Search tips
Search criteria

Results 1-25 (55)

Clipboard (0)

Select a Filter Below

more »
Year of Publication
more »
1.  Genetic and Environmental Influences on Individual Differences in Frequency of Play with Pets among Middle-Aged Men: A Behavioral Genetic Analysis 
Anthrozoos  2012;25(4):441-456.
There is growing evidence that pet ownership and human–animal interaction (HAI) have benefits for human physical and psychological well-being. However, there may be pre-existing characteristics related to patterns of pet ownership and interactions with pets that could potentially bias results of research on HAI. The present study uses a behavioral genetic design to estimate the degree to which genetic and environmental factors contribute to individual differences in frequency of play with pets among adult men. Participants were from the ongoing longitudinal Vietnam Era Twin Study of Aging (VETSA), a population-based sample of 1,237 monozygotic (MZ) and dizygotic (DZ) twins aged 51–60 years. Results demonstrate that MZ twins have higher correlations than DZ twins on frequency of pet play, suggesting that genetic factors play a role in individual differences in interactions with pets. Structural equation modeling revealed that, according to the best model, genetic factors accounted for as much as 37% of the variance in pet play, although the majority of variance (63–71%) was due to environmental factors that are unique to each twin. Shared environmental factors, which would include childhood exposure to pets, overall accounted for <10% of the variance in adult frequency of pet play, and were not statistically significant. These results suggest that the effects of childhood exposure to pets on pet ownership and interaction patterns in adulthood may be mediated primarily by genetically-influenced characteristics.
PMCID: PMC4286882  PMID: 25580056
genetics; pets; twins
2.  Analysis of Quantitative Magnetic Resonance Imaging and Biomechanical Parameters on Human Discs with Different Grades of Degeneration 
Journal of magnetic resonance imaging : JMRI  2013;38(6):10.1002/jmri.24120.
To establish relationships between quantitative magnetic resonance imaging (qMRI) and biomechanical parameters to help inform and interpret alterations of human intervertebral discs (IVD) with different grades of degeneration.
Materials and Methods
The properties of the nucleus pulposus (NP) and annulus fibrosus (AF) tissues of each IVD of 10 lumbar spines (range 32–77 years) were analyzed by qMRI (relaxation times T1 and T2, magnetization transfer ratio MTR and apparent diffusion coefficient ADC), and tested in confined compression and dynamic shear.
T1 and T2 significantly decreased in both the NP and AF with increasing degeneration grades while the MTR increased significantly with grade 4. In contrast with the others qMRI parameters, the ADC had a tendency to decrease with increasing grade. Disc degeneration caused a decrease in the aggregate modulus, hydraulic permeability and shear modulus magnitude along with an increase in phase angle in the AF. On the other hand, disc degeneration of NPs decreased the shear modulus and the phase angle.
Our studies indicate that qMRI can be used as a non-invasive diagnostic tool in the detection of IVDs properties with potential to help interpret and to detect early, middle and late stages of degeneration. QMRI of the human IVD can therefore become a very important diagnostic assessment tool in determining the functional state of the disc.
PMCID: PMC3735720  PMID: 23633131
Quantitative MRI; intervertebral disc degeneration; biomechanics; permeability; shear modulus
3.  Genetic and Environmental Influences of Daily and Intra-individual Variation in Testosterone Levels in Middle-Aged Men 
Psychoneuroendocrinology  2013;38(10):2163-2172.
Testosterone regulates numerous physiological processes, and evidence suggests that it plays a critical role in male aging. It has yet to be determined whether the heritability of testosterone varies in accordance with its diurnal rhythm. Similarly, it is unclear whether changes in testosterone level throughout the day are genetically influenced. The aim of the present study was to determine the degree to which genetic and environmental factors contribute to individual differences in testosterone throughout the day in middle-aged men.
Saliva-based measures of free testosterone, sampled at multiple time-points both at-home and in-lab, were collected from 783 male twins (193 monozygotic pairs, 196 dizygotic pairs, 5 unpaired twins) as part of the Vietnam Era Twin Study of Aging (VETSA). The average age of participants was 55.9 years (SD=2.6).
Testosterone levels declined substantially over the course of the day, with 32%–39% of the change occurring in the first 30 minutes after waking. Heritability estimates for specific time-points ranged from .02 to .39. The heritability of the average at-home and in-lab testosterone values were notably higher (.42 and .47 respectively). Daily rates of change showed some evidence of genetic influence, with heritability estimates ranging from .15 to .29, whereas there were no observable genetic influences on coefficients of variation.
Genetic influences account for a significant proportion of the variance in average testosterone levels, while environmental factors account for the majority of intra-individual variability. These results highlight the need to explore both genetic and individual-specific environmental factors as determinants of free testosterone levels in aging men.
