A Longitudinal Twin Study of the Direction of Effects between ADHD Symptoms and IQ

Contains fulltext : 155112.PDF (publisher's version ) (Open Access)While the negative association between ADHD symptoms and IQ is well documented, our knowledge about the direction and aetiology of this association is limited. Here, we examine the association of ADHD symptoms with verbal and performance IQ longitudinally in a population-based sample of twins. In a population-based sample of 4,771 twin pairs, DSM-IV ADHD symptoms were obtained from the Conners' Parent Rating Scale-Revised. Verbal (vocabulary) and performance (Raven's Progressive Matrices) IQ were assessed online. ADHD symptom ratings and IQ scores were obtained at ages 12, 14 and 16 years. Making use of the genetic sensitivity and time-ordered nature of our data, we use a cross-lagged model to examine the direction of effects, while modelling the aetiologies of the association between ADHD symptoms with vocabulary and Raven's scores over time. Although time-specific aetiological influences emerged for each trait at ages 14 and 16 years, the aetiological factors involved in the association between ADHD symptoms and IQ were stable over time. ADHD symptoms and IQ scores significantly predicted each other over time. ADHD symptoms at age 12 years were a significantly stronger predictor of vocabulary and Raven's scores at age 14 years than vice versa, whereas no differential predictive effects emerged from age 14 to 16 years. The results suggest that ADHD symptoms may put adolescents at risk for decreased IQ scores. Persistent genetic influences seem to underlie the association of ADHD symptoms and IQ over time. Early intervention is likely to be key to reducing ADHD symptoms and the associated risk for lower IQ

Genetic etiology in cases of recovered and persistent stuttering in an unselected, longitudinal sample of young twins

The contribution of genetic factors in the persistence of and early recovery from stuttering was assessed

Genetic etiology in cases of recovered and persistent stuttering in an unselected, longitudinal sample of young twins

The contribution of genetic factors in the persistence of and early recovery from stuttering was assessed

Age-related differences and heritability of the perisylvian language networks

Acquisition of language skills depends on the progressive maturation of specialized brain networks that are usually lateralized in adult population. However, how genetic and environmental factors relate to the age-related differences in lateralization of these language pathways is still not known. We recruited 101 healthy right-handed subjects aged 9–40 years to investigate age-related differences in the anatomy of perisylvian language pathways and 86 adult twins (52 monozygotic and 34 dizygotic) to understand how heritability factors influence language anatomy. Diffusion tractography was used to dissect and extract indirect volume measures from the three segments of the arcuate fasciculus connecting Wernicke's to Broca's region (i.e., long segment), Broca's to Geschwind's region (i.e., anterior segment), and Wernicke's to Geschwind's region (i.e., posterior segment). We found that the long and anterior arcuate segments are lateralized before adolescence and their lateralization remains stable throughout adolescence and early adulthood. Conversely, the posterior segment shows right lateralization in childhood but becomes progressively bilateral during adolescence, driven by a reduction in volume in the right hemisphere. Analysis of the twin sample showed that genetic and shared environmental factors influence the anatomy of those segments that lateralize earlier, whereas specific environmental effects drive the variability in the volume of the posterior segment that continues to change in adolescence and adulthood. Our results suggest that the age-related differences in the lateralization of the language perisylvian pathways are related to the relative contribution of genetic and environmental effects specific to each segment. SIGNIFICANCE STATEMENT Our study shows that, by early childhood, frontotemporal (long segment) and frontoparietal (anterior segment) connections of the arcuate fasciculus are left and right lateralized, respectively, and remain lateralized throughout adolescence and early adulthood. In contrast, temporoparietal (posterior segment) connections are right lateralized in childhood, but become progressively bilateral during adolescence. Preliminary twin analysis suggested that lateralization of the arcuate fasciculus is a heterogeneous process that depends on the interplay between genetic and environment factors specific to each segment. Tracts that exhibit higher age effects later in life (i.e., posterior segment) appear to be influenced more by specific environmental factors

Proportions of the phenotypic correlations between ADHD symptoms and Raven’s Standard Progressive Matrice scores due to genetic (A), shared environmental (C) and non-shared environmental (E) influences.

<p>ADHD = attention deficit hyperactivity disorder; r_ph = phenotypic correlation</p><p>^aProportions of the phenotypic correlation due to total genetic or environmental influences (i.e. transmitted plus age-specific effects).</p><p>^bProportions of the phenotypic correlation due to time-specific genetic or environmental influences specific to early adolescence.</p><p>Figures in parentheses refer to the absolute contributions of A, C and E respectively to the phenotypic correlations between ADHD symptoms and Raven’s scores.</p><p>Proportions of the phenotypic correlations between ADHD symptoms and Raven’s Standard Progressive Matrice scores due to genetic (A), shared environmental (C) and non-shared environmental (E) influences.</p

Phenotypic correlations between ADHD symptom and Raven’s Standard Progressive Matrices scores.

<p>95% confidence intervals are provided in brackets.</p><p>Phenotypic correlations between ADHD symptom and Raven’s Standard Progressive Matrices scores.</p

Cross-lagged path model of vocabulary and ADHD symptom scores.

<p>95% confidence intervals are provided in brackets. Values in square brackets [] represent time-specific genetic and environmental contributions to ADHD symptoms and vocabulary scores. Asterisks indicate the significantly greater path at the p = 0.05 level. Non-significant paths are indicated by dashed lines.</p

Transmission of genetic (A), shared environmental (C) and non-shared environmental (E) influences between ADHD symptoms and vocabulary scores over time.

<p><i>Note</i>: Percentages in parentheses refer to the proportion of variance at the age indicated transmitted from the previous time point, i.e. transmitted from time 1 to time 2 and from time 2 to time 3. For each trait, percentages within each column add up to 100%, and, thus, may not perfectly correspond to proportions derivable from parameter estimates in this table, due to rounding error.</p><p>Transmission of genetic (A), shared environmental (C) and non-shared environmental (E) influences between ADHD symptoms and vocabulary scores over time.</p

Phenotypic correlations between ADHD symptom and vocabulary scores.

<p>95% confidence intervals are provided in brackets.</p><p>Phenotypic correlations between ADHD symptom and vocabulary scores.</p

Transmission of genetic (A), shared environmental (C) and non-shared environmental (E) influences between ADHD symptoms and Raven’s Standard Progressive Matrices over time.

<p><i>Note</i>: Percentages in parentheses refer to the proportion of variance at the age indicated transmitted from the previous time point, i.e. transmitted from time 1 to time 2 and from time 2 to time 3. For each trait, percentages within each column add up to 100% and, thus, may not perfectly correspond to proportions derivable from parameter estimates in this table, due to rounding error.</p><p>Transmission of genetic (A), shared environmental (C) and non-shared environmental (E) influences between ADHD symptoms and Raven’s Standard Progressive Matrices over time.</p