Studies have found negative associations between socioeconomic position and attention deficit/hyperactivity disorder (ADHD), but it remains unclear if this association is causal. The aim of this study was to determine the extent to which the association between family income in early childhood and subsequent ADHD depends on measured and unmeasured selection factors.
A total of 811,803 individuals born in Sweden between 1992 and 2000 were included in this nationwide population-based cohort study. Diagnosis of ADHD was assessed via the Swedish national Patient Register and the Swedish Prescribed Drug Register. Annual family income during offspring's first 5 years in life was collected prospectively from the Swedish Integrated Database for Labour Market Research and divided into quartiles by (lower) family disposable income. We predicted ADHD from family income while controlling for covariates and also comparing differently exposed cousins and siblings to control for unmeasured familial confounding.
The crude analyses suggested that children exposed to lower income levels were at increased risk for ADHD (HRQuartile1 = 2.52; 95% CI, 2.42–2.63; HRQuartile2 = 1.52; 95% CI, 1.45–1.58; HRQuartile3 = 1.20; 95% CI, 1.14–1.15). This dose-dependent association decreased after adjustment for measured covariates (HRQuartile1 = 2.09; 95% CI, 2.00–2.19; HRQuartile2 = 1.36; 95% CI, 1.30–1.42; HRQuartile3 = 1.13; 95% CI, 1.08–1.18). Although the association was attenuated in cousin comparisons (HRQuartile1 = 1.61; 95% CI, 1.40–1.84; HRQuartile2 = 1.28; 95% CI, 1.12–1.45; HRQuartile3 = 1.14; 95% CI, 1.01–1.28) and sibling comparison models (HRQuartile1 = 1.37; 95% CI, 1.07–1.75; HRQuartile2 = 1.37; 95% CI, 1.12–1.68; HRQuartile3 = 1.23; 95% CI, 1.04–1.45), it remained statistically significant across all levels of decreased disposable family income.
Our results indicated that low family income in early childhood was associated with increased likelihood of ADHD. The link remained even after controlling for unmeasured selection factors, highlighting family income in early childhood as a marker of causal factors for ADHD.
"parenting behavior and parent depression, Tung et al., 2014] and environmental [i.e. media use, Nikkelen et al., 2014 and family income, Larsson et al., 2014] factors mediate the link between genetic variation and ADHD symptoms. The integration of all these factors in one viable model of ADHD is the ultimate goal, but lies beyond the scope of this study, addressing the various factors previously associated with ADHD symptoms. "
[Show abstract][Hide abstract] ABSTRACT: Fear of strangers is a developmental milestone in childhood that encompasses behavioral inhibition and decreased novelty seeking. Children with attention deficit/hyperactivity disorder (ADHD) often exhibit fearless and impulsive behaviors, similar to those observed in children with atypically low levels of stranger fear. It is currently unknown whether these behaviors share common underlying biological mechanisms. Polymorphisms in the dopamine receptor 4 gene (DRD4) have been implicated in the risk for developing ADHD symptoms in childhood. Here we investigate whether (1) DRD4 variable number tandem repeats (VNTRs) are associated with both stranger fear and ADHD symptoms, and (2) stranger fear in preschoolers mediates the link between DRD4 VNTRs and ADHD in later childhood. Stranger fear was observed in a large sample (N=589) of 3-year-old Caucasian children and ADHD symptoms were assessed by a validated, mother-rated questionnaire at 6 years. We found evidence that longer DRD4 variants were associated with increased ADHD symptoms at 6 years, and that this relationship was partially mediated by lower levels of observed stranger fear at 3 years. Our results suggest a common underlying neurobiological mechanism in the association between low stranger fear and ADHD symptoms; variation in DRD4 may be an important contributor to this mechanism.
