Haplotypes of catechol-O-methyltransferase modulate intelligence-related brain white matter integrity

Impact of COMT haplotypes on functional connectivity density and its association with the gene expression of dopamine receptors

Catechol-O-methyltransferase (COMT) affects brain connectivity via modulating the dopamine system, with an expected greater effect of haplotypes than single-nucleotide polymorphism (SNP). The action pathway from COMT to dopamine to connectivity is theoretically dependent on the gene expression of dopamine receptors. Here, we aimed to investigate the impact of COMT haplotypes on brain functional connectivity density (FCD) in hundreds of healthy young subjects, and to disclose the association between the COMT-FCD statistical map and the spatial expression of the dopamine receptor genes. We found an inverted U-shaped modulation of COMT haplotypes on FCD in the left inferior parietal lobule that is mainly connected to the frontal and parietal cortices, with APS homozygotes exhibiting greater FCD than the other five groups. However, we failed to identify any significant effect of any SNP on FCD. Utilizing gene expression data collected from Allen human brain atlas, we found the COMT-FCD statistical map was significantly associated with the expression patterns of the dopamine receptor genes. Our results suggest that COMT haplotypes have greater impact on functional connectivity than a single genetic variation and that the association between COMT and functional connectivity may be dependent on the gene expression of dopamine receptors.

Catechol O-methyltransferase (COMT) functional haplotype is associated with recurrence of affective symptoms: A prospective birth cohort study

BACKGROUND

Catechol-O-methyltransferase (COMT) polymorphisms play an essential role in dopamine availability in the brain. However, there has been no study investigating whether a functional four-SNP (rs6269-rs4633-rs4818-rs4680) haplotype is associated with affective symptoms over the life course.

METHODS

We tested this using 2093 members of the Medical Research Council National Survey of Health and Development (MRC NSHD), who had been followed up since birth in 1946, and had data for COMT genotypes, adolescent emotional problems (age 13-15) and at least one measure of adult affective symptoms at ages 36, 43, 53, or 60-64 years. First, differences in the levels of affective symptoms by the functional haplotype using SNPs rs6269, rs4818, and rs4680 were tested in a structural equation model framework. Second, interactions between affective symptoms by COMT haplotype were tested under an additive model. Finally, a quadratic regressor (haplotype2) was used in a curvilinear model, to test for a possible inverted-U trend in affective symptoms according to COMT-related dopamine availability.

RESULTS

Women had a significant interaction between COMT haplotypes and adolescent emotional problem on affective symptoms at age 53. Post hoc analysis showed a significant positive association between adolescent emotional problems and affective symptoms at age 53 years in the middle dopamine availability group (valA/valB or met/met; β = .11, p = .007). For men, no significant interactions were observed.

CONCLUSIONS

Combination of the COMT functional haplotype model and inverted-U model may shed light on the effect of dopaminergic regulation on the trajectory of affective symptoms over the life course.

Sex-specific effects of COMT Val158Met polymorphism on corpus callosum structure: A whole-brain diffusion-weighted imaging study

BACKGROUND

Genetic polymorphisms play a significant role in determining brain morphology, including white matter structure and may thus influence the development of brain functions. The main objective of this study was to examine the effect of Val158Met (rs4680) polymorphism of Catechol-O-Methyltransferase (COMT) gene on white matter connectivity in healthy adults.

METHODS

We used a whole-brain diffusion-weighted imaging method with Tract-Based Spatial Statistics (TBSS) analysis to examine white matter structural integrity in intrinsic brain networks on a sample of healthy subjects (N = 82).

RESULTS

Results revealed a sex-specific effect of COMT on corpus callosum (CC): in males only, Val homozygotes had significantly higher fractional anisotropy (FA) compared to Met-carriers. Volume-of-interest analysis showed a genotype by sex interaction on FA in genu and rostral midbody of CC, whereby Val males demonstrated higher FA than Met females.

CONCLUSIONS

These results demonstrate the key effect of genes by sex interaction, rather than their individual contribution, on the corpus callosum anatomy.

