Maternal smoking has consistently been associated with multiple adverse childhood outcomes including externalizing disorders. In contrast the association between maternal smoking during pregnancy (MSDP) and internalizing (anxiety and depressive) disorders in offspring has received less investigation.

We conducted a nationwide cohort study including 957635 individuals born in Denmark between 1991 and 2007. Data on MSDP and diagnoses of depression or anxiety disorders were derived from national registers and patients were followed up from the age of 5 years to the end of 2012. Hazard rate ratios (HRRs) were estimated using stratified Cox regression models. Sibling data were used to disentangle individual- and familial-level effects of MSDP and to control for unmeasured familial confounding.

At the population level, offspring exposed to MSDP were at increased risk for both severe depression [HRR 1.29, 95% confidence interval (CI) 1.22–1.36] and severe anxiety disorders (HRR 1.26, 95% CI 1.20–1.32) even when controlling for maternal and paternal traits. However, there was no association between MSDP and internalizing disorders when controlling for the mother's propensity for MSDP (depression: HRR 1.11, 95% CI 0.94–1.30; anxiety disorders: HRR 0.94, 95% CI 0.80–1.11) or comparing differentially exposed siblings (depression: HRR 1.18, 95% CI 0.75–1.89; anxiety disorders: HRR 0.87, 95% CI 0.55–1.36).

The results suggest that familial background factors account for the association between MSDP and severe internalizing disorders not the specific exposure to MSDP.

There is a lack of evidence pointing to the efficacy of any specific psychotherapy for adults with anorexia nervosa (AN). The aim of this study was to compare three psychological treatments for AN: Specialist Supportive Clinical Management, Maudsley Model Anorexia Nervosa Treatment for Adults and Enhanced Cognitive Behavioural Therapy.

A multi-centre randomised controlled trial was conducted with outcomes assessed at pre-, mid- and post-treatment, and 6- and 12-month follow-up by researchers blind to treatment allocation. All analyses were intention-to-treat. One hundred and twenty individuals meeting diagnostic criteria for AN were recruited from outpatient treatment settings in three Australian cities and offered 25–40 sessions over a 10-month period. Primary outcomes were body mass index (BMI) and eating disorder psychopathology. Secondary outcomes included depression, anxiety, stress and psychosocial impairment.

Treatment was completed by 60% of participants and 52.5% of the total sample completed 12-month follow-up. Completion rates did not differ between treatments. There were no significant differences between treatments on continuous outcomes; all resulted in clinically significant improvements in BMI, eating disorder psychopathology, general psychopathology and psychosocial impairment that were maintained over follow-up. There were no significant differences between treatments with regard to the achievement of a healthy weight (mean = 50%) or remission (mean = 28.3%) at 12-month follow-up.

The findings add to the evidence base for these three psychological treatments for adults with AN, but the results underscore the need for continued efforts to improve outpatient treatments for this disorder.

Australian New Zealand Clinical Trials Registry (ACTRN 12611000725965) http://www.anzctr.org.au/

Job loss, debt and financial difficulties are associated with increased risk of mental illness and suicide in the general population. Interventions targeting people in debt or unemployed might help reduce these effects.

We searched MEDLINE, Embase, The Cochrane Library, Web of Science, and PsycINFO (January 2016) for randomized controlled trials (RCTs) of interventions to reduce the effects of unemployment and debt on mental health in general population samples. We assessed papers for inclusion, extracted data and assessed risk of bias.

Eleven RCTs (n = 5303 participants) met the inclusion criteria. All recruited participants were unemployed. Five RCTs assessed ‘job-club’ interventions, two cognitive behaviour therapy (CBT) and a single RCT assessed each of emotional competency training, expressive writing, guided imagery and debt advice. All studies were at high risk of bias. ‘Job club’ interventions led to improvements in levels of depression up to 2 years post-intervention; effects were strongest among those at increased risk of depression (improvements of up to 0.2–0.3 s.d. in depression scores). There was mixed evidence for effectiveness of group CBT on symptoms of depression. An RCT of debt advice found no effect but had poor uptake. Single trials of three other interventions showed no evidence of benefit.