PMCID: PMC3775872  PMID: 23639251
Testosterone; Heritability; Twin Study; Diurnal Variation; Aging; Men; Middle-Age
4.  Greater frequency of CD5-negative CD8+ T cells against human immunodeficiency virus type 1 than other viruses is consistent with adaptation to antigenic variation 
The CD5 protein antagonizes phosphorylation events downstream of T cell receptor (TCR) engagement to decrease T cell responsiveness. CD5-negative T cell clones respond preferentially over their CD5+ counterparts against cells with low human histocompatibility-linked leukocyte antigen (HLA) levels. In human immunodeficiency virus type 1 (HIV-1) infection, CD5-CD8+ T cells increase in prevalence with disease progression.
To investigate potential causes of this expansion of CD5-CD8+ T cells in HIV-1 infection, we compared CD5 expression on CD8+ T cells reactive against HIV-1 peptides, common viral peptides and a self peptide that together span a broad range of TCR avidities in the context of the common HLA-A2 class I restriction molecule. Following stimulation, CD5 expression on peptide-specific CD8+ T cells was assessed by flow cytometry.
In healthy controls, there was no significant difference in the CD5+ percentage of CD8+ T cells specific for common viral peptides, but a lower percentage of those responding against a common self peptide expressed CD5. The same relationship occurred in HIV-infected individuals, however, a lower percentage of HIV peptide-specific CD8+ T cells than other viral peptide-specific CD8+ T cells expressed CD5. In terms of overall CD5 expression level at the peptide-specific responder population level, HIV-specific CD8+ T cells resembled those responsive against the self peptide, despite much higher avidity TCR/HLA/peptide interactions.
This deficit in CD5 expression selective for HIV-specific CD8+ T cells is consistent with in vivo adaptation to low avidity HIV peptide variants and has potential consequences for CD8+ T cell expansion, cross-reactivity and autoreactivity.
PMCID: PMC4167305  PMID: 25237383
CD5; CD8+ T cell; HIV; T cell receptor; Peptide; Avidity; HLA class I
5.  Molecular profiling of human mammary gland links breast cancer risk to a p27+ cell population with progenitor characteristics 
Cell stem cell  2013;13(1):117-130.
Early full-term pregnancy is one of the most effective natural protections against breast cancer. To investigate this effect, we have characterized the global gene expression and epigenetic profiles of multiple cell types from normal breast tissue of nulliparous and parous women, and carriers of BRCA1 or BRCA2 mutations. We found significant differences in CD44+ progenitor cells, where the levels of many stem cell-related genes and pathways, including the cell cycle regulator p27, are lower in parous women without BRCA1/BRCA2 mutations. We also noted a significant reduction in the frequency of CD44+p27+ cells in parous women, and showed using explant cultures that parity-related signaling pathways play a role in regulating the number of p27+ cells and their proliferation. Our results suggest that pathways controlling p27+ mammary epithelial cells and the numbers of these cells relate to breast cancer risk, and can be explored for cancer risk assessment and prevention.
PMCID: PMC3703476  PMID: 23770079
6.  Natural Killer Cell Function and Dysfunction in Hepatitis C Virus Infection 
BioMed Research International  2014;2014:903764.
Viruses must continually adapt against dynamic innate and adaptive responses of the host immune system to establish chronic infection. Only a small minority (~20%) of those exposed to hepatitis C virus (HCV) spontaneously clear infection, leaving approximately 200 million people worldwide chronically infected with HCV. A number of recent research studies suggest that establishment and maintenance of chronic HCV infection involve natural killer (NK) cell dysfunction. This relationship is illustrated in vitro by disruption of typical NK cell responses including both cell-mediated cytotoxicity and cytokine production. Expression of a number of activating NK cell receptors in vivo is also affected in chronic HCV infection. Thus, direct in vivo and in vitro evidence of compromised NK function in chronic HCV infection in conjunction with significant epidemiological associations between the outcome of HCV infection and certain combinations of NK cell regulatory receptor and class I human histocompatibility linked antigen (HLA) genotypes indicate that NK cells are important in the immune response against HCV infection. In this review, we highlight evidence suggesting that selective impairment of NK cell activity is related to establishment of chronic HCV infection.
PMCID: PMC4095668  PMID: 25057504
7.  Salivary Cortisol and Prefrontal Cortical Thickness in Middle-Aged Men: A Twin Study 
NeuroImage  2010;53(3):1093-1102.