White matter alterations related to attention-deficit hyperactivity disorder and COMT val(158)met polymorphism: children with valine homozygote attention-deficit hyperactivity disorder have altered white matter connectivity in the right cingulum (cingulate gyrus)

INTRODUCTION

In this article, the COMT gene val(158)met polymorphism and attention-deficit hyperactivity disorder (ADHD)-related differences in diffusion-tensor-imaging-measured white matter (WM) structure in children with ADHD and controls were investigated.

PATIENTS AND METHODS

A total of 71 children diagnosed with ADHD and 24 controls aged 8-15 years were recruited. Using diffusion tensor imaging, COMT polymorphism and ADHD-related WM alterations were investigated, and any interaction effect between the COMT polymorphism and ADHD was also examined. The effects of age, sex, and estimated total IQ were controlled by multivariate analysis of covariance (MANCOVA).

RESULTS

First, an interaction between the COMT val(158)met polymorphism and ADHD in the right (R) cingulum (cingulate gyrus) (CGC) was found. According to this, valine (val) homozygote ADHD-diagnosed children had significantly lower fractional anisotropy (FA) and higher radial diffusivity (RD) in the R-CGC than ADHD-diagnosed methionine (met) carriers, and val homozygote controls had higher FA and lower RD in the R-CGC than val homozygote ADHD patients. Second, met carriers had higher FA and axial diffusivity in the left (L)-uncinate fasciculus and lower RD in the L-posterior corona radiata and L-posterior thalamic radiation (include optic radiation) than the val homozygotes, independent of ADHD diagnosis. Third, children with ADHD had lower FA in the L-CGC and R-retrolenticular part of the internal capsule than the controls, independent of the COMT polymorphism.

CONCLUSION

Significant differences reported here may be evidence that the COMT gene val(158)met polymorphism variants, as well as ADHD, could affect brain development. ADHD and the COMT polymorphism might be interactively affecting WM development in the R-CGC to alter the WM connectivity in children with val homozygote ADHD.

Developmental differences in intra-individual variability in children with ADHD and ASD

BACKGROUND

Intra-individual variability reflects temporal variation within an individual's performance on a cognitive task. Children with developmental disorders, such as ADHD and ASD show increased levels of intra-individual variability. In typical development, intra-individual variability decreases sharply between the ages 6 and 20. The tight link between intra-individual variability and age has led to the suggestion that it may be marker of neural development. As there is accumulating evidence that ADHD and ASD are characterised by atypical neurodevelopmental trajectories, we set out to explore developmental changes in intra-individual variability in subjects with ADHD and ASD.

METHOD

We used propensity score matching to match a cross-sectional sample of children with ADHD, ASD and control subjects (N = 405, aged 6-19 years old) for age, IQ and gender. We used ex-Gaussian distribution parameters to characterise intra-individual variability on fast responses (sigma) and slow responses (tau).

RESULT

Results showed that there was a similar decrease in mean response times with age across groups, and an interaction between age and group for measures of variability, where there was a much lower rate of change in the variability parameters (sigma and tau) for subjects with ASD compared with the other two groups. Subjects with ADHD had higher intra-individual variability, reflected by both sigma and tau, but the rate of decrease in variability with age was similar to that of the controls.

CONCLUSION

These results suggest that subjects with ADHD, ASD and controls differ in the rate at which intra-individual variability decreases during development, and support the idea that intra-individual variability may be a marker of neural development, mimicking the neurodevelopmental changes in these disorders.

Dosage effects of BDNF Val66Met polymorphism on cortical surface area and functional connectivity

The single nucleotide polymorphism (SNP) that leads to a valine-to-methionine substitution at codon 66 (Val66Met) in BDNF is correlated with differences in cognitive and memory functions, as well as with several neurological and psychiatric disorders. MRI studies have already shown that this genetic variant contributes to changes in cortical thickness and volume, but whether the Val66Met polymorphism affects the cortical surface area of healthy subjects remains unclear. Here, we used multimodal MRI to study whether this polymorphism would affect the cortical morphology and resting-state functional connectivity of a large sample of healthy Han Chinese human subjects. An SNP-wise general linear model analysis revealed a "dosage effect" of the Met allele, specifically a stepwise increase in cortical surface area of the right anterior insular cortex with increasing numbers of the Met allele. Moreover, we found enhanced functional connectivity between the anterior insular and the dorsolateral prefrontal cortices that was linked with the dosage of the Met allele. In conclusion, these data demonstrated a "dosage effect" of BDNF Val66Met on normal cortical structure and function, suggesting a new path for exploring the mechanisms underlying the effects of genotype on cognition.