‘Job-club’ interventions may be effective in reducing depressive symptoms in unemployed people, particularly those at high risk of depression. Evidence for CBT-type interventions is mixed; further trials are needed. However the studies are old and at high risk of bias. Future intervention studies should follow CONSORT guidelines and address issues of poor uptake.

Depression is one of the most common and debilitating non-motor symptoms of Parkinson's disease (PD). The neurocognitive mechanisms underlying depression in PD are unclear and treatment is often suboptimal.

We investigated the role of striatal dopamine in reversal learning from reward and punishment by combining a controlled medication withdrawal procedure with functional magnetic resonance imaging in 22 non-depressed PD patients and 19 PD patients with past or present depression.

PD patients with a depression (history) exhibited impaired reward v. punishment reversal learning as well as reduced reward v. punishment-related BOLD signal in the striatum (putamen) compared with non-depressed PD patients. No effects of dopaminergic medication were observed.

The present findings demonstrate that impairments in reversal learning from reward v. punishment and associated striatal signalling depend on the presence of (a history of) depression in PD.

A growing body of neuropsychological and neurobiological research shows a relationship between functioning of the prefrontal cortex and criminal and violent behaviour. The prefrontal cortex is crucial for executive functions such as inhibition, attention, working memory, set-shifting and planning. A deficit in these functions – a prefrontal deficit – may result in antisocial, impulsive or even aggressive behaviour. While several meta-analyses show large effect sizes for the relationship between a prefrontal deficit, executive dysfunction and criminality, there are few studies investigating differences in executive functions between violent and non-violent offenders. Considering the relevance of identifying risk factors for violent offending, the current study explores whether a distinction between violent and non-violent offenders can be made using an extensive neuropsychological test battery.

Male remand prisoners (N = 130) in Penitentiary Institution Amsterdam Over-Amstel were administered an extensive neuropsychological test battery (Cambridge Automated Neuropsychological Test Battery; CANTAB) measuring response inhibition, planning, attention, set-shifting, working memory and impulsivity/reward sensitivity.

Violent offenders performed significantly worse on the stop-signal task (partial correlation r = 0.205, p = 0.024), a task measuring response inhibition. No further differences were found between violent and non-violent offenders. Explorative analyses revealed a significant relationship between recidivism and planning (partial correlation r = −0.209, p = 0.016).

Violent offenders show worse response inhibition compared to non-violent offenders, suggesting a more pronounced prefrontal deficit in violent offenders than in non-violent offenders.

It has been demonstrated that negatively distorted self-referential processing, in which individuals evaluate one's own self, is a pathogenic mechanism in subthreshold depression that has a considerable impact on the quality of life and carries an elevated risk of developing major depression. Behavioural activation (BA) is an effective intervention for depression, including subthreshold depression. However, brain mechanisms underlying BA are not fully understood. We sought to examine the effect of BA on neural activation during other perspective self-referential processing in subthreshold depression.

A total of 56 subjects underwent functional magnetic resonance imaging scans during a self-referential task with two viewpoints (self/other) and two emotional valences (positive/negative) on two occasions. Between scans, while the intervention group (n = 27) received BA therapy, the control group (n = 29) did not.

The intervention group showed improvement in depressive symptoms, increased activation in the dorsal medial prefrontal cortex (dmPFC), and increased reaction times during other perspective self-referential processing for positive words after the intervention. Also, there was a positive correlation between increased activation in the dmPFC and improvement of depressive symptoms. Additionally, there was a positive correlation between improvement of depressive symptoms and increased reaction times.

BA increased dmPFC activation during other perspective self-referential processing with improvement of depressive symptoms and increased reaction times which were associated with improvement of self-monitoring function. Our results suggest that BA improved depressive symptoms and objective monitoring function for subthreshold depression.

