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Meta-Analysis of Alzheimer's Disease Risk with Obesity, Diabetes, and Related DisordersBackground: Late-onset Alzheimer’s disease (AD) is a multifactorial and heterogeneous disorder with major risk factors including advanced age, presence of an apolipoprotein E 4 (APOE4) allele, and family history of AD. Other risk factors may be obesity and diabetes and related disorders, which are highly prevalent. Methods: We reviewed longitudinal epidemiological studies of body mass, diabetes, metabolic syndrome, and glucose and insulin levels on risk for AD. We conducted meta-analyses of the results from these studies. Results: For obesity assessed by body mass index, the pooled effect size for AD was 1.59 (95% confidence interval [CI] 1.02–2.5; z 2.0; p .042), and for diabetes, the pooled effect size for AD was 1.54 (95% CI 1.33–1.79; z 5.7; p .001). Egger’s test did not find significant evidence for publication bias in the meta-analysis for obesity (t 1.4, p .21) or for diabetes (t .86, p .42). Since these disorders are highly comorbid, we conducted a meta-analysis combining all studies of obesity, diabetes, and abnormal glucose or insulin levels, which yielded a highly significant pooled effect size for AD of 1.63 (95% CI 1.39 –1.92; z 5.9; p .001). Conclusions: Obesity and diabetes significantly and independently increase risk for AD. Though the level of risk is less than that with the APOE4 allele, the high prevalence of these disorders may result in substantial increases in future incidence of AD. Physiological changes common to obesity and diabetes plausibly promote AD.
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RASD2, MYH9, and CACNG2 Genes at Chromosome 22q12 Associated with the Subgroup of Schizophrenia with Non-Deficit in Sustained Attention and Executive FunctionBackground: In a previous linkage study of schizophrenia that included Taiwanese samples, the marker D22S278 (22q12.3) was significantly linked to schizophrenia (p .001). Methods: We conducted fine mapping of the implicated genomic region, with 47 validated single nucleotide polymorphism (SNP) markers around 1 Mb of D22S278, in a Taiwanese sample of 218 pedigrees with at least 2 siblings affected with schizophrenia. We examined the association of these SNPs and their haplotypes with schizophrenia and with subgroups defined by the presence and absence of deficits in sustained attention as assessed by undegraded and degraded continuous performance tests (CPTs). We also examined subgroups defined by deficits in categories achieved in the Wisconsin Card Sort Test (WCST). Results: Three of five candidate vulnerability genes (RASD2, APOL5, MYH9, EIF3S7, and CACNG2), which had marginally significant associations with schizophrenia, had significant associations with schizophrenic patients who did not have deficits in sustained attention on the undegraded CPT (RASD2 gene SNP rs736212; p .0008 with single locus analysis) and the degraded CPT (MYH9 gene haplotype 1-1-1-1 of SNP rs3752463 - rs1557540 - rs713839 - rs739097; p .0059 with haplotype analysis). We also found a significant association for patients who showed no deficits in executive function as measured by categories achieved in the WCST (CACNG2 gene haplotype 2-1-1-1 of SNP rs2267360 - rs140526 - rs1883987 - rs916269; p .0163 with haplotype analysis). Conclusions: The genes RASD2, MYH9, and CACNG2 might be vulnerability genes for neuropsychologically defined subgroups of schizophrenic patients.
