Clinical variables and genetic loading for schizophrenia: analysis of published Danish adoption study data.

Schizophrenia shows considerable clinical variation, but the relationship between clinical variables and degree of genetic loading for schizophrenia is unclear. We investigated this by analyzing published data from the adoption study of Kety et al. (1994) in Denmark.

Age and birth cohort effects on rates of alcohol dependence.

Background: Epidemiological studies of traits such as alcohol dependence and depression have often found lifetime rates in younger individuals exceeding those found in older individuals. This suggests additional influences of birth cohort or period effects so that individuals in later-born cohorts have an increased lifetime risk.

Methods: Data from the Collaborative Study on the Genetics of Alcoholism were used to investigate secular trends for alcoholism and related conditions and to examine risk predictors while taking the cohort effect into account.

The genetic basis for psychiatric illness in man.

Following the influential genetic studies of Heston and Kety, there has been growing acceptance of the role of genes in determining behaviour. It is now recognized that most types of behaviour, from normal variations in traits such as personality to complex psychiatric disorders, are influenced not only by environmental factors but also by multiple genes. While twin and adoption studies have been vital in demonstrating the heritability of behaviour, the focus is now on the identification of the genes involved using the molecular genetic strategies linkage analysis and allelic association.

Psychopathology in the postgenomic era.

We are rapidly approaching the postgenomic era in which we will know all of the 3 billion DNA bases in the human genome sequence and all of the variations in the genome sequence that are ultimately responsible for genetic influence on behavior. These ongoing advances and new techniques will make it easier to identify genes associated with psychopathology. Progress in identifying such genes has been slower than some experts expected, probably because many genes are involved for each phenotype, which means the effect of any one gene is small.

Neuroticism, extraversion, life events and depression. The Cardiff Depression Study.

Background: Certain personality traits may mediate the relationship between familiality and adversity in causing depression.

Aims: To examine whether the neuroticism and extraversion scales of the Eysenck Personality Inventory (EPI) represent enduring traits underlying the vulnerability to respond to adversity by developing depressive episodes.

Method: A total of 108 subjects with depression and their siblings were compared with 105 healthy control subjects and their siblings.

Familiality of clinical characteristics in schizophrenia.

Few studies have assessed the familiality of clinical characteristics in schizophrenia. Therefore, we set out to investigate the familiality of the following characteristics; age of onset, course of disorder, employment status at onset, impairment during disorder, marital status at onset, mode of onset and premorbid functioning. Clinical characteristics were recorded using the Operational Criteria Checklist for Psychotic Illness for 155 subjects with an RDC diagnosis of schizophrenia, schizoaffective disorder, or psychosis of unknown origin, from 61 families multiply affected by schizophrenia.

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.

Observer effects and heritability of childhood attention-deficit hyperactivity disorder symptoms.

Background: Twin studies have found that childhood attention-deficit hyperactivity disorder (ADHD) has a strong genetic component. Estimates of heritability, the extent of non-additive genetic effects and of 'sibling contrast' effects vary between different studies.

Aims: To use multiple informants to assess the extent to which observer effects influence such estimates in an epidemiological sample of twins.

Association of DRD4 in children with ADHD and comorbid conduct problems.

Recent family and twin study findings suggest that ADHD when comorbid with conduct problems may represent a particularly familial and heritable form of ADHD. Although several independent groups have shown association between the DRD4 7 repeat allele and ADHD, others have failed to replicate this finding. Previous TDT analyses of UK and Eire samples had also been negative.

Heritability of Schneider's first-rank symptoms.

Background: Schneider's first-rank symptoms are given particular weight when making a diagnosis of schizophrenia, but the nuclear syndrome, characterised by one or more first-rank symptoms, has been found previously to have no heritability.

Aims: To estimate the heritability of the nuclear syndrome.

Method: A total of 224 twin pairs (106 monozygotic, 118 same-gender dizygotic) were ascertained from the Maudsley Twin Register in London via probands with any psychosis.