Females are more likely than males to develop major depressive disorder (MDD). The current study used fMRI to compare the neural correlates of autobiographical memory (AM) recall between males and females diagnosed with MDD. AM overgenerality is a persistent cognitive deficit in MDD, the magnitude of which is correlated with depressive severity only in females. Delineating the neurobiological correlates of this deficit may elucidate the nature of sex-differences in the diathesis for developing MDD.

Participants included unmedicated males and females diagnosed with MDD (n = 20/group), and an age and sex matched healthy control group. AM recall in response to positive, negative, and neutral cue words was compared with a semantic memory task.

The behavioral properties of AMs did not differ between MDD males and females. In contrast, main effects of sex on cerebral hemodynamic activity were observed in left dorsolateral prefrontal cortex and parahippocampal gyrus during recall of positive specific memories, and middle prefrontal cortex (mPFC), and precuneus during recall of negative specific memories. Moreover, main effects of diagnosis on regional hemodynamic activity were observed in left ventrolateral prefrontal cortex and mPFC during positive specific memory recall, and dorsal anterior cingulate cortex during negative specific memory recall. Sex × diagnosis interactions were evident in the dorsomedial prefrontal cortex, caudate, and precuneus during positive memory recall, and in the posterior cingulate cortex, insula, precuneus and thalamus during negative specific memory recall.

The differential hemodynamic changes conceivably may reflect sex-specific cognitive strategies during recall of AMs irrespective of the phenomenological properties of those memories.

Although repeatedly associated with white matter microstructural alterations, bipolar disorder (BD) has been relatively unexplored using complex network analysis. This method combines structural and diffusion magnetic resonance imaging (MRI) to model the brain as a network and evaluate its topological properties. A group of highly interconnected high-density structures, termed the ‘rich-club’, represents an important network for integration of brain functioning. This study aimed to assess structural and rich-club connectivity properties in BD through graph theory analyses.

We obtained structural and diffusion MRI scans from 42 euthymic patients with BD type I and 43 age- and gender-matched healthy volunteers. Weighted fractional anisotropy connections mapped between cortical and subcortical structures defined the neuroanatomical networks. Next, we examined between-group differences in features of graph properties and sub-networks.

Patients exhibited significantly reduced clustering coefficient and global efficiency, compared with controls globally and regionally in frontal and occipital regions. Additionally, patients displayed weaker sub-network connectivity in distributed regions. Rich-club analysis revealed subtly reduced density in patients, which did not withstand multiple comparison correction. However, hub identification in most participants indicated differentially affected rich-club membership in the BD group, with two hubs absent when compared with controls, namely the superior frontal gyrus and thalamus.

This graph theory analysis presents a thorough investigation of topological features of connectivity in euthymic BD. Abnormalities of global and local measures and network components provide further neuroanatomically specific evidence for distributed dysconnectivity as a trait feature of BD.

Childbirth is a potent trigger for the onset of psychiatric illness in women including postpartum depression (PPD) and postpartum psychosis (PP). Medical complications occurring during pregnancy and/or childbirth have been linked to postpartum psychiatric illness and sociodemographic factors. We evaluated if pregnancy and obstetrical predictors have similar effects on different types of postpartum psychiatric disorders.

A population-based cohort study using Danish registers was conducted in 392 458 primiparous women with a singleton delivery between 1995 and 2012 and no previous psychiatric history. The main outcome was first-onset postpartum psychiatric episodes. Incidence rate ratios (IRRs) were calculated for any psychiatric contact in four quarters for the first year postpartum.

