Genetic and Environmental Regulation on Longitudinal Change of Metabolic Phenotypes in Danish and Chinese Adult Twins

Longitudinal analysis of sibling correlation on blood pressure using mixed modeling

PURPOSE

Although moderate to high genetic contribution to blood pressure variation have been estimated in numerous studies, the genetic control over the longitudinal change in blood pressure has been less frequently investigated because of the requirement of longitudinal design.

METHODS

Based on blood pressure data from a large-scale family-based longitudinal survey, we introduced hierarchical modeling of longitudinal family data in combination with fractional polynomials for fitting nonlinear age patterns of blood pressure and the mixed-effect models for estimating sibling correlation on blood pressure to assess the genetic and shared environmental effects on blood pressure level as well as on the rate of change in blood pressure over ages.

RESULTS

Significant sibling correlations were estimated on the levels of systolic blood pressure (0.2, 95% CI: 0.10-0.30) and diastolic blood pressure (0.28, 95% CI: 0.18-0.38), whereas for the longitudinal change or the rate of change, significant correlation was estimated only for diastolic blood pressure (0.13, 95% CI: 0.04-0.23). In the sex-specific analysis, similar pattern is observed, but statistical significance was only reached in female siblings with correlation estimates higher than the overall sample.

CONCLUSION

The rate of change in blood pressure is mainly influenced by individual's unique environment; and the genetic and common family environment may play a role in regulating the longitudinal change of diastolic but not systolic blood pressure.

Longitudinal Investigation into Genetics in the Conservation of Metabolic Phenotypes in Danish and Chinese Twins

Longitudinal twin studies on long term conservation of individual metabolic phenotypes can help to explore the genetic and environmental basis in maintaining metabolic homeostasis and metabolic health. We performed a longitudinal twin study on 12 metabolic phenotypes from Danish twins followed up for 12 years and Chinese twins traced for 7 years. The study covered a relatively large sample of 502 pairs of Danish adult twins with a mean age at intake of 38 years and a total of 181 Chinese adult twin pairs with a mean baseline age of 39.5 years. Bivariate twin models were fitted to the longitudinal measurements taken at two time points (at baseline and follow-up) to estimate the genetic and environmental contributions to phenotype variation and correlation at and between the two time points. High genetic components in the regulation of intra-individual phenotype correlation or stability over time were estimated in both Danish (h²>0.75 except fasting blood glucose) and Chinese (h²>0.72 except blood pressure) twins; moderate to high genetic contribution to phenotype variation at the two time points were also estimated except for the low genetic regulation on glucose in Danish and on blood pressure in Chinese twins. Meanwhile the bivariate twin models estimated shared environmental contributions to the variance and covariance in fasting blood glucose in Danish twins, and in systolic and diastolic blood pressure, low and high density lipoprotein cholesterol in Chinese twins. Overall, our longitudinal twin study on long-term stability of metabolic phenotypes in Danish and Chinese twins identified a common pattern of high genetic control over phenotype conservation, and at the same time revealed population-specific patterns of genetic and common environmental regulation on the variance as well as covariance of glucose and blood pressure.