Attention deficit hyperactivity disorder (ADHD) and executive functioning in affected and unaffected adolescents and their parents: challenging the endophenotype construct

Socioeconomic disadvantage and parental mood/affective problems links negative parenting and executive dysfunction in children born very preterm

Poverty increases the risk of poorer executive function (EF) in children born full-term (FT). Stressors associated with poverty, including variability in parenting behavior, may explain links between poverty and poorer EF, but this remains unclear for children born very preterm (VPT). We examine socioeconomic and parental psychosocial adversity on parenting behavior, and whether these factors independently or jointly influence EF in children born VPT. At age five years, 154 children (VPT = 88, FT = 66) completed parent-child interaction and EF tasks. Parental sensitivity, intrusiveness, cognitive stimulation, and positive and negative regard were coded with the Parent-Child Interaction Rating Scale. Socioeconomic adversity spanned maternal demographic stressors, Income-to-Needs ratio, and Area Deprivation Index. Parents completed measures of depression, anxiety, inattention/hyperactivity, parenting stress, and social-communication interaction (SCI) problems. Parental SCI problems were associated with parenting behavior in parents of children born VPT, whereas socioeconomic adversity was significant in parents of FT children. Negative parenting behaviors, but not positive parenting behaviors, were related to child EF. This association was explained by parental depression/anxiety symptoms and socioeconomic adversity. Results persisted after adjustment for parent and child IQ. Findings may inform research on dyadic interventions that embed treatment for parental mood/affective symptoms and SCI problems to improve childhood EF.

Neuroanatomical markers of familial risk in adolescents with conduct disorder and their unaffected relatives

BACKGROUND

Previous studies have reported brain structure abnormalities in conduct disorder (CD), but it is unclear whether these neuroanatomical alterations mediate the effects of familial (genetic and environmental) risk for CD. We investigated brain structure in adolescents with CD and their unaffected relatives (URs) to identify neuroanatomical markers of familial risk for CD.

METHODS

Forty-one adolescents with CD, 24 URs of CD probands, and 38 healthy controls (aged 12-18), underwent structural magnetic resonance imaging. We performed surface-based morphometry analyses, testing for group differences in cortical volume, thickness, surface area, and folding. We also assessed the volume of key subcortical structures.

RESULTS

The CD and UR groups both displayed structural alterations (lower surface area and folding) in left inferior parietal cortex compared with controls. In contrast, CD participants showed lower insula and pars opercularis volume than controls, and lower surface area and folding in these regions than controls and URs. The URs showed greater folding in rostral anterior cingulate and inferior temporal cortex than controls and greater medial orbitofrontal folding than CD participants. The surface area and volume differences were not significant when controlling for attention-deficit/hyperactivity disorder comorbidity. There were no group differences in subcortical volumes.

CONCLUSIONS

These findings suggest that alterations in inferior parietal cortical structure partly mediate the effects of familial risk for CD. These structural changes merit investigation as candidate endophenotypes for CD. Neuroanatomical changes in medial orbitofrontal and anterior cingulate cortex differentiated between URs and the other groups, potentially reflecting neural mechanisms of resilience to CD.

An Exploration of Sleep and Family Factors in Young Children at Familial Risk for ADHD

Objective: The aim of the current study was to examine relations between sleep problems and family factors and early markers of ADHD in young children with and without a familial risk for ADHD.Methods: Differences in sleep behavior and family functioning in children under 6 years with (n = 72) and without (n = 139) a familial risk for ADHD were investigated. The influence of family and sleep factors on the development of early temperament markers of ADHD (effortful control and negative affect) was explored. Parents/caregivers completed questionnaires on family functioning, child sleep behavior, and general regulatory behaviors.Results: A significant difference was observed between high-risk and low-risk groups for family functioning in the infant/toddler (<3 years) and preschool (>3 years) cohorts. Parents of infants/toddlers in the high-risk group reported poorer infant sleep. However, there were no sleep differences reported for the preschool cohort. Family functioning was found to predict effortful control, while sleep quality predicted negative affect.Conclusion: The results of this study highlight potential family and sleep issues for young children with a familial history of ADHD and the potential influence of these factors on early temperament markers of ADHD. Future research should explore these relations further in order to better establish whether early sleep and family interventions could mitigate later ADHD symptomatology.