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Advanced Paternal Age and Early Onset of Schizophrenia in Sporadic Cases: Not Confounded by Parental Polygenic Risk for SchizophreniaBACKGROUND:Whether paternal age effect on schizophrenia is a causation or just an association due to con-founding by selection into late parenthood is still debated. We investigated the association between paternal age andearly onset of schizophrenia in offspring, controlling for both paternal and maternal predisposition to schizophrenia asempirically estimated using polygenic risk score (PRS) derived from the Psychiatric Genomics Consortium.METHODS:Among 2923 sporadic schizophrenia cases selected from the Schizophrenia Trio Genomic Research inTaiwan project, 1649 had parents’genotyping data. The relationships of paternal schizophrenia PRS to paternal ageatfirst birth (AFB) and of maternal schizophrenia PRS to maternal AFB were examined. A logistic regression model ofpatients’early onset of schizophrenia (#18 years old) on paternal age was conducted.RESULTS:Advanced paternal age over 20 years exhibited a trend of an increasing proportion of early onset ofschizophrenia (odds ratio per 10-year increase in paternal age = 1.28,p= .007) after adjusting for maternal age, sex,and age. Older paternal AFB also exhibited an increasing trend of paternal schizophrenia PRS. Additionally, aU-shaped relationship between maternal AFB and maternal schizophrenia PRS was observed. After adjusting forboth paternal and maternal schizophrenia PRS, the association of paternal age with patients’early onset ofschizophrenia remained (odds ratio = 1.29,p= .04).CONCLUSIONS:The association between paternal age and early onset of schizophrenia was not confounded byparental PRS for schizophrenia, which partially captures parental genetic vulnerability to schizophrenia. Ourfindingssupport an independent role of paternal age per se in increased risk of early onset of schizophrenia in offspring
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A Twin Study of Sexual Behavior in MenThe role of genetic and environmental influences on age of initiation of first sexual relations and engaging in sexual activity with multiple partners (10 or more partners in 1 year) was investigated in male twins (N = 6, 744) from the Vietnam Era Twin Registry. Individual differences in both types of sexual behaviors were heritable, but only age of onset of sexual relations was significantly influenced by the environment shared by the twins. There was a moderate negative correlation between age of initiation of sexual relations and the multiple partners variable; initiating sexual relations earlier was associated with a higher probability of having multiple partners. The additive genetic influence on age of initiation also influenced the multiple partners variable. The substantial unique environmental influences on each variable were uncorrelated with each other. The data suggest that the observed association between age of initiation of sexual relations and having multiple partners is due to genetic influences common to both behaviors.
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Associations Between ADHD and Psychoactive Substance use Disorders:Findings from a Longitudinal Study of High-Risk Siblings of ADHD ChildrenThe purpose of this study was to determine whether the single nucleotide polymorphisms (SNPs) within candidate genes for attention deficit hyperactivity disorder (ADHD) are associated with the age at onset for ADHD. One hundred and forty-three SNPs were genotyped across five candidate genes (DRD5, SLC6A3, HTR1B, SNAP25, DRD4) for ADHD in 229 families with at least one affected offspring. SNPs with the highest estimated power to detect an association with age at onset were selected for each candidate gene, using a power-based screening procedure that does not compromise the nominal significance level. A time-to-onset analysis for family-based samples was performed on these SNPs to determine if an association exists with age at onset for ADHD. Seven consecutive SNPs surrounding the D5 dopamine receptor gene (DRD5), were associated with the age at onset for ADHD; FDR adjusted q-values ranged from 0.008 to 0.023. This analysis indicates that individuals with the risk genotype develop ADHD earlier than individuals with any other genotype. A haplotype analysis across the 6 significant SNPs that were in linkage disequilibrium with one another, CTCATA, was also found to be significant (p-value = 0.02). We did not observe significant associations with age at onset for the other candidate loci tested. Although definitive conclusions await independent replication, these results suggest that a variant in DRD5 may affect age at onset for ADHD
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Further evidence of an association between maternal smoking during pregnancy and attention deficit hyperactivity disorder: Findings from a high-risk sample of siblingsThe authors investigated the relationship between attentiondeficit/byperactivity disorder (ADHD) and cigarette smoking in siblings of ADHD and non-ADHD probands. They conducted a 4-year follow-up of siblings from ADHD and control-group families. In the siblings of ADHD probands, ADHD was associated with higher rates and earlier onset of cigarette smoking. There was also a significant positive association between cigarette smoking and conduct disorder, major depression, and drug abuse in the siblings, even after adjusting for confounding variables. Moreover, smoking was found to be familial among ADHD families but not control-group families. Our findings indicate that ADHD is a risk factor for early initiation of cigarette smoking in the high-risk siblings of ADHD probands
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Substance Use Disorders in High-Risk Adolescent OffspringObjective: To examine the risk for substance use disorders (SUD) in offspring of SUD parents who were not selected due to referral to SUD treatment centers. Method: The original sample was ascertained through two groups of index children: 140 ADHD probands and 120 non-ADHD comparison probands. These groups had 174 and 129 biological siblings and 279 and 240 parents, respectively. Results: We found that: 1) parental SUD was associated with SUD and all SUD subtypes in the offspring; 2) parental alcohol use disorders were associated with alcohol use disorders in the offspring as well as co-occurring alcohol and drug use disorders but not drug use disorders alone in the offspring; and 3) drug use disorders in the parents were associated with drug use disorders but not alcohol use disorders in the offspring. Conclusions: These findings suggest that alcoholism and drug abuse may breed true from parents to their offspring, but further work with larger samples is needed to confirm this idea. Our findings also suggest a possible common diathesis that is expressed as comorbid alcohol and drug use in the offspring of alcoholic parents. If confirmed, these findings may be useful for the development of preventive and early intervention strategies for adolescents at high risk for SUD based on parental history of SUD.
