Application of an automated parcellation method to the analysis of pediatric brain volumes

Neuroimaging Phenotypes Associated With Risk and Resilience for Psychosis and Autism Spectrum Disorders in 22q11.2 Microdeletion Syndrome

Identification of biological risk factors that contribute to the development of complex neuropsychiatric disorders such as psychosis and autism spectrum disorder (ASD) is key for early intervention and detection. Furthermore, parsing the biological heterogeneity associated with these neuropsychiatric syndromes will help us understand the neural mechanisms underlying psychiatric symptom development. The 22q11.2 microdeletion syndrome (22q11DS) is caused by a recurrent genetic mutation that carries significantly increased risk for developing psychosis and/or ASD. In this review, I provide an brief introduction to 22q11DS and discuss common phenotyping strategies that are used to assess psychosis and ASD in this population. I then summarize neuroimaging phenotypes associated with psychosis and ASD in 22q11.DS. Next, I discuss challenges within the field and provide practical suggestions to overcome these obstacles. Finally, I discuss future directions for moving 22q11DS risk and resilience research forward.

Imaging genetics in neurodevelopmental psychopathology

Neurodevelopmental disorders are defined by highly heritable problems during development and brain growth. Attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorders (ASDs), and intellectual disability (ID) are frequent neurodevelopmental disorders, with common comorbidity among them. Imaging genetics studies on the role of disease-linked genetic variants on brain structure and function have been performed to unravel the etiology of these disorders. Here, we reviewed imaging genetics literature on these disorders attempting to understand the mechanisms of individual disorders and their clinical overlap. For ADHD and ASD, we selected replicated candidate genes implicated through common genetic variants. For ID, which is mainly caused by rare variants, we included genes for relatively frequent forms of ID occurring comorbid with ADHD or ASD. We reviewed case-control studies and studies of risk variants in healthy individuals. Imaging genetics studies for ADHD were retrieved for SLC6A3/DAT1, DRD2, DRD4, NOS1, and SLC6A4/5HTT. For ASD, studies on CNTNAP2, MET, OXTR, and SLC6A4/5HTT were found. For ID, we reviewed the genes FMR1, TSC1 and TSC2, NF1, and MECP2. Alterations in brain volume, activity, and connectivity were observed. Several findings were consistent across studies, implicating, for example, SLC6A4/5HTT in brain activation and functional connectivity related to emotion regulation. However, many studies had small sample sizes, and hypothesis-based, brain region-specific studies were common. Results from available studies confirm that imaging genetics can provide insight into the link between genes, disease-related behavior, and the brain. However, the field is still in its early stages, and conclusions about shared mechanisms cannot yet be drawn.

Developmental variation in amygdala volumes among children with posttraumatic stress

This article examined associations between indices of maturation (age and Tanner stage) and amygdala volumes in 24 youth (aged 7-14) with posttraumatic stress disorder symptoms and a matched control group. Fifteen of the youth with exposure to trauma were also re-evaluated one year later. A positive association between maturation and right amygdala volumes was observed in the trauma group but not in controls. Associations with maturation remained when controlling for a number of possible covariates and over time. Developmentally younger youth (Tanner stage 1 and 2) showed increases and older (Tanner stage 3 and 4) decreases in right amygdala volumes.

Fragile X-associated disorders: a clinical overview

Fragile X Syndrome (FraX) is the most common inherited cause of learning disability worldwide. FraX is an X-linked neuro-developmental disorder involving an unstable trinucleotide repeat expansion of cytosine guanine guanine (CGG). Individuals with the full mutation of FraX have >200 GG repeats with premutation carriers having 55-200 GG repeats. A wide spectrum of physical, behavioural, cognitive, psychiatric and medical problems have been associated with both full mutation and premutation carriers of FraX. In this review, we detail the clinical profile and examine the aetiology, epidemiology, neuropathology, neuroimaging findings and possible management strategies for individuals with both the full mutation and premutation of FraX.

Neuroanatomic predictors to prodromal psychosis in velocardiofacial syndrome (22q11.2 deletion syndrome): a longitudinal study

BACKGROUND

Up to 30% of young adults with velocardiofacial syndrome (VCFS; 22q11.2 deletion syndrome) develop schizophrenia or psychosis. Identifying the neuroanatomic trajectories that increase risk for psychosis in youth with this genetic disorder is of great interest.

