Funding:

2002-2008  NIMH RO1 MH/HD 62152: The Neuroanatomy of Adult ADHD: An MRI Morphometric Study” (Larry J. Seidman, Ph.D., PI).

2002-2005  March of Dimes Foundation (MOD): “Brain Function and Structure in Adults with
Dyslexia and Attention Deficit/Hyperactivity Disorder: Relationship to Obstetric Factors” (Larry J. Seidman, Ph.D., PI).

The specific aims of this project, defining the neuroanatomical basis of ADHD, have been supported primarily by two grants funded from 2002-2008 (see below).  The goals of these studies are to examine brain structure and functioning in children and adults with and without ADHD using neuropsychological tests, functional magnetic resonance imaging (fMRI) and structural MRI.  We: 1) examined the neuroanatomic bases of ADHD in children and adults; 2) measured the relationship of brain structure, function, and neuropsychological dysfunctions in ADHD; 3) studied the heterogeneity of brain abnormalities in ADHD; 4) evaluated the effects of gender and age on brain abnormalities in ADHD; 5) created a resource for brain-gene studies of adult ADHD; and 6) will relate measures of brain function, structure and neuropsychological function to obstetric factors.

In the first (NIMH funded) study, a total of 285 subjects have been brain imaged under this and other related protocols (see below) and after a number of subjects were excluded for bad scans, a final sample of 279 was formed. This includes 96 controls, 151 persons with ADHD (36 with comorbid bipolar disorder), 18 persons with bipolar disorder, 10 relatives of persons with ADHD, and 4 persons with ADHD NOS due to later age of onset. 79 participants were between ages 10-19 (31 controls) and 43 persons with ADHD, and 200 were twenty years of age or older. Thirty-three persons with ADHD were psychotropically naïve at the time of brain imaging. These include participants imaged in collaboration with Dr. Valera when she carried out her NRSA post-doctoral fellowship (Dr. Seidman, mentor: F32 MH065040: “A Functional MRI Study of Working Memory in ADHD Adults), in collaboration with Dr. Biederman, who was supported by NARSAD, and the rest collected solely under this grant. All 279 subjects brains have had comprehensive morphometric analyses carried out at the MGH Center for Morphometric Analysis including general segmentation and cortical parcellation and an additional 137 had specialized cerebellar parcellation analyses. Although not originally part of the grant aims, a pilot study of 76 participants received diffusion tensor imaging (DTI) scans including 56 controls and 17 persons with ADHD. In addition, functional MRI data was collected on 235 of the 279 participants 12 and older using the n-back (2-back task) and multi-source interference (MSIT) task. In addition to support from this grant, patients and controls were sampled from the "Testing the Validity of Adult Attention Deficit Hyperactivity Disorder" (Faraone, MH 57934-05) study, the “A Genetic Linkage Study of Children with Attention Deficit Hyperactivity Disorder” (Faraone, HD 37694) study, the “Adult Outcome of Attention Deficit Hyperactivity Disorder” (Biederman, HD 36317-07) study, the “Long Term Outcome of ADHD in Girls” (Biederman, MH 50657-08) study, the NARSAD Distinguished Investigator Award to Dr. Beiderman (“Neuropsychology and Neuroimaging Study of Mania”), the “Open Label Phase I/II Study of the Safety and Dopamine Transporter Binding Properties of C-11 Altropane in Normal Human Subjects and in Patients with ADHD” (Spencer, MH 064019), and the “Open-Label Phase I/II Study of Dopamine Transporter Receptor Occupancy with OROS Methylphenidate and Immediate Release Methylphenidate as Measured with C-11 Altropane in Human Subjects” (Spencer, 2003-P-002058).  Dr. Faraone’s, Dr. Biederman’s, and Dr. Spencer’s studies include structured psychiatric interviews, diagnostic procedures, neuropsychological tests, and blood draws for genetic analyses.  All were IRB approved at MGH Participants were also recruited from the community and received the same clinical measures as subjects from Dr. Faraone’s, Dr. Biederman’s, Dr. Spencer’s studies.