PPD and postpartum acute stress reactions were associated with pregnancy and obstetrical complications. For PPD, hyperemesis gravidarum [IRR 2.69, 95% confidence interval (CI) 1.93–3.73], gestational hypertension (IRR 1.84, 95% CI 1.33–2.55), pre-eclampsia (IRR 1.45, 95% CI 1.14–1.84) and Cesarean section (C-section) (IRR 1.32, 95% CI 1.13–1.53) were associated with increased risk. For postpartum acute stress, hyperemesis gravidarum (IRR 1.93, 95% CI 1.38–2.71), preterm birth (IRR 1.51, 95% CI 1.30–1.75), gestational diabetes (IRR 1.42, 95% CI 1.03–1.97) and C-section (IRR 1.36, 95% CI 1.20–1.55) were associated with increased risk. In contrast, risk of PP was not associated with pregnancy or obstetrical complications.

Pregnancy and obstetrical complications can increase the risk for PPD and acute stress reactions but not PP. Identification of postpartum women requiring secondary care is needed to develop targeted approaches for screening and treatment. Future work should focus on understanding the contributions of psychological stressors and underlying biology on the development of postpartum psychiatric illness.

We reanalyzed data from a previously published randomized component study that aimed to test the incremental effect of systematic exposure in an internet-delivered cognitive behavioral treatment (ICBT) for irritable bowel syndrome (IBS).

Three hundred and nine individuals with IBS were randomly assigned to either the full treatment protocol (experimental condition) or the same treatment protocol without systematic exposure (control). Participants were assessed weekly for IBS symptoms over the active treatment phase. We used a complier average causal effect (CACE) analysis, in the growth mixture modeling framework, to (1) examine the specific effect of exposure among those who received the intervention (i.e. compliers), and (2) explore the associations of pre-treatment patient characteristics with compliance status and outcome changes.

Fifty-five per cent of those assigned to the experimental condition were classified as compliers. The CACE analysis that took into account compliance status demonstrated that the magnitude of the incremental effect of systematic exposure on IBS symptoms was larger than the effect observed in an intention-to-treat analysis that ignored compliance status (d = 0.81 v. d = 0.44). Patients with university education showed more improvement during the exposure phase of the treatment. Pre-treatment patient characteristics did not predict compliance status.

The effect of systematic exposure on IBS symptoms is of substantial magnitude among those individuals who actually receive the intervention (CACE). Studying the subsample of individuals who discontinue treatment prematurely and tailoring interventions to improve compliance may increase overall improvement rates in ICBT for IBS.

Given the concerns regarding the adverse health outcomes associated with weight gain and metabolic syndrome in relation to use of second-generation antipsychotics (SGAs), we aimed in this study to explore whether the increase in the use of SGAs would have any impacts on the trend of excess mortality in people with schizophrenia and bipolar disorder (BPD).

Two nationwide samples of individuals with schizophrenia and BPD were identified in Taiwan's National Health Insurance Research Database in 2003 and in 2008, respectively. Age- and gender-standardized mortality ratios (SMRs) were calculated for each of the 3-year observation periods. The SMRs were compared between the calendar year cohorts, by disease group, and by causes of death.

The mortality gap for people with schizophrenia decreased slightly, revealing an SMR of 3.40 (95% CI 3.30–3.50) for the 2003 cohort and 3.14 (3.06–3.23) for the 2008 cohort. The mortality gap for BPD individuals remained relatively stable with only those aged 15–44 years having an SMR rising significantly from 7.04 (6.38–7.76) to 9.10 (8.44–9.79). Additionally, in this group of BPD patients aged 15–44 years, the natural-cause-SMR increased from 5.65 (4.93–6.44) to 7.16 (6.46–7.91).

Compared with the general population, the gap in the excess mortality for people with schizophrenia reduced slightly. However, the over 200% difference between the cohorts in the excess mortality for BPD individuals aged 15–44 years could be a warning sign. Future research to further examine the related factors underlying those changes is warranted.

The attributional theory of paranoia suggests that paranoid beliefs may protect individuals from low self-esteem and distress (Bentall et al. 2001). The current study tested this theory by investigating a hypothesis that paranoid beliefs in combination with low perceived deservedness of persecution (poor-me beliefs) confer protection against the distress caused by social but not activity related stress.

