Attention Deficit/Hyperactivity Disorders (ADHD) are typically diagnosed in terms of Inattention Problems (INP) and Hyperactivity/Impulsivity Problems (HIP). However, considerable evidence supports an additional set of attentional problems designated as Sluggish Cognitive Tempo (SCT), characterized by lethargy, daydreaming, and confusion. To test relations between genetic and environmental influences on SCT, INP, and HIP, Moruzzi et al. (2014) analyzed scores for the three different kinds of problems rated on the CBCL/6-18 for 796 8-17-year-old Italian twins.

The three kinds of problems were significantly intercorrelated and were influenced by both genetic and environmental factors. However, the three kinds of problems were sufficiently distinct from each other to indicate different etiologies. INP and HIP problems were more strongly influenced by genetic factors than was SCT, which was more strongly influenced by environmental factors. The authors concluded that “genetic twin analyses of the SCT, INP and HIP indicate moderate genetic overlap between the three components, providing some support to an ADHD syndrome that encompasses SCT symptoms” (p. 73).


Moruzzi, S., Rijsdijk, F., & Battaglia, M. (2014). A twin study of the relationships among inattention, hyperactivity/impulsivity and sluggish cognitive tempo problems. Journal of Abnormal Child Psychology, 42, 63-75.