Although glucocorticoid receptors are highly expressed in the prefrontal cortex, the hippocampus remains the predominant focus in the literature examining relationships between cortisol and brain. We examined phenotypic and genetic associations of cortisol levels with the thickness of prefrontal and anterior cingulate cortex regions, and with hippocampal volume in a sample of 388 middle-aged male twins who were 51–59 years old. Small but significant negative phenotypic associations were found between cortisol levels and the thickness of left dorsolateral (superior frontal gyrus, left rostral middle frontal gyrus) and ventrolateral (pars opercularis, pars triangularis, pars orbitalis) prefrontal regions, and right dorsolateral (superior frontal gyrus) and medial orbital frontal cortex. Most of the associations remained significant after adjusting for general cognitive ability, cardiovascular risk factors, and depression. Bivariate genetic analyses suggested that some of the associations were primarily accounted for by shared genetic influences; that is, some of the genes that tend to result in increased cortisol levels also tend to result in reduced prefrontal cortical thickness. Aging has been associated with reduced efficiency of hypothalamic-pituitary-adrenal function, with frontal lobe shrinkage, and with increases in health problems, but our present data do not allow us to determine the direction of effects. Moreover, the degree or the direction of the observed associations and the extent of their shared genetic underpinnings may well change as these individuals age. Longitudinal assessments are underway to elucidate the direction of the associations and the genetic underpinnings of longitudinal phenotypes for changes in cortisol and brain morphology.
PMCID: PMC4034538  PMID: 20156572
heritability; magnetic resonance imaging (MRI); hippocampus; HPA axis structure; genetic correlation
8.  Cognitive Reserve Moderates the Association Between Hippocampal Volume and Episodic Memory in Middle Age 
Neuropsychologia  2013;51(6):1124-1131.
Cognitive reserve is hypothesized to help people withstand greater brain pathology without manifesting clinical symptoms, and may be regarded as a preventive factor of dementia. It is unclear whether the effect of cognitive reserve is evident only among the older adults or after conversion to dementia, or if it can also be seen earlier in life before the prominent effects of cognitive aging become apparent. While finding a main effect of cognitive reserve on cognitive outcome may be consistent with the reserve hypothesis, in our view, it is unnecessary to invoke the idea of reserve if only a main effect is present. Rather, it is the interaction between a measure of reserve and a brain measure on cognitive outcome that is key for confirming that the effects of brain pathology affect people differently according to their cognitive reserve. We studied whether general cognitive ability at an average age of 20 years, as a direct measure of cognitive reserve, moderates the association between hippocampal volume and episodic memory performance in 494 middle-aged men ages 51 to 60. Whereas there was no statistically significant direct relationship between hippocampal volume and episodic memory performance in middle age, we found a statistically significant interaction such that there was a positive association between hippocampal volume and episodic memory only among people with lower general cognitive ability at age 20, i.e., lower levels of cognitive reserve. Our results provide support for the hypothesis that cognitive reserve moderates the relationship between brain structure and cognition in middle age, well before the onset of dementia.
PMCID: PMC3660613  PMID: 23499725
cognitive reserve; general cognitive ability; episodic memory; hippocampus; verbal learning
9.  Short Communication: Antibody Responses to Human Immunodeficiency Virus Envelope from Infections with Multiple Subtypes Utilize the 1F7-Idiotypic Repertoire 
A common idiotype of anti-HIV antibodies (Abs), designated as 1F7, was recently observed on anti-HIV broadly neutralizing Abs (BnAbs). The presence of the 1F7-idiotype on BnAbs suggests that continuous selection of 1F7-idiotypic Abs may allow these clones to achieve the somatic hypermutation necessary for broad neutralization. As the selection of type-specific BnAbs occurs in the setting of infections with a wide array of HIV subtypes, we investigated Abs from subjects infected with diverse subtypes for the selection of 1F7-idiotypic Abs. We observed the 1F7-idiotype on antiviral Abs in infections with various HIV subtypes. Furthermore, gp140-specific 1F7-idiotypic Abs recognized the gp140 antigens from several HIV subtypes. These results demonstrate that the 1F7-idiotype is a common characteristic of Abs from infections with diverse HIV subtypes, and suggests that early cross-reactivity of 1F7-idiotypic clones may act in conjunction with somatic hypermutation to produce BnAbs.
PMCID: PMC3636582  PMID: 23265432
10.  Positioning of APOBEC3G/F Mutational Hotspots in the Human Immunodeficiency Virus Genome Favors Reduced Recognition by CD8+ T Cells 
PLoS ONE  2014;9(4):e93428.
