Nathan Gillespie | Virginia Commonwealth University (original) (raw)

Papers by Nathan Gillespie

Research paper thumbnail of Tests of measurement invariance across age in the Delusion Symptoms States Inventory scales of depression, anxiety and general psychological distress in a sample of Australian twins

Research paper thumbnail of Direction of Causation Models

Research paper thumbnail of Shared Genetic and Environmental Influences on Early Temperament and Preschool Psychiatric Disorders in Hispanic Twins

Twin research and human genetics : the official journal of the International Society for Twin Studies, Jan 2, 2015

Objective: Despite an increasing recognition that psychiatric disorders can be diagnosed as early... more Objective: Despite an increasing recognition that psychiatric disorders can be diagnosed as early as preschool, little is known how early genetic and environmental risk factors contribute to the development of psychiatric disorders during this very early period of development. Method: We assessed infant temperament at age 1, and attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and separation anxiety disorder (SAD) at ages 3 through 5 years in a sample of Hispanic twins. Genetic, shared, and non-shared environmental effects were estimated for each temperamental construct and psychiatric disorder using the statistical program MX. Multivariate genetic models were fitted to determine whether the same or different sets of genes and environments account for the co-occurrence between early temperament and preschool psychiatric disorders. Results: Additive genetic factors accounted for 61% of the variance in ADHD, 21% in ODD, and 28% in SAD. Shared envir...

Research paper thumbnail of Characterization and photochemistry of 13-desmethyl bacteriorhodopsin

The journal of physical chemistry. B, Jan 25, 2005

The photochemistry of the 13-desmethyl (DM) analogue of bacteriorhodopsin (BR) is examined by usi... more The photochemistry of the 13-desmethyl (DM) analogue of bacteriorhodopsin (BR) is examined by using spectroscopy, molecular orbital theory, and chromophore extraction followed by conformational analysis. The removal of the 13-methyl group permits the direct photochemical formation of a thermally stable, photochemically reversible state, P1(DM) (lambda(max) = 525 nm), which can be generated efficiently by exciting the resting state, bR(DM) with yellow or red light (lambda > 590 nm). Chromophore extraction analysis reveals that the retinal configuration in P1(DM) is 9-cis, identical to that of the retinal configuration in the native BR P1 state. Fourier transform infrared and Raman experiments on P1(DM) indicate an anti configuration around the C15=N bond, as would be expected of an O-state photoproduct. However, low-temperature spectroscopy and ambient, time-resolved studies indicate that the P1(DM) state forms primarily via thermal relaxation from the L(D)(DM) state. Theoretical ...

Research paper thumbnail of Two-Photon and Fluorescence Spectroscopy and the Effect of Environment on the Photochemical Properties of Peridinin in Solution and in the Peridinin-Chlorophyll-Protein from Amphidinium carterae†

The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll... more The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll-protein (PCP) complex are studied by using one-photon and two-photon spectroscopy, solvent effects, and quantum theory. Two-photon excitation spectra, two-...

Research paper thumbnail of Low Birth Weight in MZ Twins Discordant for Birth Weight is Associated with Shorter Telomere Length and lower IQ, but not Anxiety/Depression in Later Life

Twin Research and Human Genetics, 2015

Shorter telomere length (TL) has found to be associated with lower birth weight and with lower co... more Shorter telomere length (TL) has found to be associated with lower birth weight and with lower cognitive ability and psychiatric disorders. However, the direction of causation of these associations and the extent to which they are genetically or environmentally mediated are unclear. Within-pair comparisons of monozygotic (MZ) and dizygotic (DZ) twins can throw light on these questions. We investigated correlations of within pair differences in telomere length, IQ, and anxiety/depression in an initial sample from Brisbane (242 MZ pairs, 245 DZ same sex (DZSS) pairs) and in replication samples from Amsterdam (514 MZ pairs, 233 DZSS pairs) and Melbourne (19 pairs selected for extreme high or low birth weight difference). Intrapair differences of birth weight and telomere length were significantly correlated in MZ twins, but not in DZSS twins. Greater intra-pair differences of telomere length were observed in the 10% of MZ twins with the greatest difference in birth weight compared to the bottom 90% in both samples and also in the Melbourne sample. Intra-pair differences of telomere length and IQ, but not of TL and anxiety/depression, were correlated in MZ twins, and to a smaller extent in DZSS twins. Our findings suggest that the same prenatal effects that reduce birth weight also influence telomere length in MZ twins. The association between telomere length and IQ is partly driven by the same prenatal effects that decrease birth weight.