METHODS

We acquired high-resolution anatomic magnetic resonance images and measures of psychiatric function on 72 youth with VCFS, 26 unaffected siblings, and 24 age-matched community control subjects at two time points: between late childhood (mean age 11.9 years) and mid-adolescence (mean age 15.1 years).

RESULTS

With the exception of cranial gray matter and orbitofrontal prefrontal cortex, neuroanatomic trajectories in youth with VCFS were comparable to unaffected siblings and community control subjects during this developmental window. However, in youth with VCFS, longitudinal decreases in the volumes of cranial gray and white matter, prefrontal cortex, mesial temporal lobe, and cerebellum were associated with increased combined prodromal symptoms at Time 2. In contrast, only decreases in temporal lobe gray matter volumes (p < .002) and verbal IQ (p < .002) predicted specifically to positive prodromal symptoms of psychosis at Time 2.

CONCLUSIONS

These findings are in line with studies of non-VCFS individuals at risk for schizophrenia and suggest that early decrements in temporal lobe gray matter may be predictive of increased risk of prodromal psychotic symptoms in youth with VCFS.

Cingulate gyrus morphology in children and adolescents with fetal alcohol spectrum disorders

Alcohol consumption during pregnancy can lead to a variety of cognitive and other birth defects, collectively termed fetal alcohol spectrum disorders (FASD), and including the Fetal Alcohol Syndrome (FAS). This study examined the impact of gestational alcohol exposure on the morphology of the cingulate gyrus, given this region's role in cognitive control, attention, and emotional regulation, all of which are affected in children with FASD. Thirty-one youth (ages 8-16) with histories of heavy prenatal alcohol exposure (n=21) and demographically matched comparison subjects (n=10) underwent structural magnetic resonance imaging. The cingulate gyrus was manually delineated, and parcellated volumes of grey and white matter were compared across groups. Alcohol-exposed individuals had significantly smaller raw cingulate grey matter, white matter, and tissue volumes compared with controls. After adjustment for respective cranial tissue constituents, only white matter volumes remained significantly reduced, and this held regardless of whether or not the child qualified for a diagnosis of FAS. A correlation between posterior cingulate grey matter volume and the WISC-III Freedom from Distractibility Index was also observed in alcohol-exposed children. These data suggest that cingulate white matter is compromised beyond global white matter hypoplasia in alcohol-exposed individuals, regardless of FAS diagnosis. The observed volumetric reductions in the cingulate gyrus may contribute to the disruptive and emotionally dysregulated behavioral profile commonly observed in this population.

Gyrification patterns in monozygotic twin pairs varying in discordance for autism

In order to disentangle genetic and environmental contributions to cortical anomalies in children with autism, we investigated cortical folding patterns in a cohort of 14 monozygotic (MZ) twin pairs who displayed a range of phenotypic discordance for autism, and 14 typically developing community controls. Cortical folding was assessed with the gyrification index, which was calculated on high resolution anatomic MR images. We found that the cortical folding patterns across most lobar regions of the cerebral cortex was highly discordant within MZ twin pairs. In addition, children with autism and their co-twins exhibited increased cortical folding in the right parietal lobe, relative to age- and gender-matched typical developing children. Increased folding in the right parietal lobe was associated with more symptoms of autism for co-twins. Finally, the robust association between cortical folding and IQ observed in typical children was not observed in either children with autism or their co-twins. These findings, which contribute to our understanding of the limits of genetic liability in autism, suggest that anomalies in the structural integrity of the cortex in this PDD may disrupt the association between cortical folding and intelligence that has been reported in typical individuals, and may account, in part, for the deficits in visual spatial attention and in social cognition that have been reported in children with autism.

Neuroimaging and neuropsychological follow-up study in a pediatric brain tumor patient treated with surgery and radiation

Intracranial tumors are the most common neoplasms of childhood, accounting for approximately 20% of all pediatric malignancies. Radiation therapy has led directly to significant increases in survival of children with certain types of intracranial tumors; however, given the aggressive nature of this therapy, children are at risk for exhibiting changes in brain structure, neuronal biochemistry, and neurocognitive functioning. In this case report, we present neuropsychological, magnetic resonance imaging, proton magnetic resonance spectroscopic imaging, and diffusion tensor imaging data for two adolescents (one patient with ependymal spinal cord tumor with intracranial metastases, and one healthy, typically developing control) from three time points as defined by the patient's radiation schedule (baseline before the patient's radiation therapy, 6 months following completion of the patient's radiation, and 27 months following the patient's radiation). In the patient, there were progressive decreases in gray and white matter volumes as well as early decreases in mean N-acetyl aspartate/choline (NAA/Cho) ratios and fractional anisotropy (FA) in regions with normal appearance on conventional MRI. At the last follow-up, NAA/Cho and FA tended to change in the direction to normal values in selected regions. At the same time, the patient had initial reduction in language and motor skills, followed by return to baseline, but later onset delay in visuospatial and visual perceptual skills. Results are discussed in terms of sensitivity of the four techniques to early and late effects of treatment, and avenues for future investigations.

