, there was a strong association of increased 3p21 LOH with increasing polynuclear aromatic hydrocarbon-DNA adducts levels (P = 0.03), as well as an increased prevalence LOH with earlier age of smoking initiation (P = 0.02). Our results confirm that 3p21 LOH is strongly associated with measures of biologically effective dose of exposure to tobacco carcinogens. Our results also suggest that alterations of hMLH1 are not related to any of the reported associations, because there was no evidence of microsatellite instability. Finally, LOH in 3p21 may be an early molecular event in NSCLC, because it is significantly associated with a tendency to start smoking at a young age.

Implications and prognostic value of K-ras mutation for early-stage lung cancer in women.

BACKGROUND: Because there is no clear consensus as to the predictive value of K-ras gene mutation for survival in patients with lung cancer, we examined the occurrence of K-ras mutations in a large, prospective case series of non-small-cell lung cancer (NSCLC). Our goals were to define the patient characteristics associated with K-ras mutation and to determine whether mutation of this gene might be a biomarker of patient prognosis. METHODS: Consecutive, newly diagnosed patients with lung cancer treated with potentially curative resection over a 4-year period were recruited for study. The mutation status of K-ras codon 12 in each patient's tumor DNA was determined by means of polymerase chain reaction-restriction fragment length polymorphism analysis of archived pathology specimens. Analyses were restricted to adenocarcinoma. RESULTS: There was a statistically significant association between female sex and K-ras mutation after adjustment for carcinogen exposures (odds ratio = 3.3; 95% confidence interval [CI] = 1.3-7.9); mutations were found only in smokers. Comparison of Kaplan-Meier curves indicated a strong association between K-ras mutation and decreased patient survival (two-sided P =.009); analysis stratified by pathologic staging groups revealed that this association was statistically significant only for stage I tumors (two-sided P =.002). Cox proportional hazards modeling indicated that K-ras codon 12 mutation was a statistically significant predictor of patient survival, after adjustment for the effects of age, sex, and stage (risk ratio = 1.8; 95% CI = 1.1-3.1). CONCLUSIONS: After adjustment for environmental exposures, non-small-cell lung tumors in women appear to be more likely than those in men to harbor K-ras mutations, suggesting a possible role of estrogen exposure in either the initiation or the selection of K-ras mutant clones in adenocarcinoma. In addition, our data suggest that K-ras codon 12 mutation is a marker of aggressive NSCLC, as evidenced by its association with decreased patient survival, particularly for early-stage disease.

k-ras mutation and occupational asbestos exposure in lung adenocarcinoma: asbestos-related cancer without asbestosis.

Environmental carcinogen exposure is requisite for the development of nearly all lung cancer, and it is well known that asbestos exposure interacts synergistically with tobacco smoke to induce lung cancer. However, the precise molecular lesions induced by asbestos are unknown. Furthermore, it is also unknown whether asbestos carcinogenesis proceeds in a fashion independent of or dependent upon the induction of fibrosis in workers with high asbestos exposures. Previous studies have suggested that asbestos is associated with the presence of a k-ras mutation in adenocarcinoma of the lung. We aimed to test whether occupational asbestos exposure was associated with k-ras codon 12 mutations in lung adenocarcinoma tumors and to determine whether this was conditional on the presence of asbestosis. All newly diagnosed, resectable lung cancer patients receiving treatment at the Massachusetts General Hospital between November 1992 and December 1996 were eligible to participate. Because k-ras mutation is very strongly associated with adenocarcinoma, and men were more likely to be occupationally exposed to asbestos, the study was restricted to males with this histological diagnosis. There were 84 male patients with available questionnaire-derived work history data and paraffin-embedded tumor tissue for determination of k-ras mutation status. Chest radiographic evaluation was done for all of the patients who reported occupational exposure to asbestos. The prevalence of k-ras mutation was higher among those with a history of occupational asbestos exposure (crude odds ratio, 4.8; 95% confidence interval, 1.5-15.4) compared to those without asbestos exposure, and this association remained after adjustment for age and pack-years smoked (adjusted odds ratio, 6.9; 95% confidence interval, 1.7-28.6). An index score that weights both the dates of exposure and the estimated intensity of exposure indicated that those with k-ras mutations had significantly greater asbestos exposures than those without mutations (P < 0.01). Analysis of the descriptive components of exposure indicated that the duration of exposure was not associated with k-ras mutation, but that the time since initial exposure was significantly associated with mutation status. The association of k-ras mutation and reported asbestos exposure was not dependent on the presence of radiographic evidence of asbestos-related disease. These data suggest that asbestos exposure increases the likelihood of mutation at k-ras codon 12 and that this process occurs independently of the induction of interstitial fibrosis.

Chromosome 3p14 alterations in lung cancer: evidence that FHIT exon deletion is a target of tobacco carcinogens and asbestos.

