Early temperament, such as socio-emotional development and activity level, varies widely, yet its underlying biological associations are not understood. We identified genetic variation associated with infant and toddler temperament using genome-wide association meta-analyses. We studied parent-rated emotionality, activity, shyness and sociability (n = 43,963-72,663) in the second and third postnatal years and a cross-age average. Cross-age single nucleotide polymorphism heritabilities for…