Paranoid symptoms, perceived deservedness of persecution, self-esteem, mood, and stress levels of individuals diagnosed with schizophrenia spectrum disorders (N = 91) and healthy controls (N = 52) were assessed in the context of daily life using the experience sampling method.

Individuals holding poor-me beliefs (poor-me individuals) showed blunted sensitivity to social but not activity stress. In contrast, individuals holding paranoid beliefs in combination with high perceived deservedness of persecution (bad-me individuals) showed heightened sensitivity to social stress. No consistent differences in reactions to activity stress emerged. Although both poor-me and bad-me individuals reported low self-esteem, this disturbance was particularly characteristic of bad-me individuals.

The results suggest that poor-me paranoid beliefs may protect individuals against the distress associated with unpleasant social situations. The specificity of reactions to social stress is discussed in the context of wider literature. Future directions for research are suggested.

This paper addresses the levels of psychological distress experienced at age 42 years by men and women born in 1958 and 1970. Comparing these cohorts born 12 years apart, we ask whether psychological distress has increased, and, if so, whether this increase can be explained by differences in their childhood conditions.

Data were utilized from two well-known population-based birth cohorts, the National Child Development Study and the 1970 British Cohort Study. Latent variable models and causal mediation methods were employed.

After establishing the measurement equivalence of psychological distress in the two cohorts we found that men and women born in 1970 reported higher levels of psychological distress compared with those born in 1958. These differences were more pronounced in men (b = 0.314, 95% confidence interval 0.252–0.375), with the magnitude of the effect being twice as strong compared with women (b = 0.147, 95% confidence interval 0.076–0.218). The effect of all hypothesized early-life mediators in explaining these differences was modest.

Our findings have implications for public health policy, indicating a higher average level of psychological distress among a cohort born in 1970 compared with a generation born 12 years earlier. Due to increases in life expectancy, more recently born cohorts are expected to live longer, which implies – if such differences persist – that they are likely to spend more years with mental health-related morbidity compared with earlier-born cohorts.

Functional neurological disorders (FNDs), also known as conversion disorder, are unexplained neurological symptoms unrelated to a neurological cause. The disorder is common, yet poorly understood. The symptoms are experienced as involuntary but have similarities to voluntary processes. Here we studied intention awareness in FND.

A total of 26 FND patients and 25 healthy volunteers participated in this functional magnetic resonance study using Libet's clock.

FND is characterized by delayed awareness of the intention to move relative to the movement itself. The reporting of intention was more precise, suggesting that these findings are reliable and unrelated to non-specific attentional deficits. That these findings were more prominent with aberrant positive functional movement symptoms rather than negative symptoms may be relevant to impairments in timing for an inhibitory veto process. Attention towards intention relative to movement was associated with lower right inferior parietal cortex activity in FND, a region early in the processing of intention. During rest, aberrant functional connectivity was observed with the right inferior parietal cortex and other motor intention regions.

The results converge with observations of low inferior parietal activity comparing involuntary with voluntary movement in FND, emphasizing core deficiencies in intention. Heightened precision of this impaired intention is consistent with Bayesian theories of impaired top-down priors that might influence the sense of involuntariness. A primary impairment in voluntary motor intention at an early processing stage might explain clinical observations of slowed effortful voluntary movement, heightened self-directed attention and underlie functional movements. These findings further suggest novel therapeutic targets.

Late-life depression (LLD) is associated with a decline in physical activity. Typically this is assessed by self-report questionnaires and, more recently, with actigraphy. We sought to explore the utility of a bespoke activity monitor to characterize activity profiles in LLD more precisely.

The activity monitor was worn for 7 days by 29 adults with LLD and 30 healthy controls. Subjects underwent neuropsychological assessment and quality of life (QoL) (36-item Short-Form Health Survey) and activities of daily living (ADL) scales (Instrumental Activities of Daily Living Scale) were administered.