Aim 1. Identifying the neuroanatomic bases of ADHD in children and adults:
To this date, we have completed a number of publications examining this aim. These studies are summarized below:

Many investigators have hypothesized that attention-deficit/hyperactivity disorder (ADHD) involves structural and functional brain abnormalities in frontal–striatal circuitry. Although our review suggests that there is substantial support for this hypothesis, a growing literature demonstrates widespread abnormalities affecting other cortical regions and the cerebellum. Because there is only one report studying adults with ADHD, this summary is based on children. A key limitation of the literature is that most of the studies until recently have been underpowered, using samples of fewer than 20 subjects per group. Nevertheless, these studies are largely consistent with the most comprehensive and definitive study (Castellanos et al 2002). Moreover, studies differ in the degree to which they address the influence of medications, comorbidities, or gender, and most have not addressed potentially important sources of heterogeneity such as family history of ADHD, subtype, or perinatal complications. Despite these limitations, a relatively consistent picture has emerged. The most replicated alterations in ADHD in childhood include significantly smaller volumes in the dorsolateral prefrontal cortex (DLPFC), caudate, pallidum, corpus callosum, and cerebellum. These results suggest that the brain is altered in a more widespread manner than has been previously hypothesized. Developmental studies are needed to address the evolution of this brain disorder into adulthood (Seidman et al., 2005).

Convergent data from neuroimaging, neuropsychological, genetic, and neurochemical studies in ADHD have implicated dysfunction of DLPFC and dorsal anterior cingulate (dACC) cortical structures, which form the cortical arm of the frontostriatal network supporting executive functions. Furthermore, besides the DLPFC and dACC, structural and functional imaging studies have shown abnormalities in key brain regions within distributed cortical networks supporting attention. The conceptualization of neural systems biology in ADHD aims at the understanding of what organizing principles have been altered during development within the brain of a person with ADHD. Characterizing these neural systems using neuroimaging could be critical for the description of structural endophenotypes and may provide the capability of in vivo categorization and correlation with behavior and genes (Makris et al., 2009).

Although there are many structural neuroimaging studies of ADHD in children, there are inconsistencies across studies and no consensus regarding which brain regions show the most robust area or volumetric reductions relative to control subjects. Our goal was to statistically analyze structural imaging data via a meta-analysis to help resolve these issues. We searched the MEDLINE and PsycINFO databases through January 2005. Studies must have been written in English, used MRI, and presented the means and standard deviations of regions assessed. Data were extracted by one of the authors and verified independently by another author. Analyses were performed using STATA with metan, metabias, and metainf programs. A meta-analysis including all regions across all studies indicated global reductions for ADHD subjects compared with control subjects, standardized mean difference  =.408, p < .001. Regions most frequently assessed and showing the largest differences included cerebellar regions, the splenium of the corpus callosum, total and right cerebral volume, and right caudate. Several frontal regions assessed in only two studies also showed large significant differences. This meta-analysis provides a quantitative analysis of neuroanatomical abnormalities in ADHD and information that can be used to guide future studies (Valera et al., 2007).

Gray and white matter volume deficits have been reported in a number of studies of children with ADHD; however, there is a paucity of structural MRI studies of adults with ADHD. This structural MRI study used an a priori region of interest approach. Twenty-four adults with DSM-IV ADHD and 18 healthy controls comparable on age, socioeconomic status, sex, handedness, education, IQ, and achievement test performance had an MRI on a 1.5T Siemens scanner. Cortical and sub-cortical gray and white matter were segmented. Image parcellation divided the neocortex into 48 gyral-based units per hemisphere. Based on a priori hypotheses we focused on prefrontal, anterior cingulate cortex (ACC) and overall gray matter volumes. General linear analyses of the volumes of brain regions, adjusting for age, sex, and total cerebral volumes, were used to compare groups. Relative to controls, ADHD adults had significantly smaller overall cortical gray matter, prefrontal and ACC volumes. Adults with ADHD have volume differences in brain regions in areas involved in attention and executive control. These data, largely consistent with studies of children, support the idea that adults with ADHD have a valid disorder with persistent biological features (Seidman at al., 2006).

