Genes Do Not Control The Variability Of Blood Pressure In Twins

Not only does the level of blood pressure reveal something about one’s own health risk, but so do its fluctuations. It has to do with the nervous system. Swedish researchers have now investigated the role of genes in this process in twins.

High blood pressure is one of the most important health risks in industrialized countries. The dangerous thing about increased pressure in the vessels is that over time it can damage vital organs such as the heart, brain, kidneys, and eyes. In order to find out who is affected and particularly at risk, doctors often only looked at the height itself. Today, however, we know that fluctuations in blood pressure (blood pressure variability) also reveals something about the future health risk. The more pronounced the variability of systolic blood pressure, the higher the long-term risk of coronary heart disease, stroke, kidney failure, and premature death.

But what is responsible for the fact that one person’s blood pressure fluctuates particularly strongly during the day, while another person’s blood pressure varies in narrow ranges? If genes had something to do with it, researchers around Linda Lundblad (1) thought that this would be seen in a twin study. Since identical twins are almost genetically indistinguishable, the researchers examined eight such pairs. However, they did not measure their blood pressure, but the so-called muscular sympathetic nerve activity, meaning the activity of nerves of the sympathetic nervous system, which transmit their signals directly to muscles.

The sympathetic nervous system is a very old human system. It controls subconsciously ongoing processes, which put the body into increased readiness to perform. Among other things, the sympathetic nervous system plays an important role in regulating blood pressure. When activated by stress, for example, the sympathetic system increases the heart rate and the constriction of the blood vessels, and the result — blood pressure rises. A constantly high level of sympathetic activity can, therefore, lead to increased blood pressure fluctuations, especially during the day.

In the study, the researchers wanted to find out whether the activity of the nerves that control the constriction of the vessels during excitation is controlled less by the genes than the activity of the nerves at rest. In fact, the results of all identical twins were similar at rest, but only in four of eight pairs during excitement. The researchers conclude that the genes have far less influence on changes during excitation than at rest.

But how can the differences be explained? If it’s not the genetic make-up, it should be the environmental influences. The twins of this study, however, grew up together, went to the same school, and also spent much of their free time together. There were no differences in major life events. The results, therefore, suggest that the differences measured are more likely to be due to subtle — non-shared — environmental influences. Whether epigenetic factors, i.e. changes in the genetic material caused by environmental factors, are also involved in this has yet to be investigated, the authors write. However, it must be emphasized that the number of twins examined was very small. It, therefore, remains to be seen whether larger studies will be able to confirm the results of the researchers.

For the authors, however, their study is already a reason to consider how to reduce the risk of cardiovascular diseases in patients. They write that the effectiveness of behavioral therapies still needs to be confirmed. But even today, we already know that sport and exercise have an effect. If one compares two twins who move at different rates and intensity, the more fit twin is 32 percent less likely to die of cardiovascular disease than his twin siblings. Whether changes in sympathetic nerve activity after excitement also contribute to this connection still has to be investigated.

This is part 25 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon. Further studies in twin research can be found at TwinHealth website. Translation was done with the assistance of DeepL translator.

Reference:

1. Lundblad LC, Eskelin JJ, Karlsson T, Wallin BG, Elam M. Sympathetic Nerve Activity in Monozygotic Twins: Identical at Rest but Not During Arousal. Hypertension. 2017 May;69(5):964-969.