Physical activity was significantly reduced in LLD compared with controls (t = 3.63, p < 0.001), primarily in the morning. LLD subjects showed slower fine motor movements (t = 3.49, p < 0.001). In LLD patients, activity reductions were related to reduced ADL (r = 0.61, p < 0.001), lower QoL (r = 0.65, p < 0.001), associative learning (r = 0.40, p = 0.036), and higher Montgomery–Åsberg Depression Rating Scale score (r = −0.37, p < 0.05).

Patients with LLD had a significant reduction in general physical activity compared with healthy controls. Assessment of specific activity parameters further revealed the correlates of impairments associated with LLD. Our study suggests that novel wearable technology has the potential to provide an objective way of monitoring real-world function.

Laboratory tasks to delineate anxiety disorder features are used to refine classification and inform our understanding of etiological mechanisms. The present study examines laboratory measures of response inhibition, specifically the inhibition of a pre-potent motor response, in clinical anxiety. Data on associations between anxiety and response inhibition remain inconsistent, perhaps because of dissociable effects of clinical anxiety and experimentally manipulated state anxiety. Few studies directly assess the independent and interacting effects of these two anxiety types (state v. disorder) on response inhibition. The current study accomplished this goal, by manipulating state anxiety in healthy and clinically anxious individuals while they complete a response inhibition task.

The study employs the threat-of-shock paradigm, one of the best-established manipulations for robustly increasing state anxiety. Participants included 82 adults (41 healthy; 41 patients with an anxiety disorder). A go/nogo task with highly frequent go trials was administered during alternating periods of safety and shock threat. Signal detection theory was used to quantify response bias and signal-detection sensitivity.

There were independent effects of anxiety and clinical anxiety on response inhibition. In both groups, heightened anxiety facilitated response inhibition, leading to reduced nogo commission errors. Compared with the healthy group, clinical anxiety was associated with excessive response inhibition and increased go omission errors in both the safe and threat conditions.

Response inhibition and its impact on go omission errors appear to be a promising behavioral marker of clinical anxiety. These results have implications for a dimensional view of clinical anxiety.

Previous findings have been mixed regarding the relationship between maternal depressive symptoms and child cognitive development. The objective of this study was to systematically review relevant literature and to perform a meta-analysis.

Three electronic databases (PubMed, EMBASE, PsycINFO) were searched. Initial screening was conducted independently by two reviewers. Studies selected for detailed review were read in full and included based on a set of criteria. Data from selected studies were abstracted onto a standardized form. Meta-analysis using the inverse variance approach and random-effects models was conducted.

The univariate analysis of 14 studies revealed that maternal depressive symptoms are related to lower cognitive scores among children aged ⩽56 months (Cohen's d = −0.25, 95% CI −0.39 to −0.12). The synthesis of studies controlling for confounding variables showed that the mean cognitive score for children 6–8 weeks post-partum whose mothers had high depressive symptoms during the first few weeks postpartum was approximately 4.2 units lower on the Mental Developmental Index (MDI) of the Bayley Scales of Infant and Toddler Development (BSID) compared with children with non-symptomatic mothers (B̂ = −4.17, 95% CI −8.01 to −0.32).

The results indicated that maternal depressive symptoms are related to lower cognitive scores in early infancy, after adjusting for confounding factors. An integrated approach for supporting child cognitive development may include program efforts that promote maternal mental health in addition to family economic wellbeing, responsive caregiving, and child nutrition.

Adolescence is a key time period for the emergence of psychosocial and mental health difficulties. To promote adolescent adaptive (‘resilient’) psychosocial functioning (PSF), appropriate conceptualisation and quantification of such functioning and its predictors is a crucial first step. Here, we quantify resilient functioning as the degree to which an individual functions better or worse than expected given their self-reported childhood family experiences, and relate this to adolescent family and friendship support.