ADHD has been associated with structural alterations in brain networks influencing cognitive and motor behavior. Volumetric studies in children identify abnormalities in cortical, striatal, callosal, and cerebellar regions. In a prior volumetric study we found that ADHD adults had significantly smaller overall cortical gray matter, prefrontal and anterior cingulate volumes than matched controls. Thickness and surface area are additional indicators of integrity of cytoarchitecture in the cortex. To expand upon our earlier results and further refine the regions of structural abnormality, we carried out a structural MRI study of cortical thickness in the same sample of adults with ADHD (n = 24) and controls (n = 18), hypothesizing that the cortical networks underlying attention and executive function (EF) would be most affected. Compared to healthy adults, adults with ADHD showed selective thinning of cerebral cortex in the networks that subserve attention and EF. In the present study we found significant cortical thinning in ADHD in a distinct cortical network supporting attention especially in the right hemisphere involving the inferior parietal lobule, the dorsolateral prefrontal and the anterior cingulate cortex. This is the first documentation that ADHD in adults is associated with thinner cortex in the cortical network that modulates attention (Makris et al., 2007).

ADHD has been hypothesized to be due, in part, to structural defects in brain networks influencing cognitive, affective and motor behaviors.  Although the current literature on fiber tracts is very limited in ADHD, gray matter abnormalities suggest that white matter connections may be altered selectively in neural systems.  A prior study (Ashtari and others, 2005), using DT-MRI showed alterations to be present within the frontal and cerebellar white matter in children and adolescents with ADHD.  In this study of DT-MRI in adults with childhood ADHD (funded by the March of Dimes Foundation), we hypothesized that the fiber pathways subserving attention and executive functions would be altered.  To this end, the cingulum bundle and the superior longitudinal fascicle II (SLF II) were investigated in vivo in 12 adults with childhood onset ADHD and 17 demographically comparable unaffected controls using DT-MRI.  Relative to the controls, the fractional anisotropy (FA) values were significantly smaller in both regions of interest in the right hemisphere, indicating an alteration of anatomical connections within the attention and executive function cerebral systems in adults with childhood ADHD.  The demonstration of FA abnormalities in the cingulum bundle and SLF II in adults with childhood ADHD provides further support for persistent structural abnormalities into adulthood (Makris et al., 2008).

Although ADHD and bipolar disorder (BPD) frequently co-occur and represent a particularly morbid clinical form of both disorders, neuroimaging research addressing this comorbidity is scarce.   Our aim was to evaluate the morphometric MRI underpinnings of the comorbidity of ADHD with BPD testing the hypothesis that subjects with this comorbidity would have neuroanatomical correlates of both disorders. Morphometric MRI findings were compared between 31 adults with ADHD and BPD with those of 18 with BPD, 26 with ADHD, and 23 healthy controls. The volumes (cm3) of our regions of interest were estimated as a function of ADHD status, BPD status, age, sex, and omnibus brain volume using linear regression models.  When BPD was associated with a significantly smaller orbital prefrontal cortex and larger right thalamus, this pattern was found in comorbid subjects with ADHD plus BPD.  Likewise, when ADHD was associated with significantly less neocortical gray matter, less overall frontal lobe and superior prefrontal cortex volumes, a smaller right anterior cingulate cortex, and less cerebellar gray matter, so did comorbid ADHD plus BPD subjects.  Results support the hypothesis that ADHD and BPD independently contribute to volumetric alterations of selective and distinct brain structures. In the comorbid state of ADHD plus BPD, the profile of brain volumetric abnormalities consists of structures that are altered in both disorders individually. Attention to comorbidity is necessary to help clarify the heterogeneous neuroanatomy of both BPD and ADHD (Biederman et al., 2008).