Psychiatry Research 09/2014; 220(3). DOI:10.1016/j.psychres.2014.09.004 · 2.47 Impact Factor
"Despite the prominence of the developmental psychopathology perspective, the social context of ADHD is surprisingly neglected today. Both Russell et al. (this issue, 2014) and Larsson et al. (this issue, 2014) take strides toward remedying this state of affairs. Both studies relied on population-wide surveys. "
[Show abstract][Hide abstract] ABSTRACT: In the 1950's, many experts believed hyperkinesis was a neurotic reaction to inner conflicts arising from early family experiences. In the 1990's, many experts believed ADHD to be ‘genetic’ (without a mechanistic explanation of what that meant). Both views appear naïve today in a scientific world grappling with the complexity of highly plastic gene expression, gene x environment interplay, and epigenetic, context-dependent emergence of psychopathology. Both views also fail to account for the uncomfortable fact that ADHD is also associated with social disadvantage – a level of analysis required in a developmental psychopathology approach. That developmental psychopathology approach, pioneered a generation ago, initially emphasized the accumulation of risk and protective factors, and emerged in a contemporary systemic approach that seeks to determine whether it is risk accumulation (e.g., allostatic load) or specific risk factors (e.g., family process) that mechanistically shape psychopathology. Despite the prominence of the developmental psychopathology perspective, the social context of ADHD is surprisingly neglected today. Both Russell et al. (this issue, 2014) and Larsson et al. (this issue, 2014) take strides toward remedying this state of affairs.
Journal of Child Psychology and Psychiatry 05/2014; 55(5). DOI:10.1111/jcpp.12237 · 6.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Importance
The prevention of suicidal behavior is one of the most important tasks for mental health clinicians. Although a few studies have indicated an increased risk of suicidal behavior among individuals with attention-deficit/hyperactivity disorder, the development of more effective ways of identifying and modifying the risk is hampered by our limited understanding of the underlying mechanisms for this association.Objective
To explore whether attention-deficit/hyperactivity disorder and suicidal behavior share genetic and environmental risk factors.Design, Setting, and Participants
Matched cohort design across different levels of family relatedness recorded from January 1, 1987, to December 31, 2009. We identified 51 707 patients with attention-deficit/hyperactivity disorder (through patient and prescribed drug registers) in Sweden and their relatives by linking longitudinal population-based registers. Control participants were matched 1:5 on sex and birth year.Main Outcomes and Measures
Any record of suicide attempt or completed suicide defined by discharge diagnoses of the International Classification of Diseases.Results
Individuals with attention-deficit/hyperactivity disorder (probands) had increased risks of attempted and completed suicide, even after adjusting for comorbid psychiatric disorders (odds ratio [OR] = 3.62 [95% CI, 3.29-3.98] and 5.91 [95% CI, 2.45-14.27], respectively). The highest familial risk was observed among first-degree relatives (attempted suicide: OR = 2.42 [95% CI, 2.36-2.49] among parents of probands with ADHD and OR = 2.28 [95% CI, 2.17-2.40] among full siblings of probands with ADHD; completed suicide: OR = 2.24 [95% CI, 2.06-2.43] and OR = 2.23 [1.83-2.73], respectively), whereas the risk was considerably lower among more genetically distant relatives (attempted suicide: OR = 1.59 [95% CI, 1.47-1.73] among maternal half siblings, OR = 1.57 [95% CI, 1.45-1.70] among paternal half siblings, and OR = 1.39 [95% CI, 1.35-1.43] among cousins; completed suicide: OR = 1.51 [95% CI, 1.08-2.10], OR = 2.02 [95% CI, 1.47-2.79], and OR = 1.51 [95% CI, 1.36-1.67], respectively). These familial aggregation patterns remained similar across sex, after excluding relatives with attention-deficit/hyperactivity disorder and probands with suicidal behavior, and after excluding probands and relatives with severe comorbid disorders.Conclusions and Relevance
Attention-deficit/hyperactivity disorder is associated with an increased risk of both attempted and completed suicide. The pattern of familial risks across different levels of relatedness suggests that shared genetic factors are important for this association. This is an important first step toward identifying the underlying mechanisms for the risk of suicidal behavior in patients with attention-deficit/hyperactivity disorder and suggests that individuals with attention-deficit/hyperactivity disorder and their family members are important targets for suicide prevention and treatment.
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