Increased Risk of Traumatic Injuries Among Parents of Children with Attention Deficit/Hyperactivity Disorder: A Nationwide Population-Based Study

Children with attention deficit/hyperactivity disorder (ADHD) are vulnerable to traumatic injuries. Parents of children with ADHD experience undesirable impacts more frequently than parents of children without ADHD. The aim of this study was to evaluate whether traumatic injuries are more prevalent in parents of children with ADHD than in parents of children without ADHD. We compared the prevalence of traumatic injuries between parents of children with and without ADHD by using data from the Taiwan Maternal and Child Health Database from 2004 to 2017. The Cox proportional-hazards regression model was used to examine differences in burn injury, fracture, and traumatic brain injury between parents of children with and without ADHD after adjustment for age, urbanicity, and income level. In total, 81,401 fathers and 87,549 mothers who had at least one offspring with ADHD and 1,646,100 fathers and 1,730,941 mothers with no offspring with ADHD were included in the analysis. The results indicated that both fathers and mothers of children with ADHD had higher risks of burn injury, fracture, and traumatic brain injury than fathers and mothers of children without ADHD. Mothers of children with ADHD had higher risks for all kinds of traumatic events than fathers of children with ADHD.

Parent Psychopathology and Neurocognitive Functioning in Children With ADHD

Objective: The objective of this study was to examine the association between parent mental health (ADHD and depression) and offspring performance on neurocognitive tasks in children with ADHD. Method: The clinical sample consisted of 570 children (85% males, mean age: 10.77 years) with ADHD who completed neurocognitive tasks measuring working memory, attention set-shifting, and motivational deficits. Questionnaire measures were used to assess ADHD and depression symptom presence in parents. Results: Controlling for ADHD severity, children of parents with ADHD had poorer working memory (B = -0.25, 95% confidence interval [CI] [-0.45, -0.07], p = .01) and increased errors on the extra dimensional shift stage of the set-shifting task (B = 0.26 95% CI [0.02, 0.50], p = .04). Parent depression was not associated with offspring performance on any of the assessed neurocognitive tasks. Conclusion: Children with ADHD who have a parent with ADHD symptom presence are a subgroup of children who may have additional neurocognitive impairments that have potential implications when implementing interventions that target cognition and learning.

A Twin Study of Inhibitory Control at Age Two and ADHD Behavior Problems at Age Three

Low levels of childhood inhibitory control (IC) are phenotypically and genetically associated with externalizing behavior problems and attention deficit hyperactivity disorder (ADHD). Unfortunately, there is little research on this topic in early childhood, when IC first emerges. This investigation extends the previous findings of contemporaneous genetic covariance between parent-rated and laboratory-assessed IC and ADHD at age 2 by examining longitudinal links between IC at age two and ADHD behavior problems at age three in a sample of 314 same-sex twin pairs (145 monozygotic or MZ, 169 dizygotic or DZ). There were significant phenotypic associations between both parent and laboratory IC assessments at age two and later ADHD behavioral problems (correlations ranged from - .15 to - .44). In our model-fitting strategy, we included measures of ADHD and IC at age 2 as predictors of ADHD at age 3. Longitudinal genetic analyses showed that phenotypic covariance between age two IC and ADHD behavior problems one year later were explained by overlapping genetic variance (genetic correlations ranged from - .28 to - .60). However, these effects were not unique to IC and reflect variance shared with ADHD at age 2. Parent-rated IC at age two showed higher phenotypic and genetic covariance with ADHD at age three than lab ratings of IC at age two. This is the first investigation examining genetic covariance between parent and lab-based IC at age two and ADHD behavior problems at age three. Findings show that after accounting for co-occurring ADHD, early temperamental IC is not a unique genetic risk factor for later ADHD.

