Twin studies help find the role of genetics in diseases

 

We all know that family members often resemble each other in many ways. Similarly, many diseases and their risk factors are more frequent in relatives of the patient than in the population on average, but is the similarity between near relatives due to common genes or a common (family) environment?

An answer to this question has been sought for nearly one hundred years with the help of twin studies. Twin studies are based on the fact that there are genetically two kinds of twins: monozygotic or "identical", who have the same genotype, and dizygotic or "non-identical", whose genotypes are like those of two siblings in general. Therefore, the greater similarity of identical twins compared to non-identical twins as regards the phenomenon under study is considered a sign of the impact of the genotype. The issue can also be approached by studying differences between monozygotic twins, because those are indicative of the impact of external factors. This way, we have been able to show that smoking increases intervertebral disc degeneration regardless of genetic predisposition.

Relatively much twin research has been carried out in Finland. For example, a follow-up study of adult twins begun at the Department of Public Health 25 years ago recently gave new results on the causes of cancer (New England Journal of Medicine, 2000). The results are based on a combined Nordic analysis, incorporating results from Finland, Sweden and Denmark. The data comprised approximately 90,000 adult twins, a good 10,000 of whom had contracted cancer during the follow-up period of several decades. A total of 28 different forms of cancer were studied, and only in three cases was there evidence of significant genetic component. Over 200 scientific articles and some one dozen doctoral dissertations have been published on the adult twin study. The Department of Public Health is, at present, carrying out two extensive studies on the health, health-related behaviour and general development of adolescent twins. The subjects comprise twins born in 1974-1979 and 1983-1987. These projects include researchers from the Universities of Helsinki, Jyväskylä, Oulu and Turku.

Further information:
Professor Jaakko Kaprio, Department of Public Health,
P.O. Box 41 FIN-00014 University of Helsinki,
Tel: +358 9 19127595,
Email: jaakko.kaprio@helsinki.fi
Web: http://kate.pc.helsinki.fi/twin/twinhome.html