Due to constitutive expression in cells targeted by human immunodeficiency virus (HIV), and immediate mode of viral restriction upon HIV entry into the host cell, APOBEC3G (A3G) and APOBEC3F (A3F) have been considered primarily as agents of innate immunity. Recent bioinformatic and mouse model studies hint at the possibility that mutation of the HIV genome by these enzymes may also affect adaptive immunity but whether this occurs in HIV-infected individuals has not been examined. We evaluated whether APOBEC-mediated mutations within common HIV CD8+ T cell epitopes can potentially enhance or diminish activation of HIV-specific CD8+ T cells from infected individuals. We compared ex vivo activation of CD8+ T lymphocytes from HIV-infected individuals by wild type HIV peptide epitopes and synthetic variants bearing simulated A3G/F-induced mutations by measuring interferon-γ (IFN-γ) production. We found that A3G/F-induced mutations consistently diminished HIV-specific CD8+ T cell responses against the common epitopes we tested. If this reflects a significant trend in vivo, then adaptation by HIV to enrich sequences that are favored for mutation by A3G/F (A3G/F hotspots) in portions of its genome that encode immunogenic CD8+ T cell epitopes would favor CTL escape. Indeed, we found the most frequently mutated A3G motif (CCC) is enriched up to 6-fold within viral genomic sequences encoding immunodominant CD8+ T cell epitopes in Gag, Pol and Nef. Within each gene, A3G/F hotspots are more abundant in sequences encoding epitopes that are commonly recognized due to their HLA restriction. Thus, in our system, mutations of the HIV genome, mimicking A3G/F activity, appeared to abrogate or severely reduce CTL recognition. We suggest that the physiological significance of this potential effect in facilitating CTL escape is echoed in the adaptation of the HIV genome to enrich A3G/F hotspots in sequences encoding CTL epitopes that are more immunogenic at the population level.
PMCID: PMC3982959  PMID: 24722422
11.  Intraglandular Injection of Botulinum Toxin A Reduces Tear Production in Rabbits 
Ophthalmic plastic and reconstructive surgery  2013;29(1):10.1097/IOP.0b013e31826e8a86.
To develop an animal model and investigate the dose-dependent effect of an intraglandular injection of botulinum toxin A (BTX-A) on tear production.
In a volume of 0.1-ml, 0.625-, 1.25-, or 2.5-U BTX-A was injected transconjunctivally in the superolateral lobe of the lacrimal gland of adult New Zealand white female rabbits. In the contralateral lacrimal gland, 0.1 ml of 0.9% sodium chloride was injected. Prior to injection and at 1-week postinjection, photographs were taken to evaluate pre- and postoperative eyelid position. Fluorescein and Rose Bengal stain were used to evaluate the corneal surface, and Schirmer test was used to assess tear production.
Glands injected with the intermediate (1.25 U) and the highest (2.5 U) doses of BTX-A displayed a statistically significant decrease in tear production (p = 0.002 and 0.007, respectively) compared with the contralateral saline-injected glands at 1 week. No corneal pathologic factors from excessive dryness were observed following the injection. While postinjection ptosis was observed (p = 0.025), no difference was seen between BTX-A and saline-injected eyes.
In rabbits, intraglandular injection of BTX-A resulted in decreased tear production at 1 week. No additional reduction in tear production was seen with a BTX-A dose greater than 1.25 U, suggesting glandular receptor saturation at this dose. Despite suppression of tear production, no corneal pathologic factors were observed. Further studies are needed to refine this animal model with the ultimate goal of determining optimum delivery route and concentration to reduction in tear production while minimizing side effects in patients.
PMCID: PMC3823535  PMID: 23128538
12.  A Multivariate Twin Study of Hippocampal Volume, Self-Esteem and Well-Being in Middle Aged Men 
Genes, Brain, and Behavior  2012;11(5):539-544.
Self-esteem and well-being are important for successful aging, and some evidence suggests that self-esteem and well-being are associated with hippocampal volume, cognition, and stress responsivity. Whereas most of this evidence is based on studies of older adults, we investigated self-esteem, well-being and hippocampal volume in 474 male middle-age twins. Self-esteem was significantly positively correlated with hippocampal volume (.09, p=.03 for left hippocampus, .10, p=.04 for right). Correlations for well-being were not significant (ps ≫.05). There were strong phenotypic correlations between self-esteem and well-being (.72, p<.001) and between left and right hippocampal volume (.72, p<.001). In multivariate genetic analyses, a 2-factor AE model with well-being and self-esteem on one factor and left and right hippocampal volumes on the other factor fit the data better than Cholesky, independent pathway or common pathway models. The correlation between the two genetic factors was .12 (p=.03); the correlation between the environmental factors was .09 (p>05). Our results indicate that largely different genetic and environmental factors underlie self-esteem and well-being on the one hand and hippocampal volume on the other.
PMCID: PMC3389179  PMID: 22471516
self-esteem; well-being; hippocampus; twins; heritability; aging
13.  Hierarchical Genetic Organization of Human Cortical Surface Area 
Science (New York, N.Y.)  2012;335(6076):1634-1636.
Surface area of the cerebral cortex is a highly heritable trait, yet little is known about genetic influences on regional cortical differentiation in humans. Using a data-driven, fuzzy clustering technique with magnetic resonance imaging data from 406 twins, we parceled cortical surface area into genetic subdivisions, creating a human brain atlas based solely on genetically informative data. Boundaries of the genetic divisions corresponded largely to meaningful structural and functional regions; however, the divisions represented previously undescribed phenotypes different from conventional (non–genetically based) parcellation systems. The genetic organization of cortical area was hierarchical, modular, and predominantly bilaterally symmetric across hemispheres. We also found that the results were consistent with human-specific regions being subdivisions of previously described, genetically based lobar regionalization patterns.
