Effect of parental age on children's intelligence in the Southwestern China Prospective twin registry

Abstract

Average parental age has been increasing in recent years for social and financial reasons. Previous research has shown that parental age is positively associated with increased health problems in the offspring. To assess the influence of parental age on intelligence during childhood and adolescence, we investigated twins between 6 and 16 years old in the Southwestern China Prospective Twin Registry. We assessed intelligence using the Chinese edition of Wechsler Intelligence Scale for Children-Revised (WISC-R) on 178 monozygotic and 155 dizygotic twin pairs. Advanced maternal age was not associated with increased total IQ in male and female offspring, explaining less than 1% of the variance. The heritability of total IQ was 17% (95% CI: 0–39%), with shared environment explaining 57% (95% CI: 36–73%) of the variance. Similarly, for performance IQ, the influence of parental age was not significant, with heritability accounting for 12% (95% CI: 0–38%) of the variance and shared environment 51% (95% CI: 28–67%). Paternal age was associated with higher verbal IQ, explaining approximately 2% of variance. Finally, the variance of verbal IQ was greater in females than in males, with genetic and shared environmental influences equal across the sexes.