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Characteristics of Adults with Attention Deficit Hyperactivity Disorder Plus Substance Use Disorder: The Role of Psychiatric ComorbidityThe objective of the study was to investigate the characteristics of adults with Attention Deficit Hyperactivity Disorder (ADHD) or substance use disorder (SUD), especially in the context of comorbid psychiatric disorders. Subjects were adults (n ¼ 78) participating in a controlled family study of ADHD and SUD. Four groups were identified based on a diagnosis of ADHD or SUD: ADHD, SUD, ADHDþSUD, and neither ADHD nor SUD. All diagnoses were determined by structured clinical interview for DSM IV. Rates of psychiatric comorbidity were lowest in the controls, intermediate in the ADHD and SUD groups, and highest in the ADHDþSUD group. Relative to controls, the ADHD, SUD, and ADHDþSUD groups had higher rates of major depression (z ¼ 1.98, p ¼ 0.05), conduct disorder (z ¼ 2.0, p ¼ 0.04), antisocial personality disorder (z ¼ 2.6, p ¼ 0.009), agoraphobia (z ¼ 2.5, p ¼ 0.01) and social phobia (z ¼ 2.7, p ¼ 0.007). Higher rates of psychiatric comorbidity, especially mood and anxiety disorders, exist in subjects with SUDþADHD relative to subjects with SUD, ADHD, or controls. Clinicians need to be attentive to other psychiatric disorders that may occur in the large group of adults with ADHDþSUD.
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Influence of Parental SUD and ADHD on ADHD in their Offspring: Preliminary Results from a Pilot-controlled Family StudyAs part of a pilot-controlled family-based study of the children of parents with and without substance use disorders (SUD), the influence of parental SUD and ADHD on the risk for ADHD in offspring was evaluated. Using structured psychiatric interviews, 96 families (183 youth; mean age 11.6 years) were assessed. To evaluate the effect of parental ADHD and SUD, the offspring were stratified into four groups based on parental status: children of parents with neither ADHD nor SUD, children of parents with SUD only, children of parents with ADHD only, and children of parents with both ADHD and SUD. Using generalized estimating equation models, parental SUD and ADHD were used to predict ADHD in the offspring. The rate of children with ADHD increased among children of parents with neither disorder (3%), children of parents with SUD (13%), children of parents with ADHD (25%), and children of parents with both ADHD and SUD (50%) (p ¼ :001). Children of parents with ADHD or ADHD plus SUD were more likely to have ADHD in comparison to children of parents with neither diagnosis (p < 0:05). Children of parents with ADHD plus SUD were at greater risk of ADHD in comparison to children of parents with SUD only (p ¼ 0:01). Despite the small sample size, the results of this study seem to suggest that the offspring of SUD or ADHD parents are at elevated risk for ADHD compared to controls. The offspring of parents with both ADHD and SUD appear to be at the highest risk for ADHD, highlighting the need for careful screening of this group of youth for ADHD. Replication studies clarifying the nature and strength of the association are necessary.
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Substance Use among ADHD Adults: Implications of Late Onset and Subthreshold DiagnosesDiagnosing ADHD in adults is difficult when the diagnostician cannot establish an onset prior to the DSM-IV criterion of age seven or if the number of symptoms does not achieve the DSM threshold for diagnosis. These diagnostic issues are an even larger concern for clinicians faced with adults with substance use disorders (SUD). The present study compared four groups of adults: full ADHD subjects who met all DSM-IV criteria for childhood onset ADHD, late onset ADHD subjects who met all criteria except the age at onset criterion, subthreshold ADHD subjects who did not meet full symptom criteria, and nonADHD subjects who did not meet any of the above criteria. Diagnoses were by the Structured Clinical Interview for DSM-IV, and the Drug Use Severity Index (DUSI) was used for self-report of substance use. Cigarette and marijuana use was significantly greater in all ADHD groups relative to non-ADHD controls. Although usage rates of other drugs failed to reach significance, the ADHD groups were more likely to have used each drug (except alcohol) compared with the non-ADHD group. The late onset and full ADHD groups were more likely to have endorsed ever having a problem due to use of cigarettes, alcohol, or marijuana and reported more trouble resisting use of drugs or alcohol. The full ADHD group was more likely than the other groups to have reported ‘‘getting high’’ as their reason for using their preferred drug. Adults with ADHD have elevated rates of substance use and related impairment. Data about late onset ADHD provides further support for the idea that the DSM-IV age at onset criterion is too stringent. In contrast, subthreshold ADHD seems to be a milder form of the disorder, or perhaps a heterogeneous group of true ADHD cases and false positives.
