Birthweight has implications for physical and mental health in later life. Using data from Caucasian twins collected in Australia, the Netherlands and the United States, and from East Asian twins collected in Japan and South Korea, we compared the total phenotypic, genetic and environmental variances of birthweight between Caucasians and East Asians. Model-fitting analyses yielded four major findings. First, for both males and females, the total phenotypic variances of birthweight were about 45% larger in Caucasians than in East Asians. The larger phenotypic variances were mainly attributable to a greater shared environmental variance of birthweight in Caucasians (ranging from 62% to 67% of variance) than Asians (48% to 53%). Second, the genetic variance of birthweight was equal in Caucasians and East Asians for both males and females, explaining a maximum of 17% of variance. Third, small variations in total phenotypic variances of birthweight within Caucasians and within East Asians were mainly due to differences in nonshared environmental variances. We speculate that maternal effects (both genetic and environmental) explain the large shared environmental variance in birthweight and may account for the differences in phenotypic variance in birthweight between Caucasians and East Asians. Recent molecular findings and specific environmental factors that are subsumed by maternal effects are discussed.
Bibliographical noteFunding Information:
We would like to thank the twins in all five countries for their participation. We wish to thank Ann Eldridge and Marlene Grace for participant recruitment and phenotype collection of Australian twin data. The Australian work was supported by grants from the GenomEUtwin grant (EU/QLRT-2001-01254), Queensland Cancer Fund, the Australian National Health and Medical Research Council (950998, 981339 and 241944), and the US National
Cancer Institute (CA88363). The Minnesota Twin Family Study was supported in part by United States Public Health Services grants AA09367 and DA05147. The Netherlands Twin Register was supported in part by grants NWO 480-04-004, NWO 904-57-94, & NIMH, RO1 MH58799-03. The Seoul Twin Family Study was supported by Korea Research Foundation Grant (KRF-2001-041-C00548) and the Brain Korea 21 Research Fellowship award given to the first author.