Catechol-O-methyltransferase Val158Met polymorphism on the relationship between white matter hyperintensity and cognition in healthy people

Background

White matter lesions can be easily observed on T2-weighted MR images, and are termed white matter hyperintensities (WMH). Their presence may be correlated with cognitive impairment; however, the relationship between regional WMH volume and catechol-O-methyltransferase (COMT) Val158Met polymorphism in healthy populations remains unclear.

Methods

We recruited 315 ethnic Chinese adults with a mean age of 54.9±21.8 years (range: 21–89 y) to examine the genetic effect of COMT on regional WMH and the manner in which they interact to affect cognitive function in a healthy adult population. Cognitive tests, structural MRI scans, and genotyping of COMT were conducted for each participant.

Results

Negative correlations between the Digit Span Forward (DSF) score and frontal WMH volumes (r = −.123, P = .032, uncorrected) were noted. For the genetic effect of COMT, no significant difference in cognitive performance was observed among 3 genotypic groups. However, differences in WMH volumes over the subcortical region (P = .016, uncorrected), whole brain (P = .047, uncorrected), and a trend over the frontal region (P = .050, uncorrected) were observed among 3 COMT genotypic groups. Met homozygotes and Met/Val heterozygotes exhibited larger WMH volumes in these brain regions than the Val homozygotes. Furthermore, a correlation between the DSF and regional WMH volume was observed only in Met homozygotes. The effect size (cohen’s f) revealed a small effect.

Conclusions

The results indicate that COMT might modulate WMH volumes and the effects of WMH on cognition.

Predicting planning performance from structural connectivity between left and right mid-dorsolateral prefrontal cortex: moderating effects of age during postadolescence and midadulthood

Complex cognitive abilities such as planning are known to critically rely on activity of bilateral mid-dorsolateral prefrontal cortex (mid-dlPFC). However, the functional relevance of the structural connectivity between left and right mid-dlPFC is yet unknown. Here, we applied global tractography to derive streamline counts as estimates of the structural connectivity between mid-dlPFC homologs and related it to planning performance in the Tower of London task across early to midadulthood, assuming a moderating effect of age. Multiple regression analyses with interaction effects revealed that streamline counts between left and right mid-dlPFC were negatively associated with planning performance specifically in early postadolescence. From the fourth life decade on, there was a trend for a reversed, positive association. These differential findings were corroborated by converging results from fractional anisotropy and white-matter density estimates in the genu of the corpus callosum where fibers connecting mid-dlPFC homologs traversed. Moreover, the results for streamline counts were regionally specific, marking the strength of mid-dlPFC connectivity as critical in predicting interindividual differences in planning performance across different stages of adulthood. Taken together, present findings provide first evidence for nonadditive effects of age on the relation between complex cognitive abilities and the structural connectivity of mid-dlPFC homologs.

Association between the Catechol O-methyltransferase (COMT) Val158met polymorphism and different dimensions of impulsivity

Background

Impulsivity is a multidimensional construct which has been associated with dopaminergic neurotransmission. Nonetheless, until this moment, few studies addressed the relationship between different types of impulsivity and the single nucleotide polymorphism caused by a substitution of valine (val) with methionine (met) in the 158 codon of the Catechol-o-Methyltransferase gene (COMT-val158met). The present study aimed to investigate the association between val158met COMT polymorphism and impulsive behavior measured by two neuropsychological tests.

Methodology/Principal Findings

We administered two neuropsychological tests, a Continuous Performance Task and the Iowa Gambling Task were applied to 195 healthy participants to characterize their levels of motor, attentional and non-planning impulsivity. Then, subjects were grouped by genotype, and their scores on impulsivity measures were compared. There were no significant differences between group scores on attentional and motor impulsivity. Those participants who were homozygous for the met allele performed worse in the Iowa Gambling Task than val/val and val/met subjects.

