Background: Causes of variation in cardiovascular risk factors include biological variation within individuals, and more permanent differences between individuals, which are at least partly genetic in origin. We have compared the magnitude of genetic and non-genetic factors within and across occasions through repeated measures of plasma cholesterol in twin subjects, and have also determined how far the same genes affect cholesterol levels at different ages.
Methods: Data on plasma total cholesterol were extracted for 208 twin pairs who had provided blood on up to six occasions across a period of 17 years. They were aged 18-30 years at the time of first study and 30-47 at the time of the last. Multivariate models of variation due to genetic, shared environmental and unique environmental factors were fitted to the multi-occasion data and the proportions of variation due to these factors were estimated.
Results: One genetic factor influenced plasma cholesterol on all occasions and a second genetic factor only influenced cholesterol results on the fifth and sixth occasions 10-17 years after the first. Environmental factors did not have significant long-term effects.
Conclusions: We conclude that individuals' long-term mean plasma cholesterol values are strongly genetically determined, but that some of these genes are age-specific in their effects.