Study Designs in Genetic Epidemiology

Genetic epidemiology, as a relatively new issue, aims to explore the independent role of genetic-environmental determinants of diseases. Genetic epidemiology studies, depending on the objective, encompass the most preliminary surveys from the attempts to find family history in the occurrence of diseases to the most advanced surveys including specific strategies by clinical trials in the prevention of genetic diseases. Different objectives in genetic epidemiology studies require special methods and study designs. In this review, chief designs including familial aggregation, heritability, segregation, linkage, and association are evaluated; likewise, the purpose of diverse kinds of studies and analyses is briefly discussed. The utilization of study designs and related analyses according to the aims are the main issues and necessary in the accurate implementation of the study. Some methodological issues in relation to studies on tuberculosis are also reported. Attention to these issues might be useful in the implementation of these methods in the studies designed for the prevention and treatment of genetic disorders. 1. Introduction Epidemiology is the study of distribution and determinants of disease frequency in human populations and the use of this information to control and promote health [1]. The goal of epidemiologic research is to collect valid and precise information on the causes, prevention, and treatment of disease [1]. Genetic epidemiology is the study of the role of genes and their interaction with environmental factors in the occurrence of disease in human populations [2]. The branch of genetic epidemiology is still quite young, although the parents of that (epidemiology and genetics) have rather long history [3]. The objectives of epidemiological studies in genetic science are to determine the risks related to allelic variants of candidate genes, to map more accurately regions of the genome for which there is evidence of linkage to disease susceptibility, and to contribute cases to a genome-wide search for susceptibility genes [4]. 2. Study Designs in Classic Epidemiology The selection of one design over another in studies depends on the particular research question [3] and also on cost, time, and ethical considerations. The most common types of studies are listed with brief explanations about them in Table 1 [1, 5–8]. Table 1: Main study designs in classic epidemiology. 3. Study Designs in Genetic Epidemiology Similar to classical epidemiology, observational studies in genetic epidemiology are divided into descriptive and analytical