Research paper thumbnail of A comparison of early family life events amongst monozygotic twin women with lifetime anorexia nervosa, bulimia nervosa, or major depression

International Journal of Eating Disorders, 2007

Objectives: To investigate the differential profile of early family life events associated with l... more Objectives: To investigate the differential profile of early family life events associated with lifetime anorexia nervosa (AN), bulimia nervosa (BN), and major depression (MD).

Research paper thumbnail of Direction of causation modeling between cross-sectional measures of parenting and psychological distress in female twins

Behavior genetics, 2003

Under certain conditions, cross-sectional analysis of cross-twin intertrait correlations can prov... more Under certain conditions, cross-sectional analysis of cross-twin intertrait correlations can provide important information about the direction of causation (DOC) between two variables. A community-based sample of Australian female twins aged 18 to 45 years was mailed an extensive Health and Lifestyle Questionnaire (HLQ) that covered a wide range of personality and behavioral measures. Included were self-report measures of recent psychological distress and perceived childhood environment (PBI). Factor analysis of the PBI yielded three interpretable dimensions: Coldness, Overprotection, and Autonomy. Univariate analysis revealed that parental Overprotection and Autonomy were best explained by additive genetic, shared, and nonshared environmental effects (ACE), whereas the best-fitting model for PBI Coldness and the three measures of psychological distress (Depression, Phobic Anxiety, and Somatic Distress) included only additive genetic and nonshared environmental effects (AE). A commo...

Research paper thumbnail of Retinal microvessels reflect familial vulnerability to psychotic symptoms: A comparison of twins discordant for psychotic symptoms and controls

Schizophrenia Research, 2015

Mounting evidence suggests that individuals with schizophrenia have an underlying vulnerability t... more Mounting evidence suggests that individuals with schizophrenia have an underlying vulnerability to cardiovascular disease, and a recent study suggested that this vulnerability might be reflected in the retinal microvasculature. The purpose of this study was to test the hypothesis that the retinal microvessels reflect familial vulnerability to psychotic symptoms. Participants were 531 adolescent and young adult twins who took part in the Brisbane Longitudinal Twin Study and the Twins Eye Study in Tasmania. The twins had photographs taken of their retina when they were adolescents or young adults (M age=20.6years), and retinal vessel diameter was assessed using computer software. The twins completed an assessment of psychosis symptoms approximately six years later. We compared retinal venular diameters of individuals with one or more symptoms of psychosis (n=45), their unaffected co-twins (n=24), and controls (n=462). Individuals with one or more symptoms of psychosis had wider venules (standardized mean=0.29) than controls (standardized mean=-0.04; p=.03), and unaffected co-twins had venular diameters that were intermediate (standardized mean=0.13) between the two groups, suggesting that wide venules may represent a proxy marker of familial vulnerability to psychosis symptoms. Consistent with previous work, there were no differences in arteriolar diameter between individuals with and without symptoms of psychosis. Findings suggest that wide retinal venules may serve as a proxy marker of familial liability to psychosis symptoms. The pathophysiological mechanisms linking psychosis and cardiovascular disease may be operative from early in life, possibly at the level of the microvasculature.

Research paper thumbnail of Characterization of the Branched-Photocycle Intermediates P and Q of Bacteriorhodopsin

The Journal of Physical Chemistry B, 2002

The bacteriorhodopsin branched-photocycle intermediates P and Q are studied with respect to chrom... more The bacteriorhodopsin branched-photocycle intermediates P and Q are studied with respect to chromophore isomeric content, photochemical origin, kinetic heterogeneity, and photoreversibility. These blue-shifted species are compared to products with similar ...

