Stroke and Twins
Twins have provided valuable insights into stroke and related diseases. Observing how and when twins develop stroke and related diseases have already provided valuable insight into both the genetic and environmental risk for stroke.
The genetic contribution to stroke, its strength and its overall impact on the population, have been debated for many years. One of the strongest pieces of evidence suggesting a genetic contribution to stroke came from a large study of 32,000 twins who were followed for many decades. By comparing the rate of concordance between twins, an estimate of the genetic contribution to stroke can be made. More specifically, concordance rates look at instances where one twin has had a stroke and examines whether the other twin has had a stroke. These rates are compared between monozygotic (identical) twins and dizygotic (fraternal) twins. Because identical twins are genetically identical, if a higher rate of concordance for stroke (or other disease) is found among identical twins when compared to fraternal twins, this indicates a genetic contribution to stroke. This is what was found and provides some of the most convincing evidence for the overall importance of genetics to stroke risk.
Twin studies can be a valuable tool in understanding the specific causes, and new methods of preventing, stroke. Twin studies provide estimates of specific genetic contribution to stroke. There may be deficiencies in enzymes, vulnerabilities to environmental exposures, or susceptibility to medical conditions (e.g., diabetes). By defining the genetic contributions to stroke, interventions can be devised and started early in life, a time when small changes can mean huge differences in risk over the course of a lifetime.
Twin studies are also a powerful tool to study environmental causes of stroke. By looking at differences in the environment between monozygotic twins, additional risk factors for stroke can be defined. For example, by examining differences in living situations (e.g., married, divorced, widowed, life stress, socio-economic conditions), differences in subsequent stroke rates, and because monozygotic twins are genetically identical, difference in the rate of stroke must be attributed to the environment. This is the critical first step in devising therapeutic interventions.
Over the past decade the importance of the genetic contributions to stroke has become obvious. Combining large scale clinical epidemiological studies such as twins studies with bench research into the molecular and cellular processes will provide the best blend of approaches to advance our understanding of the mechanisms, and ultimately the prevention, of stroke and related diseases.