Associations between performance on the Rey-Osterrieth Complex Figure and regional brain volumes in children with and without velocardiofacial syndrome

Ninety-two children with velocardiofacial syndrome (VCFS), a genetic disorder caused by a microdeletion of chromosome 22q11.2 and an age, race, and gender-ratio comparable sample of 59 control participants were included in the project. Participants received an MRI as well as a comprehensive neuropsychological battery; the primary outcome measure in the current report is the Rey-Osterrieth Complex Figure (ROCF). Children with VCFS performed less well on the ROCF and have lower whole brain volume compared to controls. After controlling for whole brain volume differences, children with VCFS have bilaterally less parietal lobe gray and white matter yet more frontal lobe white matter. Brain-behavior relationships include: (a) for both groups, parietal volumes (both gray and white matter) predicted ROCF Copy Organization performance and frontal volumes (both gray and white matter) predicted ROCF Copy Accuracy performance; (b) for controls, frontal white matter also predicted ROCF Copy Organization performance; (c) ROCF Recall Organization performance was best predicted by frontal gray matter volume only in our controls; ROCF Recall Accuracy performance was best predicted by frontal gray matter volume in both groups; and (d) in children with VCFS, performance on the ROCF-Copy Structural Elements Accuracy scale was predicted by right hemisphere white matter volume. Our hypotheses were also retested using IQ-matched and whole brain volume-matched subsamples. Identical results were obtained in these analyses. Assumptions about the organization of and the localization of the brain structures that subserve specific cognitive functions in the typically developing brain may not apply in the abnormally developing brain.

Neuroimaging correlates of parent ratings of working memory in typically developing children

The purpose of the present study was to investigate construct validity of parent ratings of working memory in children, using a multi-trait/multi-method design including neuroimaging, rating scales, and performance-based measures. Thirty-five typically developing children completed performance-based tests of working memory and nonexecutive function (EF) skills, received volumetric MRI, and were rated by parents on both EF-specific and broad behavior rating scales. After controlling for total cerebral volume and age, parent ratings of working memory were significantly correlated with frontal gray, but not temporal, parietal, or occipital gray, or any lobar white matter volumes. Performance-based measures of working memory were also moderately correlated with frontal lobe gray matter volume; however, non-EF parent ratings and non-EF performance-based measures were not correlated with frontal lobe volumes. Results provide preliminary support for the convergent and discriminant validity of parent ratings of working memory, and emphasize their utility in exploring brain-behavior relationships in children. Rating scales that directly examine EF skills may potentially have ecological validity, not only for "everyday" function, but also as correlates of brain volume. (JINS, 2009, 15, 31-41.).

Relationship of temporal lobe volumes to neuropsychological test performance in healthy children

Ecological validity of neuropsychological assessment includes the ability of tests to predict real-world functioning and/or covary with brain structures. Studies have examined the relationship between adaptive skills and test performance, with less focus on the association between regional brain volumes and neurobehavioral function in healthy children. The present study examined the relationship between temporal lobe gray matter volumes and performance on two neuropsychological tests hypothesized to measure temporal lobe functioning (visual perception-VP; peabody picture vocabulary test, third edition-PPVT-III) in 48 healthy children ages 5-18 years. After controlling for age and gender, left and right temporal and left occipital volumes were significant predictors of VP. Left and right frontal and temporal volumes were significant predictors of PPVT-III. Temporal volume emerged as the strongest lobar correlate with both tests. These results provide convergent and discriminant validity supporting VP as a measure of the "what" system; but suggest the PPVT-III as a complex measure of receptive vocabulary, potentially involving executive function demands.

Selective cerebral volume reduction in Rett syndrome: a multiple-approach MR imaging study

BACKGROUND AND PURPOSE

Previous studies have examined volumetric abnormalities in Rett syndrome (RTT), using MR imaging and focusing on selective changes. However, these studies preceded the identification of MECP2 as the gene mutated in most RTT cases. We studied regional brain volume changes as noted by MR imaging in girls with RTT who had mutations in the MECP2 gene and more or less severe clinical outcomes to further characterize the neuroanatomy of RTT and its correlations with clinical severity.

