Biomedical subjects

J K Hewitt

Publications and source records attributed to J K Hewitt.

At least 37 records · Page 2Linked to original sources

PubMed1999

Tobacco, alcohol and drug use in eight- to sixteen-year-old twins: the Virginia Twin Study of Adolescent Behavioral Development.

OBJECTIVE: This study reports prevalences of lifetime and current alcohol, tobacco and drug use in adolescents; examines associations between substance use and a number of putative risk factors; and estimates the contribution of genetic, shared and unique environmental influences on substance use. METHOD: Substance use data were collected using the Child and Adolescent Psychiatric Assessment on a population sample of 1,412 male and female monozygotic and dizygotic twin pairs, aged 8 through 16, from the Virginia Twin Study of Adolescent Behavioral Development. RESULTS: Heritabilities were estimated to be 84% and 82% for liability to lifetime and current tobacco use, respectively. For alcohol use the role of genes and environment varied according to the context of reporting. Liability to lifetime alcohol use was estimated to be under environmental control, with 71% of the variation shared by members of a twin pair and 29% unique to individual twins. Lifetime alcohol use without the permission of a parent or guardian and current use of alcohol were predominantly explained by genetic factors (h2 = 72% and 74%). The role of genetic factors increased and that of unique environmental factors decreased with increasing severity of alcohol use. Lifetime use of any drug showed a heritability of 45%, with the shared environment accounting for 47% of the variation. Shared environmental factors explained most of the variation in marijuana use. CONCLUSIONS: Genetic factors explained a significant proportion of the variation in the use of tobacco, alcohol and other drugs. Shared environmental factors contributed significantly to lifetime alcohol use and other drug use.

Adolescent↗

PubMed1998

A family history and direct interview study of the familial aggregation of substance abuse: the adolescent substance abuse study.

The adolescent substance abuse (ASA) study collected information concerning drug use and psychopathology on male adolescent probands in treatment for substance abuse and also on matched control adolescents, as well as all available family members of both groups. Information was obtained through direct interview and the family history method of assessment. Both methods revealed greater alcohol and drug use, conduct disorder (CD) and antisocial personality disorder (ASP) in the relatives of treatment probands as compared with control relatives. These results suggest familial transmission, not only for alcohol abuse, but also for non-alcohol substance abuse. Familial transmission for CD and ASP is also evident for both male and female relatives, although the prevalence of these disorders is significantly greater in males than females.

Adolescent↗

PubMed1998

Assortative mating for major psychiatric diagnoses in two population-based samples.

BACKGROUND: Previous studies on assortment for psychiatric disorders have reported discrepant findings. We aimed to test whether there is a significant association for psychiatric diagnoses, including alcoholism, generalized anxiety disorder, major depressive disorder, panic disorder and phobias between husbands and wives in two population-based samples. We further evaluated whether marital resemblance occurs primarily within or across psychiatric disorders and if assortment for psychopathology is primary or secondary to assortment for correlated variables. METHODS: A model for mate selection addressed whether the correlation between mates for psychiatric disorders arises from direct assortment (primary homogamy) or through correlation with other variables for which assortment occurs (secondary homogamy) or through cross-variable assortment. The model accounted for within-person co-morbidity as well as across-spouse data. RESULTS: Findings suggested that a moderate degree of assortment exists both within and across psychiatric diagnoses. Only a small amount of the observed marital resemblance for mental illness could be explained by assortment for correlated variables such as age, religious attendance and education. Similar results were obtained for the two samples separately and confirmed in their joint analysis, revealing that the co-morbidity and assortment findings, except for the marital correlation for age, religious attendance and education, replicate across samples. CONCLUSIONS: Significant but moderate primary assortment exists for psychiatric disorders. The bias in twin studies that have ignored the small amount of assortment is negligible.

Adolescent↗

PubMed1998

Sex differences and non-additivity in the effects of genes on personality.

New large-sample data show that non-additive genetic effects, probably epistatic interactions between loci, and sex-limited gene expression are significant features of the genetic architecture of human personality as measured by questionnaire scales of extraversion and neuroticism. Three large data sets--new data on large samples (n = 20,554) of US twins, their spouses, parents, siblings and children, correlations for Australian twins (n = 7,532), and previously published twin data from Finland (n = 14,288)--are subjected to an integrated analysis to test alternative hypotheses about the genetic causes of family resemblance in personality. When allowance is made for differences in reliability of the scales, the combined data are consistent with the same model for variation. There are significant amounts of genetic non-additivity for both dimensions of personality. The evidence favours additive x additive epistatic interactions rather than dominance. In the case of neuroticism, there is especially strong evidence of sex differences in genetic architecture favouring a greater relative contribution of non-additive genetic effects in males. The data confirm previous claims to find no major contribution of the shared environment of twins and siblings to these dimensions of personality. Correlations between spouses are zero, and the correlations for very large samples of siblings and non-identical twins do not differ significantly.

