A twin study of genetic relationships between psychotic symptoms.

Objective: Biometrical model fitting was applied to clinical data from twins to investigate whether operationally defined schizophrenic, schizoaffective, and manic syndromes share genetic risk factors.

Method: Seventy-seven monozygotic and 89 same-sex dizygotic twin pairs in which the proband met the Research Diagnostic Criteria (RDC) for lifetime-ever schizophrenic, schizoaffective, or manic syndrome were ascertained from the Maudsley Twin Register in London. The syndromes were defined non-hierarchically.

Genetic and gender influences on nocturnal bladder control--a study of 2900 3-year-old twin pairs.

Objective: The present study of over 2900 twin pairs born in England and Wales in 1994 examines the influences of genetics and gender on nocturnal bladder control at 3 years of age.

Materials And Method: Parent report data was analysed in terms of means and components of variance, using a sex-limitation model to explore genetic and environmental variation within and between the sexes.

Results: Both genetics and gender are seen to influence acquisition: bladder control at 3 years is moderately heritable (24%), and girls show on average slightly increased acquisition compared with boys, even within opposite-sex pairs.

GENESiS: creating a composite index of the vulnerability to anxiety and depression in a community-based sample of siblings.

There is considerable evidence for a unitary and dimensional view of the genetic vulnerability to symptoms of anxiety and depression. The GENESiS (Genetic Environmental-Nature of Emotional States in Siblings) Study aims to use a multivariate approach to detect genetic loci that contribute to individual differences in this vulnerability dimension. The study used the UK General Practice Research Framework to generate a community-based sample of siblings.

QTL association analysis of the DRD4 exon 3 VNTR polymorphism in a population sample of children screened with a parent rating scale for ADHD symptoms.

Current developments in molecular genetics have led to a rapid increase in research aimed at the identification of genetic variation that influences complex human phenotypes. One phenotype that has aroused a great deal of interest is the behavioral trait hyperactivity and the related clinical disorder attention-deficit hyperactivity disorder (ADHD). The driving force behind the molecular genetic research in this area is the overwhelming evidence from quantitative genetic studies that show high heritablility (h(2) = 0.

Analytic power calculation for QTL linkage analysis of small pedigrees.

Power calculation for QTL linkage analysis can be performed via simple algebraic formulas for small pedigrees, but requires intensive computation for large pedigrees, in order to evaluate the expectation of the test statistic over all possible inheritance vectors at the test position. In this report, we show that the non-centrality parameter for an arbitrary pedigree can be approximated by the sum of the variances of the correlations between all pairs of relatives, each variance being weighted by a factor that is determined by the mean correlation of the pair. We show that this approximation is sufficiently accurate for practical purposes in small to moderately large pedigrees, and that large sibships are more efficient than other family structures under a range of genetic models.

Life events and depression in a community sample of siblings.

Background: The overall aim of the GENESiS project is to identify quantitative trait loci (QTLs) for anxiety/depression, and to examine the interaction between these loci and psychosocial adversity. Here we present life-events data with the aim of clarifying: (i) the aetiology of life events as inferred from sibling correlations; (ii) the relationship between life events and measures of anxiety and depression, as well as neuroticism; and (iii) the interaction between life events and neuroticism on anxiety/depression indices.

Methods: We assessed the occurrence of one network and three personal life-event categories and multiple indices of anxiety/depression including General Health Questionnaire, Anhedonic Depression, Anxious Arousal and Neuroticism in a large community-based sample of2150 sib pairs, 410 trios and 81 quads.

The genetic basis of the relation between speed-of-information-processing and IQ.

The relationship of speed-of-information-processing (SIP), as derived from reaction times (RTs) on experimental tasks, and intelligence has been extensively studied. SIP is suggested to measure the efficiency with which subjects can perform basic cognitive operations underlying a wide range of intellectual abilities. Observed phenotypic correlations between RT and IQ typically are in the -0.

Genetic mediation of the correlation between peripheral nerve conduction velocity and IQ.

Variation in peripheral nerve conduction velocity (PNCV) and intelligence was studied in 18-year-old Dutch twins. It has been suggested that both brain nerve conduction velocity and PNCV are positively correlated with intelligence (Reed, 1984) and that heritable differences in nerve conduction velocity may explain part of the well-established heritability of intelligence. The relationship among IQ, obtained with the Wechsler Adult Intelligence Scale, and median nerve PNCV was examined in 159 twin pairs.

Genetic analysis of peripheral nerve conduction velocity in twins.

We studied variation in peripheral nerve conduction velocity (PNCV) and intelligence in a group of 16-year-old Dutch twins. It has been suggested that both brain nerve conduction velocity and PNCV are positively correlated with intelligence (Reed, 1984) and that heritable differences in NCV may explain part of the well established heritability of intelligence. The Standard Progressive Matrices test was administered to 210 twin pairs to obtain IQ scores.

Effect of depression on psychomotor skills, eye movements and recognition-memory.

In this study 12 depressed outpatients were compared to 12 healthy controls with respect to their performance on a number of cognitive tasks, including a recognition-memory task, and their eye movements and pupil size were recorded while watching a traffic film. The recognition-memory task consisted of words with intermediate hedonic tone (neutral words), words with high hedonic tone ('good' words) and words with low hedonic tone ('bad' words). Patients performed slower on perceptual-motor tasks which could be characterized as effort-demanding, while no difference between groups was found on effortless tasks.