Advantages of linking national registries with twin registries for epidemiological research

Abstract

Linking national registries with twin data represents an opportunity to produce epidemiological research of
high quality. National registries contain information on a broad array of variables, some of which cannot be
measured reliably in regular health surveys. By taking kinship into consideration, twin studies have the
benefit of being able to identify confounding stemming from genetic or shared environmental sources. In
this paper, we use examples from our own interview and questionnaire-based twin studies from the Norwegian
Twin Registry (NTR) on mental disorders, alcohol use and socioeconomic status linked to registry
data on medical benefits to demonstrate the value. In the first example, we examined to what extent genetic
and environmental factors contributed to sick leave and disability pension and the association between these
two types of benefits. In the second example, we explored the genetic and environmental relationship
between personality disorders and sick leave. In the third example, a co-twin control design was applied to
explore whether there is a true protective relationship between moderate alcohol consumption and health.
The fourth example shows to what degree anxiety and depression are associated with later sick leave granted
for not only mental disorders, but also somatic disorders, adjusted for confounding by genetic and shared
environmental factors. In the fifth example, we address the socioeconomic gradient in sick leave, adjusting
for non-observed confounders associated with the family in a co-twin control design. Our examples illustrate
some of the potentials obtainable by linking national registries with twin data. The efforts that have been
made to create the NTR in Norway and the International Network of Twin Studies (INTR) internationally
make these types of linkage studies easier to conduct and available to more researchers. As there are still
many areas to explore, we encourage epidemiological researchers to make use of this possibility.