Workshop: Twins: a powerful study design to examine the role of genetics and environment for work incapacity
Authors:   Organised by: Karolinska Institutet Chair persons: Pia Svedberg - Sweden
Published: November 2019

Twin design is an important tool to analyze the role of genetic and environmental factors, and to better understand causal mechanisms in public health research. Twin studies have reliably shown that genetic factors are important not only for physiological traits but also for psychological and health behavioral traits as well as for health-related work incapacity in terms of sick leave and disability pension.

As many countries face an aging workforce, it is becoming ever more important to understand the underlying causes of work incapacity across the entire working life. In the past decade, twin data in combination with national register data have been used to deepen our understanding of the role of genetic and environmental influences on the complex processes of sick leave and disability pension. The aim of this workshop is to present and discuss methods and results of studies based on the large Swedish, Finnish and Norwegian twin cohorts.

Linear structural equations are intensively utilized in modern methods of twin studies. A variety of models are available to answer different research questions, such as the dynamics behind associations between traits and developmental processes in longitudinal designs - models also applicable in health at work and social security. Further, analyzing twin pairs discordant for an outcome or risk factor (co-twin control) provides a unique possibility to control for familial (genetic and shared environmental) factors, since cases and controls are matched optimally being twins. Findings based on twin cohorts suggest that familial factors are relevant to many risk factors as well as for work incapacity. By controlling for these unobserved confounding factors, the co-twin control design may provide more accurate estimates of risk factors for work incapacity and complement the epidemiological findings of unrelated subjects. Based on population-based twin cohort studies with long follow-up, indications also exist that familial confounding may have different roles in the associations between risk factors and work incapacity. For example, in regard to various disability pension diagnosis groups and depending on study designs (one vs. two time points, longer vs. shorter follow-up etc.).

Results from prospective studies on various risk factors, including adolescents’ mental health problems, for future sick leave and disability pension will be presented. Another presentation focuses on the stability and change in genetic and environmental factors influencing work incapacity from age 18 until retirement and the likelihood of causality between educational attainment, lifestyle and work incapacity. Finally, results on adverse outcomes of sick leave due to mental disorders using an open cohort design adjusting for familial factors will be presented.

During the time of rapid development in molecular genetics, the twin study design has maintained its importance and will continue to cast light on different aspects of work incapacity.

Key messages

Twin design offers a unique tool in public health research to examine and control for familial (genetic and shared environmental) factors. Genetic factors seem to play an important role in understanding the complex causes of work incapacity in terms of sick leave and disability pension.