Twin registers across the globe: what's out there in 2002?
Twin research offers the greatest power for the genetic analysis of complex multifactorial traits and diseases in humans. Modern twin analyses extend beyond the classical twin study for estimating the heritability of a trait. The human genome project can fulfil its promises only after functional characterisation of single genes in the context of genetic background and environment. Twin research can make a major contribution in that regard. Twin research is greatly facilitated by the willingness, motivation, cooperation, and generosity of the participants and their families. A second important aspect is the availability of twin registries that serve as a resource for genetic epidemiology. Currently, there is no systematic overview of the twin collections worldwide. This special issue will help to overcome the limited accessibility of this resource by providing basic information on most of the existing twin registers. Furthermore, an additional goal is to facilitate collaboration between registers. Some basic principles, potentials, and problems will be exemplified by my personal experience in the Berlin Twin Study.