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Family-based life course epidemiology is the approach to clarify long-term effects of accumulations and chains of biological and social risk exposures in one's life trajectory, namely, before and during conception, infancy, childhood, young adulthood and later adult life. Both genetic and environmental factors are considered. One of the theoretical rationales is the 'developmental origin of health and disease (DOHaD)' hypothesis. According to this theory, the causes of adult diseases are attributed to predictive adaptive responses and biological programming or epigenetic changes during a critical period of early life. If the environment later in life after birth is different from what is predicted, a mismatch has happened, leading to the development of a disease. This theory is supported by many epidemiologic studies, animal experiments, and evolution theory of biology. Longitudinal twin-family data are very powerful and useful information in the family-based life course genetic epidemiologic study.

The importance of twin research in the field of preventive medicine is described from the viewpoint of gene-environment interaction. The recent advancements in twin research in Japan and other countries are the major topics in this paper. The historical background of the Japan Society for Twin Studies is described. The Center for Twin Research of Osaka University is also described as the first center of this kind in Japan. The advancement of epigenetic research is described as a new global trend of twin research, particularly in European countries. Other new trends in twin research in Asian countries, such as China, Indonesia, Russia, Iran, and Malaysia, are also described.

Zygosity on multiple pregnancies is important factor of prognosis in fetus and new bones. In the past, determination of zygosity has been made mainly on the basis of histological and microscopic observations. Such a morphological distinction, however is not sufficient. Fragment analysis based on capillary electrophoresis has been developed as a rapid and accurate technique for DNA typing. To elucidate the clinical availability of fragment analysis, we examined the zygosity of nine multiple pregnancies (three twins and six triplets) by fragment analysis of microsatellite DNAs and other common DNA tests (PCR-SSCP assay and VNTR analysis using agarose gel electrophoresis). Fragment analysis and PCR-SSCP identified the heterozygosity in two of three twins and all of six triplets including one presumable dizygotic triplet, while VNTR analysis failed to recognize one of two dizygotic twins and three of five trizygotic triplets. Although detection efficiency of PCR-SSCP seems to be similar to that of fragment analysis, PCR-SSCP could not separate the several microsatellite DNAs that fragment analysis showed to be heterozygous. Moreover, fragment analysis could detect a minor population possessing the different DNA types (> 5%) in the same cell suspension. The present results suggest that fragment analysis of microsatellite DNAs may be an excellent and beneficial method for clinical application of zygosity determination in multiple pregnancies.

Twenty-two twins' families were investigated to determine the influence of a genetic factor in the etiology of allergic diseases in children. Zygosity was confirmed by eight red cell blood types and HLA type. Eight pairs of monozygotic twins were divided by a probability of monozygosity as calculated from Essen-Möller's method. Concordance rate of allergic disease and asthma were 88% in MZ, 86% in DZ, 75%, 73% and that of positive rate of DF-specific IgE antibody were 60% in MZ, 58% in DZ. In DZ, not sharing the same HLA haplotypes, concordance of the positive rate of DF-specific IgE antibody was 0%. Concomitant coefficiency of total serum IgE levels were 0.593 in MZ, 0.063 in DZ. These data suggested that IgE production may be influenced by genetic factors.

Tracheal dimensions were analyzed radiographically in 17 pairs of healthy high school boys (12 pairs of monozygotic twins and 5 pairs of dizygotic twins). Coefficients of variation in interindividual extra- and intrathoracic tracheal widths, tracheal depth, tracheal length, and cross sectional area ranged from 9.6 to 17.3%. Genetic influence was found in intrathoracic as well as extrathoracic tracheal widths at maximal expiration and in extrathoracic tracheal width at maximal inspiration. Intrathoracic tracheal width remained the same at either maximal inspiration or expiration. However, extrathoracic tracheal width became larger at maximal inspiration regardless of great changes in pleural pressure. These results indicate that tracheal rings may be influenced by genetic factors and that extrathoracic width may be enlarged during maximal inspiration.