Research paper thumbnail of A Finite Mixture Model for Genotype and Environment Interactions: Detecting Latent Population Heterogeneity

Twin Research and Human Genetics, 2006

Research paper thumbnail of The Sensitivity of Variance Component Estimates to Underreporting: Method and Application to Substance Abuse Data

Twin Research and Human Genetics, 2007

Research paper thumbnail of Comparing Factor, Class, and Mixture Models of Cannabis Initiation and DSM Cannabis Use Disorder Criteria, Including Craving, in the Brisbane Longitudinal Twin Study

Twin Research and Human Genetics, 2014

Accumulating evidence suggests that the Diagnostic and Statistical Manual of Mental Disorders (DS... more Accumulating evidence suggests that the Diagnostic and Statistical Manual of Mental Disorders (DSM) diagnostic criteria for cannabis abuse and dependence are best represented by a single underlying factor. However, it remains possible that models with additional factors, or latent class models or hybrid models, may better explain the data. Using structured interviews, 626 adult male and female twins provided complete data on symptoms of cannabis abuse and dependence, plus a craving criterion. We compared latent factor analysis, latent class analysis, and factor mixture modeling using normal theory marginal maximum likelihood for ordinal data. Our aim was to derive a parsimonious, best-fitting cannabis use disorder (CUD) phenotype based on DSM-IV criteria and determine whether DSM-5 craving loads onto a general factor. When compared with latent class and mixture models, factor models provided a better fit to the data. When conditioned on initiation and cannabis use, the association between criteria for abuse, dependence, withdrawal, and craving were best explained by two correlated latent factors for males and females: a general risk factor to CUD and a factor capturing the symptoms of social and occupational impairment as a consequence of frequent use. Secondary analyses revealed a modest increase in the prevalence of DSM-5 CUD compared with DSM-IV cannabis abuse or dependence. It is concluded that, in addition to a general factor with loadings on cannabis use and symptoms of abuse, dependence, withdrawal, and craving, a second clinically relevant factor defined by features of social and occupational impairment was also found for frequent cannabis use.

Research paper thumbnail of Genetic Simplex Modeling of Eysenck's Dimensions of Personality in a Sample of Young Australian Twins

Twin Research, 2004

The relative stability and magnitude of genetic and environmental effects underlying major dimens... more The relative stability and magnitude of genetic and environmental effects underlying major dimensions of adolescent personality across time were investigated. The Junior Eysenck Personality Questionnaire was administered to over 540 twin pairs at ages 12, 14 and 16 years. Their personality scores were analyzed using genetic simplex modeling which explicitly took into account the longitudinal nature of the data. With the exception of the dimension lie, multivariate model fitting results revealed that familial aggregation was entirely explained by additive genetic effects. Results from simplex model fitting suggest that large proportions of the additive genetic variance observed at ages 14 and 16 years could be explained by genetic effects present at the age of 12 years. There was also evidence for smaller but significant genetic innovations at 14 and 16 years of age for male and female neuroticism, at 14 years for male extraversion, at 14 and 16 years for female psychoticism, and at 14 years for male psychoticism.

Research paper thumbnail of A Genome Scan for Eye Color in 502 Twin Families: Most Variation is due to a QTL on Chromosome 15q

Twin Research, 2004

We have rated eye color on a 3-point scale (1 = blue/grey, 2 = hazel/green, 3 = brown) in 502 twi... more We have rated eye color on a 3-point scale (1 = blue/grey, 2 = hazel/green, 3 = brown) in 502 twin families and carried out a 5-10 cM genome scan (400-757 markers). We analyzed eye color as a threshold trait and performed multipoint sib pair linkage analysis using variance components analysis in Mx. A lod of 19.2 was found at the marker D15S1002, less than 1 cM from OCA2, which has been previously implicated in eye color variation. We estimate that 74% of variance in eye color liability is due to this QTL and a further 18% due to polygenic effects. However, a large shoulder on this peak suggests that other loci affecting eye color may be telomeric of OCA2 and inflating the QTL estimate. No other peaks reached genome-wide significance, although lods > 2 were seen on 5p and 14q and lods >1 were additionally seen on chromosomes 2, 3, 6, 7, 8, 9, 17 and 18. Most of these secondary peaks were reduced or eliminated when we repeated the scan as a two locus analysis with the 15q linkage included, although this does not necessarily exclude them as false positives. We also estimated the interaction between the 15q QTL and the other marker locus but there was only minor evidence for additive x additive epistasis. Elaborating the analysis to the full two-locus model including non-additive main effects and interactions did not strengthen the evidence for epistasis. We conclude that most variation in…

