Background: Reading disability (RD) and attention deficit/hyperactivity disorder (ADHD) are comorbid and genetically correlated, especially the inattentive dimension of ADHD (ADHD‐I). However, ...previous research indicates that RD and ADHD enter into opposite gene by environment (G × E) interactions.
Methods: This study used behavioral genetic methods to replicate these opposite G × E interactions in a sample of same‐sex monozygotic and dizygotic twin pairs from the Colorado Learning Disabilities Research Center (CLDRC; DeFries et al., 1997) and to test a genetic hypothesis for why these opposite interactions occur.
Results: We replicated opposite G × E interactions for RD (bioecological) and ADHD‐I (diathesis‐stress) with parental education in the same sample of participants. The genetic hypothesis for this opposite pattern of interactions is that only genes specific to each disorder enter into these opposite interactions, not the shared genes underlying their comorbidity. To test this hypothesis, we used single models with an exploratory three‐way interaction, in which the G × E interactions for each disorder were moderated by comorbidity. Neither three‐way interaction was significant. The heritability of RD did not vary as a function of parental education and ADHD‐I. Similarly, the heritability of ADHD‐I did not vary as a function of parental education and RD.
Conclusions: We documented opposite G × E interactions in RD and ADHD‐I in the same overall twin sample, but the explanation for this apparent paradox remains unclear. Examining specific genes and more specific environmental factors may help resolve the paradox.
The relationship between the
p
factor and cognition in youth has largely focused on general cognition (IQ) and executive functions (EF). Another cognitive construct, processing speed (PS), is ...dissociable from IQ and EF, but has received less research attention despite being related to many different mental health symptoms. The present sample included 795 youth, ages 11–16 from the Colorado Learning Disabilities Research Center (CLDRC) sample. Confirmatory factor analyses tested multiple
p
factor models, with the primary model being a second-order, multi-reporter
p
factor. We then tested the correlation between the
p
factor and a latent PS factor. There was a significant, negative correlation between the
p
factor and PS (
r
(87) = -0.42,
p
< .001), indicating that slower processing speed is associated with higher general mental health symptoms. This association is stronger than previously reported associations with IQ or EF. This finding was robust across models that used different raters (youth and caregiver) and modeling approaches (second-order vs. bifactor). Our findings indicate that PS is related to general psychopathology symptoms. This research points to processing speed as an important transdiagnostic construct that warrants further exploration across development.
Several quantitative trait loci (QTLs) that influence developmental dyslexia (reading disability RD) have been mapped to chromosome regions by linkage analysis. The most consistently replicated area ...of linkage is on chromosome 6p23-21.3. We used association analysis in 223 siblings from the United Kingdom to identify an underlying QTL on 6p22.2. Our association study implicates a 77-kb region spanning the gene
TTRAP and the first four exons of the neighboring uncharacterized gene
KIAA0319. The region of association is also directly upstream of a third gene,
THEM2. We found evidence of these associations in a second sample of siblings from the United Kingdom, as well as in an independent sample of twin-based sibships from Colorado. One main RD risk haplotype that has a frequency of ∼12% was found in both the U.K. and U.S. samples. The haplotype is not distinguished by any protein-coding polymorphisms, and, therefore, the functional variation may relate to gene expression. The QTL influences a broad range of reading-related cognitive abilities but has no significant impact on general cognitive performance in these samples. In addition, the QTL effect may be largely limited to the severe range of reading disability.
This study investigated the association between reading disability (RD) and internalizing
and externalizing psychopathology in a large community sample of twins with (N = 209) and
without RD (N = ...192). The primary goals were to clarify the relation between RD and
comorbid psychopathology, to test for gender differences in the behavioral correlates of RD,
and to test if common familial influences contributed to the association between RD and
other disorders. Results indicated that individuals with RD exhibited significantly higher
rates of all internalizing and externalizing disorders than individuals without RD. However,
logistic regression analyses indicated that RD was not significantly associated with symptoms
of aggression, delinquency, oppositional defiant disorder, or conduct disorder after
controlling for the significant relation between RD and ADHD. In contrast, relations
between RD and symptoms of anxiety and depression remained significant even after
controlling for comorbid ADHD, suggesting that internalizing difficulties may be specifically
associated with RD. Analyses of gender differences indicated that the significant relation
between RD and internalizing symptoms was largely restricted to girls, whereas the
association between RD and externalizing psychopathology was stronger for boys. Finally,
preliminary etiological analyses suggested that common familial factors predispose both
probands with RD and their non-RD siblings to exhibit externalizing behaviors, whereas
elevations of internalizing symptomatology are restricted to individuals with RD.
Reversal errors play a prominent role in theories of reading disability. We examined reversal errors in the writing of letters by 5- to 6-year-old children. Of the 130 children, 92 had a history of ...difficulty in producing speech sounds, a risk factor for reading problems. Children were more likely to reverse letter forms that face left, such as and , than forms that face right, such as and . We propose that this asymmetry reflects statistical learning: Children implicitly learn that the right-facing pattern is more typical of Latin letters. The degree of asymmetry that a child showed was not related to the child's reading skill at Time 2, 2¾ years later. Although children who went on to become poorer readers made more errors in the letter writing task than children who went on to become better readers, they were no more likely to make reversal errors.