MATERIALS AND METHODS

Complementary semiautomated Talairach- and voxel-based approaches were used to study spoiled gradient-recalled acquisition sequence MR imaging scans from 23 girls with MECP2 mutations/RTT, including a pair of discordant monozygotic twins and 25 age-matched control girls. Both absolute and relative volumetric changes were examined to account for the well-documented global reduction in brain volume seen in RTT.

RESULTS

Absolute volumetric reductions were observed throughout the brain in RTT. Selective/relative decreases in parietal lobe gray matter, particularly in the dorsal parietal region, and mild, diffuse reductions in cortical white matter were observed in the RTT group compared with control subjects. In girls with RTT and a more severe phenotype, anterior frontal lobe volumes were relatively more reduced. Twin comparisons revealed selective preservation of the occipital cortex.

CONCLUSION

Selective reductions of dorsal parietal gray matter and preservation of the occipital cortex seem to be basic neuroanatomic features of RTT, whereas preferential reduction of the anterior frontal lobe appears to be a correlate of clinical severity in this disorder. The most affected brain regions include those that may underlie key functional deficits observed in RTT.

Impact of ventricular enlargement on the measurement of metabolic activity in spatially normalized PET

In pathologic brains with morphological alterations, the process of spatial normalization, as performed by SPM methods, may introduce a confounding effect in the measurement of metabolic activity data. To investigate the effect of the spatial normalization of PET images, we analyzed MRI and PET studies of 20 schizophrenic patients and 18 controls. Using a Talairach-based segmentation procedure and manual segmentation, we measured regional metabolic activity in the untransformed brains and after their spatial normalization. The effect of spatial normalization seems minimal for large ROIs like the main brain lobes, even in brains showing pronounced morphological abnormalities. However, the caudate nucleus shows a considerable change in metabolic activity values after normalization. This normalization effect is much larger in patients than in controls, and leads to artifactual differences between them. We obtained incorrect results (SPM analysis) regarding functional differences between patients and controls in the caudate due to this bias introduced by the spatial normalization. There was a significant correlation between the size of the lateral ventricles and the underestimation of metabolic activity of the caudate. Normalization bias seems to arise from a misalignment of the caudate in the normalized space, pixel overlap between the normalized caudate, and the caudate of the template being on average lower than 50% in both groups. Spatial normalization of the PET images of pathologic brains may introduce a potential source of error that should be taken into account in the analysis of functional data, in particular, in the study of small brain nuclei like the caudate.

Autistic Spectrum Disorders in Velo-cardio Facial Syndrome (22q11.2 Deletion)

The extent to which the phenotype of children comorbid for velocardiofacial syndrome (VCFS) and autism spectrum disorders (ASD) differs from that of VCFS-only has not been studied. The sample consisted of 41 children (20 females) with VCFS, ranging in age from 6.5 years to 15.8 years. Eight children with VCFS met formal DSM-IV diagnostic criteria for autism based upon the ADI-R. These eight plus an additional nine participants met diagnostic criteria for an autistic spectrum disorder (VCFS + ASD). Ninety-four percent of the children with VCFS + ASD had a co-occurring psychiatric disorder while 60% of children with VCFS had a psychiatric disorder. Children with VCFS + ASD had larger right amygdala volumes. All other neuroanatomic regions of interest were statistically similar between the two groups.

Abnormal patterns of cortical gyrification in velo-cardio-facial syndrome (deletion 22q11.2): an MRI study

Velo-cardio-facial syndrome (VCFS), also known as 22q11.2 deletion syndrome, is a common genetic condition associated with increased risk for developing schizophrenia. Given that cortical malformations play an integral role in the pattern of neuroanatomical alterations associated with VCFS, the aim of the present study was to quantify and localize gyral abnormalities. Magnetic resonance images were obtained on a 1.5 T scanner. The gyrification index (GI), a measure of the degree of cortical complexity, was differentially calculated for each lobe using a semi-automated protocol. The GI was calculated for 37 patients affected by VCFS as well as for 36 comparison individuals group-matched for age, handedness, and gender. The subjects affected by VCFS showed a significant decrease in the GI in the frontal and parietal lobes compared with the control group. The pattern of decreased gyrification in the frontal and parietal lobes further defines the structural changes associated with the syndrome and suggests underlying abnormalities in neural connectivity. Aberrant connectivity may be partially responsible for the cognitive and behavioral impairments in the syndrome, as well as the high incidence of schizophrenia among affected individuals.