Conclusions/Significance

Our results suggest that met allele of val158met COMT polymorphism is associated with poor performance in decision-making/cognitive impulsivity task. The results reinforce the hypothesis that val and met alleles of the val158met polymorphism show functional dissociation and are related to different prefrontal processes.

COMT rs4680 Met is not always the 'smart allele': Val allele is associated with better working memory and larger hippocampal volume in healthy Chinese

Catechol-O-methyltransferase (COMT) Val158Met (rs4680) polymorphism plays a crucial role in regulating brain dopamine level. Converging evidence from Caucasian samples showed that, compared with rs4680 Val allele, the Met allele was linked to lower COMT activity, which in turn was linked to better cognitive performance such as working memory (WM) and to a larger hippocampus (a brain region important for WM). However, some behavioral studies have shown that the function of rs4680 appears to vary across different ethnic groups, with Chinese subjects showing an opposite pattern as that for Caucasians (i.e. the Val allele is linked to better cognitive functions related to WM in Chinese). Using a sample of healthy Han Chinese college students (ages from 19 to 21 years), this study investigated the association of COMT Val158Met genotype with behavioral data on a two-back WM task (n = 443, 189M/254F) and T1 MRI data (n = 320, 134M/186F). Results showed that, compared to the Met allele, the Val allele was associated with larger hippocampal volume (the right hippocampus: β = -0.118, t = -2.367, P = 0.019, and the left hippocampus: β = -0.099, t = -1.949, P = 0.052) and better WM performance (β = -0.110, t = -2.315, P = 0.021). These results add to the growing literature on differentiated effects of COMT rs4680 polymorphism on WM across populations and offer a brain structural mechanism for such population-specific genetic effects.

Antipsychotic medications and cognitive functioning in bipolar disorder: moderating effects of COMT Val108/158 Met genotype

BACKGROUND

There is a negative association between the use of antipsychotics and cognitive functioning in bipolar patients, which may be mediated by altered dopamine signaling in selected brain areas, and moderation thereof by genetic sequence variation such as COMT Val108/158Met. The interaction between antipsychotic drug use and the COMT Val108/158Met genotype on two-year cognitive functioning in bipolar patients was examined.

METHODS

Interaction between the COMT Val108/158Met and antipsychotics on a composite cognitive measure was examined in 51 bipolar patients who were assessed 12 times at two-monthly intervals over a period of two years (379 observations).

RESULTS

There was a significant negative effect of the interaction between antipsychotic medications and Val allele load on the composite cognitive measure in bipolar patients (p < 0.001).

CONCLUSIONS

The negative effects of antipsychotics on cognitive functioning in bipolar disorder may be moderated by the COMT Val 108/158 Met genotype, with a negative effect of Val allele load. If replicated, the results may be indicative of pharmacogenetic interactions in bipolar disorder.

Genetics of ageing-related changes in brain white matter integrity - a review

White matter (WM) plays a vital role in the efficient transfer of information between grey matter regions. Modern imaging techniques such as diffusion tensor imaging (DTI) have enabled the examination of WM microstructural changes across the lifespan, but there is limited knowledge about the role genetics plays in the pattern and aetiology of age-related WM microstructural changes. Family and twin studies suggest that the heritability of WM integrity measures changes over the lifespan, with the common DTI measure, fractional anisotropy (FA), showing moderate to high heritability in adults. However, few heritability studies have been undertaken in older adults. Linkage studies in middle-aged adults suggest that specific regions on chromosomes 3 and 15 may harbour genetic variants for WM integrity. A number of studies have investigated candidate genes, with the APOE ɛ4 polymorphism being the most frequently studied. Although these candidate gene studies suggest associations of particular genes with WM integrity measures in some specific brain regions, the findings remain inconsistent due to differences in their methodologies, samples and the outcome measures used. The APOE ɛ4 allele has been associated with decreased WM integrity (FA) in the cingulum, corpus callosum and parahippocampal gyrus. Only one genome-wide association study of global WM integrity measures in older adults has been published, and reported suggestive single nucleotide polymorphisms await replication. Overall, genetic age-related WM integrity studies are lacking and a concerted effort to examine the genetic determinants of age-related decline in WM integrity is clearly needed to improve our understanding of the ageing brain.