Background
The onset of hyperactivity/impulsivity and attention problems (HAP) is typically younger than that of conduct problems (CP), and some research supports a directional relation wherein HAP ...precedes CP. Studies have tested this theory using between‐person and between‐group comparisons, with conflicting results. In contrast, prior research has not examined the effects of within‐person fluctuations in HAP on CP.
Method
This study tested the hypothesis that within‐person variation in HAP would positively predict subsequent within‐person variation in CP, in two population samples of youth (N = 620) who participated in identical methods of assessment over the course of 30 months. Three‐level, hierarchical models were used to test for within‐person, longitudinal associations between HAP and CP, as well as moderating effects of between‐person and between‐family demographics.
Results
We found a small but significant association in the expected direction for older youth, but the opposite effect in younger and non‐Caucasian youth. These results were replicated across both samples.
Conclusions
The process by which early HAP relates to later CP may vary by age and racial identity.
Evaluation of social-cognitive skills in 23 young children with autism or other developmental delays found tests involving others' attention were more difficult for children with autism than tests ...involving others' behavior. However, the typical developmental pattern of first sharing, then following, and then directing attention or behavior was evident. Some intercorrelations among social-cognitive skills were found. (Contains references.) (Author/DB)
Approximately 60% of children with reading difficulties (RD) meet criteria for at least one co-occurring disorder. The most common of these, attention deficit-hyperactivity disorder (ADHD), occurs in ...20-40% of individuals with RD. Recent studies have suggested that genetic influences are responsible. To assess the genetic etiologies of RD and the comorbidity of RD and two ADHD symptom dimensions -- inattention (IN) and hyperactivity/impulsivity (H/I) -- we are conducting the first longitudinal twin study of RD and ADHD. Data from twin pairs in which at least one member of the pair met criteria for proband status for RD at initial assessment, and were reassessed 5 years later, were subjected to DeFries-Fulker (DF) analysis. Analyses of reading composite data indicated that over 60% of the proband deficit at initial assessment was due to genetic influences, and that reading deficits at follow-up were due substantially to the same genetic influences. When a bivariate DF model was fitted to reading performance and IN data, genetic influences accounted for 60% of contemporaneous comorbidity and over 60% of the longitudinal relationship. In contrast, analysis of the comorbidity between reading performance and H/I indicated that common genetic influences accounted for only about 20% of the contemporaneous and about 10% of the longitudinal relationships. Results indicate that (1) genetic influences on RD are substantial and highly stable; (2) the comorbidity between RD and IN is due largely to genetic influences, both contemporaneously and longitudinally; and (3) genetic influences contribute significantly less to the comorbidity between RD and H/I.
Recent structural and functional imaging work, as well as neuropathology and neuropsychology studies, provide strong empirical support for the involvement of frontal cortex in autism. The Cambridge ...Neuropsychological Test Automated Battery (CANTAB) is a computer-administered set of neuropsychological tests developed to examine specific components of cognition. Previous studies document the role of frontal cortex in performance of two CANTAB subtests: the Stockings of Cambridge, a planning task, and the Intradimensional/Extradimensional Shift task, a measure of cognitive set shifting. To examine the integrity of frontal functions, these subtests were administered to 79 participants with autism and 70 typical controls recruited from seven universities who are part of the Collaborative Programs of Excellence in Autism network. The two groups were matched on age, sex, and fullscale IQ. Significant group differences were found in performance on both subtests, with the autism group showing deficits in planning efficiency and extradimensional shifting relative to controls. Deficits were found in both lower- and higher-IQ individuals with autism across the age range of 6 to 47 years. Impairment on the CANTAB executive function subtests did not predict autism severity or specific autism symptoms (as measured by the ADI-R and ADOS), but it was correlated with adaptive behavior. If these CANTAB subtests do indeed measure prefrontal function, as suggested by previous research with animals and lesion patients, this adds to the accumulating evidence of frontal involvement in autism and indicates that this brain region should remain an active area of investigation.
Four genes have recently been proposed as candidates for dyslexia: dyslexia susceptibility 1 candidate 1 (
DYX1C1), roundabout
Drosophila homolog 1 (
ROBO1), doublecortin domain-containing protein 2 ...(
DCDC2) and
KIAA0319. Each gene is implicated in global brain-development processes such as neural migration and axonal guidance, with the exception of
DYX1C1, the function of which is still unknown. The most immediate clinical prospect of the discovery of these genes is the possibility of early identification of dyslexia via genetic screening. However, research efforts have yet to identify a functional mutation in any of these genes. When causal variants are identified, they will need to be considered within a multifactorial framework, which is likely to involve gene–gene and gene–environment interactions, to make accurate predictions of diagnostic status.
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