Children's reading performance is correlated with white matter structure measured by diffusion tensor imaging

We investigated the white matter structure in children (n = 14) with a wide range of reading performance levels using diffusion tensor imaging (DTI), a form of magnetic resonance imaging. White matter structure in a left temporo-parietal region that had been previously described as covarying with reading skill in adult readers also differs between children who are normal and poor readers. Specifically, the white matter structure measured using fractional anisotropy (FA) and coherence index (CI) significantly correlated with behavioral measurements of reading, spelling, and rapid naming performance. In general, lower anisotropy and lower coherence were associated with lower performance scores. Although the magnitude of the differences in children are smaller than those in adults, the results support the hypothesis that the structure of left temporoparietal neural pathways is a significant component of the neural system needed to develop fluent reading.

Gray matter alteration in dyslexia: converging evidence from volumetric and voxel-by-voxel MRI analyses

Affecting up to 4-10% of the population, dyslexia is a highly prevalent, childhood onset developmental disorder adversely influencing multiple domains of adaptive functioning throughout the lifespan. The present brain imaging study was conducted in order to investigate the neuroanatomical correlates of developmental dyslexia. The MRI brain scans of 10 males with dyslexia and 14 matched controls were analyzed with (1) a classical volumetric method measuring gray and white matter lobar volumes and (2) a voxel-by-voxel method. The voxel-by-voxel method identifies changes in tissue density and localizes morphologic alterations without limiting the analyses to predefined regions. Subsequent correlations between gray matter density and neuropsychological performance on specific phonological processing tasks (rhyme judgment) were conducted. Volumetric analyses revealed significantly reduced gray matter volumes in both temporal lobes in dyslexic individuals. The voxel-by-voxel analyses further localized changes to the left temporal lobe, revealing reduced gray matter density in the middle and inferior temporal gyri. Conversely, increased gray matter density was found in the precentral gyri bilaterally. As a combined group, the dyslexic and control subjects demonstrated positive correlations between performance on the rhyme judgment tasks and gray matter density in the middle and inferior frontal gyri, and the middle temporal gyri bilaterally. The current study indicates that dyslexia is associated with a structural gray matter deficit involving a complex fronto-temporal network implicated in phonological processing.

Frontal and caudate alterations in velocardiofacial syndrome (deletion at chromosome 22q11.2)

This study investigated the morphology of the frontal lobe and the caudate nucleus in velocardiofacial syndrome, a neurogenetic disorder caused by a microdeletion at chromosome 22q11.2 and frequently associated with severe psychiatric disturbances. Volumes of the caudate nucleus and subregions of the frontal lobe were compared on magnetic resonance images of 10 children with velocardiofacial syndrome and 10 age- and gender-matched controls. Frontal deep white matter was reduced significantly (by about 23%) in subjects with velocardiofacial syndrome relative to controls. Frontal and prefrontal volumes were also reduced in subjects with velocardiofacial syndrome, although not disproportionately to whole brain volume. The volume of the right caudate nucleus was increased in children with velocardiofacial syndrome. Associations between right caudate and right frontal regions were noted in controls but not in children with velocardiofacial syndrome. These findings suggest frontostriatal dysfunction in children with velocardiofacial syndrome. Insofar as up to 30% of adults with velocardiofacial syndrome (also known as chromosome 22q11 deletion syndrome) develop schizophrenia and frontostriatal dysfunction has been noted in schizophrenia, the findings support the hypothesis that velocardiofacial syndrome might represent a neurodevelopmental model of schizophrenia.

Brain development in Turner syndrome: a magnetic resonance imaging study

Turner syndrome (TS) results from the absence of an X chromosome in females. This genetic condition is associated with specific cognitive deficits and variations in brain volumes. The goal of this study was to use high-resolution magnetic resonance imaging (MRI) to determine morphological variations in TS and to investigate the effects of parental origin of the X chromosome on brain development in TS. MRI brain scans were acquired from 26 girls with TS and 26 age- and gender-matched controls. Seventeen of the TS subjects had a maternally inherited X chromosome (Xm), and nine of the subjects had a paternally inherited X chromosome (Xp). Rater-blind morphometric analyses were conducted to compare tissue volume differences between girls with TS and controls. Three-way analyses were used to compare subgroups and controls. Subjects with TS demonstrated bilateral decreases in parietal gray and occipital white matter accompanied by increased cerebellar gray matter. Subjects with Xm showed decreased occipital white matter and increased cerebellar gray matter compared to controls. No differences were found in comparisons between subjects with Xp and controls or between subjects with Xm and Xp. Results suggest that X monosomy affects posterior cerebral and cerebellar anatomy in TS. While differences between comparisons of Xm and Xp to controls might suggest an imprinting effect, no significant differences were found when the two subgroups were directly compared to each other. Further investigation into the possible role of genomic imprinting is therefore warranted.

