A Longitudinal Twin Study on the Association Between Inattentive and Hyperactive-Impulsive ADHD Symptoms

DSM-IV distinguishes two symptom domains of attention deficit hyperactivity disorder (ADHD): inattentiveness and hyperactivity-impulsivity. The present study examines the aetiologies and developmental relations underlying the associations between inattentiveness and hyperactivity-impulsivity over time, based on a representative population sample from the United Kingdom of approximately 7,000 twin pairs. ADHD symptoms were assessed as continuous dimensions using the DSM-IV items from the Conners’ Parent Rating Scale at two ages: middle childhood (age 1) and early adolescence (age 2). Quantitative genetic cross-lagged analyses showed that the association of the ADHD dimensions over time is influenced by stable as well as newly developing genetic factors. Moreover the longitudinal relationship between the ADHD dimensions appears to be unidirectional, with hyperactivity-impulsivity in middle childhood predicting the presence of inattentiveness in early adolescence, but not vice versa. Thus, hyperactivity-impulsivity may serve to exacerbate inattentiveness over time. Findings are discussed in the context of developmental changes in ADHD symptoms.     

A Twin Study of ADHD Symptoms in Early Adolescence: Hyperactivity-impulsivity and Inattentiveness Show Substantial Genetic Overlap but Also Genetic Specificity

A previous paper in this journal revealed substantial genetic overlap between the ADHD dimensions of hyperactivity-impulsivity and inattentiveness in a sample of 8-year old twins drawn from a UK-representative population sample. Four years later, when the twins were 12 years old, more than 5,500 pairs drawn from the same sample were rated again on the DSM-IV based Revised Conners’ Parent Rating Scale to assess symptoms on both ADHD dimensions. Heritabilities were high (around 70%) for both hyperactivity-impulsivity and inattentiveness and evidence for etiological sex differences was absent. The critical finding was a genetic correlation of 0.55, indicating that hyperactivity-impulsivity and inattentiveness are substantially influenced by the same genes but that the two dimensions also show large and significant unique genetic effects. These results in early adolescence confirm our findings in middle childhood, providing evidence for substantial genetic overlap as well as genetic heterogeneity of the ADHD dimensions. Future genetic studies should investigate the ADHD dimensions separately.     

Psychometric properties of the Highly Sensitive Child scale across developmental stage,gender, and country

Adolescents differ in their degree of Environmental Sensitivity, that is, the ability to perceive and process information about their environment. The present study aimed to investigate the psychometric properties of the Highly Sensitive Child scale (HSC), a self-report measure of Environmental Sensitivity, in two Belgian and UK samples with a total of 3056 adolescents. First, the factor structure, internal consistency, dimensionality, and construct validity of the HSC scale were examined. Second, measurement invariance of the HSC scale across developmental stage, gender, and country was tested. Results supported a bifactor model with a general sensitivity factor and three group factors: Ease of Excitation (EOE), Low Sensory Threshold (LST), and Aesthetic Sensitivity (AES). Cronbach’s alpha and McDonalds’s (hierarchical) omega indicated that the HSC scale is a reliable measure of Environmental Sensitivity, except for AES. Furthermore, AES was associated with different personality traits than EOE and LST. Second, the HSC scale was partially measurement invariant across developmental stage, gender, and country. The results provide important insights in the psychometrics of a first measurement of Environmental Sensitivity in early to late adolescents. Implications for further research are discussed.

     

More Than Just IQ: School Achievement Is Predicted by Self-Perceived Abilities—But for Genetic Rather Than Environmental Reasons

ABSTRACT— Evidence suggests that children's self-perceptions of their abilities predict their school achievement even after one accounts for their tested cognitive ability (IQ). However, the roles of nature and nurture in the association between school achievement and self-perceived abilities (SPAs), independent of IQ, is unknown. Here we reveal that there are substantial genetic influences on SPAs and that there is genetic covariance between SPAs and achievement independent of IQ. Although it has been assumed that the origins of SPAs are environmental, this first genetic analysis of SPAs yielded a heritability of 51% in a sample of 3,785 pairs of twins, whereas shared environment accounted for only 2% of the variance in SPAs. Moreover, multivariate genetic analyses indicated that SPAs predict school achievement independently of IQ for genetic rather than environmental reasons. It should therefore be possible to identify "SPA genes" that predict school achievement independently of "IQ genes."