Diseases in Twins↗

PubMed1998

Exploring the genetic and environmental etiology of high general cognitive ability in fourteen- to thirty-six-month-old twins.

Although numerous theories have attempted to explain the origins of high general cognitive ability (g), the genetic and environmental etiology of high g during infancy and early childhood has not previously been investigated. We report results of a twin study of high cognitive ability at 14, 20, 24, and 36 months using twins from the more than 600 children participating in the MacArthur Longitudinal Twin Study. High g groups were formed from the ninetieth percentile and above at each age, with IQ equivalent means at or above 126 across the ages. Results suggest increasing genetic influence and increasing genetic stability from 14 to 36 months using DeFries-Fulker multiple regression analyses. However, genetic influences are substantial when examining individuals who possess high g scores averaged across all 4 ages. These results suggest that, although high cognitive ability may be genetically influenced in early childhood, these influences differ in magnitude from 14 to 36 months.

Child Development↗

PubMed1997

The familial aggregation of depressive symptoms, antisocial behavior, and alcohol abuse.

This study describes results from an ongoing family study of adolescent boys and their families designed to investigate potential risk factors for substance abuse. The adolescent treatment probands have severe drug and alcohol related problems and were recruited through a residential rehabilitation program. To date, the sample includes 251 individuals: 39 male probands and their families and 34 control families matched for age and geographic location (zip code). Probands and participating family members are given a structured interview which assesses alcohol and drug problems, and various psychiatric symptoms. The purpose of the present study was to examine the coaggregation of depressive symptoms, antisocial behavior, and alcohol misuse. Multivariate pedigree analyses were performed using a model that allowed for the estimation of vertical familial transmission, residual sibling resemblance, and assortative mating. Spouse correlations were estimated at .57, .21, and .31 for antisocial behavior, depressive symptoms, and alcohol abuse, respectively. Residual sibling environment (i.e., sibling resemblance unaccounted for by parent-offspring transmission) was not found for alcohol problem symptoms, but did contribute to resemblance for antisocial behavior and depressive symptoms. The proportion of variance accounted for by vertical familial transmission was estimated at approximately 30 to 40%. More important, correlations among the transmissible family factors for these psychiatric syndromes ranged from .58 to .73, suggesting substantial overlap among the underlying familial antecedents for these disorders.

Adolescent↗

PubMed1997

The Virginia Twin Study of Adolescent Behavioral Development. Influences of age, sex, and impairment on rates of disorder.

BACKGROUND: The Virginia Twin Study of Adolescent Behavioral Development is a cohort-longitudinal epidemiological study that uses the genetic twin design to study the development and maintenance of child psychiatric disorders. We determined the rates of DSM-III-R disorders, disorders with impairment, and age, sex, and comorbidity effects. METHODS: Families of 2762 white twins aged 8 to 16 years participated. Twins and their parents were asked systematically about risk factors and current psychiatric symptoms by means of investigator-based psychiatric interviews and questionnaires. The DSM-III-R diagnoses were made for major depressive disorder, separation anxiety, overanxious disorder, simple phobia, social phobia, agoraphobia, oppositional defiant disorder, conduct disorder, and attention deficit hyperactivity disorder. RESULTS: The 3-month point prevalence for any DSM-III-R disorders was 413 per 1000, and that for disorders with associated impairment was 142 per 1000. Emotional disorders with impairment occurred in 89 per 1000, with girls being more commonly affected; behavioral disorders had a prevalence of 71 per 1000, with boys being more frequently affected. The proportion with disorder who also had functional impairment varied across disorders; anxiety and phobic disorders were particularly likely not to be accompanied by impairment. Rates of emotional and behavioral disorders increased over the age range. There was extensive comorbidity among disorders. CONCLUSIONS: The prevalence rates and patterns of findings from this study of twins are consistent with those of other epidemiological studies, supporting previous findings of few differences in rates of psychiatric disorder between twins and singletons. The importance of including measures of functional impairment is evident by its effect on rates of disorder and patterns of comorbidity.

Adolescent↗

PubMed1997

Genetic and environmental influences on child reports of manifest anxiety and symptoms of separation anxiety and overanxious disorders: a community-based twin study.