We used Principal Component and regression analyses to investigate the relationship between childhood family experiences and PSF (psychiatric symptomatology, personality traits and mental wellbeing) in healthy adolescents (the Neuroscience in Psychiatry Network; N = 2389; ages 14–24). Residuals from the relation between childhood family experiences and PSF reflect resilient functioning; the degree to which an individual is functioning better, or worse, than expected given their childhood family experiences. Next, we relate family and friendship support with resilient functioning both cross-sectionally and 1 year later.

Friendship and family support were positive predictors of immediate resilient PSF, with friendship support being the strongest predictor. However, whereas friendship support was a significant positive predictor of later resilient functioning, family support had a negative relationship with later resilient PSF.

We show that friendship support, but not family support, is an important positive predictor of both immediate and later resilient PSF in adolescence and early adulthood. Interventions that promote the skills needed to acquire and sustain adolescent friendships may be crucial in increasing adolescent resilient PSF.

The objective of this study was to determine whether hatha yoga is an efficacious adjunctive intervention for individuals with continued depressive symptoms despite antidepressant treatment.

We conducted a randomized controlled trial of weekly yoga classes (n = 63) v. health education classes (Healthy Living Workshop; HLW; n = 59) in individuals with elevated depression symptoms and antidepressant medication use. HLW served as an attention-control group. The intervention period was 10 weeks, with follow-up assessments 3 and 6 months afterwards. The primary outcome was depression symptom severity assessed by blind rater at 10 weeks. Secondary outcomes included depression symptoms over the entire intervention and follow-up periods, social and role functioning, general health perceptions, pain, and physical functioning.

At 10 weeks, we did not find a statistically significant difference between groups in depression symptoms (b = −0.82, s.e. = 0.88, p = 0.36). However, over the entire intervention and follow-up period, when controlling for baseline, yoga participants showed lower levels of depression than HLW participants (b = −1.38, s.e. = 0.57, p = 0.02). At 6-month follow-up, 51% of yoga participants demonstrated a response (⩾50% reduction in depression symptoms) compared with 31% of HLW participants (odds ratio = 2.31; p = 0.04). Yoga participants showed significantly better social and role functioning and general health perceptions over time.

Although we did not see a difference in depression symptoms at the end of the intervention period, yoga participants showed fewer depression symptoms over the entire follow-up period. Benefits of yoga may accumulate over time.

Genetic–epidemiological studies that estimate the contributions of genetic factors to variation in tic symptoms are scarce. We estimated the extent to which genetic and environmental influences contribute to tics, employing various phenotypic definitions ranging between mild and severe symptomatology, in a large population-based adult twin-family sample.

In an extended twin-family design, we analysed lifetime tic data reported by adult mono- and dizygotic twins (n = 8323) and their family members (n = 7164; parents and siblings) from 7311 families in the Netherlands Twin Register. We measured tics by the abbreviated version of the Schedule for Tourette and Other Behavioral Syndromes. Heritability was estimated by genetic structural equation modeling for four tic disorder definitions: three dichotomous and one trichotomous phenotype, characterized by increasingly strictly defined criteria.

Prevalence rates of the different tic disorders in our sample varied between 0.3 and 4.5% depending on tic disorder definition. Tic frequencies decreased with increasing age. Heritability estimates varied between 0.25 and 0.37, depending on phenotypic definitions. None of the phenotypes showed evidence of assortative mating, effects of shared environment or non-additive genetic effects.

Heritabilities of mild and severe tic phenotypes were estimated to be moderate. Overlapping confidence intervals of the heritability estimates suggest overlapping genetic liabilities between the various tic phenotypes. The most lenient phenotype (defined only by tic characteristics, excluding criteria B, C and D of DSM-IV) rendered sufficiently reliable heritability estimates. These findings have implications in phenotypic definitions for future genetic studies.