Summary of Results of analyses: Volumetric and surface area (i.e., thickness) measures indicate that adults with ADHD have structural brain abnormalities (reductions) in overall gray matter, DLPFC, cerebellum, anterior cingulate cortex and the inferior parietal lobule, consistent with a network that regulates attention and executive control. The abnormalities are largely bilateral, but greater involvement of the right hemisphere is suggested by abnormalities in white matter, thus far measured in the cingulum bundle and right superior longitudinal fascicle (SLF) II. In contrast to results reported in the literature on children with ADHD, no significant differences were noted in the basal ganglia (i.e., caudate, pallidum and putamen), consistent, in part, with the Castellanos finding of “normalization” of caudate volume by late teenage years. Areas that we had proposed to be abnormal in ADHD based on theoretical reasons, such as thalamus and nucleus accumbens, were not significantly different than controls. While the abnormalities are not accounted for by comorbidity, some findings are observed in patients with ADHD+BP, such as volume reductions in orbital PFC. Thus, careful attention to the nature of comorbidity is necessary to understand neuroanatomical deviations in persons with ADHD+ comorbid disorders. We have yet to test for differences in corpus callosum, and also to directly test child and adult samples to determine if the results are comparable using the same methods. These results strongly support the validity of adult ADHD from the point of view of the presence of anatomical abnormalities in networks subserving attention and executive control.

Aim 2. Relating brain structure, function and neuropsychological dysfunctions:
We hypothesized that ADHD symptoms can be accounted for by structural and functional abnormalities in fronto-subcortical networks. Our specific hypotheses involve response inhibition and working memory. We predict that response inhibition deficits will be associated with a smaller anterior cingulate, caudate and pallidum, and altered blood flow in the ACC and DLPFC. We also predict that working memory deficits will be associated with smaller DLPFC and with reduced blood flow in DLPFC, ACC and parietal cortex.

The objective of this first analysis was to identify the neural correlates of ADHD adults during performance on a verbal working memory task.  A sample of un-medicated adults with ADHD (N=20) and controls (N=20) group matched on age, sex, and estimated IQ was assessed.  A 2-back task of working memory was used to examine neural function, and the blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) response was used as a measure of neural activity during working memory performance. Working memory performance on the 2-back task did not differ significantly between ADHD adults and controls.  However, compared to controls, ADHD adults showed significantly decreased activity in cerebellar and occipital regions, and a trend toward decreased activation in an a priori region of the prefrontal cortex (p < .07).  In conclusion, ADHD adults showed altered patterns of neural activity despite comparable task performance.  These findings suggest that the cerebellum is involved in the pathophysiology of at least some cognitive deficits associated with ADHD, and emphasize the need for additional research aimed at elucidating the role of the cerebellum in ADHD symptomatology (Valera et al., 2005).

Although ADHD in adults is associated with significant morbidity and dysfunction and afflicts both sexes, relatively few imaging studies have examined females and none have had sufficient power to adequately examine sex differences. We sought to examine sex differences in neural functioning of ADHD adults during performance on a verbal working memory task. Participants were 44 adults with ADHD matched on age, sex, and estimated IQ to 49 controls. Accuracy and reaction time on an n-back task were measures of working memory performance. The blood-oxygenation-level dependent functional magnetic resonance imaging response was used as a measure of neural activity.  A group by sex ANOVA showed no between-group differences in either reaction time or percent correct for the working memory task. For imaging data, with both sexes combined, ADHD adults showed less activity than controls in prefrontal regions. However, sex-by-group analyses revealed an interaction, such that male ADHD adults showed significantly less activity lateralized to right frontal, temporal and subcortical regions, as well as left occipital and cerebellar regions relative to male controls, whereas female ADHD adults showed no differences from female controls. Exploratory correlation analyses revealed negative associations between working memory related activation and number of hyperactive symptoms for males and number of inattentive symptoms for females. Male but not female adults with ADHD showed significantly altered patterns of neural activity during performance on a verbal working memory task. Males and females showed different associations between neural activity and ADHD symptoms (Valera et al., in Press).