Dopamine transporter genotype modulates brain activity during a working memory task in children with ADHD

Dopamine active transporter gene (DAT1) is a candidate gene associated with attention-deficit/hyperactivity disorder (ADHD). The DAT1 variable number tandem repeat (VNTR)-3' polymorphism is functional and 9R carriers have been shown to produce more DAT than 10R homozygotes. We used functional magnetic resonance imaging (fMRI) to investigate the effects of this polymorphism on the neural substrates of working memory (WM) in a small but selected population of children with ADHD, naïve of any psychotropic treatment and without comorbidity. MRI and genotype data were obtained for 36 children (mean age: 10,36 +/- 1,49 years) with combined-type ADHD (9R n = 15) and 25 typically developing children (TDC) (mean age: 9,55 +/- 1,25 years) (9R n = 12). WM performance was similar between conditions. We found a cross-over interaction effect between gene (9R vs. 10R) and diagnosis (TDC vs. ADHD) in the orbito-frontal gyrus, cerebellum and inferior temporal lobe. In these areas, WM-related activity was higher for 9R carriers in ADHD subjects and lower in TDC. In ADHD children only, 10R homozygotes exhibited higher WM-related activity than 9R carriers in a network encompassing the parietal and the temporal lobes, the ventral visual cortex, the orbito-frontal gyrus and the head of the caudate nucleus. There was no significant results in TDC group. Our preliminary findings suggest that DAT1 VNTR polymorphism can modulate WM-related brain activity ADHD children.

Parenting Stress and Broader Phenotype in Parents of Children with Attention Deficit Hyperactivity Disorder, Dyslexia or Typical Development

In the present study parenting stress and the broader phenotype are investigated in two highly common developmental disorders, namely Attention Deficit Hyperactivity Disorder (ADHD) and specific reading impairment (dyslexia). Within a total sample of 130 parents, 27 were parents of children with ADHD (P-ADHD), 38 were parents of children with a diagnosis of dyslexia (P-DYS) and the other 65 participants were parents of children with typical development (P-TD). A battery of cognitive tasks was administered which included verbal and non-verbal Intellectual Quotient (IQ), reading speed (passage and nonwords), verbal fluency and the Attention Network Task (ANT). Reading history, symptoms of ADHD in adults and parenting stress were measured through questionnaires. Group differences evidenced that the P-DYS group had lower scores in the reading tasks, in the verbal fluency task and in the reading history questionnaire. Conversely, the P-ADHD group had more transversal cognitive weaknesses (IQ, reading tasks, verbal fluency) and the highest scores in parenting stress and ADHD symptoms, together with poor reading history. The groups did not differ in the ANT task. Parenting stress was predicted, on the whole sample, by lower socioeconomic status (SES) and number of family members and higher ADHD symptoms. Implications for research and clinical settings are discussed.

Working Memory and Vigilance as Multivariate Endophenotypes Related to Common Genetic Risk for Attention-Deficit/Hyperactivity Disorder

OBJECTIVE

Understanding the role of endophenotypes is essential for process models of psychopathology. This study examined which candidate cognitive endophenotypes statistically mediate common variant genetic risk for attention-deficit/hyperactivity disorder (ADHD).

METHOD

A case-control design using community-recruited volunteer children 7 to 11 years of age (n = 656, n = 435 ADHD), of whom 514 were of homogenous European ancestry for the primary models (n = 337 ADHD, 177 non-ADHD). Children were assessed with a multi-informant, best-estimate diagnostic procedure and laboratory measures of working memory, response inhibition, executive functioning, arousal/attention, temporal information processing, and processing speed. Latent variables were created for the candidate cognitive measures and for parent- and teacher-rated ADHD dimensions. Polygenic risk scores (PGS) were computed using a discovery sample of 20,183 individuals with ADHD and 35,191 controls from the Psychiatric Genetics Consortium. Cognitive measures that survived multiple testing correction for association with the PGS were evaluated for mediation with ADHD using structural equation models.