Diffusion magnetic resonance imaging for Brainnetome: a critical review

Increasing evidence shows that the human brain is a highly self-organized system that shows attributes of small-worldness, hierarchy and modularity. The "connectome" was conceived several years ago to identify the underpinning physical connectivities of brain networks. The need for an integration of multi-spatial and -temporal approaches is becoming apparent. Therefore, the "Brainnetome" (brain-net-ome) project was proposed. Diffusion magnetic resonance imaging (dMRI) is a non-invasive way to study the anatomy of brain networks. Here, we review the principles of dMRI, its methodologies, and some of its clinical applications for the Brainnetome. Future research in this field is discussed.

White matter integrity, fiber count, and other fallacies: the do's and don'ts of diffusion MRI

Diffusion-weighted MRI (DW-MRI) has been increasingly used in imaging neuroscience over the last decade. An early form of this technique, diffusion tensor imaging (DTI) was rapidly implemented by major MRI scanner companies as a scanner selling point. Due to the ease of use of such implementations, and the plausibility of some of their results, DTI was leapt on by imaging neuroscientists who saw it as a powerful and unique new tool for exploring the structural connectivity of human brain. However, DTI is a rather approximate technique, and its results have frequently been given implausible interpretations that have escaped proper critique and have appeared misleadingly in journals of high reputation. In order to encourage the use of improved DW-MRI methods, which have a better chance of characterizing the actual fiber structure of white matter, and to warn against the misuse and misinterpretation of DTI, we review the physics of DW-MRI, indicate currently preferred methodology, and explain the limits of interpretation of its results. We conclude with a list of 'Do's and Don'ts' which define good practice in this expanding area of imaging neuroscience.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

The effects of psychosis risk variants on brain connectivity: a review

In light of observed changes in connectivity in schizophrenia and the highly heritable nature of the disease, neural connectivity may serve as an important intermediate phenotype for schizophrenia. However, how individual variants confer altered connectivity and which measure of brain connectivity is more proximal to the underlying genetic architecture (i.e., functional or structural) has not been well delineated. In this review we consider these issues and the relative sensitivity of imaging methodologies to schizophrenia-related changes in connectivity. We searched PubMed for studies considering schizophrenia risk genes AND functional or structural connectivity. Where data was available, summary statistics were used to determine an estimate of effect size (i.e., Cohen's d). A random-effects meta-analysis was used to consider (1) the largest effect and (2) all significant effects between functional and structural studies. Schizophrenia risk variants involved in neurotransmission, neurodevelopment and myelin function were found to be associated with altered neural connectivity. On average, schizophrenia risk genes had a large effect on functional (mean d = 0.76) and structural connectivity (mean d = 1.04). The examination of the largest effect size indicated that the outcomes of functional and structural studies were comparable (Q = 2.17, p > 0.05). Conversely, consideration of effect size estimates for all significant effects suggest that reported effect sizes in structural connectivity studies were more variable than in functional connectivity studies, and that there was a significant lack of homogeneity across the modalities (Q = 6.928, p = 0.008). Given the more variable profile of effect sizes associated with structural connectivity, these data may suggest that structural imaging methods are more sensitive to a wider range of effects, as opposed to functional studies which may only be able to determine large effects. These conclusions are limited by methodological considerations, and require further investigation involving larger samples, multiple genes, and novel analysis techniques for confirmation.

Disruptive mRNA folding increases translational efficiency of catechol-O-methyltransferase variant

Catechol-O-methyltransferase (COMT) is a major enzyme controlling catecholamine levels that plays a central role in cognition, affective mood and pain perception. There are three common COMT haplotypes in the human population reported to have functional effects, divergent in two synonymous and one nonsynonymous position. We demonstrate that one of the haplotypes, carrying the non-synonymous variation known to code for a less stable protein, exhibits increased protein expression in vitro. This increased protein expression, which would compensate for lower protein stability, is solely produced by a synonymous variation (C¹⁶⁶T) situated within the haplotype and located in the 5′ region of the RNA transcript. Based on mRNA secondary structure predictions, we suggest that structural destabilization near the start codon caused by the T allele could be related to the observed increase in COMT expression. Our folding simulations of the tertiary mRNA structures demonstrate that destabilization by the T allele lowers the folding transition barrier, thus decreasing the probability of occupying its native state. These data suggest a novel structural mechanism whereby functional synonymous variations near the translation initiation codon affect the translation efficiency via entropy-driven changes in mRNA dynamics and present another example of stable compensatory genetic variations in the human population.