Research paper thumbnail of Do the Genetic or Environmental Determinants of Anxiety and Depression Change with Age? A Longitudinal Study of Australian Twins

Twin Research, 2004

Because the determinants of anxiety and depression in late adolescence and early adulthood may di... more Because the determinants of anxiety and depression in late adolescence and early adulthood may differ from those in later life, we investigated the temporal stability and magnitude of genetic and environmental correlates of symptoms of anxiety and depression across the life span. Data were collected from a population-based Australian sample of 4364 complete twin pairs and 777 singletons aged 20 to 96 years who were followed-up over three studies between 1980 and 1996. Each study contained the 14-item self-report DSSI/sAD scale which was used to measure recently experienced symptoms of anxiety and depression. Symptom scores were then divided and assigned to age intervals according to each subject's age at time of participation. We fitted genetic simplex models to take into account the longitudinal nature of the data. For male anxiety and depression, the best fitting simplex models comprised a single genetic innovation at age 20 which was transmitted, and explained genetic variation in anxiety and depression at ages 30, 40, 50 and 60. Most of the lifetime genetic variation in female anxiety and depression could also be explained by innovations at age 20 which were transmitted to all other ages; however, there were also smaller age-dependent genetic innovations at 30 for anxiety and at 40 and 70 for depression. Although the genetic determinants of anxiety and depression appear relatively stable across the lifespan for males and females, there is some evidence to support additional mid-life and late age gene action in females for depression. The fact that midlife onset for anxiety occurs one decade before depression is also consistent with a causal relationship (anxiety leading to depression) between these conditions. These findings have significance for large scale depression prevention projects.

Research paper thumbnail of Optimization of bacteriorhodopsin for bioelectronic devices

Trends in Biotechnology, 2002

Research paper thumbnail of Biomolecular Electronics:  Protein-Based Associative Processors and Volumetric Memories

The Journal of Physical Chemistry B, 1999

The promise of new architectures and more cost-effective miniaturization has prompted interest in... more The promise of new architectures and more cost-effective miniaturization has prompted interest in molecular and biomolecular electronics. Bioelectronics offers valuable near-term potential, because evolution and natural selection have optimized many biological ...

Research paper thumbnail of Two-Photon and Fluorescence Spectroscopy and the Effect of Environment on the Photochemical Properties of Peridinin in Solution and in the Peridinin-Chlorophyll-Protein from Amphidinium carterae †

The Journal of Physical Chemistry A, 2003

The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll... more The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll-protein (PCP) complex are studied by using one-photon and two-photon spectroscopy, solvent effects, and quantum theory. Two-photon excitation spectra, two-...

Research paper thumbnail of Perceived social support in a large community sample

Social Psychiatry and Psychiatric Epidemiology, 2004

The positive health and wellbeing effects of social support have been consistently demonstrated i... more The positive health and wellbeing effects of social support have been consistently demonstrated in the literature since the late 1970s. However, a better understanding of the effects of age and sex is required. We examined the factor structure and reliability of Kessler's Perceived Social Support (KPSS) measure in a community-based sample that comprised younger and older adult cohorts from the Australian Twin Registry (ATR), totalling 11,389 males and females aged 18-95, of whom 887 were retested 25 months later. Factor analysis consistently identified seven factors: support from spouse, twin, children, parents, relatives, friends and helping support. Internal reliability for the seven dimensions ranged from 0.87 to 0.71 and test-retest reliability ranged from 0.75 to 0.48. Perceived support was only marginally higher in females. Age dependencies were explored. Across the age range, there was a slight decline (more marked in females) in the perceived support from spouse, parent and friend, a slight increase in perceived relative and helping support for males but none for females, a substantial increase in the perceived support from children for males and females and a negligible decline in total KPSS for females against a negligible increase for males. The perceived support from twin remained constant. Females were more likely to have a confidant, although this declined with age whilst increasing with age for males. Total scores for perceived social support conflate heterogeneous patterns on sub-scales that differ markedly by age and sex. Our paper describes these relationships in detail in a very large Australian sample.