RESULTS

Results were essentially identical in the homogeneous European ancestry subgroup (n = 514) and in the full sample (N = 656). For the European population, the PGS was associated with ADHD diagnosis (Nagelkerke R2 = 0.045; β = 0.233, SE = 0.053, p = .000011) and multi-indicator dimensional ADHD latent variables by parent report (β = 0.185, SE = 0.043) and teacher report (β = 0.165, SE = 0.042). The PGS effect was statistically mediated by working memory (indirect effect, β = 0.101, SE = 0.029, 95% CI = 0.05, 0.16, p = .00049, 43% of genetic effect accounted for) and arousal/alertness (indirect effect β = 0.115, 95% CI = 0.04, 0.20, SE = 0.041, p = .005, 49% of genetic effect accounted for).

CONCLUSION

This is the first clear demonstration from molecular genetic data that working memory and arousal regulation are promising cognitive endophenotypes for ADHD with regard to mediating genetic risk from common genetic variants.

Cognitive Functioning in Adolescents with Self-Reported ADHD and Depression: Results from a Population-Based Study

This study aims to assess cognitive functioning differences among adolescents with retrospectively self-reported: ADHD and an onset of depression, only ADHD, only depression, and neither ADHD nor depression. Data from the Tracking Adolescents’ Individual Lives Survey (TRAILS) cohort was used in this study. Neuropsychological functioning was assessed in 1549 adolescents, at baseline and follow-up (mean ages 11 and 19 years). The Composite International Diagnostic Interview was used to classify adolescents into 4 groups: ADHD with onset of depression, only ADHD, only depression, and neither ADHD nor depression. Linear mixed effects models were used to analyse group differences in cognitive functioning at baseline and follow-up, and the change in cognitive functioning between these 2 time-points. Results showed a significant main effect of group on response time variability at baseline, working memory maintenance at follow up, and change in response time variability scores between baseline and follow-up. As compared to the healthy and depressed-only groups, adolescents with only ADHD showed longer response time variability at baseline and, which declined between baseline and follow-up. Adolescents with ADHD plus depression showed higher reaction time for working memory maintenance than the depressed only and healthy groups at follow-up. In conclusion, adolescents with self-reported ADHD show poorer cognitive functioning than healthy adolescents and those with only depression. Amongst adolescents with ADHD, specific cognitive domains show poor functioning depending on the presence or absence of comorbid depression. While adolescents with only ADHD have lower reaction time variability, those with comorbid depression have poorer working memory maintenance.

Changing ASD-ADHD symptom co-occurrence across the lifespan with adolescence as crucial time window: Illustrating the need to go beyond childhood

Literature on the co-occurrence between Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) is strongly biased by a focus on childhood age. A review of the adolescent and adult literature was made on core and related symptoms of ADHD and ASD. In addition, an empirical approach was used including 17,173 ASD-ADHD symptom ratings from participants aged 0 to 84 years. Results indicate that ASD/ADHD constellations peak during adolescence and are lower in early childhood and old age. We hypothesize that on the border of the expected transition to independent adulthood, ASD and ADHD co-occur most because social adaptation and EF skills matter most. Lower correlations in childhood and older age may be due to more diffuse symptoms reflecting respectively still differentiating and de-differentiating EF functions. We plea for a strong research focus in adolescence which may -after early childhood- be a second crucial time window for catching-up pattern explaining more optimal outcomes. We discuss obstacles and oppportunities of a full lifespan approach into old age.

