Nicotine and familial vulnerability to schizophrenia: a discordant twin study

Tobacco use is significantly associated with schizophrenia. However, it is not clear if smoking is associated with the illness itself, treatment, or underlying vulnerability to the disease. Smoking was studied in a sample of schizophrenic probands (n = 24), their unaffected co-twins (n = 24), and controls (n = 3,347). Unaffected co-twins had higher rates of daily smoking than controls. Probands and co-twins were more frequently unsuccessful in attempts to quit than controls. Probands reported shaky hands and depression following smoking cessation more often than controls, whereas unaffected co-twins reported difficulty concentrating, drowsiness, nervousness, and headache following smoking cessation more often than controls. Results are consistent with the hypothesis that nicotine use is influenced by familial vulnerability to schizophrenia, not just clinical schizophrenia per se.     

A twin study of the association between pathological gambling and antisocial personality disorder

Many individuals with a history of pathological gambling (PG) also have a history of engaging in antisocial behaviors, and this has often been interpreted as a result of the former causing the latter. In a sample of 7,869 men in 4,497 twin pairs from the Vietnam Era Twin Registry, the authors examined (a) the association between PG and antisocial personality disorder (ASPD), (b) the extent to which PG might be differentially associated with childhood conduct disorder (CD) and adult antisocial behavior (AAB), and (c) the contribution of genetic and environmental factors to the association of PG with ASPD, CD, and AAB. PG was significantly associated with all 3 antisocial behavior disorders, and the association of PG with ASPD, CD, and AAB was predominantly explained by genetic factors. The results of this study suggest that the greater-than-chance co-occurrence of PG and antisocial behavior disorders is partially due to their sharing a common genetic vulnerability. The antisocial behavior observed among many individuals with PG probably cannot be interpreted as being simply a consequence of the PG.     

Genetic transmission of major affective disorders: quantitative models and linkage analyses

We comprehensively reviewed 2 types of studies aimed at specifying the mode of inheritance of major affective disorders: quantitative models and linkage analyses. Quantitative models attempt to represent the genetic mechanism responsible for the familial distribution of a disorder. Despite efforts to refine models by incorporating the bipolar-unipolar distinction or the sex effect, consistent support for a specific mode of transmission has not been found. Some mixed genetic models support single major locus inheritance, but transmission probabilities do not conform to Mendelian expectations. Linkage analysis is a more powerful technique used for testing the single gene hypothesis. Linkage results have also been inconsistent, showing moderate support for an X-linked variant of bipolar-related disorder and equivocal support for linkages to Chromosomes 6 and 11. However, relatively few genetic loci have been examined. Methodological factors, genetic heterogeneity, and phenotypic heterogeneity are discussed as potential explanations for inconsistent findings.     

Issues in Professional Training to Implement Evidence‐based Parenting Programs: The Preferences of Indigenous Practitioners

Indigenous children have elevated risk for poor health, behavioural, emotional, and social outcomes. Significant evidence exists that parenting programs can reduce family risk factors and improve outcomes for children and families; however, mainstream programs have had slower uptake in Indigenous communities than other communities. Culturally sensitive delivery of evidence‐based programs can enhance engagement of parents, yet the development of a workforce to deliver programs to Indigenous parents faces many obstacles. This project seeks to identify professional training processes that enhance Indigenous practitioners’ skills and confidence in delivering an evidence‐based parenting program. A survey of trained parenting practitioners via an online practitioner network assessed their views of the training and post‐training support processes they had experienced. Respondents were 57 Indigenous and 720 non‐Indigenous practitioners from 15 countries. Most training processes were rated equally helpful by Indigenous and non‐Indigenous practitioners. However, several training processes were identified as important for the delivery of culturally competent training, such as tailoring the pace of training and simplifying the language in teaching resources. Practitioners with higher ratings of the helpfulness of peer support following training reported higher program uptake and implementation. Qualitative themes also focused on the helpfulness of program resources, and having a peer support network and mentoring. Increasing access to appropriate, flexibly delivered training and post‐training support for Indigenous professionals will support the development of a skilled workforce with local knowledge and connections, and further increase the reach of evidence‐based services in Indigenous communities.     

The paradox of normal neuropsychological function in schizophrenia

Mounting evidence suggests that compromised neurocognitive function is a core feature of schizophrenia. However, some studies have found neuropsychologically normal schizophrenia patients. To address this apparent contradiction, we blindly rated individual neuropsychological profiles of 75 schizophrenia patients and 91 control participants on the basis of methods developed by L. J. Seidman, S. V. Faraone, W. S. Kremen, J. R. Pepple, M. J. Lyons, and M. T. Tsuang (1993). Almost one-quarter of the patients were classified as neuropsychologically within normal limits (WNL). Despite significantly worse neuropsychological performance, WNL patients had higher estimated premorbid ability than did controls. Compared to a subset of controls matched on overall neuropsychological function, WNL patients had higher estimated premorbid ability and current IQs. Our results favor the view that even neuropsychologically normal schizophrenia patients have compromised cognitive function relative to their presumed expected or premorbid level of intellectual ability.     

Neuropsychological functioning among the nonpsychotic relatives of schizophrenic patients: a 4-year follow-up study

In a prior study of 54 relatives of patients with schizophrenia and 72 control participants, 3 neuropsychological functions met the criteria for risk indicators of the schizophrenia genotype: executive functioning, memory, and auditory attention. In an assessment of the stability of these findings, the sample was reexamined 4 years after the initial assessment. Three test scores were found to differ between groups (Immediate Verbal Memory, Delayed Verbal Memory, and Dichotic Listening Digits Detected) or to show a significant Group x Gender interaction (immediate and delayed verbal and visual memories). None of the test scores showed Group x Time interactions, suggesting that the discriminating power of the tests was stable over time. Evidence for deficits in working memory and rule learning on the object alternation test was also found. These results support the idea that neuropsychological dysfunction among relatives of patients with schizophrenia is a stable trait caused by the familial predisposition to schizophrenia.     

A twin study of spatial and non-spatial delayed response performance in middle age

Delayed alternation and object alternation are classic spatial and non-spatial delayed response tasks. We tested 632 middle-aged male veteran twins on variants of these tasks in order to compare test difficulty, measure their inter-correlation, test order effects, and estimate heritabilities (proportion of observed variance due to genetic influences). Non-spatial alternation (NSA), which may involve greater reliance on processing of subgoals, was significantly more difficult than spatial alternation (SA). Despite their similarities, NSA and SA scores were uncorrelated. NSA performance was worse when administered second; there was no SA order effect. NSA scores were modestly heritable (h(2)=.25; 26); SA was not. There was shared genetic variance between NSA scores and general intellectual ability (r(g)=.55; .67), but this also suggests genetic influences specific to NSA. Compared with findings from small, selected control samples, high "failure" rates in this community-based sample raise concerns about interpretation of brain dysfunction in elderly or patient samples.