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Psychoactive substance use disorders in adults with attention deficit hyperactivity disorder (ADHD): effects of ADHD and psychiatric comorbidityObjective: The authors evaluated the association between attention deficit hyperactivity disorder (ADHD) and psychoactive substance use disorders in adults with ADHD, attending to comorbidity with mood, anxiety, and antisocial disorders. It was hypothesized that psychiatric comorbidity would be a risk factor for psychoactive substance use disorders. Method: Findings for 120 referred adults with a clinical diagnosis ofchildhood-onset ADHD were compared with those for non-ADHD adult comparison subjects (N=268). All childhood and adult diagnoses were obtained by structured psychiatric interviews for DSM-III-R. Rı ıiiIt.ıi There was a significantly higher lifetime risk for psychoactive substance use disorders in the ADHD adults than in the comparison subjects (52% versus 27%). Although the two groups did not differ in the rate ofalcohol use disorders, the ADHD adults had significantly higher rates ofdrug and drug plus alcohol use disorders than the comparison subjects. ADHD significantly increased the risk for substance use disorders independently ofpsychiatric comorbidity. Antisocial disorders significantly increased the risk for substance use disorders independently ofADHD status. Mood and anxiety disorders increased the risk for substance use disorders in both the ADHD and comparison subjects, but more demonstrably in the comparison subjects. Conclusions: Although psychiatric comorbidity increased the risk for psychoactive substance use disorders in adults with ADHD, by itself ADHD was a significant risk factor for substance use disorders. More information is needed to further delineate risk and protective factors mediating the development of substance use disorders in persons with ADHD.
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Six-week, double-blind, placebo-controlled study of desipramine for adult attention deficit hyperactivity disorderO bjective: The factor structures of individual positive and negative symptoms as well as global ratings were examined in a diagnostically heterogeneous group of subjects. Method: Subjects were identified through a clinical and family study of patients with major psychoses at a VA medical center and evaluated with the Scale for the Assessment of N egative Symptoms and the Scale for the Assessment of Positive Symptoms. For the examination of global-level factor structures (N =630), both principal-component analysis and factor analysis with orthogonal rotation were used. Factor analysis was used for the examination of item-level factor structures as well (N =549). Results: The principal-component analysis of global ratings revealed three factors: negative symptoms, positive symptoms, and disorganization. The factor analysis of global ratings revealed a negative symptom factor and a positive symptom factor. The itemlevel factor analysis revealed two negative symptom factors (diminished expression and disordered relating), two positive symptom factors (bizarre delusions and auditory hallucinations), and a disorganization factor. Conclusions: The generation of additional meaningful factors at the item level suggests that important information about symptoms is lost when only global ratings are viewed. Future work should explore clinical and pathological correlates of the more differentiated item-level symptom dimensions
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Revisiting the factor structure for positive and negative symptoms: evidence from a large heterogeneous group of psychiatric patientsO bjective: The factor structures of individual positive and negative symptoms as well as global ratings were examined in a diagnostically heterogeneous group of subjects. Method: Subjects were identified through a clinical and family study of patients with major psychoses at a VA medical center and evaluated with the Scale for the Assessment of N egative Symptoms and the Scale for the Assessment of Positive Symptoms. For the examination of global-level factor structures (N =630), both principal-component analysis and factor analysis with orthogonal rotation were used. Factor analysis was used for the examination of item-level factor structures as well (N =549). Results: The principal-component analysis of global ratings revealed three factors: negative symptoms, positive symptoms, and disorganization. The factor analysis of global ratings revealed a negative symptom factor and a positive symptom factor. The itemlevel factor analysis revealed two negative symptom factors (diminished expression and disordered relating), two positive symptom factors (bizarre delusions and auditory hallucinations), and a disorganization factor. Conclusions: The generation of additional meaningful factors at the item level suggests that important information about symptoms is lost when only global ratings are viewed. Future work should explore clinical and pathological correlates of the more differentiated item-level symptom dimensions
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Dopamine D4 Gene 7-Repeat Allele and Attention Deficit Hyperactivity DisorderObjective: Family, twin, and adoption studies show attention deficit hyperactivity disorder (ADHD) to have a substantial genetic component, and some studies have reported an association between ADHD and the dopamine D4 (DRD4) gene. Method: The authors recruited 27 triads that comprised an ADHD adult, his or her spouse, and their ADHD child. These triads were assessed for ADHD, and their DNA was genotyped for DRD4 alleles. Results: A multiallelic transmission disequilibrium test suggested an association between ADHD and the DRD4 7-repeat allele. Among family members, the number of 7-repeat alleles predicted the diagnosis of ADHD. Conclusions: Prior reports of an association between ADHD and DRD4 generalize to families recruited through clinically referred ADHD adults. However, because there are some conflicting studies, further work is needed to clarify the role of DRD4 in the etiology of the disorder.