Neuropsychological performance measures as intermediate phenotypes for attention-deficit/hyperactivity disorder: A multiple mediation analysis

Genetic influences on dopaminergic neurotransmission have been implicated in attention-deficit hyperactivity disorder (ADHD) and are theorized to impact cognitive functioning via alterations in frontal-striatal circuitry. Neuropsychological functioning has been proposed to account for the potential associations between dopamine candidate genes and ADHD. However, to date, this mediation hypothesis has not been directly tested. Participants were 498 youth ages 6-17 years (mean M = 10.8 years, SD = 2.4 years, 55.0% male). All youth completed a multistage, multiple-informant assessment procedure to identify ADHD and non-ADHD cases, as well as a comprehensive neuropsychological battery. Youth provided a saliva sample for DNA analyses; the 480 base pair variable number of tandem repeat polymorphism of the dopamine active transporter 1 gene (DAT1) and the 120 base pair promoter polymorphism of the dopamine receptor D4 gene (DRD4) were genotyped. Multiple mediation analysis revealed significant indirect associations between DAT1 genotype and inattention, hyperactivity-impulsivity, and oppositionality, with specific indirect effects through response inhibition. The results highlight the role of neurocognitive task performance, particularly response inhibition, as a potential intermediate phenotype for ADHD, further elucidating the relationship between genetic polymorphisms and externalizing psychopathology.

Gently restless: association of ADHD-like traits with response inhibition and interference control

Impairment of inhibition-related functions is one of the most pronounced cognitive deficits found in attention-deficit/hyperactivity disorder (ADHD). Compelling evidence from studies of unaffected relatives of patients with ADHD and of ADHD-like traits in healthy subjects suggest the continuous distribution of ADHD symptoms in the population. A more subtle inhibitory deficit can also be found in healthy relatives of patients and in subjects with high ADHD-like traits. Here, we examined the relationship between inhibitory performance and ADHD-like traits, for the first time, in a large sample of healthy adults by applying multiple, widely used tests of inhibition-related functions. ADHD-like traits, in general, were independently predicted by Stroop interference score and, at trend level, by go/no-go commission error rate while controlling for socio-demographic factors, verbal intelligence and neuroticism. Additionally, higher inattentive traits were related to worse Stroop performance at trend level, and higher hyperactive/impulsive traits were significantly associated with more go/no-go commission errors. ADHD-like traits were strongly related to neuroticism. The study shows that individual differences in ADHD-like traits are related to variance in fundamental inhibition-related functions over and above effects of negative affect regulation, but the relationships tend to be small. The results suggest the quasi-dimensionality of ADHD and raise further questions about the relationship between genetic factors and the deficit of inhibition-related functions in the ADHD spectrum.

Moderators of neuropsychological mechanism in attention-deficit hyperactivity disorder

Neuropsychological measures have been proposed as both a way to tap mechanisms and as endophenotypes for child ADHD. However, substantial evidence supporting heterogeneity in neuropsychological performance among youth with ADHD as well as apparent effect differences by sex, age, and comorbidity have slowed progress. To address this, it is important to understand sibling effects in relation to these moderators. 461 youth ages 6-17 years (54.8 % male, including 251 youth with ADHD, 107 of their unaffected biological siblings, and 103 non-ADHD controls) completed diagnostic interviews and a theoretically informed battery of neuropsychological functioning. A structural equation model was used to consolidate neuropsychological domains. Group differences between unaffected siblings of youth with ADHD and controls across each domain were first examined as the primary endophenotype test for ADHD. Moderation of these effects was evaluated via investigation of interactions between diagnostic group and both proband and individual level characteristics, including sex, age, and comorbidity status. Unaffected siblings performed worse than control youth in the domains of inhibition, response time variability, and temporal information processing. Individual age moderated these effects, such that differences between controls and unaffected siblings were pronounced among younger children (ages 6-10 years) but absent among older youth (ages 11-17 years). Evidence for moderation of effects by proband sex and comorbidity status produced more variable and smaller effects. Results support the utility of inhibition, response time variability, and temporal processing as useful endophenotypes for ADHD in future genetic associations studies of the disorder, but suggest this value will vary by age among unaffected family members.

