Twin studies of cardiorespiratory disease, daily cardiovascular activity and imaging

Twin studies have helped gain insight into the role of heritability in disease and disease processes. Given the large burden cardiorespiratory diseases place on society, these diseases have featured largely in twin studies. In part A of this chapter, a brief overview of the outcomes of such studies is provided for a wide variety of cardiovascular and respiratory diseases. A moderate to high influence of genes is seen for the vast majority of these diseases. This highlights the importance of screening high-risk individuals, as well as studying gene-by-environment interactions. While studying the disease itself is important, insight into the processes leading up to the disease may increase our understanding of disease development. By studying cardiovascular function for prolonged periods of time in nonpatient populations, valuable insights can be obtained in normal day cardiovascular functioning. In part B of this chapter, we review twin studies in which indices of cardiovascular function were recorded throughout the day and night using ambulatory monitoring. Here too, it is evident that heritability influences the variation of everyday blood pressure and heart action. Another way of gaining insight into the physiological processes underlying disease development is through imaging studies. In part C of this chapter, we discuss the inclusion of twins in imaging studies. Twin studies of imaging data are still sparse and cover a wide variety of traits. Studies including both monozygotic and dizygotic twins generally point to a role for genetic factors, though the degree differs across the traits. Within imaging studies, the twin discordant design is also often applied, demonstrating the occurrence of gene-by-environment interaction. Overall, twin studies have shown that genetic factors play an important role in individual variation in many physiological diseases and disease processes. Future studies are expected to provide more insight into the interplay of genetic and environmental factors with respect to physiological function and risk. Of particular interest are studies looking into epigenetic mechanisms, which are gradually emerging and may further help the development of more personalized medicine, based on genetic vulnerability as well as lifestyle and environment.