Genetic and environmental influences in the determination of individual differences in self-reported symptoms of separation anxiety (SAD), overanxious disorder (OAD), and manifest anxiety (MANX) were evaluated in children and adolescents for three age groups (8-10, 11-13, and 14-16). Symptom counts for SAD and OAD were assessed for 1,412 twin pairs using the children's version of the Child and Adolescent Psychiatric Assessment, and MANX scores were based on child report from the Revised Children's Manifest Anxiety Scales. Despite significant age and gender differences in thresholds of liability for child reports of symptoms of SAD and OAD, additive genetic and environmental effects could be set equal across age and gender for these variables. For MANX, however, the best-fitting model was a common effects sex-limitation model with estimates of heritability varying dependent upon age and gender. Parameter estimates from the ACE models of OAD and SAD showed that additive genetic variation was a necessary component in the explanation of individual differences in child-reported symptoms of OAD (h2 = .37) across gender, but does not appear to be a major contributor to the explanation of individual differences in symptoms of SAD reported by children. Shared environmental effects (c2 = .40) were found to play a moderate role for SAD but could be dropped from the model for OAD and from all of the age groups for MANX, although the parameter approached significance among 11 yr to 13-year-old males.

Adolescent↗

PubMed1997

Genetic and developmental influences on infant mouse ultrasonic calling. I. A diallel analysis of the calls of 3-day olds.

Ultrasonic calls produced by young mice reliably elicit investigation and retrieval by adults. While there are large individual differences in the characteristics of these calls, little work has been done to partition that variation. We completed a 4 x 4 diallel cross and Hayman analyses on several characteristics of these cries. The major result was the detection of directional dominance toward a higher rate of calling, longer calls, and calls of lower overall frequency with a greater bandwidth. Within the context of biometrical genetic theory, we conclude that calls with such characteristics may have important fitness value. Extending this idea, we propose that within the population sampled for this study (the animals of the four inbred strains and 12 F1 hybrid groups), the calls most effectively eliciting investigation and retrieval would be calls with the average hybrid values of the diallel cross.

Animals↗

PubMed1997

The genetics of obesity: what have genetic studies told us about the environment.

Genetic studies have shown that both childhood and adult body mass index are substantially heritable. The evidence for shared family environmental influences is largely absent, even though there are clear indications that secular changes in energy expenditure have brought about a significant increase in the prevalence of obesity. This apparent inconsistency may be explained by the dual phenomena of the near-universality of access to environments that facilitate reductions in energy expenditure (e.g., TV as a recreational pastime), together with heritable individual differences in the response to or utilization of these environments. The impact of changes in nonshared environments on body weight can be estimated from biometrical genetical studies and is found to be both small and relatively short-lived. Genetic and environmental results from longitudinal studies are consistent with what is known about the changing distribution of adiposity during adulthood and clinical experience of the difficulty of maintaining behavioral-induced weight loss.

Adolescent↗

PubMed1997

Exploring the genetic etiology of low general cognitive ability from 14 to 36 months.

The genetic and environmental etiology of low general cognitive ability (g) during infancy and early childhood has not previously been investigated. The current study examined the genetic etiology of low cognitive ability at 14, 20, 24, and 36 months with twins from the MacArthur Longitudinal Twin Study. Low g groups were formed from the lowest 10th percentile at each age. Univariate probandwise concordance rates and DeFries-Fulker (J. C. DeFries & D. W. Fulker, 1985, 1988) multiple regression techniques suggest genetic etiology in low general cognitive ability groups. The stability of low general cognitive ability over time also appears to be primarily due to genetic factors. Although replication is necessary, these results suggest that the genetic etiology of low g during infancy and early childhood is at least as great as the heritability of g in the unselected population.

Aptitude↗

PubMed1997

Genetics and developmental psychopathology: 1. Phenotypic assessment in the Virginia Twin Study of Adolescent Behavioral Development.

