ORIGINAL ARTICLE Variations in Heritability of Cortisol Reactivity to Stress as a Function of Early Familial Adversity Among 19-Month-Old Twins

Context: Cortisol reactivity is a marker of vulnerability for a variety of stress-related diseases that likely arise from the contributions of both genetic and environmental sources of influence. However, little is known about gene-environment interplay in early cortisol reactivity. Objectives: To examine the genetic and environmen-tal contributions to early cortisol reactivity in a population-based sample of 19-month-old twins and to determine whether these contributions vary as a function of early familial adversity. Design: A variant of the twin method, with genetic and environment contributions to cortisol reactivity esti-mated as a function of familial adversity. Familial adver-sity was defined as the presence of 7 risk factors during perinatal and postnatal development (eg, at 6 and 19 months of age): maternal smoking during pregnancy, low birth weight, low family income, low maternal educa-tional level, single parenthood, young motherhood, and maternal hostile or reactive behaviors. Twins exposed to 4 or more risk factors at either time were considered as having been exposed to high (vs low) familial adversity (23.4 % of the sample)