MRI parcellation of the frontal lobe in boys with attention deficit hyperactivity disorder or Tourette syndrome

Dysfunction of frontal-striatal-thalamic-frontal circuitry has been hypothesized to underlie both attention deficit hyperactivity disorder (ADHD) and Tourette syndrome (TS). Several research groups have therefore used anatomic magnetic resonance imaging (aMRI) to obtain volumetric measurements of subregions of the frontal lobe in these disorders. Most previous studies have relied on subparcellation methods that utilize callosal landmarks to derive subregions of the frontal lobe. In contrast, we present here an investigation of frontal lobe morphometry in ADHD and TS based on a reliable frontal subparcellation protocol that combines contiguous sulcal/gyral boundaries to derive frontal lobe modules based on prior functional studies. This highly reliable procedure subdivides the frontal lobe into five major modules: prefrontal, premotor, motor (precentral gyrus), anterior cingulate, and deep white matter. The first four modules are also segmented into gray and gyral white matter compartments. The protocol was applied to T1-weighted, SPGR coronal MRI images of 13 school-aged boys with ADHD, 13 boys with TS, and 13 age- and gender-matched controls. In ADHD, we found volumetric reductions in both the gray and white matter of the prefrontal cortex. These findings, in conjunction with previous reports on basal ganglia abnormalities, suggest that prefrontal-striatal pathways may be anomalous in ADHD. In TS, we found volumetric decreases in the left deep frontal white matter. Decreases in deep white matter suggest the presence of abnormalities in long associational and projection fiber bundles in TS. The findings of this study both confirm and extend our knowledge of the neurobiology of ADHD and TS, indicating that the reliable parcellation method presented has the potential of increasing our understanding of the role of the frontal lobe in developmental and psychiatric disorders.

Smaller prefrontal and premotor volumes in boys with attention-deficit/hyperactivity disorder

BACKGROUND

Anatomic magnetic resonance imaging (MRI) studies of attention-deficit/hyperactivity disorder (ADHD) have been limited by use of callosal rather than sulcal/gyral landmarks in defining cerebral lobes and functionally relevant sublobar regions (e.g., prefrontal cortex). We present an investigation of cerebral volumes in ADHD using a Talairach-based approach that uses cortical landmarks to define functionally relevant regions.

METHODS

Volumes were compared between groups of 12 boys with ADHD and 12 age- and gender-matched control subjects, using a series of multiple analyses of variance.

RESULTS

Boys with ADHD had (on average) 8.3% smaller total cerebral volumes. Significant reductions in lobar volumes were seen only for the frontal lobes. Within the frontal lobes, a reduction was seen in both gray and white matter volumes, with some evidence suggesting lateralization of these findings: reduction in frontal white matter volume was specific to the left hemisphere; there was a bilateral reduction in frontal gray matter volume but more so in the right hemisphere. Subparcellation of the frontal lobe revealed smaller prefrontal, premotor, and deep white matter volumes.

CONCLUSIONS

Findings suggest that ADHD is associated with decreased frontal lobe gray and white matter volumes. More than one subdivision of the frontal lobes appears to be reduced in volume, suggesting that the clinical picture of ADHD encompasses dysfunctions attributable to anomalous development of both premotor and prefrontal cortices.

