Epidemiology and Genetics
Epidemiology and genetics are two distinct disciplines that converge into a new field of human science. Genetic epidemiology is a broad term used for the study of genetics and inheritance of disease. Genetic epidemiology is a science that deals with etiology, distribution, and control of disease in groups of relatives, as well as inherited causes of diseases in populations. In particular, genetic epidemiology is a discipline which focuses on the role of genetic factors and their interaction with environmental factors in the occurrence of disease. Genetic epidemiology can proceed with little or no understanding of the genetic mechanisms involved in disease. Major analytical components of the discipline can be identified in the concept of the qualitative trait,i.e., the gene as an unit of transmission across generations, and in the quantitative trait, i.e., the possible inheritance of a trait such as measurable anthropomorphic characteristics. These two components must be integrated with epidemiologic techniques able to describe causal associations between genetic characteristics and the given data, e.g., mortality and morbidity, into specific groups of individuals.
A proper classification of the etiology of genetic diseases include: single gene causation--the disease is due to a single gene mutation leading to an anomalous protein function and phenotypic manifestations; Chromosomal causation--anomalies in chromosome number (aneuploidies, polyploidies) or in chromosome structure (rearrangements of genetic material within or between chromosomes); Multifactorial causation-- an arbitrary classification where genetic factors are involved as being a co-factor either in the disease or its precursors. Perinatal diseases as well as oral cleft and neural tube defects are examples. Cancer genetics and psychiatric genetics represent another broad example of multifactorial causation.
All of these diseases stand to benefit from genetic epidemiology. In fact, a major goal of genetic epidemiology is the possibility of preventing a disease, or to provide a reliable probability of the occurrence of the disease with a very low rate of false positive cases. The final target can be considered the possibility of reducing morbidity and mortality. Furthermore, because of continuing progress in molecular biology, the concept and the prospective of genetic epidemiology changes over time.
Aided by advances in computer technology, scientists developed complex algorithms for the analysis of genetic models, the description of the transmission of the disease, and genetic-environmental interactions. Sophisticated mathematical techniques are now used for assessing classification, diagnosis, prognosis and treatment of many genetic disorders. Strategies of analysis include population study and family study. Population study must be considered as a broad and reliable study with an impact on public health programs. They evaluate the distribution and the determinants of genetic traits. Family study approaches are more specific, and are usually confirmed by other independent observations. By means of several statistical tools, genetic epidemiologic studies evaluate risk factors, inheritance and possible models of inheritance. Different kinds of studies are based upon the number of cases enrolled and the method of collection of the sample (prospective or retrospective). A challenge for the investigator is to achieve a result able to be applied with as low a bias as possible to the general population.
Analysis of a proper sample size, as well as study type (prospective, case-control, etc.,) are techniques belonging to epidemiology and statistics. They were developed in order to produce reliable information from a study regarding the association of genetic and environmental factors. Descriptive studies consider genetic trait frequency, geographic distribution differences, and prevalence of certain conditions in different populations. Analytic studies consider association, probability of occurrence, inheritance, and identification of specific groups of individuals. Methods of analysis utilize computer-assisted procedures and specialized software. Briefly, the parameters most often investigated include odds ratio, relative risk, likelihood ratio, logistic regression, Cox regression, linkage analysis, cluster analyses, and latent class analysis. Some parameters, as well as odds ratio and relative risk, yield an association between one or more factors. The disease can be expressed as risk or probability of occurrence with and without a determined characteristic. Logistic and Cox regressions are multivariate techniques for the simultaneous evaluation of risk factors (intended as odds ratio) upon an outcome. Other tools attempt to classify, or find the probability relating to classification of, subjects or families with homogeneous characteristics into specific groups. Linkage analysis (by analysis of two or more genetic loci), cluster analysis, and latent class analysis belong to this broad group of tests.
Thus, genetic epidemiology arises from varied scientific disciplines, including genetics, epidemiology and statistics. The strategies involved in genetic epidemiology encompass population studies and family studies. Sophisticated mathematical tools are now involved, and computer technology is playing a predominant role in the development of the discipline. Multidisciplinary collaboration is crucial to understanding the role of genetic and environmental factors in disease processes.
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