The role of age in association analyses of ADHD and related neurocognitive functioning: A proof of concept for dopaminergic and serotonergic genes

Elucidating genetic mechanisms involved in Attention-Deficit/Hyperactivity Disorder (ADHD) has been challenging. Relatively unexplored is the fact that genetic mechanisms can differ with age. The current study explored the association between dopaminergic and serotonergic genes, ADHD symptoms, and neurocognitive functioning in relation to age. Associations of three genetic ADHD risk factors, DAT1, DRD4, and 5-HTT with symptoms and six neurocognitive measures were explored in two samples of the NeuroIMAGE study: 756 children, adolescents, and young adults with ADHD, their siblings, and controls (M age 17 years, SD 3.2), and 393 parents with and without ADHD (M age 48 years, SD 4.8). Association analyses were performed in both samples, and effects were compared to address dichotomous age effects. Gene*age interactions were examined to address continuous age effects. Moderating effects of age were found for DRD4-7R carriership and ADHD symptoms in the adult group only; in the adolescents the 5-HTT LL genotype was differentially associated with inhibition and with motor timing at different ages, and to inhibition in adults; DAT1 10-6 haplotype carriership showed differential working memory performance depending on age. None of our effects survived correction for multiple comparisons. Our results are preliminary, but may point to differential genotype-phenotype associations at different ages. This can be seen as a proof of concept for the importance of age in dopaminergic and serotonergic genetic association analyses. Our findings are consistent with the idea that genetic and neurocognitive mechanisms underlying ADHD may change throughout life. © 2015 Wiley Periodicals, Inc.

Using Sibling Designs to Understand Neurodevelopmental Disorders: From Genes and Environments to Prevention Programming

Neurodevelopmental disorders represent a broad class of childhood neurological conditions that have a significant bearing on the wellbeing of children, families, and communities. In this review, we draw on evidence from two common and widely studied neurodevelopmental disorders-autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD)-to demonstrate the utility of genetically informed sibling designs in uncovering the nature and pathogenesis of these conditions. Specifically, we examine how twin, recurrence risk, and infant prospective tracking studies have contributed to our understanding of genetic and environmental liabilities towards neurodevelopmental morbidity through their impact on neurocognitive processes and structural/functional neuroanatomy. It is suggested that the siblings of children with ASD and ADHD are at risk not only of clinically elevated problems in these areas, but also of subthreshold symptoms and/or subtle impairments in various neurocognitive skills and other domains of psychosocial health. Finally, we close with a discussion on the practical relevance of sibling designs and how these might be used in the service of early screening, prevention, and intervention efforts that aim to alleviate the negative downstream consequences associated with disorders of neurodevelopment.

Neurocognitive predictors of substance use disorders and nicotine dependence in ADHD probands, their unaffected siblings, and controls: a 4-year prospective follow-up

BACKGROUND

Attention-Deficit/Hyperactivity Disorder (ADHD) is a risk factor for substance use disorders (SUDs) and nicotine dependence (ND). Neurocognitive deficits may predict the increased risk of developing SUDs and nicotine dependence.

METHODS

This study comprised three groups derived from the Dutch part of the International Multicenter ADHD Genetics (IMAGE) study: ADHD probands (n = 294), unaffected siblings (n = 161), and controls (n = 214). At baseline (age = 12.2), a range of neurocognitive functions was assessed including executive functions (inhibition, working memory, timing), measures of motor functioning (motor timing and tracking) and IQ. After a mean follow-up of 4.2 years, SUDs and ND were assessed.

RESULTS

None of the neurocognitive functions predicted later SUDs or ND in ADHD probands, even after controlling for medication use and conduct disorder. Slower response inhibition predicted later nicotine dependence in unaffected siblings (OR = 2.06, 95% CI = 1.22-3.48), and lower IQ predicted increased risk for SUDs in controls (OR = 1.96, 95% CI = 1.12-3.44).