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Age-Dependent Decline of Symptoms of Attention Deficit Hyperactivity Disorder: Impact of Remission Definition and Symptom TypeObjective: Symptom decline in attention deficit hyperactivity disorder (ADHD) was examined with different definitions of remission. Method: Symptoms in 128 boys were measured five times over 4 years. The prevalences of syndromatic (less than full syndrome), symptomatic (less than subthreshold diagnosis), and functional (full recovery) remission were estimated as a function of age with multivariate logistic regression. Results: Age was significantly associated with decline in total ADHD symptoms and symptoms of hyperactivity, impulsivity, and inattention. Symptoms of inattention remitted for fewer subjects than did symptoms of hyperactivity or impulsivity. The proportion of subjects experiencing remission varied considerably with the definition used (highest for syndromatic remission, lowest for functional remission). Conclusions: These results indicate that differences in reported remission rates reflect the definition used rather than the disorder’s course. They provide systematic support for the clinical observation that hyperactivity and impulsivity symptoms tend to decline at a higher rate than inattention symptoms.
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A Controlled Study of Behavioral Inhibition in Children of Parents With Panic Disorder and DepressionObjective: “Behavioral inhibition to the unfamiliar” has been proposed as a precursor to anxiety disorders. Children with behavioral inhibition are cautious, quiet, introverted, and shy in unfamiliar situations. Several lines of evidence suggest that behavioral inhibition is an index of anxiety proneness. The authors sought to replicate prior findings and examine the specificity of the association between behavioral inhibition and anxiety. Method: Laboratory-based behavioral observations were used to assess behavioral inhibition in 129 young children of parents with panic disorder and major depression, 22 children of parents with panic disorder without major depression, 49 children of parents with major depression without panic disorder, and 84 children of parents without anxiety disorders or major depression (comparison group). A standard definition of behavioral inhibition based on previous research (“dichotomous behavioral inhibition”) was compared with two other definitions. Results: Dichotomous behavioral inhibition was most frequent among the children of parents with panic disorder plus major depression (29% versus 12% in comparison subjects). For all definitions, the univariate effects of parental major depression were significant (conferring a twofold risk for behavioral inhibition), and for most definitions the effects of parental panic disorder conferred a twofold risk as well. Conclusions: These results suggest that the comorbidity of panic disorder and major depression accounts for much of the observed familial link between parental panic disorder and childhood behavioral inhibition. Further work is needed to elucidate the role of parental major depression in conferring risk for behavioral inhibition in children.
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Patterns of Psychopathology and Dysfunction in High-Risk Children of Parents With Panic Disorder and Major DepressionObjective: The purpose of the study was to evaluate 1) whether an underlying familial predisposition is shared by all anxiety disorders or whether specific risks are associated with specific disorders, and 2) whether panic disorder and major depression have a familial link. Method: The study compared four groups of children: 1) offspring of parents with panic disorder and comorbid major depression (N=179), 2) offspring of parents with panic disorder without comorbid major depression (N=29), 3) offspring of parents with major depression without comorbid panic disorder (N=59), and 4) offspring of parents with neither panic disorder nor major depression (N=113). Results: Parental panic disorder, regardless of comorbidity with major depression, was associated with an increased risk for panic disorder and agoraphobia in offspring. Parental major depression, regardless of comorbidity with panic disorder, was associated with increased risks for social phobia, major depression, disruptive behavior disorders, and poorer social functioning in offspring. Both parental panic disorder and parental major depression, individually or comorbidly, were associated with increased risk for separation anxiety disorder and multiple (two or more) anxiety disorders in offspring. Conclusions: These findings confirm and extend previous results documenting significant associations between the presence of panic disorder and major depression in parents and patterns of psychopathology and dysfunction in their offspring.
