Setting up and utilizing Norwegian twin panels

Abstract

In the late 1970s, a Norwegian twin panel was set up. It included all like-sexed twin pairs, born in the period 1915 to 1960, where both members were alive and had a known address in Norway at the time. The work was initiated through a grant from the National Institutes of Health in the United States. The aim was to estimate maternal effects to understand the causes of variation in traits and diseases that originate in pregnancy. However, the twin panel was also utilized for estimating genetic and environmental effects on a series of phenotypes, for instance lipoproteins, receptors, coagulation factors, cognitive abilities, educational attainment and left-handedness. A short zygosity questionnaire was sent together with the first invitation letter to the twins. Later questionnaires on general health, lifestyles and pregnancy outcomes were sent out. One important finding was that the fetal genotype had much stronger influence on variation in fetal growth than what had been assumed previously. In the early 1990s, the New Norwegian Twin Panel was created, based on information on plural births in the Medical Birth Registry of Norway (MBRN). The panel included both like-sexed and opposite-sexed pairs born in the years 1967 to 1974. After linking the MBRN to present addresses, using a national identification number, a questionnaire on zygosity, with a few items on health and social background, was sent out. This panel was later expanded to include twins born 1975-1979 and to collect more data on health, well-being and lifestyle factors. The data have been utilized for a series of sub-projects, including psychiatric interviews and the collection of DNA samples. Linkage to Norwegian health registries has provided important research opportunities for a variety of phenotypic outcomes.