Alterations in the FHIT gene region have been previously associated with smoking status and the occurrence of lung tumors. In the current study, we examined the nature of the mutations that occur at FHIT and the types of carcinogen exposures that are associated with FHIT alterations. We screened 40 primary lung tumors for the presence of point mutations within the coding exons of FHIT using PCR-single-strand conformational polymorphism. Tumors were also analyzed for allelic loss using microsatellite markers located in or near FHIT. No tumors contained point mutations within the coding region of the FHIT gene. However, several samples failed to generate a PCR product, suggesting that regions of the gene are homozygously deleted. Samples were reanalyzed for exon loss using PCR; 13 of 30 tumors failed to generate a PCR product, and 20 of 30 tumors were missing at least one FHIT exon or had loss (loss of heterozygosity or deletion) of one microsatellite marker, suggesting that regions of the gene are homozygously deleted. These data indicate that the FHIT gene has a novel pattern of mutational inactivation not seen previously with other tumor suppressor genes, most likely influenced by the proximity of the FRA3B region. There were no associations of age, sex, p53, or k-ras mutation and FHIT exon deletion. However, there was an association of smoking duration and asbestos exposure with FHIT exon loss, indicating that carcinogenic exposures may be causal in the generation of alterations in the FHIT region.

The glutathione S-transferase theta and mu deletion polymorphisms in asbestosis.

The glutathione S-transferases (GSTs) catalyze the conjugation of a wide variety of reactive, electrophilic substrates with glutathione, facilitating their excretion. There is also evidence that GSTs can catalyze glutathione conjugation of lipid radicals as well as act in the generation of leukotriene inflammatory mediators. Studying construction carpenters screened for the presence of asbestos-related diseases, we have previously reported that the constitutional deletion of GSTM1 (the gene coding for glutathione S-transferase class mu) is associated with an increased risk of asbestos-related interstitial lung disease, measured radiographically. In the current work, we have further studied this group of workers, investigating the distribution of a novel deletion polymorphism in the newly described GSTT1 gene, that codes for the GST class theta enzyme. A total of 666 carpenters were studied, and 124 (19%) had the deleted genotype. There was no association between the GSTT1 deletion and the radiographic diagnosis of either asbestos-related pleural or parenchymal disease. The GSTM1 deletion remained associated with the presence of x-ray evidence of asbestosis after adjustment for GSTT1 genotype. The GSTM1 null genotype was also associated with a family history of any malignancy. These data suggest that the association of polymorphic GSTs with asbestos-induced radiographic changes is specific for substrates of the GST class mu.

Effects of terminal nonhomology and homeology on double-strand-break-induced gene conversion tract directionality.

Double-strand breaks (DSBs) greatly enhance gene conversion in the yeast Saccharomyces cerevisiae. In prior plasmid x chromosome crosses, conversion tracts were often short ( < 53 bp) and usually extended in only one direction from a DSB in an HO recognition sequence inserted into ura3. To allow fine-structure analysis of short and unidirectional tracts, phenotypically silent markers were introduced at 3- and 6-bp intervals flanking the HO site. These markers, which created a 70-bp homeologous region (71% homology), greatly increased the proportion of bidirectional tracts. Among products with short or unidirectional tracts, 85% were highly directional, converting markers on only one side (the nearest marker being 6 bp from the HO site). A DSB in an HO site insertion creates terminal nonhomologies. The high degree of directionality is a likely consequence of the precise cleavage at homology/nonhomology borders in hybrid DNA by Rad1/10 endonuclease. In contrast, terminal homeology alone yielded mostly unidirectional tracts. Thus, nonhomology flanked by homeology yields primarily bidirectional tracts, but terminal homeology or nonhomology alone yields primarily unidirectional tracts. These results are inconsistent with uni- and bidirectional tracts arising from one- and two-ended invasion mechanisms, respectively, as reduced homology would be expected to favor one-ended events. Tract spectra with terminal homeology alone with similar in RAD1 and rad1 cells, indicating that the high proportion of bidirectional tracts seen with homeology flanking nonhomology is not a consequence of Rad1/10 cleavage at homology/homeology boundaries. Instead, tract directionality appears to reflect the influence of the degree of broken-end homology on mismatch repair.

Ethnic differences in the prevalence of the homozygous deleted genotype of glutathione S-transferase theta.

In humans the glutathione S-transferase (GST) genes encode four classes of proteins (GST) important in the detoxification of reactive electrophiles. Recently, a gene deletion polymorphism was discovered within the GST class theta locus that leads to a functional deficiency in GST theta activity within circulating red blood cells. In this study we have examined the ethnic distribution of this polymorphism using a polymerase chain reaction (PCR)-based genotyping method. Five different ethnic groups were studied: North American Caucasians, African-Americans, Mexican-Americans, Chinese and Koreans. The prevalence of the null genotype was highest among Chinese (64.4%), followed by Koreans (60.2%), African-Americans (21.8%) and Caucasians (20.4%), whereas the prevalence was lowest among Mexican-Americans (9.7%). Interestingly, the prevalence of the deleted genotype in Caucasians differed significantly when 257 individuals drawn from a nation wide organization were compared with 185 people from the New England area (23.7 versus 15.7%, P < 0.05, chi 2 test). These results indicate that there are major differences in the prevalence of this trait attributable to ethnicity and that ethnic origin even among Caucasians should be considered in studies of gene-environment interaction involving this polymorphism.