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Traumatic Brain Injury and Schizophrenia in Members of Schizophrenia and Bipolar Disorder PedigreesObjective: Schizophrenia following a traumatic brain injury could be a phenocopy of genetic schizophrenia or the consequence of a gene-environment interaction. Alternatively, traumatic brain injury and schizophrenia could be spuriously associated if those who are predisposed to develop schizophrenia have greater amounts of trauma for other reasons. The authors investigated the relationship between traumatic brain injury and psychiatric diagnoses in a large group of subjects from families with at least two biologically related first-degree relatives with schizophrenia, schizoaffective disorder, or bipolar disorder. Method: The Diagnostic Interview for Genetic Studies was used to determine history of traumatic brain injury and diagnosis for 1,275 members of multiplex bipolar disorder pedigrees and 565 members of multiplex schizophrenia pedigrees. Results: Rates of traumatic brain injury were significantly higher for those with a diagnosis of schizophrenia, bipolar disorder, and depression than for those with no mental illness. However, multivariate analysis of within-pedigree data showed that mental illness was related to traumatic brain injury only in the schizophrenia pedigrees. Independent of diagnoses, family members of those with schizophrenia were more likely to have had traumatic brain injury than were members of the bipolar disorder pedigrees. The members of the schizophrenia pedigrees also failed to show the gender difference for traumatic brain injury (more common in men than in women) that was expected and was present in the bipolar disorder pedigrees. Subjects with a schizophrenia diagnosis who were members of the bipolar disorder pedigrees (and thus had less genetic vulnerability to schizophrenia) were less likely to have had traumatic brain injury (4.5%) than were subjects with schizophrenia who were members of the schizophrenia pedigrees (and who had greater genetic vulnerability to schizophrenia) (19.6%). Conclusions: Members of the schizophrenia pedigrees, even those without a schizophrenia diagnosis, had greater exposure to traumatic brain injury compared to members of the bipolar disorder pedigrees. Within the schizophrenia pedigrees, traumatic brain injury was associated with a greater risk of schizophrenia, consistent with synergistic effects between genetic vulnerability for schizophrenia and traumatic brain injury. Posttraumatic-braininjury schizophrenia in multiplex schizophrenia pedigrees does not appear to be a phenocopy of the genetic disorder.
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Impact of Tic Disorders on ADHD Outcome Across the Life Cycle: Findings From a Large Group of Adults With and Without ADHDObjective: The impact of tic disorders on the outcome of attention deficit hyperactivity disorder (ADHD) remains a subject of high scientific and clinical interest. To evaluate the impact of comorbid ADHD and tic disorders from a lifespan perspective, the authors systematically examined data from adults with and without ADHD. Method: They comprehensively evaluated 312 consecutively referred adults with ADHD and 252 comparison subjects without ADHD. Tic disorders were characterized along with a wide range of neuropsychiatric correlates, including other comorbid disorders as well as indexes of function in the domains of school, cognition, and interpersonal functioning. Results: A significantly greater proportion of adults with ADHD (12%) than those without ADHD (4%) had tic disorders. Tic disorders followed a mostly remitting course and had little impact on functional capacities. In addition, tic disorders were not associated with stimulant use. Conclusions: These findings in adults with ADHD confirm and extend previous findings in young subjects with ADHD, documenting that although individuals with ADHD are at greater risk for tic disorders, the presence of tic disorders has a limited impact on ADHD outcome.
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Meta-Analysis of the Association Between the 7-Repeat Allele of the Dopamine D4Receptor Gene and Attention Deficit Hyperactivity DisorderObjective: Family, twin, and adoption studies show attention deficit hyperactivity disorder (ADHD) to have a substantial genetic component. Although several studies have shown an association between ADHD and the 7-repeat allele of the dopamine D4 receptor gene (DRD4), several studies have not. Thus, the status of the ADHD-DRD4 association is uncertain. Method: Meta-analysis was applied to case-control and family-based studies of the association between ADHD and DRD4 to assess the joint evidence for the association, the influence of individual studies, and evidence for publication bias. Results: For both the case-control and family-based studies, the authors found 1) support for the association between ADHD and DRD4, 2) no evidence that this association was accounted for by any one study, and 3) no evidence for publication bias. Conclusions: Although the association between ADHD and DRD4 is small, these results suggest that it is real. Further studies are needed to clarify what variant of DRD4 (or some nearby gene) accounts for this association.