PMCID: PMC3690329  PMID: 22461613
14.  Genetic and Environmental Influences of White and Gray Matter Signal Contrast: A New Phenotype for Imaging Genetics? 
Neuroimage  2012;60(3):1686-1695.
The estimation of cortical thickness is in part dependent on the degree of contrast in T1 signal intensity between white matter and gray matter along the cortical mantle. The ratio of white matter to gray matter signal (WM/GM contrast) has been found to vary as a function of age and Alzheimer’s disease status, suggesting a biological component to what might otherwise be labeled as a nuisance variable. The aim of the present study was to determine if measures of WM/GM contrast are genetically influenced, as well as the degree to which this phenotype may be related to the genetic and environmental determinants of cortical thickness. Participants were 514 male twins (130 monozygotic, 97 dizygotic pairs, and 60 unpaired individuals) from the Vietnam Era Twin Study of Aging. Ages ranged from 51 to 59 years. Measures of WM/GM contrast and cortical thickness were derived for 66 cortical regions of interest (ROI) using FreeSurfer-based methods. Univariate and bivariate twin analyses were used in order to estimate the heritability of WM/GM contrast, as well as the degree of shared genetic and environmental variance between WM/GM contrast and cortical thickness. WM/GM contrast was found to be significantly heritable in the majority of ROIs. The average heritability across individual ROIs was highest in the occipital lobe (.50), and lowest in the cingulate cortex (.24). Significant phenotypic correlations between WM/GM contrast and cortical thickness were observed for most of the ROIs. The majority of the phenotypic correlations were negative, ranging from −.11 to −.54. Of the 66 associations, only 17 significant genetic correlations were found, ranging from −.16 to −.34, indicating small amounts of shared genetic variance. The majority of the phenotypic correlations were accounted for by small unique environmental effects common between WM/GM contrast and cortical thickness. These findings demonstrate that like cortical thickness, WM/GM contrast is a genetically influenced brain structure phenotype. The lack of significant genetic correlations with cortical thickness suggests that this measure potentially represents a unique source of genetic variance, one that has yet to be explored by the field of imaging genetics.
PMCID: PMC3328105  PMID: 22500923
15.  The anti-idiotypic antibody 1F7 stimulates monocyte interleukin-10 production and induces endotoxin tolerance 
Pathogens that establish chronic infection elicit immune responses with suppressive cytokines dominating over pro-inflammatory cytokines. Chronic hepatitis C virus (HCV) infection, human immunodeficiency virus (HIV) infection and simian immunodeficiency virus (SIV) infection are associated with high levels of antiviral antibodies expressing a common idiotype specifically recognized by the 1F7 monoclonal antibody (mAb). The 1F7 mAb is a murine IgMκ antibody raised against immunoglobulin pooled from the plasma of multiple HIV-infected individuals. In this study, we investigated direct effects of the 1F7 mAb itself on peripheral blood mononuclear cells (PBMC).
Isolated monocytes or PBMC from healthy controls were incubated with the 1F7 mAb or IgMκ mAb control. Cytokine production was measured in cell culture supernatants by ELISA and cells producing interleukin-10 (IL-10) were identified by subset depletion and intracellular flow cytometry. Endotoxin tolerance was assessed by exposing monocytes to lipopolysaccharide (LPS) following 1F7 mAb or IgMκ mAb control pre-treatment and comparing tumor necrosis factor (TNF)-α levels in cell culture supernatants.
The 1F7 mAb stimulated monocytes and CD36+ lymphocytes to produce IL-10 in a time and dose-dependent manner. Treatment of monocytes with 1F7 mAb also reduced their subsequent responsiveness to LPS stimulation.
Induction of antibodies expressing the 1F7 idiotype by chronic pathogens may facilitate IL-10 production and progression to chronic infection. Direct effects of IL-10 from human monocytes stimulated by 1F7-like antibodies, followed by monocyte transition to an alternatively activated phenotype illustrated by endotoxin tolerance, are two complementary features favouring a tolerogenic or non-responsive immunological environment.
PMCID: PMC3635981  PMID: 23561395
Hepatitis C virus; Monocyte; Interleukin-10; Idiotype; Endotoxin tolerance
16.  Genetic Architecture of the Delis-Kaplan Executive Function System Trail Making Test: Evidence for Distinct Genetic Influences on Executive Function 
Neuropsychology  2011;26(2):238-250.
To examine how genes and environments contribute to relationships among Trail Making test conditions and the extent to which these conditions have unique genetic and environmental influences.
Participants included 1237 middle-aged male twins from the Vietnam-Era Twin Study of Aging (VESTA). The Delis-Kaplan Executive Function System Trail Making test included visual searching, number and letter sequencing, and set-shifting components.