Previous studies have reported hypofunction and structural abnormalities of the dorsal anterior midcingulate cortex (daMCC) in ADHD. Stimulant medications are effective treatments for ADHD, but their mechanism-of-action has not been established. We hypothesized that, compared to placebo, the extended-action osmotic-release oral system of methylphenidate (MPH-OROS, Concerta®) would increase functional MRI activation in daMCC and other fronto-parietal regions that subserve attention during the Multi-Source Interference Task (MSIT). Twenty-one adults with ADHD were randomized to six weeks of treatment with either MPH-OROS (n = 11) or placebo (n = 10). Subjects underwent fMRI twice while performing the MSIT (Baseline Scan 1, t = 0, and Scan 2, t = 6 weeks). Random effects, repeated measures, general linear model (GLM) analyses were used to compare daMCC (and whole-brain) fMRI activation during the MSIT via standard group-averaged methods. Additional individual-based daMCC volume-of-interest (VOI) confirmatory analyses and behavioral data are also presented. Performance (reaction times and accuracy) and baseline fMRI measures in daMCC and other a priori brain regions did not differ between groups. At treatment completion, a stringent random effects comparison of daMCC activation during the MSIT showed ADHD subjects on MPH-OROS had significantly higher daMCC fMRI activation than did those given placebo (P < .05, corrected for multiple comparisons). Activity in daMCC was related to clinical response at six weeks, with MPH-responders showing higher daMCC activation than placebo failures (P < .01). Individual-based daMCC VOI analyses confirmed the group-averaged findings. MPH-OROS increased activation of daMCC during the MSIT, and thus may act, in part, by normalizing hypofunction of daMCC and fronto-parietal regions in ADHD (Bush et al., 2008).

Although ADHD is associated both with brain alterations in attention and EF circuitry and with genetic variations within the dopamine system (including the dopamine transporter gene [SLC6A3]), few studies have directly investigated how genetic variations are linked to brain alterations. We sought to examine how a polymorphism in the 3’ untranslated region (UTR) of SLC6A3, associated with ADHD in meta-analysis, might contribute to variation in dorsal anterior cingulate cortex (dACC) function in subjects with ADHD.  We collected fMRI scans of 42 individuals with ADHD, all of European descent and over the age of 17, while they performed the Multi-Source Interference Task (MSIT), a cognitive task shown to activate dACC.  SLC6A3 3’ UTR variable number tandem repeat (VNTR) polymorphisms were genotyped and brain activity was compared for groups based on allele status. ADHD individuals homozygous for the 10R allele showed significant hypoactivation in the left dACC compared to 9R-carriers. Exploratory analysis also showed trends toward hypoactivation in the 10R homozygotes in left cerebellar vermis and right lateral prefrontal cortex. Further breakdown of genotype groups showed similar activation in individuals heterozygous and homozygous for the 9R allele. Alterations in activation of attention and EF networks found previously to be involved in ADHD are likely influenced by SLC6A3 genotype. This genotype may contribute to heterogeneity of brain alterations found within ADHD samples (Brown et al., In Press).

Summary of Results for Aim 2: Our results thus far strongly support the presence of dysfunction in DLPFC, dACC, and the cerebellum in ADHD, again supporting the validity of adult ADHD from a biological point of view. In general, despite normal performance that is statistically indistinguishable from controls on both the 2-back and MSIT, there is clear evidence of hypofunction of these regions in persons unmedicated at the time of scanning, especially in males with ADHD. To some extent, this disturbance can be ameliorated in dACC by classic ADHD medications such as Concerta. Of interest is that the dACC hypoactivation is at least partly influenced in the 10R homozygotes of the dopamine transporter gene [SLC6A3]. To this date, analyses have not supported the hypothesis of striatal involvement, consistent with the absence of structural alterations in the striatum in our adult subjects. Ongoing analyses are designed to test structure-function associations.

