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Biomedical subjects

Gregory L Wallace

Publications and source records attributed to Gregory L Wallace.

9 recordsLinked to original sources
PubMed2007

A multivariate analysis of neuroanatomic relationships in a genetically informative pediatric sample.

An important component of brain mapping is an understanding of the relationships between neuroanatomic structures, as well as the nature of shared causal factors. Prior twin studies have demonstrated that much of individual differences in human anatomy are caused by genetic differences, but information is limited on whether different structures share common genetic factors. We performed a multivariate statistical genetic analysis on volumetric MRI measures (cerebrum, cerebellum, lateral ventricles, corpus callosum, thalamus, and basal ganglia) from a pediatric sample of 326 twins and 158 singletons. Our results suggest that the great majority of variability in cerebrum, cerebellum, thalamus and basal ganglia is determined by a single genetic factor. Though most (75%) of the variability in corpus callosum was explained by additive genetic effects these were largely independent of other structures. We also observed relatively small but significant environmental effects common to multiple neuroanatomic regions, particularly between thalamus, basal ganglia, and lateral ventricles. These findings are concordant with prior volumetric twin studies and support radial models of brain evolution.

Adolescent↗
PubMed2007

XXY (Klinefelter syndrome): a pediatric quantitative brain magnetic resonance imaging case-control study.

OBJECTIVE: An extra X chromosome in males (XXY), known as Klinefelter syndrome, is associated with characteristic physical, cognitive, and behavioral features of variable severity. The objective of this study was to examine possible neuroanatomical substrates of these cognitive and behavioral features during childhood and adolescence. METHODS: MRI brain scans were acquired for 42 XXY and 87 healthy XY age-matched control males. We compared these 2 groups on regional brain volumes and cortical thickness. RESULTS: Total cerebral volume and all lobar volumes except parietal white matter were significantly smaller in the XXY group, whereas lateral-ventricle volume was larger. Consistent with the cognitive profile, the cortex was significantly thinner in the XXY group in left inferior frontal, temporal, and superior motor regions. CONCLUSION: The brain-imaging findings of preferentially affected frontal, temporal, and motor regions and relative sparing of parietal regions are consistent with observed cognitive and behavioral strengths and weaknesses in XXY subjects.

Adolescent↗
PubMed2006

Puberty-related influences on brain development.

Puberty is a time of striking changes in cognition and behavior. To indirectly assess the effects of puberty-related influences on the underlying neuroanatomy of these behavioral changes we will review and synthesize neuroimaging data from typically developing children and adolescents and from those with anomalous hormone or sex chromosome profiles. The trajectories (size by age) of brain morphometry differ between boys and girls, with girls generally reaching peak gray matter thickness 1-2 years earlier than boys. Both boys and girls with congenital adrenal hyperplasia (characterized by high levels of intrauterine testosterone), have smaller amygdala volume but the brain morphometry of girls with CAH did not otherwise significantly differ from controls. Subjects with XXY have gray matter reductions in the insula, temporal gyri, amygdala, hippocampus, and cingulate-areas consistent with the language-based learning difficulties common in this group.

Adolescent↗
PubMed2006

A pediatric twin study of brain morphometry.

BACKGROUND: Longitudinal pediatric neuroimaging studies have demonstrated increasing volumes of white matter and regionally-specific inverted U shaped developmental trajectories of gray matter volumes during childhood and adolescence. Studies of monozygotic and dyzygotic twins during this developmental period allow exploration of genetic and non-genetic influences on these developmental trajectories. METHOD: Magnetic resonance imaging brain scans were acquired on a pediatric sample of 90 monozygotic twin pairs, 38 same-sex dyzygotic twin pairs, and 158 unrelated typically developing singletons. Structural equation modeling was used to estimate the additive genetic, common environment, and unique environment effects, as well as age by heritability interactions, on measures of brain volumes from these images. RESULTS: Consistent with previous adult studies, additive genetic effects accounted for a substantial portion of variability in nearly all brain regions with the notable exception of the cerebellum. Significant age by heritability interactions were observed with gray matter volumes showing a reduction in heritability with increasing age, while white matter volume heritability increased with greater age. CONCLUSION: Understanding the relative contributions of genetic and nongenetic factors on developmental brain trajectories may have implications for better understanding brain-based disorders and typical cognitive development.

Adolescent↗
PubMed2005

Disorganization: the forgotten executive dysfunction in high-functioning autism (HFA) spectrum disorders.

Executive function (EF) abilities were investigated in 72 children with high-functioning autism (HFA) spectrum disorders through the collection of parent ratings and performance on laboratory measures of EF. In addition, discrepancy analysis was used to isolate executive functioning on tasks that carry multiple demands. Comparison of HFA and Asperger Disorder (AD) groups did not reveal consistent differences in EF. Results did indicate global EF deficits in the combined group of children with HFA and AD. Within the EF domain, specific deficits in flexibility and organization were most prominent.

Adolescent↗
PubMed2004

Annotation: the savant syndrome.

BACKGROUND: Whilst interest has focused on the origin and nature of the savant syndrome for over a century, it is only within the past two decades that empirical group studies have been carried out. METHODS: The following annotation briefly reviews relevant research and also attempts to address outstanding issues in this research area. Traditionally, savants have been defined as intellectually impaired individuals who nevertheless display exceptional skills within specific domains. However, within the extant literature, cases of savants with developmental and other clinical disorders, but with average intellectual functioning, are increasingly reported. RESULTS: We thus propose that focus should diverge away from IQ scores to encompass discrepancies between functional impairments and unexpected skills. It has long been observed that savant skills are more prevalent in individuals with autism than in those with other disorders. Therefore, in this annotation we seek to explore the parameters of the savant syndrome by considering these skills within the context of neuropsychological accounts of autism. A striking finding amongst those with savant skills, but without the diagnosis of autism, is the presence of cognitive features and behavioural traits associated with the disorder. CONCLUSIONS: We thus conclude that autism (or autistic traits) and savant skills are inextricably linked and we should therefore look to autism in our quest to solve the puzzle of the savant syndrome.

Affect↗
PubMed2004

Effects of hormones and sex chromosomes on stress-influenced regions of the developing pediatric brain.

Recently discovered sexual dimorphism within developing brain structures such as the amygdala and hippocampus suggests that biological factors may account for many of the sex differences in stress reactivity. In this study, we have relied on studies of naturally occurring anomalous processes, such as congenital adrenal hyperplasia (CAH) and Klinefelter's syndrome (XXY), to observe the effects of hormones and sex chromosomes on brain structures thought to influence an individual's vulnerability to stress. Brain magnetic resonance imaging (MRI) scans were obtained both from 16 boys with classic CAH and 34 age- and sex-matched controls and from 20 XXY children and 40 age-matched controls. Smaller amygdala volumes were observed in boys with CAH than in matched controls, and in XXY patients than in matched controls. XXY patients were also found to have smaller hippocampus volumes when compared with matched controls. Acknowledging that hormone and sex chromosome effects upon the developing human brain are widespread and complex, it is difficult to conclude, with any certainty, the etiology of the differences found in this study. Future studies that examine longitudinal data and/or other diagnostic groups, however, may help to better elucidate specific hormone and sex chromosome effects upon stress-related structures in the brain.

Adolescent↗