Phenotypic correlations among Trails conditions ranged from 0.29 – 0.60, and genes accounted for the majority (58–84%) of each correlation. Overall heritability ranged from 0.34 to 0.62 across conditions. Phenotypic factor analysis suggested a single factor. In contrast, genetic models revealed a single common genetic factor but also unique genetic influences separate from the common factor. Genetic variance (i.e., heritability) of number and letter sequencing was completely explained by the common genetic factor while unique genetic influences separate from the common factor accounted for 57% and 21% of the heritabilities of visual search and set-shifting, respectively. After accounting for general cognitive ability, unique genetic influences accounted for 64% and 31% of those heritabilities.
A common genetic factor, most likely representing a combination of speed and sequencing accounted for most of the correlation among Trails 1–4. Distinct genetic factors, however, accounted for a portion of variance in visual scanning and set-shifting. Thus, although traditional phenotypic shared variance analysis techniques suggest only one general factor underlying different neuropsychological functions in non-patient populations, examining the genetic underpinnings of cognitive processes with twin analysis can uncover more complex etiological processes.
PMCID: PMC3295889  PMID: 22201299
executive function; genetics; heritability; twins; middle-age; speed; trail making
17.  A Comparison of Heritability Maps of Cortical Surface Area and Thickness and the Influence of Adjustment for Whole Brain Measures: A Magnetic Resonance Imaging Twin Study 
Understanding the genetic and environmental contributions to measures of brain structure such as surface area and cortical thickness is important for a better understanding of the nature of brain-behavior relationships and changes due to development or disease. Continuous spatial maps of genetic influences on these structural features can contribute to our understanding of regional patterns of heritability, since it remains to be seen whether genetic contributions to brain structure respect the boundaries of any traditional parcellation approaches. Using data from magnetic resonance imaging scans collected on a large sample of monozygotic and dizygotic twins in the Vietnam Era Twin Study of Aging, we created maps of the heritability of areal expansion (a vertex-based area measure) and cortical thickness and examined the degree to which these maps were affected by adjustment for total surface area and mean cortical thickness. We also compared the approach of estimating regional heritability based on the average heritability of vertices within the region to the more traditional region-of-interest (ROI)-based approach. The results suggested high heritability across the cortex for areal expansion and, to a slightly lesser degree, for cortical thickness. There was a great deal of genetic overlap between global and regional measures for surface area, so maps of region-specific genetic influences on surface area revealed more modest heritabilities. There was greater inter-regional variability in heritabilities when calculated using the traditional ROI-based approach compared to summarizing vertex-by-vertex heritabilities within regions. Discrepancies between the approaches were greatest in small regions and tended to be larger for surface area than for cortical thickness measures. Implications regarding brain phenotypes for future genetic association studies are discussed.
PMCID: PMC3549553  PMID: 22856366
surface area; cortical thickness; region of interest; heritability maps
18.  Genetic Influences on Hippocampal Volume Differ as a Function of Testosterone Level in Middle-Aged Men 
NeuroImage  2011;59(2):1123-1131.
The hippocampus expresses a large number of androgen receptors; therefore, in men it is potentially vulnerable to the gradual age-related decline of testosterone levels. In the present study we sought to elucidate the nature of the relationship between testosterone and hippocampal volume in a sample of middle-aged male twins (average age 55.8 years). We found no evidence for a correlation between testosterone level and hippocampal volume, as well as no indication of shared genetic influences. However, a significant moderating effect of testosterone on the genetic and environmental determinants of hippocampal volume was observed. Genetic influences on hippocampal volume increased substantially as a function of increasing testosterone level, while environmental influences either decreased or remained stable. These findings provide evidence for an apparent gene-by-hormone interaction on hippocampal volume. To the best of our knowledge, this is the first study to demonstrate that the heritability of a brain structure in adults may be modified by an endogenous biological factor.
PMCID: PMC3230702  PMID: 21983185
Heritability; Hippocampal Volume; Testosterone; Twin Study; Aging
19.  Heritability of brain ventricle volume: Converging evidence from inconsistent results 
Neurobiology of aging  2010;33(1):1-8.
Twin studies generally show great consistency for the heritability of brain structures. Ironically, the lateral ventricles—perhaps the most reliably measured brain regions of interest—are the most inconsistent when it comes to estimating genetic influences on their volume. Heritability estimates in twin studies have ranged from zero to almost 0.80. Here we aggregate heritability estimates from extant twin studies, and we review and re-interpret some of the findings. Based on our revised estimates, we conclude that lateral ventricular volume is indeed heritable. The weighted average heritability of the revised estimates was 0.54. Although accumulated environmental insults might seem most logical as the predominant cause of age-related ventricular expansion, the data strongly suggest that genetic influences on lateral ventricular volume are increasing with age. Genetic influences accounted for 32-35% of the variance in lateral ventricular volume in childhood, but about 75% of the variance in late middle and older age. These conclusions have implications for the basic understanding of the genetic and environmental underpinnings of normative and pathological brain aging.