Aim 3. Assessing the heterogeneity of brain abnormalities in ADHD:
Because a familial subgroup (with at least one first degree relative with ADHD) may index a more biologically robust entity, we predicted that adults with a family history of ADHD will have a higher frequency of individuals with structural abnormalities in the ACC, caudate and pallidum, and with functional abnormalities in the ACC and DLPFC, than those without a family history. Considering that neuroanatomical abnormalities have been associated with both ADHD and LD, we hypothesize that persons with ADHD+LD will demonstrate structural brain abnormalities associated with both disorders. We also predict that a subgroup of persons with ADHD will be identified as impaired on executive functions, and that they will have more evidence of structural and functional brain abnormalities in prefrontal cortex, caudate, pallidum and ACC.

To this date, our focus on heterogeneity has addressed a few important issues involving the presence or absence of learning disabilities on neuropsychological performance (Seidman et al., 2006), the effect of dopamine D4 receptor on PFC volumes (Monuteaux et al., 2008), and the role of medications on ACC volumes (Makris et al., In Press).

The authors’ goal was to assess neuropsychological performance in girls with ADHD and evaluate the role of comorbid learning disabilities (LDs). Participants were 140 girls with ADHD and 122 girls without ADHD, ages 6–17 years. Neuropsychological performance was measured in a standardized manner, blind to clinical status. LD was defined by a combined regression-based and low-achievement classification. ADHD was associated with modest, but significant, neuropsychological impairment, as measured by an aggregate measure of performance and on the Stroop Color–Word Test, independent of age, social class, IQ, and psychiatric comorbidity. Neuropsychological deficits were most impaired in girls with both ADHD and an LD and in those without medications. These results extend to females the previously documented association of LDs with neuropsychological functioning in males with ADHD.

An emerging literature has demonstrated an association between the dopamine D4 receptor (DRD4) gene and volumetric brain abnormalities in children with ADHD.  However, these results have not been extended to adults and have not addressed the impact of comorbidity.  Our objective was to examine the DRD4 7R gene and volumetric brain abnormalities in adults with ADHD while accounting for comorbidity with bipolar disorder.  Subjects were male and female adult outpatient referrals stratified into two diagnostic groups: 24 with ADHD, 19 with ADHD and bipolar disorder (BPD), as well as 20 male and female adult community controls without ADHD or BPD.  We measured volumes (cm3) of a priori selected brain regions (superior frontal, middle frontal, anterior cingulate, and cerebellum cortices) by structural MRI. Among adults with ADHD, subjects with the 7-repeat allele of the DRD4 gene had a significantly smaller mean volume in the superior frontal cortex and cerebellum cortex compared to subjects without this allele.  In contrast, no such effects were detected in the adults with ADHD+BPD or controls. Our findings suggest that volumetric abnormalities in the DLPFC and cerebellum may represent an intermediate neuroanatomical phenotype between DRD4 genotype and the clinical expression of ADHD in adults, but only in ADHD subjects without comorbid BPD.  These result support the heterogeneity of ADHD and provides insights as to its underlying pathophysiology.  

We sought to examine preliminary results of brain alterations in anterior cingulate cortex (ACC) in treatment-naïve adults with ADHD.  The ACC is a central brain node for the integration of cognitive control and allocation of attention, affect and drive. Thus its anatomical alteration may give rise to impulsivity, hyperactivity and inattention, which are cardinal behavioral manifestations of ADHD. Segmentation and parcellation of the ACC was performed on controls (n=22) and treatment-naïve adults with ADHD (n=13). There was a 21% volume reduction in the left ACC of the treatment-naïve group. These results raise the possibility that in ADHD there are volumetric deficits persistent into adulthood, that are independent of medical treatment.

Summary of Results for Aim 3: Our results suggest that structural brain alterations in ADHD may be selectively found in persons with specific genotypes such as those mediated by the DRD4 7R gene. The role of medication was explored in a pilot study, and neuropsychological data was reported to demonstrate the important of comorbid LD. Ongoing analyses are designed to test heterogeneity of brain abnormalities.