Research paper thumbnail of Tests of measurement invariance across age in the Delusion Symptoms States Inventory scales of depression, anxiety and general psychological distress in a sample of Australian twins

Research paper thumbnail of Direction of Causation Models

Research paper thumbnail of Shared Genetic and Environmental Influences on Early Temperament and Preschool Psychiatric Disorders in Hispanic Twins

Twin research and human genetics : the official journal of the International Society for Twin Studies, Jan 2, 2015

Objective: Despite an increasing recognition that psychiatric disorders can be diagnosed as early... more Objective: Despite an increasing recognition that psychiatric disorders can be diagnosed as early as preschool, little is known how early genetic and environmental risk factors contribute to the development of psychiatric disorders during this very early period of development. Method: We assessed infant temperament at age 1, and attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and separation anxiety disorder (SAD) at ages 3 through 5 years in a sample of Hispanic twins. Genetic, shared, and non-shared environmental effects were estimated for each temperamental construct and psychiatric disorder using the statistical program MX. Multivariate genetic models were fitted to determine whether the same or different sets of genes and environments account for the co-occurrence between early temperament and preschool psychiatric disorders. Results: Additive genetic factors accounted for 61% of the variance in ADHD, 21% in ODD, and 28% in SAD. Shared envir...

Research paper thumbnail of Characterization and photochemistry of 13-desmethyl bacteriorhodopsin

The journal of physical chemistry. B, Jan 25, 2005

The photochemistry of the 13-desmethyl (DM) analogue of bacteriorhodopsin (BR) is examined by usi... more The photochemistry of the 13-desmethyl (DM) analogue of bacteriorhodopsin (BR) is examined by using spectroscopy, molecular orbital theory, and chromophore extraction followed by conformational analysis. The removal of the 13-methyl group permits the direct photochemical formation of a thermally stable, photochemically reversible state, P1(DM) (lambda(max) = 525 nm), which can be generated efficiently by exciting the resting state, bR(DM) with yellow or red light (lambda > 590 nm). Chromophore extraction analysis reveals that the retinal configuration in P1(DM) is 9-cis, identical to that of the retinal configuration in the native BR P1 state. Fourier transform infrared and Raman experiments on P1(DM) indicate an anti configuration around the C15=N bond, as would be expected of an O-state photoproduct. However, low-temperature spectroscopy and ambient, time-resolved studies indicate that the P1(DM) state forms primarily via thermal relaxation from the L(D)(DM) state. Theoretical ...

Research paper thumbnail of Two-Photon and Fluorescence Spectroscopy and the Effect of Environment on the Photochemical Properties of Peridinin in Solution and in the Peridinin-Chlorophyll-Protein from Amphidinium carterae†

The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll... more The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll-protein (PCP) complex are studied by using one-photon and two-photon spectroscopy, solvent effects, and quantum theory. Two-photon excitation spectra, two-...

Research paper thumbnail of Low Birth Weight in MZ Twins Discordant for Birth Weight is Associated with Shorter Telomere Length and lower IQ, but not Anxiety/Depression in Later Life

Twin Research and Human Genetics, 2015

Shorter telomere length (TL) has found to be associated with lower birth weight and with lower co... more Shorter telomere length (TL) has found to be associated with lower birth weight and with lower cognitive ability and psychiatric disorders. However, the direction of causation of these associations and the extent to which they are genetically or environmentally mediated are unclear. Within-pair comparisons of monozygotic (MZ) and dizygotic (DZ) twins can throw light on these questions. We investigated correlations of within pair differences in telomere length, IQ, and anxiety/depression in an initial sample from Brisbane (242 MZ pairs, 245 DZ same sex (DZSS) pairs) and in replication samples from Amsterdam (514 MZ pairs, 233 DZSS pairs) and Melbourne (19 pairs selected for extreme high or low birth weight difference). Intrapair differences of birth weight and telomere length were significantly correlated in MZ twins, but not in DZSS twins. Greater intra-pair differences of telomere length were observed in the 10% of MZ twins with the greatest difference in birth weight compared to the bottom 90% in both samples and also in the Melbourne sample. Intra-pair differences of telomere length and IQ, but not of TL and anxiety/depression, were correlated in MZ twins, and to a smaller extent in DZSS twins. Our findings suggest that the same prenatal effects that reduce birth weight also influence telomere length in MZ twins. The association between telomere length and IQ is partly driven by the same prenatal effects that decrease birth weight.

