Résumé·s
Background
Difficult temperament in infancy is a risk factor for forms of later internalizing and externalizing
psychopathology, including depression and anxiety. A better understanding of the roots
of difficult temperament requires assessment of its early development with a genetically
informative design. The goal of this study was to estimate genetic and environmental contributions
to individual differences in infant negative emotionality, their persistence over time
and their influences on stability between 5 and 18 months of age.
Method
Participants were 244 monozygotic and 394 dizygotic twin pairs (49.7% male) recruited
from birth. Mothers rated their twins for negative emotionality at 5 and 18 months. Longitudinal
analysis of stability and innovation between the two time points was performed in Mplus.
Results
There were substantial and similar heritability (approximately 31%) and shared environmental
(57.3%) contributions to negative emotionality at both 5 and 18 months. The trait's interindividual
stability across time was both genetically- and environmentally- mediated.
Evidence of innovative effects (i.e., variance at 18 months independent from variance at 5
months) indicated that negative emotionality is developmentally dynamic and affected by
persistent and new genetic and environmental factors at 18 months. Conclusions
In the first two years of life, ongoing genetic and environmental influences support temperamental
negative emotionality but new genetic and environmental factors also indicate
dynamic change of those factors across time. A better understanding of the source and timing
of factors on temperament in early development, and role of sex, could improve efforts
to prevent related psychopathology.