Aim 4. Exploring the effects of gender on brain abnormalities in ADHD:
Because there is no structural brain imaging data available for adult ADHD, virtually nothing is known about whether the predicted effects will be similar for males and females with the disorder. We will determine whether results found in preliminary structural MRI studies of girls and functional imaging studies of women will be replicated: more left lateralized abnormalities in females than males with ADHD.

ADHD is known to have neuropsychological correlates, characterized mainly by
executive function deficits.  However, most available data are based on studies of boys through age 12.  Our goal was to assess whether girls with ADHD express neuropsychological features similar to those found in boys, and whether these impairments are found in both pre-teen and teen samples. Subjects were 101 girls and 103 boys with DSM-III-R ADHD, and 109 comparison girls and 70 boys without ADHD, ages 9 to 17 years.  Information on neuropsychological performance was obtained in a standardized manner blind to clinical status.  Primary regression analyses controlled for age, SES, learning disability and psychiatric co-morbidity. Girls and boys with ADHD were significantly more impaired on some measures of executive functions than healthy comparisons, but did not differ significantly from each other.  With the exception of one test score there were no significant sex by diagnosis interactions.  Moreover, there were no more significant interactions between age, gender and diagnosis than would be expected by chance. Neuropsychological measures of executive functions were comparably impaired in girls compared to boys with ADHD, and these impairments are found at ages 9-12 and ages 13-17. These findings suggest that executive dysfunctions are correlates of ADHD regardless of gender and age, at least through the late teen years (Seidman et al., 2005, Valera et al., In Press).

Summary of Results for Aim 4: Our results suggest that structural brain alterations in the PFC in ADHD may be selectively found in persons with specific genotypes such as those mediated by the DRD4 7R gene. The role of medication was explored in a pilot study, and neuropsychological data was reported to demonstrate the important role of comorbid LD. Ongoing analyses are designed to test heterogeneity of brain abnormalities.

Aim 5. Creating a resource for future studies of brain abnormalities in ADHD including associations with genetic anomalies:
The proposed work will provide a resource for future studies of brain abnormalities in ADHD.  This resource will consist of the clinical data and DNA samples being collected.  Although it would be premature to propose a study of the association between gene variants and brain abnormalities in ADHD, we believe that when ADHD susceptibility genes have been discovered and confirmed, our DNA-imaging resource will provide a useful means of testing hypotheses about gene-brain associations.

One hundred twenty four people with ADHD and 68 controls have brain imaging data as well as genetic data collected under a number of protocols in Dr. Biederman’s lab. We have carried out two pilot studies of imaging genetics with these datasets.

As noted above, we measured volumes (cm3) of a priori selected brain regions (superior frontal, middle frontal, anterior cingulate, and cerebellum cortices) by structural MRI. Among adults with ADHD, subjects with the 7-repeat allele of the DRD4 gene had a significantly smaller mean volume in the superior frontal cortex and cerebellum cortex compared to subjects without this allele.  In contrast, no such effects were detected in the adults with ADHD+BPD or controls. Our findings suggest that volumetric abnormalities in the DLPFC and cerebellum may represent an intermediate neuroanatomical phenotype between DRD4 genotype and the clinical expression of ADHD in adults, but only in ADHD subjects without comorbid BPD (Monuteaux et al., 2008).

As noted above, ADHD individuals homozygous for the 10R allele showed significant hypoactivation in the left dACC compared to 9R-carriers. Exploratory analysis also showed trends toward hypoactivation in the 10R homozygotes in left cerebellar vermis and right lateral prefrontal cortex. Further breakdown of genotype groups showed similar activation in individuals heterozygous and homozygous for the 9R allele. Alterations in activation of attention and EF networks found previously to be involved in ADHD are likely influenced by SLC6A3 genotype (Brown et al., In Press).

Summary of Results for Aim 5: Our results suggest that structural and functional brain alterations in ADHD may be selectively found in persons with specific genotypes such as those mediated by the DRD4 7R and the DAT1 SLC6A3 genotype. These data are quite promising and novel. As noted below in “D” (Plans), we intend to seek additional funding to analyze these data in full.