Research paper thumbnail of A comparison of early family life events amongst monozygotic twin women with lifetime anorexia nervosa, bulimia nervosa, or major depression

International Journal of Eating Disorders, 2007

Objectives: To investigate the differential profile of early family life events associated with l... more Objectives: To investigate the differential profile of early family life events associated with lifetime anorexia nervosa (AN), bulimia nervosa (BN), and major depression (MD).

Research paper thumbnail of Direction of causation modeling between cross-sectional measures of parenting and psychological distress in female twins

Behavior genetics, 2003

Under certain conditions, cross-sectional analysis of cross-twin intertrait correlations can prov... more Under certain conditions, cross-sectional analysis of cross-twin intertrait correlations can provide important information about the direction of causation (DOC) between two variables. A community-based sample of Australian female twins aged 18 to 45 years was mailed an extensive Health and Lifestyle Questionnaire (HLQ) that covered a wide range of personality and behavioral measures. Included were self-report measures of recent psychological distress and perceived childhood environment (PBI). Factor analysis of the PBI yielded three interpretable dimensions: Coldness, Overprotection, and Autonomy. Univariate analysis revealed that parental Overprotection and Autonomy were best explained by additive genetic, shared, and nonshared environmental effects (ACE), whereas the best-fitting model for PBI Coldness and the three measures of psychological distress (Depression, Phobic Anxiety, and Somatic Distress) included only additive genetic and nonshared environmental effects (AE). A commo...

Research paper thumbnail of Retinal microvessels reflect familial vulnerability to psychotic symptoms: A comparison of twins discordant for psychotic symptoms and controls

Schizophrenia Research, 2015

Mounting evidence suggests that individuals with schizophrenia have an underlying vulnerability t... more Mounting evidence suggests that individuals with schizophrenia have an underlying vulnerability to cardiovascular disease, and a recent study suggested that this vulnerability might be reflected in the retinal microvasculature. The purpose of this study was to test the hypothesis that the retinal microvessels reflect familial vulnerability to psychotic symptoms. Participants were 531 adolescent and young adult twins who took part in the Brisbane Longitudinal Twin Study and the Twins Eye Study in Tasmania. The twins had photographs taken of their retina when they were adolescents or young adults (M age=20.6years), and retinal vessel diameter was assessed using computer software. The twins completed an assessment of psychosis symptoms approximately six years later. We compared retinal venular diameters of individuals with one or more symptoms of psychosis (n=45), their unaffected co-twins (n=24), and controls (n=462). Individuals with one or more symptoms of psychosis had wider venules (standardized mean=0.29) than controls (standardized mean=-0.04; p=.03), and unaffected co-twins had venular diameters that were intermediate (standardized mean=0.13) between the two groups, suggesting that wide venules may represent a proxy marker of familial vulnerability to psychosis symptoms. Consistent with previous work, there were no differences in arteriolar diameter between individuals with and without symptoms of psychosis. Findings suggest that wide retinal venules may serve as a proxy marker of familial liability to psychosis symptoms. The pathophysiological mechanisms linking psychosis and cardiovascular disease may be operative from early in life, possibly at the level of the microvasculature.

Research paper thumbnail of Characterization of the Branched-Photocycle Intermediates P and Q of Bacteriorhodopsin

The Journal of Physical Chemistry B, 2002

The bacteriorhodopsin branched-photocycle intermediates P and Q are studied with respect to chrom... more The bacteriorhodopsin branched-photocycle intermediates P and Q are studied with respect to chromophore isomeric content, photochemical origin, kinetic heterogeneity, and photoreversibility. These blue-shifted species are compared to products with similar ...