PMCID: PMC3221930  PMID: 20363053
lateral ventricles; genetics; aging; structural MRI; twins; endophenotype; mild cognitive impairment; Alzheimer’s disease
20.  Untreated Hypertension Decreases Heritability of Cognition in Late Middle Age 
Behavior Genetics  2011;42(1):107-120.
Hypertension is a risk factor for cognitive decline, but the mechanisms underlying the effects of hypertension on cognition, particularly in midlife, are unclear. We examined whether hypertension modifies genetic influences on individual differences in cognition. Nine cognitive domains and general cognitive ability were assessed in a sample of 1237 male twins aged 51–60 who were divided into three blood pressure groups: non-hypertensive; medicated hypertensive; and unmedicated hypertensive. Heritability was significantly lower among unmedicated hypertensives compared to medicated hypertensives and non-hypertensives for visual-spatial ability (p=0.013) and episodic memory (p=0.004). There were no heritability differences between non-hypertensives and medicated hypertensives. In addition, there were no significant differences in mean level cognition across the three blood pressure groups. These results suggest that in middle-aged men, untreated hypertension suppresses normal genetic influences on individual differences in certain domains of cognition prior to the emergence of hypertension-related effects on cognitive performance. These results further suggest that antihypertensive medication may protect against or reverse this effect.
PMCID: PMC3227796  PMID: 21688193
hypertension; cognition; twins; heritability; aging
21.  Genetic Architecture of Context Processing in Late Middle Age: More Than One Underlying Mechanism 
Psychology and aging  2011;26(4):852-863.
Studies comparing young and older adults suggest a deficit in processing context information as a key mechanism underlying cognitive aging. However, the genetic architecture of context processing has not been examined. Consistent with previous results, we found evidence of functionally dissociable components of context processing accuracy in 1127 late middle-aged twins ages 51–60. One component emphasizes use of context cues to prepare responses (proactive cognitive control); the other emphasizes adjustment of responses after probes are presented (reactive control). Approximately one-quarter of the variance in each component was accounted for by genes. Multivariate twin analysis indicated that genetic factors underlying two important components of context processing were independent of one another, thus implicating more than one underlying mechanism. Slower reaction time (RT) on non-context processing trials was positively correlated with errors on the strongly proactive control component on which young adults outperform older adults, but RT was negatively correlated with errors on the strongly reactive control component on which older adults perform better. Although this RT measure was uncorrelated with chronological age in our age-homogeneous sample, slower RT was associated with performance patterns that were more like older adults. However, this did not generalize to other processing speed measures. Genetic correlations, which reflect shared genetic variance, paralleled the phenotypic correlations. There was also a positive genetic correlation between general cognitive ability and accuracy on the proactive control component, but there were still mostly distinct genetic influences underlying these measures. In contrast, the reactive control component was unrelated to general cognitive ability.
PMCID: PMC3222785  PMID: 21875218
twins; heritability; context processing; cognitive aging; processing speed
22.  Genetic Influences on Cortical Regionalization in the Human Brain 
Neuron  2011;72(4):537-544.
Animal data demonstrate that the development of distinct cortical areas is influenced by genes that exhibit highly regionalized expression patterns. In this paper, we show genetic patterning of cortical surface area derived from MRI data from 406 adult human twins. We mapped genetic correlations of areal expansion between selected seed regions and all other cortical locations, with the selection of seed points based on results from animal studies. “Marching seeds” and a data-driven, hypothesis-free, fuzzy clustering approach provided convergent validation. The results reveal strong anterior-to-posterior graded, bilaterally symmetric patterns of regionalization, largely consistent with patterns previously reported in non-human mammalian models. Broad similarities in genetic patterning between rodents and humans may suggest a conservation of cortical patterning mechanisms while dissimilarities might reflect the functionalities most essential to each species.
PMCID: PMC3222857  PMID: 22099457
23.  Tamoxifen Downregulates Ets-oncogene Family Members ETV4 and ETV5 in Benign Breast Tissue: Implications for Durable Risk Reduction 
Five years of tamoxifen reduces breast cancer risk by nearly 50% but is associated with significant side-effects and toxicities. A better understanding of the direct and indirect effects of tamoxifen in benign breast tissue could elucidate new mechanisms of breast carcinogenesis, suggest novel chemoprevention targets, and provide relevant early response biomarkers for Phase II prevention trials.
Seventy-three women at increased risk for breast cancer were randomized to tamoxifen (20 mg daily) or placebo for three months. Blood and breast tissue samples were collected at baseline and post-treatment. Sixty-nine women completed all study activities (37 tamoxifen and 32 placebo). The selected biomarkers focused on estradiol and IGFs in the blood, DNA methylation and cytology in random periareolar fine needle aspirates, and tissue morphometry, proliferation, apoptosis, and gene expression (microarray and RT-PCR) in the tissue core samples.
