Estimation of the interaction between heredity and environment for musical aptitude of twins

Effects of gene-environment interactions on cardiovascular risk factors in Chinese adolescent twins

A population-based sample of 73 male and 77 female monozygotic (MZ), and 41 male and 33 female dizygotic (DZ) Chinese adolescent twin pairs were studied to assess effects of gene-environment interactions of systolic blood pressure (SBP), diastolic blood pressure (DBP), serum cholesterol and triglyceride levels. Intrapair concordance in BP levels was found to be significantly associated with the interaction of zygosity and salty foods preference and also with that of zygosity and vegetable preference. A consistently positive and statistically significant association was observed between the intrapair difference in serum cholesterol and the interaction of zygosity and animal organ preference; while intrapair concordance in serum cholesterol was associated with the interaction of zygosity and milk consumption. Intrapair difference in serum triglycerides was associated with the interaction of zygosity and fish preference, and a significant association was also found between the intrapair concordance in serum triglycerides and the interaction of zygosity and sweets preference. These observations suggest that the impact of these environmental agents may be influenced by the genotype.

Scope and methodology of twin studies

The use of twins as a research tool is still proving its worth both by the number of scientists engaged in twin research and by the significance of their results. Old, familiar research designs are finding new applications, and new research designs are appearing. Of greatest current interest are the epidemiological studies made possible by the assembly and the aging of large numbers of twins in twin registries. As an outgrowth partly of the twin registries, partly of conceptual and mathematical progress, new methods have emerged for diagnosis of twin types and for analysis of twin data. One line of development started with the questionnaire method of zygosity diagnosis and has given rise most recently to zygosity diagnosis by principal component analysis. Another line started with probability calculations and has led to the use of generalized distance and noncentral chi-square. The appropriateness of these methods in different contexts needs to be critically considered. Also of importance are the psychologists' new methods of extracting genetic “factors”. The greatest weakness of twin studies, long recognized, is their dependence on the assumption that DZ pairs provide an adequate control on the environmental differences within MZ pairs. This may be valid with respect to environmental influences that are highly self-selected. It is debatable for self-selected influences that differ among families, and clearly untenable for most influences imposed by the social environment peculiar to twins.