Research paper thumbnail of A Finite Mixture Model for Genotype and Environment Interactions: Detecting Latent Population Heterogeneity

Twin Research and Human Genetics, 2006

Research paper thumbnail of The Sensitivity of Variance Component Estimates to Underreporting: Method and Application to Substance Abuse Data

Twin Research and Human Genetics, 2007

Research paper thumbnail of Comparing Factor, Class, and Mixture Models of Cannabis Initiation and DSM Cannabis Use Disorder Criteria, Including Craving, in the Brisbane Longitudinal Twin Study

Twin Research and Human Genetics, 2014

Accumulating evidence suggests that the Diagnostic and Statistical Manual of Mental Disorders (DS... more Accumulating evidence suggests that the Diagnostic and Statistical Manual of Mental Disorders (DSM) diagnostic criteria for cannabis abuse and dependence are best represented by a single underlying factor. However, it remains possible that models with additional factors, or latent class models or hybrid models, may better explain the data. Using structured interviews, 626 adult male and female twins provided complete data on symptoms of cannabis abuse and dependence, plus a craving criterion. We compared latent factor analysis, latent class analysis, and factor mixture modeling using normal theory marginal maximum likelihood for ordinal data. Our aim was to derive a parsimonious, best-fitting cannabis use disorder (CUD) phenotype based on DSM-IV criteria and determine whether DSM-5 craving loads onto a general factor. When compared with latent class and mixture models, factor models provided a better fit to the data. When conditioned on initiation and cannabis use, the association between criteria for abuse, dependence, withdrawal, and craving were best explained by two correlated latent factors for males and females: a general risk factor to CUD and a factor capturing the symptoms of social and occupational impairment as a consequence of frequent use. Secondary analyses revealed a modest increase in the prevalence of DSM-5 CUD compared with DSM-IV cannabis abuse or dependence. It is concluded that, in addition to a general factor with loadings on cannabis use and symptoms of abuse, dependence, withdrawal, and craving, a second clinically relevant factor defined by features of social and occupational impairment was also found for frequent cannabis use.

Research paper thumbnail of Genetic Simplex Modeling of Eysenck's Dimensions of Personality in a Sample of Young Australian Twins

Twin Research, 2004

The relative stability and magnitude of genetic and environmental effects underlying major dimens... more The relative stability and magnitude of genetic and environmental effects underlying major dimensions of adolescent personality across time were investigated. The Junior Eysenck Personality Questionnaire was administered to over 540 twin pairs at ages 12, 14 and 16 years. Their personality scores were analyzed using genetic simplex modeling which explicitly took into account the longitudinal nature of the data. With the exception of the dimension lie, multivariate model fitting results revealed that familial aggregation was entirely explained by additive genetic effects. Results from simplex model fitting suggest that large proportions of the additive genetic variance observed at ages 14 and 16 years could be explained by genetic effects present at the age of 12 years. There was also evidence for smaller but significant genetic innovations at 14 and 16 years of age for male and female neuroticism, at 14 years for male extraversion, at 14 and 16 years for female psychoticism, and at 14 years for male psychoticism.

Research paper thumbnail of A Genome Scan for Eye Color in 502 Twin Families: Most Variation is due to a QTL on Chromosome 15q

Twin Research, 2004

We have rated eye color on a 3-point scale (1 = blue/grey, 2 = hazel/green, 3 = brown) in 502 twi... more We have rated eye color on a 3-point scale (1 = blue/grey, 2 = hazel/green, 3 = brown) in 502 twin families and carried out a 5-10 cM genome scan (400-757 markers). We analyzed eye color as a threshold trait and performed multipoint sib pair linkage analysis using variance components analysis in Mx. A lod of 19.2 was found at the marker D15S1002, less than 1 cM from OCA2, which has been previously implicated in eye color variation. We estimate that 74% of variance in eye color liability is due to this QTL and a further 18% due to polygenic effects. However, a large shoulder on this peak suggests that other loci affecting eye color may be telomeric of OCA2 and inflating the QTL estimate. No other peaks reached genome-wide significance, although lods > 2 were seen on 5p and 14q and lods >1 were additionally seen on chromosomes 2, 3, 6, 7, 8, 9, 17 and 18. Most of these secondary peaks were reduced or eliminated when we repeated the scan as a two locus analysis with the 15q linkage included, although this does not necessarily exclude them as false positives. We also estimated the interaction between the 15q QTL and the other marker locus but there was only minor evidence for additive x additive epistasis. Elaborating the analysis to the full two-locus model including non-additive main effects and interactions did not strengthen the evidence for epistasis. We conclude that most variation in…