Cerebral growth in Fragile X syndrome: review and comparison with Down syndrome

Neuroimaging studies have shown selective changes in brain size in Fragile X syndrome (FraX), which include reductions in the posterior cerebellar vermis, age-dependent increases in hippocampal volume, and enlarged caudate nucleus and thalamus. Contrasting with these limbic and subcortical anomalies, much less is known about the neocortex in FraX. The present study attempted to examine cerebral and lobar-level volumetric changes in young males with FraX (2-7 years), by comparing groups of subjects with full mutation (FM) and mosaicism (Mos) with both age-matched controls and subjects with developmental language delay (DLD) and Down syndrome (DS). For this purpose, we used high resolution (i.e, SPGR) MRI scans and semi-automated methods for segmenting (tissue class) and parcellating (i.e., Talairach) the brain. In agreement with previous studies, we found no changes in overall brain or cerebrum size in FraX. Nevertheless, boys with FM FraX had relative reductions in temporal lobe volume (primarily gray matter) and relative preservation/enlargement of parietal white matter volume. While temporal lobe reductions were not specific, since they were also observed in DLD and DS subjects, parietal preservation/enlargement was only seen in FraX. The relevance of these preliminary findings was emphasized by comparisons between FraX groups, which revealed more marked changes in FM FraX than in Mos FraX (i.e., gene dosage). While cross-sectional analyses revealed marked age-dependent decreases in DS, a group showing marked global and lobar volumetric reductions, there were no changes over time in FraX. These neuroimaging data are discussed in the context of FraX neurobiology and other developmental disorders.

Neuroimaging studies in Rett syndrome

Neuroimaging is a key instrument for determining structural and in vivo functional status of the brain, non-invasively. Multiple approaches can now determine aspects of anatomic and neurochemical changes in brain, and have been utilized effectively in Rett Syndrome patients to understand the biological basis of this neurodevelopmental disorder. Studies performed at our institute include volumetric analyses of MRI, magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), cerebral blood flow measurements with MRI, and positron emission tomography scans (PET). These studies have provided considerable insight into mechanisms underlying the clinical features of this disease. Volumetric analyses suggest that decreased brain volume in RS results from global reductions in both gray and white matter of the brain. A selective vulnerability of the frontal lobes is evidenced by the preferential reduction of blood flow, increased choline and reduced n-acetyl aspartate (NAA) by MRS, and increased glucose uptake in these same regions as shown by ((18)F)-fluorodeoxyglucose (FDG) PET scans. We hypothesize that the increased glucose uptake relates to increased glutamate cycling in synapses. The resulting neuroexcitotoxic injury to the developing brain contributes to the seizures, behavioral disturbance and respiratory irregularities commonly seen in phases 1 and 2 of this disorder.

Effects of image orientation on the comparability of pediatric brain volumes using three-dimensional MR data

PURPOSE

The purpose of this study was to examine the comparability of morphometric measurements made on pediatric data sets collected at five scanner locations, each using variations on a 3D spoiled gradient-recalled echo (SPGR) pulse sequence.

METHOD

Archived MR data from 60 typically developing children were collected and separated into seven groups based on the pulse sequence used. A highly automated image-processing procedure was used to segment the brain data into white tissue, gray tissue, and CSF compartments and into various neuroanatomic regions of interest.

RESULTS

Volumetric comparisons between groups revealed differences in areas of the temporal and occipital lobes. These differences were observed when comparing data sets with different image orientations and appeared to be due to partial volume averaging (PVA) and susceptibility-induced geometric distortions.

CONCLUSION

Our results indicate that slice selection and image resolution should be controlled in volumetric studies using aggregated data from multiple centers to minimize the effects of PVA and susceptibility-induced geometric distortions.

Regional cortical white matter reductions in velocardiofacial syndrome: a volumetric MRI analysis

BACKGROUND

Velocardiofacial syndrome, caused by a microdeletion on chromosome 22q.11, is associated with craniofacial anomalies, cardiac defects, learning disabilities, and psychiatric disorders. To understand how the 22q.11 deletion affects brain development, this study examined gray and white matter volumes in major lobar brain regions of children with velocardiofacial syndrome relative to control subjects.

METHODS

Subjects were ten children with velocardiofacial syndrome and ten age- and gender-matched unaffected children. Coronal images were acquired with a 3-D spoiled gradient echo series and partitioned into 124, 1.5-mm contiguous slices. A stereotaxic grid was used to subdivide brain tissue into cerebral lobes, which were segmented into gray, white, and CSF compartments using an algorithm based on intensity values and tissue boundaries. Nonparametric statistics were used to compare lobar volumes of gray and white matter.

RESULTS

Analyses indicated that children with velocardiofacial syndrome had significantly smaller volumes in nonfrontal, but not frontal, lobar brain regions. Volume reductions affected nonfrontal white matter to a greater extent than nonfrontal gray matter.

CONCLUSIONS

The presence of white matter reductions may be related to disturbances in myelination or axonal integrity in velocardiofacial syndrome. Further work is required to delineate the nature and extent of white matter anomalies, and to link them to variation in the neurocognitive and neuropsychiatric phenotype of velocardiofacial syndrome.