Tamoxifen downregulated ets-oncogene transcription factor family members ETV4 and ETV5 and reduced breast epithelial cell proliferation independent of CYP2D6 genotypes or effects on estradiol, ESR1 or IGFs. Reduction in proliferation was correlated with downregulation of ETV4 and DNAJC12. Tamoxifen reduced the expression of ETV4- and ETV5-regulated genes implicated in epithelial-stromal interaction and tissue remodeling. Three months of tamoxifen did not affect breast tissue composition, cytological atypia, preneoplasia or apoptosis.
A plausible mechanism for the chemopreventive effects of tamoxifen is restriction of lobular expansion into stroma through downregulation of ETV4 and ETV5. Multipotential progenitor cap cells of terminal end buds may be the primary target.
PMCID: PMC3208724  PMID: 21778330
Tamoxifen; Biomarkers; Gene Expression; Proliferation; DNA Methylation
24.  Genetic and Environmental Contributions to Regional Cortical Surface Area in Humans: A Magnetic Resonance Imaging Twin Study 
Cerebral Cortex (New York, NY)  2011;21(10):2313-2321.
Cortical surface area measures appear to be functionally relevant and distinct in etiology, development, and behavioral correlates compared with other size characteristics, such as cortical thickness. Little is known about genetic and environmental influences on individual differences in regional surface area in humans. Using a large sample of adult twins, we determined relative contributions of genes and environment on variations in regional cortical surface area as measured by magnetic resonance imaging before and after adjustment for genetic and environmental influences shared with total cortical surface area. We found high heritability for total surface area and, before adjustment, moderate heritability for regional surface areas. Compared with other lobes, heritability was higher for frontal lobe and lower for medial temporal lobe. After adjustment for total surface area, regionally specific genetic influences were substantially reduced, although still significant in most regions. Unlike other lobes, left frontal heritability remained high after adjustment. Thus, global and regionally specific genetic factors both influence cortical surface areas. These findings are broadly consistent with results from animal studies regarding the evolution and development of cortical patterning and may guide future research into specific environmental and genetic determinants of variation among humans in the surface area of particular regions.
PMCID: PMC3169660  PMID: 21378112
cortex; cortical thickness; heritability
25.  Responses to pandemic ASO3-adjuvanted A/California/07/09 H1N1 influenza vaccine in human immunodeficiency virus-infected individuals 
BMC Immunology  2012;13:49.
Influenza infection may be more serious in human immunodeficiency virus (HIV)-infected individuals, therefore, vaccination against seasonal and pandemic strains is highly advised. Seasonal influenza vaccines have had no significant negative effects in well controlled HIV infection, but the impact of adjuvanted pandemic A/California/07/2009 H1N1 influenza hemaglutinin (HA) vaccine, which was used for the first time in the Canadian population as an authorized vaccine in autumn 2009, has not been extensively studied.
Assess vaccine-related effects on CD4+ T cell counts and humoral responses to the vaccine in individuals attending the Newfoundland and Labrador Provincial HIV clinic.
A single dose of ArepanrixTM split vaccine including 3.75 μg A/California/07/2009 H1N1 HA antigen and ASO3 adjuvant was administered to 81 HIV-infected individuals by intramuscular injection. Plasma samples from shortly before, and 1–5 months after vaccination were collected from 80/81 individuals to assess humoral anti-H1N1 HA responses using a sensitive microbead-based array assay. Data on CD4+ T cell counts, plasma viral load, antiretroviral therapy and patient age were collected from clinical records of 81 individuals.
Overall, 36/80 responded to vaccination either by seroconversion to H1N1 HA or with a clear increase in anti-H1N1 HA antibody levels. Approximately 1/3 (28/80) had pre-existing anti-H1N1 HA antibodies and were more likely to respond to vaccination (22/28). Responders had higher baseline CD4+ T cell counts and responders without pre-existing antibodies against H1N1 HA were younger than either non-responders or responders with pre-existing antibodies. Compared to changes in their CD4+ T cell counts observed over a similar time period one year later, vaccine recipients displayed a minor, transient fall in CD4+ T cell numbers, which was greater amongst responders.
We observed low response rates to the 2009 pandemic influenza vaccine among HIV-infected individuals without pre-existing antibodies against H1N1 HA and a minor transient fall in CD4+ T cell numbers, which was accentuated in responders. A single injection of the ArepanrixTM pandemic A/California/07/2009 H1N1 HA split vaccine may be insufficient to induce protective immunity in HIV-infected individuals without pre-existing anti-H1N1 HA responses.
PMCID: PMC3482569  PMID: 22937824
HIV; influenza; pandemic; A/California/07/2009 H1N1 HA antigen; AS03 oil in water adjuvant; inflammation; CD4+ T cells; age

Results 1-25 (55)