We introduce an overlapping cohort sequential longitudinal study of behavioral development and psychopathology in a representative sample of 1412 pairs of twins aged 8 through 16 years. Multiple phenotypic assessments involve a full psychiatric interview with each child and each parent, and supplementary parental, teacher, and child interview material and questionnaires. For the first wave of assessments, the numbers of reported DSM-III-R symptoms of Major Depressive Disorder (MDD), Separation Anxiety Disorder (SAD), Overanxious Disorder (OAD), Oppositional Defiant Disorder (ODD), Conduct Disorder (CD), and Attention Deficit Hyperactivity Disorder (ADHD), assessed through interviews, confirm patterns of age and sex trends found in other epidemiological samples, but underscore their dependence on whether the child or the parent is the informant. Correlations across domains for symptoms reported by the same informant are often as large as correlations across informants for the same domain of symptoms. Factor analyses of these symptom counts, taking account of informant view and unreliability of assessment, show the high degree of correlation between SAD and OAD, between MDD and OAD, and between CD and ODD. ADHD symptoms are relatively independent of the other domains, but show moderate correlations with CD, ODD, and MDD. Factorially derived dimensional questionnaire scales, based on child, parental, and teacher reports, show patterns of relationship to symptom counts consistent with both convergent and discriminant validity as indices of liability to clinical symptoms. Across informants, questionnaire scales provide as good a prediction of symptoms as do clinical interviews. Multitrait-multimethod confirmatory factor analysis reveals the patterns of relationship between symptoms of psychiatric disorder in children taking due account of informant and unique sources of variance. Gender differences are consistent within the correlated clusters of ODD/CD and MDD/SAD/OAD, although there are disorder-specific age trends. There are large informant-specific influences on the reporting of symptoms in clinical interviews. Dimensional questionnaire scales provide a useful source of additional information. In subsequent analyses of genetic and environmental etiology of childhood psychopathology we must expect that results may differ by informant and method of assessment. Multivariate and developmental analyses that explore the sources of these differences will shed new light on the relationship between genetic and environmentally influenced vulnerability and the manifestation of psychopathology in specific circumstances.

Adolescent↗

PubMed1997

Genetics and developmental psychopathology: 2. The main effects of genes and environment on behavioral problems in the Virginia Twin Study of Adolescent Behavioral Development.

Little is known about the contribution of genetic and environmental factors to risk for juvenile psychopathology. The Virginia Twin Study of Adolescent Behavioral Development allows these contributions to be estimated. A population-based, unselected sample of 1412 Caucasian twin pairs aged 8-16 years was ascertained through Virginia schools. Assessment of the children involved semi-structured face-to-face interviews with both twins and both parents using the Child and Adolescent Psychiatric Assessment (CAPA). Self-report questionnaires were also completed by parents, children, and teachers. Measures assessed DSM-III-R symptoms of Attention Deficit Hyperactivity Disorder (ADHD). Conduct Disorder, Oppositional Defiant Disorder, Overanxious Disorder, Separation Anxiety, and Depressive Disorder. Factorially derived questionnaire scales were also extracted. Scores were normalized and standardized by age and sex. Maximum likelihood methods were used to estimate contributions of additive and nonadditive genetic effects, the shared and unique environment, and sibling imitation or contrast effects. Estimates were tested for heterogeneity over sexes. Generally, monozygotic (MZ) twins correlated more highly than dizygotic (DZ) twins, parental ratings more than child ratings, and questionnaire scales more highly than interviews. DZ correlations were very low for measures of ADHD and DZ variances were greater than MZ variances for these variables. Correlations sometimes differed between sexes but those for boy-girl pairs were usually similar to those for like-sex pairs. Most of the measures showed small to moderate additive genetic effects and moderate to large effects of the unique individual environment. Measures of ADHD and related constructs showed marked sibling contrast effects. Some measures of oppositional behavior and conduct disorder showed shared environmental effects. There were marked sex differences in the genetic contribution to separation anxiety, otherwise similar genetic effects appear to be expressed in boys and girls. Effects of rater biases on the genetic analysis are considered. The study supports a widespread influence of genetic factors on risk to adolescent psychopathology and suggests that the contribution of different types of social influence may vary consistently across domains of measurement.

Adolescent↗

PubMed1997

Behavior genetics and eating disorders.

Behavior genetics is concerned with the genetic and environmental influences on individual differences in the vulnerability to eating disorders. We should be skeptical about simple genetic explanations for disorders whose development, maintenance, and possible remission involve the interaction of individual behaviors and environmental circumstances. Twin, family, and adoption studies can help to delineate which phenotypes are most heritable, and which are most responsive to family circumstances or individual environments. Subsequent searches for individual genetic and environmental risk factors can be guided by these results. Although there is consistent evidence of genetic factors influencing vulnerability to eating disorders, the details are far from clear, and additional studies will be useful. The further development of dimensional indices of vulnerability will improve population-based and developmental genetic research, as well as facilitating the search for individual genes.

Feeding and Eating Disorders↗

PubMed1996

The Virginia Twin-Family Study of Adolescent Behavioral Development: assessing sample biases in demographic correlates of psychopathology.