A quantitative MRI study of posterior fossa development in velocardiofacial syndrome

BACKGROUND

Velocardiofacial syndrome (VCFS) has been identified as a risk factor for developing schizophrenia. Qualitative neuroimaging studies indicated that VCFS was frequently associated with abnormal development of structures in the posterior fossa of the brain. The objective of this investigation was to identify the specific structures affected in the posterior fossa and investigate the association of these neuroanatomic variations with behaviors potentially related to later-onset psychiatric disorders.

METHODS

Twenty-four children and adolescents with VCFS individually matched for age and gender with 24 control subjects received magnetic resonance imaging scans. Analysis of covariance models were used to investigate regional brain differences. Association between brain areas and behaviors measured on the Child Behavior Checklist (CBCL) were assessed using simple regression models.

RESULTS

Children with VCFS had significantly smaller size of vermal lobules VI--VII and the pons after adjusting for overall brain size. There were no significant associations between scores on the CBCL and measures of neuroanatomic variation within the VCFS group.

CONCLUSIONS

Structural alterations of the posterior fossa in VCFS are specifically limited to cerebellar vermis lobules VI--VII and pons. Previous literature has suggested that the vermis is involved in social cognition, and alteration of lobules VI--VII could therefore partially explain the neurobehavioral profile associated with VCFS.

IV. Neuroanatomy of Williams syndrome: a high-resolution MRI study

Williams syndrome (WMS), a genetic condition resulting from a contiguous deletion on the long arm of chromosome 7, is associated with a relatively consistent profile of neurocognitive and neurobehavioral features. The distinctiveness and regularity of the profile of learning and behavioral characteristics in this genetic condition suggests that underlying neurobiological correlates may be identifiable. In this initial study, we report findings derived from a high-resolution neuroimaging study of 14 young adult subjects with WMS and an individually matched normal control group. Compared to controls, subjects with WMS were noted to have decreased overall brain and cerebral volumes, relative preservation of cerebellar and superior temporal gyrus (STG) volumes, and disproportionate volume reduction of the brainstem. Analyses also suggested that the pattern of cerebral lobe proportions in WMS may be altered compared to normal controls with a greater ratio of frontal to posterior (parietal+occipital) tissue. Assessment of tissue composition indicated that, relative to controls, individuals with WMS have relative preservation of cerebral gray matter volume and disproportionate reduction in cerebral white matter volume. However, within the cerebral gray matter tissue compartment, the right occipital lobe was noted to have excess volume loss. Combined with our growing knowledge of the function of genes in the commonly deleted region for WMS, more detailed information regarding the structure and function of the WMS brain will provide a unique opportunity for elucidating meaningful correlations amongst genetic, neurobiological, and neurobehavioral factors in humans.

Morphological alteration of temporal lobe gray matter in dyslexia: an MRI study

Functional imaging studies of developmental dyslexia have reported reduced task-related neural activity in the temporal and inferior parietal cortices. To examine the possible contribution of subtle anatomic deviations to these reductions, volumes were measured for the major lobes of the brain, the subcortical nuclei, cerebellum, and lateral ventricles on magnetic resonance imaging (MRI) scans from 16 right-handed dyslexic men, ages 18 to 40, and 14 matched controls, most of whom had previously undergone PET imaging. A specific decrease in tissue volume was localized to the temporal lobes and was particularly prominent on the left (p < .01). An analysis of tissue composition revealed that this reduction was primarily attributable to decreased gray matter within the left temporal lobe (p < .002). Further segmentation of the temporal lobe showed that this reduction was not confined to the superior temporal gyrus, the primary location of primary auditory cortex. Reductions of temporal lobe gray matter may reflect a regional decrease in neuronal number or neuropil, which in turn may result in reading impairment.

Relationship of cognitive functioning, whole brain volumes, and T2-weighted hyperintensities in neurofibromatosis-1

Using quantitative magnetic resonance imaging morphometry, we report that the whole brain volumes of patients with neurofibromatosis-1 are significantly larger than normal, confirm the prevalence of macrocephaly as about 50%, and report that macrocephaly in patients with neurofibromatosis-1 does not appear to be related to the familial or sporadic origin of the neurofibromatosis-1 or to the presence or absence of T2-weighted hyperintensities. No strong relationship emerged between the extent of neurofibromatosis-1-associated impairment of cognitive functions and degree of macrocephaly; however, the macrocephalic neurofibromatosis-1 group did have a significant verbal impairment relative to the nonmacrocephalic neurofibromatosis-1 group in vocabulary (P < .009).