van Keulen BJ, Dolan CV, Andrew R, et al. - In this prospective follow-up study of twins, researchers determined the relative contributions of genetic and environmental factors to inter-individual variations in cortisol production and metabolism throughout adolescence. The sample consisted of 218 mono- and dizygotic twins (N = 109 pairs) born between 1995 and 1996, selected from the Netherlands Twin Register. According to results, the contribution of genetic factors to inter-individual differences in the production of cortisol decreased from 12 to 17 years, suggesting a predominant function for individual circumstances. Distinct patterns of genetic and environmental influences have been observed for cortisol metabolism, with heritability that either increased with age or peaked at age 12 years.