Cancer incidences in Europe related to mortalities, and ethnohistoric, genetic, and geographic distances

Alternatives to the carcinogenicity bioassay for toxicity prediction: are we there yet?

INTRODUCTION

For decades, traditional toxicology has been the ultimate source of information on the carcinogenic potential of chemicals; however, with increasing demand on regulation of chemicals and decreasing resources for testing, opportunities to accept 'alternative' approaches have dramatically expanded. The need for tools able to identify carcinogens in shorter times and at a lower cost in terms of animal lives and money is still an open issue, and the present strategies and regulations for carcinogenicity prescreening do not adequately protect human health.

AREAS COVERED

This paper briefly summarizes the theories on the early steps of carcinogenesis and presents alternative detection methods for carcinogens based on genetic toxicology, structure-activity relationships and cell transformation assays.

EXPERT OPINION

There is evidence that the combination of Salmonella and structural alerts for the DNA-reactive carcinogens, and in vitro cell transformation assays for nongenotoxic carcinogens, permits the identification of a very large proportion of carcinogens. If implemented, this alternative strategy could improve considerably the protection of human health.

The relative role of drift and selection in shaping the human skull

Human populations across the world vary greatly in cranial morphology. It is highly debated to what extent this variability has accumulated through neutral processes (genetic drift) or through natural selection driven by climate. By taking advantage of recent work showing that geographic distance along landmasses is an excellent proxy for neutral genetic differentiation, we quantify the relative role of drift versus selection in an exceptionally large dataset of human skulls. We show that neutral processes have been much more important than climate in shaping the human cranium. We further demonstrate that a large proportion of the signal for natural selection comes from populations from extremely cold regions. More generally, we show that, if drift is not explicitly accounted for, the effect of natural selection can be greatly overestimated.

Genetic population structure analysis in New Hampshire reveals Eastern European ancestry

Genetic structure due to ancestry has been well documented among many divergent human populations. However, the ability to associate ancestry with genetic substructure without using supervised clustering has not been explored in more presumably homogeneous and admixed US populations. The goal of this study was to determine if genetic structure could be detected in a United States population from a single state where the individuals have mixed European ancestry. Using Bayesian clustering with a set of 960 single nucleotide polymorphisms (SNPs) we found evidence of population stratification in 864 individuals from New Hampshire that can be used to differentiate the population into six distinct genetic subgroups. We then correlated self-reported ancestry of the individuals with the Bayesian clustering results. Finnish and Russian/Polish/Lithuanian ancestries were most notably found to be associated with genetic substructure. The ancestral results were further explained and substantiated using New Hampshire census data from 1870 to 1930 when the largest waves of European immigrants came to the area. We also discerned distinct patterns of linkage disequilibrium (LD) between the genetic groups in the growth hormone receptor gene (GHR). To our knowledge, this is the first time such an investigation has uncovered a strong link between genetic structure and ancestry in what would otherwise be considered a homogenous US population.

Ecogeographic genetic epidemiology

Complex diseases such as cancer and heart disease result from interactions between an individual's genetics and environment, i.e. their human ecology. Rates of complex diseases have consistently demonstrated geographic patterns of incidence, or spatial "clusters" of increased incidence relative to the general population. Likewise, genetic subpopulations and environmental influences are not evenly distributed across space. Merging appropriate methods from genetic epidemiology, ecology and geography will provide a more complete understanding of the spatial interactions between genetics and environment that result in spatial patterning of disease rates. Geographic information systems (GIS), which are tools designed specifically for dealing with geographic data and performing spatial analyses to determine their relationship, are key to this kind of data integration. Here the authors introduce a new interdisciplinary paradigm, ecogeographic genetic epidemiology, which uses GIS and spatial statistical analyses to layer genetic subpopulation and environmental data with disease rates and thereby discern the complex gene-environment interactions which result in spatial patterns of incidence.

A further test of the Finno-Ugrian Suicide Hypothesis: correspondence of county suicide rates in Romania and population proportion of ethnic Hungarians

Across the 42 counties of Romania, the total suicide rate and the population percentage of ethnic Hungarians were strongly positively interrelated (79% attributable variance). Counties with the strongest Hungarian minority had suicide rates converging to (or exceeding) the suicide rate for Hungary, which rate is high. Of a set of about 20 vital statistics and socioeconomic indicators, only life expectancy predicted a significant increment of further variance in the suicide rates. However, this effect was small, adding merely 3% further variance explained to 79% already accounted for. Overall, the findings are supportive of the Finno-Ugrian Suicide Hypothesis, i.e., the notion that geographic patterns of suicide prevalence may be partially due to genetic differences between populations. Supplemental analyses of a questionnaire item which specifically queried this study's main finding indicated widespread disbelief of this fact of suicide prevalence across a variety of samples, including two samples from Romania.