Research paper thumbnail of Do the Genetic or Environmental Determinants of Anxiety and Depression Change with Age? A Longitudinal Study of Australian Twins

Twin Research, 2004

Because the determinants of anxiety and depression in late adolescence and early adulthood may di... more Because the determinants of anxiety and depression in late adolescence and early adulthood may differ from those in later life, we investigated the temporal stability and magnitude of genetic and environmental correlates of symptoms of anxiety and depression across the life span. Data were collected from a population-based Australian sample of 4364 complete twin pairs and 777 singletons aged 20 to 96 years who were followed-up over three studies between 1980 and 1996. Each study contained the 14-item self-report DSSI/sAD scale which was used to measure recently experienced symptoms of anxiety and depression. Symptom scores were then divided and assigned to age intervals according to each subject's age at time of participation. We fitted genetic simplex models to take into account the longitudinal nature of the data. For male anxiety and depression, the best fitting simplex models comprised a single genetic innovation at age 20 which was transmitted, and explained genetic variation in anxiety and depression at ages 30, 40, 50 and 60. Most of the lifetime genetic variation in female anxiety and depression could also be explained by innovations at age 20 which were transmitted to all other ages; however, there were also smaller age-dependent genetic innovations at 30 for anxiety and at 40 and 70 for depression. Although the genetic determinants of anxiety and depression appear relatively stable across the lifespan for males and females, there is some evidence to support additional mid-life and late age gene action in females for depression. The fact that midlife onset for anxiety occurs one decade before depression is also consistent with a causal relationship (anxiety leading to depression) between these conditions. These findings have significance for large scale depression prevention projects.

Research paper thumbnail of Optimization of bacteriorhodopsin for bioelectronic devices

Trends in Biotechnology, 2002

Research paper thumbnail of Biomolecular Electronics:  Protein-Based Associative Processors and Volumetric Memories

The Journal of Physical Chemistry B, 1999

The promise of new architectures and more cost-effective miniaturization has prompted interest in... more The promise of new architectures and more cost-effective miniaturization has prompted interest in molecular and biomolecular electronics. Bioelectronics offers valuable near-term potential, because evolution and natural selection have optimized many biological ...

Research paper thumbnail of Two-Photon and Fluorescence Spectroscopy and the Effect of Environment on the Photochemical Properties of Peridinin in Solution and in the Peridinin-Chlorophyll-Protein from Amphidinium carterae †

The Journal of Physical Chemistry A, 2003

The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll... more The ground and excited-state properties of peridinin in solution and in the peridinin-chlorophyll-protein (PCP) complex are studied by using one-photon and two-photon spectroscopy, solvent effects, and quantum theory. Two-photon excitation spectra, two-...

Research paper thumbnail of Perceived social support in a large community sample

Social Psychiatry and Psychiatric Epidemiology, 2004

The positive health and wellbeing effects of social support have been consistently demonstrated i... more The positive health and wellbeing effects of social support have been consistently demonstrated in the literature since the late 1970s. However, a better understanding of the effects of age and sex is required. We examined the factor structure and reliability of Kessler's Perceived Social Support (KPSS) measure in a community-based sample that comprised younger and older adult cohorts from the Australian Twin Registry (ATR), totalling 11,389 males and females aged 18-95, of whom 887 were retested 25 months later. Factor analysis consistently identified seven factors: support from spouse, twin, children, parents, relatives, friends and helping support. Internal reliability for the seven dimensions ranged from 0.87 to 0.71 and test-retest reliability ranged from 0.75 to 0.48. Perceived support was only marginally higher in females. Age dependencies were explored. Across the age range, there was a slight decline (more marked in females) in the perceived support from spouse, parent and friend, a slight increase in perceived relative and helping support for males but none for females, a substantial increase in the perceived support from children for males and females and a negligible decline in total KPSS for females against a negligible increase for males. The perceived support from twin remained constant. Females were more likely to have a confidant, although this declined with age whilst increasing with age for males. Total scores for perceived social support conflate heterogeneous patterns on sub-scales that differ markedly by age and sex. Our paper describes these relationships in detail in a very large Australian sample.