The Virginia Twin-Family Study of Adolescent Behavioral Development (VTSABD) is a current longitudinal study of psychopathology in 1412 pairs of 8-16-year-old Caucasian twins and their parents. The primary aim of the study is to evaluate family-genetic and environmental risk factors for major domains of psychopathology in families representative of the Virginia Caucasian population. In this report, we utilize census-derived indices of neighbourhood income and urban residence to identify departures from population representation arising at the time of family enrollment in the twin registry and family participation in a psychiatric interview. Furthermore, we consider whether demographic sample biases influenced prevalence rates of adult psychopathology (including major depression, generalized anxiety disorder, alcohol dependence, phobias, and panic disorder) in the VTSABD. Results indicated that families that enrolled in the twin registry (83% of those identified by Virginia schools) and that participated in the home interview (75% of those targeted) resided in urban and rural communities with a range of per capita income levels representative of the Virginia population. However, participation biases operated throughout the study and were primarily characterized by losses of families living in low income, urban communities. There was also a smaller number of families living in high income neighbourhoods that did not enroll in the twin registry or that indefinitely postponed the psychiatric interview. These biases had small effects on prevalence rates of adult psychopathology in the VTSABD sample, even though neighbourhood income was significantly related to a subset of adult diagnoses. We emphasize the usefulness of the census methodology in evaluating sample biases in population-based psychiatric genetic studies.

Adolescent↗

PubMed1996

Genetic and environmental structure of the Tridimensional Personality Questionnaire: three or four temperament dimensions?

Previous phenotypic factor analyses suggest that C. R. Cloninger's Tridimensional Personality Questionnaire (TPQ; 1987c) assesses 4 rather than 3 temperament dimensions. The purpose of this study was to determine whether Cloninger's revised 4-factor model showed incremental validity over his original model and to investigate the convergent and discriminant validity of Cloninger's dimensions in comparison to the personality dimensions proposed by H. J. Eysenck (1981) and J. A. Gray (1970). The sample included 2,420 women and 870 men (aged 50-96) from a volunteer population-based sample of twins. Joint phenotypic factor analyses supported Cloninger's 4-dimensional temperament model. A 4-dimensional genetical factor structure was also confirmed in genetic analyses of the TPQ higher order dimensions in women. For men only 3 genetic factors were necessary to explain the genetic variance among the TPQ dimensions.

Aged↗

PubMed1996

The genetics of children's oral reading performance.

Measures of reading achievement and verbal ability have been shown to be heritable. Additionally, recent evidence has been suggestive of a major gene effect on reading disability and for problem reading in a sample of normal readers. We report on the etiology of individual differences in oral reading performance, the Slosson Oral Reading Test (SORT), for which biometrical analyses have not been reported in the literature previously. Oral reading performance was measured in a large population-based sample of twins of the Virginia Twin Study of Adolescent Behavioral Development. Biometrical analyses of the SORT suggested that, in both males and females, 69% of the phenotypic variation was due to heritable influences and 13% of the variation due to shared environmental effects. While the relative importance of genetic and environmental influences is equivalent for males and females, males showed greater phenotypic variability than females.

Achievement↗

PubMed1996

Voiding function after Burch colposuspension for stress incontinence.

OBJECTIVE: To evaluate changes in voiding function before and after Burch colposuspension for genuine stress incontinence. STUDY DESIGN: Full urodynamic evaluations were performed before and three months after surgery on 21 patients undergoing Burch colposuspension for genuine stress incontinence. Sixteen patients underwent the Burch procedure alone and five underwent an abdominal sacral colpopexy for vaginal vault prolapse in addition to the Burch procedure. The preoperative and postoperative urodynamic studies were compared with each other to see what changes in voiding function had occurred as the result of surgery. RESULTS: Statistical analysis of the differences between the preoperative, and postoperative urodynamic studies using blocked analysis of variance showed dramatic decreases in both instrumented and noninstrumented peak and mean urine flow rates and an increase in detrusor pressure at peak urinary flow during voiding. A substantial but not statistically significant increase in mean residual urine was found after surgery in patients who underwent the Burch procedure alone. There were no statistically significant differences in these parameters in patients undergoing the Burch procedure combined with abdominal sacral colpopexy. Using the criteria of a flow rate of < 12 mL/sec in association with a voiding detrusor pressure > 50 cm H2O, five patients undergoing the Burch procedure alone had evidence of postoperative outflow obstruction. Three women with complete vaginal vault prolapse had functional outlet obstruction before surgery, and another three women had postoperative outlet obstruction following the combined Burch procedure and sacral colpopexy. CONCLUSIONS: Burch colposuspension produced significant changes in postoperative voiding function three months after surgery, and outflow obstruction induced by surgery appeared to be a significant potential complication. Renewed attention should be devoted to the development of durable but nonobstructive operations for the surgical cure of genuine stress incontinence.

Female↗