Social sexual inequality and sex difference in cancer incidence

Socioeconomic factors play many roles in influencing health including overall health status, lifestyle and occupational exposures, and access to preventive, diagnostic and treatment services. This paper reviews evidence on the geographical distribution of the sex differences in cancer incidence and life expectancy. The analyses reported are at the regional (Italy), continental (Europe), and world-wide scales. In agreement with other contributions on the social epidemiology of cancer, these results indicate that there is a close link between the health of the populations, and socioeconomic and cultural factors, and support the notion that environment contributes strongly to total cancer incidence. Thus, the emphasis for reducing cancer incidence needs to focus more on reducing environmental contributions. In order to improve the health status of the populations, not only applications of the present etiologic knowledge are necessary (for example, it is estimated that around up to 50% of cancers are nowadays technically preventable), but also further research on environmental topics should be stimulated. Within this perspective the indicators of health differences between genders-which are demonstrated to be very sensitive to socioeconomic and cultural factors--can play a very useful role for monitoring environmental factors, and for health planning by agencies and governments.

Africans and Asians abroad: genetic diversity in Europe

Besides its obvious intrinsic value, knowledge of population history, and of the demographic and evolutionary changes that accompany it, has proven fundamental to address applied research in human genetics. In this review we place current European genetic diversity in the context of the global human genome diversity and review the evidence supporting a recent African origin of the Europeans. We then discuss the results and the interpretation of genetic studies attempting to quantify the relative importance of various gene flow processes, both within Europe and from Asia into Europe, focusing especially on the initial, Paleolithic colonization of the continent, and on later, Paleolithic postglacial and Neolithic dispersals. Finally, we discuss how knowledge of the patterns of genetic diversity in Europe, and of their inferred generating processes, can be extremely useful in planning health care and in biomedical research.

Current practices in the spatial analysis of cancer: flies in the ointment

While many lessons have been learned from the spatial analysis of cancer, there are several caveats that apply to many, if not all such analyses. As "flies in the ointment", these can substantially detract from a spatial analysis, and if not accounted for, can lead to weakened and erroneous conclusions. This paper discusses several assumptions and limitations of spatial analysis, identifies problems of scientific inference, and concludes with potential solutions and future directions.

A new protocol for evaluating putative causes for multiple variables in a spatial setting, illustrated by its application to European cancer rates

We introduce a statistical protocol for analyzing spatially varying data, including putative explanatory variables. The procedures comprise preliminary spatial autocorrelation analysis (from an earlier study), path analysis, clustering of the resulting set of path diagrams, ordination of these diagrams, and confirmatory tests against extrinsic information. To illustrate the application of these methods, we present incidence and mortality rates of 31 organ- and sex-specific cancers in Europe; these rates vary markedly with geography and type of cancer. Additionally, we investigated three factors (ethnohistory, genetics, and geography) putatively affecting these rates. The five variables were correlated separately for the 31 cancers over European reporting stations. We analyzed the correlations by path analysis, k-means clustering, and nonmetric multidimensional scaling; coefficients of the 31 path diagrams modeling the correlations vary substantially. To simplify interpretation, we grouped the diagrams into five clusters, for which we describe the differential effects of the three putative causes on incidence and mortality. When scaled, the path coefficients intergrade without marked gaps between clusters. Ethnic differences make for differences in cancer rates, even when the populations tested are ancient and complex mixtures. Path analysis usefully decomposes a structural model involving effects and putative causes, and estimates the magnitude of the model's components. Smooth intergradation of the path coefficients suggests the putative causes are the results of multiple forces. Despite this continuity of the path diagrams of the 31 cancers, clustering offers a useful segmentation of the continuum. Etiological and other extrinsic information on the cancers map significantly into the five clusters, demonstrating their epidemiological relevance.

Inequalities in health: the value of sex-related indicators

My laboratory has previously shown that the sex differences in tumor incidence in Europe can be related to the female social condition and that the pattern of this relationship varies according to the different historical contexts. In this article, I have extended the study worldwide to all cancer registries, and I present the sex differences in life expectancy at birth. A close link between the health of the populations and socioeconomic and cultural factors was confirmed. The sex-related indicators had a distribution independent from the parent variables cancer incidence and life expectancy; thus, they carry complementary information and provide an additional, sensitive probe for monitoring the health of the populations.

The sex difference in tumor incidence is related to the female condition: models for Europe and Italy

A remarkable aspect of cancer distribution in Europe is the large spatial variability of the male-female incidence ratio, from no difference up to 50%. Given the evidence of the predominantly environmental origin of cancer, we studied the ability of a set of socioeconomic indicators of the female condition to model the spatial variability of the sex difference in tumor incidence at two different scales: between countries (Europe) and between provinces (Italy). The sex difference in tumor incidence correlated with female socioeconomic condition indicators at the same extent (r = 0.73) in both situations, but in opposite directions. In the European study the higher the sexual social equality the lower the differential tumor incidence, whereas the opposite result was shown by the between-provinces Italian study. We also investigated the relation of the female condition indicator with other social and cultural descriptors of the same populations, and we suggest explanatory models linking female condition and pathology at the continental and local scales. Overall, our analysis supports the predominantly environmental origin of cancer and stresses the importance of relating cancer patterns to societal determinants. Our analysis also suggests that the sex difference in tumor incidence is a very useful probe for exploring the social-economic cultural correlates of cancer in human populations. We emphasize the need for a thorough analysis of the empirical correlations highlighted in ecologic studies.