White matter changes in healthy adolescents at familial risk for unipolar depression: a diffusion tensor imaging study

Alterations in white matter integrity of several cortical and subcortical circuits have been reported in relation to unipolar major depressive disorder. It is not clear whether these white matter changes precede the onset of illness. In all, 13 adolescent volunteers with no personal or family history of a psychiatric disorder (controls) and 18 adolescent volunteers with no personal history of a psychiatric illness including depression, but who were at high risk for developing unipolar depression by virtue of parental depression (high-risk youth), underwent diffusion tensor imaging studies. An automated tract-based spatial statistics method, a whole-brain voxel-by-voxel analysis, was used to analyze the scans. Population average diffusion parameter values were also calculated for each tract. Adolescents at high risk for unipolar depression had lower fractional anisotropy (FA) values in the left cingulum, splenium of the corpus callosum, superior longitudinal fasciculi, uncinate, and inferior fronto-occipital fasciculi than did controls. Altered white matter integrity in healthy adolescents at familial risk for unipolar depression suggests that it might serve as a vulnerability marker for the illness.

The effects of catechol-O-methyl-transferase polymorphism Val158Met on functional connectivity in healthy young females: a resting EEG study

The catechol-O-methyl-transferase (COMT) gene has been linked to a wide spectrum of human phenotypes, including cognition, affective response, pain sensitivity, anxiety and psychosis. This study examined the modulatory effects of COMT Val158Met on neural interactions, indicated by connectivity strengths. Blood samples and resting state eyes-closed EEG signals were collected in 254 healthy young females. The COMT Val158Met polymorphism was decoded into 3 groups: Val/Val, Val/Met and Met/Met. The values of mutual information of 20 frontal-related channel pairs across delta, theta, alpha and beta frequencies were analyzed based on the time-frequency mutual information method. Our one-way ANOVA analyses revealed that the significant connection-frequency pairs were relatively left lateralized (P<0.01) and included F7-T3 and F7-C3 at delta frequency, and F3-F4, F7-T3, F7-C3, F7-P3, F3-C3, F3-F7 and F4-F8 at theta frequency. The F-test at F7-T3 and F7-C3 theta surpassed the statistical threshold of P<0.003 (after Bonferroni correction). For all the above connection-frequency pairs, there was a dose-dependent trend in the connectivity strengths of the alleles as follows: Val/Val>Val/Met>Met/Met. Our analyses complemented previous literature regarding neural modulation by the COMT Val158Met polymorphism. The implication to the pathogenesis in schizophrenia was also discussed. Further studies are needed to clarify whether there is gender difference on this gene-brain interaction.

COMT genotype affects prefrontal white matter pathways in children and adolescents

Diffusion tensor imaging is widely used to evaluate the development of white matter. Information about how alterations in major neurotransmitter systems, such as the dopamine (DA) system, influence this development in healthy children, however, is lacking. Catechol-O-metyltransferase (COMT) is the major enzyme responsible for DA degradation in prefrontal brain structures, for which there is a corresponding genetic polymorphism (val158met) that confers either a more or less efficient version of this enzyme. The result of this common genetic variation is that children may have more or less available synaptic DA in prefrontal brain regions. In the present study we examined the relation between diffusion properties of frontal white matter structures and the COMT val158met polymorphism in 40 children ages 9-15. We found that the val allele was associated with significantly elevated fractional anisotropy values and reduced axial and radial diffusivities. These results indicate that the development of white matter in healthy children is related to COMT genotype and that alterations in white matter may be related to the differential availability of prefrontal DA. This investigation paves the way for further studies of how common functional variants in the genome might influence the development of brain white matter.