Heritabilities of the metabolic syndrome phenotypes and related factors in Korean twins

Context: The genetic studies of metabolic syndrome (MetS), individual components, or latent factors of MetS phenotypes, in Asian populations are limited. Objective: This study aimed to estimate heritability of MetS and its components, and to identify latent factors clustering individual components among Korean twins and their families. Design: Data were derived from the Healthy Twin Study, an ongoing cohort study, from April 2005 to December 2008. Participants: A total of 1942 Korean adult same-sex twins and their families (728 men, 1214 women; 795 monozygotic and 229 dizygotic twin individuals with 918 nontwin family members). Main Outcome Measures: MetS phenotypes measured were waist circumference (WC), mean blood pressure (MBP), glucose, high-density lipoprotein cholesterol (HDL), and triglycerides (TG) as continuous and discrete traits. MetS was defined using Adult Treatment Panel III and International Diabetes Federation criteria. Heritability, bivariate analyses, interclass correlation, concordances, and factor analyses were conducted. Results: Significant differences in interclass correlation for WC, MBP, HDL, and glucose and in concordance rate for high WC and low HDL among monozygotic and dizygotic twins were found. MetS had heritabilities of 51-60% (P < 0.001), and phenotypes showed adjusted heritabilities ranging from 46% (for TG) to 77% (for low HDL). Factor analysis indicated two latent factors (factor 1, TG/WC/HDL; factor 2, WC/MBP/glucose) with significant heritabilities of 60-63%. Bivariate analyses exhibited different genetic and environmental interrelationships between phenotype pairs, although WC and TG showed significant genetic correlations with all other phenotypes. Conclusions: Significant genetic contributions for MetS, its related phenotypes, and latent factors comprising MetS are confirmed.