CONCLUSIONS

Cold executive functions, motor functioning, and IQ did not predict the elevated risk of SUDs and ND in ADHD. Future studies should target 'hot' executive functions such as reward processing as risk factors for SUDs or ND.

Inhibitory control and delay aversion in unaffected preschoolers with a positive family history of attention deficit hyperactivity disorder

BACKGROUND

From current theories on the etiology of attention deficit hyperactivity disorder (ADHD), it can be inferred that delay aversion (DA) and deficits in inhibitory control (IC) constitute basic deficits or endophenotypes of the disorder that already occur in the preschool period. This implies an occurrence of the characteristics in unaffected preschoolers with a positive family history of ADHD. Thus, it is hypothesized that preschoolers who are not affected by ADHD but who have first-degree relatives who suffer, or have suffered, from ADHD show deficits in IC and heightened DA in comparison to preschoolers from the general population.

METHODS

Thirty unaffected preschoolers with a positive family history of ADHD were compared with 30 control children matched with respect to age in months, gender, intelligence, and maternal education level. The groups also did not differ in terms of maternal depressive symptoms and the number of psychosocial family risks. A set of age-appropriate neuropsychological tasks on executive IC (e.g. Puppet Says, Day-Night, relying on Go-NoGo and interference paradigms) and DA (e.g. Snack Delay, Gift Wrap, relying on delay of gratification paradigm) was conducted.

RESULTS

Unaffected preschoolers showed significantly higher DA than control children (t(29) = -2.57, p < .008). The result did not change when subclinical ADHD symptoms and symptoms of oppositional defiant disorder were controlled for (F(1,29) = 5.21, p < .031). Differences in IC did not reach statistical significance.

CONCLUSION

The results are compatible with the assumption that DA constitutes a familial vulnerability marker that can be validly assessed in the preschool period. As this is the first study to address this issue in preschoolers, more research is needed to confirm and further analyze the significance of DA assessments specifically at this developmental stage.

Attention-deficit/hyperactivity disorder (ADHD) and motor timing in adolescents and their parents: familial characteristics of reaction time variability vary with age

OBJECTIVE

There is consistent evidence that attention-deficit/hyperactivity disorder (ADHD) is strongly related to impaired motor timing as reflected in decreased accuracy and increased reaction time variability (RTV). It is not known whether motor timing impairments are present in adolescents and adults with ADHD and their unaffected relatives to the same extent as has been reported in children, and whether ADHD and motor timing share familial underpinnings, as reflected in parent-offspring co-segregation and sibling cross-correlations.

METHOD

A total of 589 parents and 808 children/adolescents from families with ADHD and control families (parent/offspring average age: 48.6/17.3 years) were included. All participants were thoroughly assessed for ADHD and performed a 40-trial motor timing task (1-second interval production). Dependent neurocognitive measures included RT median (RTM: representing accuracy), RTV and ex-Gaussian component τ (τ: representing infrequent long response times). Generalized estimating equations were used for analyses.

RESULTS

Unaffected children from families with ADHD had RTV (but not RTM or τ) scores in between those of affected and control children. However, during middle-to-late adolescence, unaffected offspring were not impaired compared to control offspring and differed from ADHD probands, whereas during late adolescence/early adulthood, all offspring groups performed equally. Affected and unaffected parents of families with ADHD showed increased RTV compared to controls, regardless of age (not significant after adjusting for IQ). There were indications for shared familiality between RTV and ADHD as reflected by sibling cross-correlations and between RTM and ADHD as reflected by sibling cross-correlations and a maternal parent-offspring relation (parent-of-origin effect).

CONCLUSIONS

RTV and its familial characteristics are influenced by development during adolescence. Increased RTV in children with ADHD appears to reflect immaturities in their neurocognitive functioning. Maternal ADHD effects might be involved in transmission of RTM (not RTV), but overall RTM showed less compelling (familial) relationships with ADHD than RTV.