Personality disorders, common mental disorders and receipt of disability benefits: evidence from the British National Survey of Psychiatric Morbidity

Effectiveness of outpatient and community treatments for people with a diagnosis of 'personality disorder': systematic review and meta-analysis

BACKGROUND

Quality of care and access to effective interventions have been widely criticised as limited for people diagnosed with 'personality disorder' or who have comparable needs (described in some recent papers as "Complex Emotional Needs" (CEN). It is important to identify effective interventions and the optimal context and mode of delivery for people with CEN. We aimed to investigate the effectiveness of psychosocial interventions delivered in community and outpatient settings in treating symptoms associated with 'personality disorder', and the moderating effects of treatment-related variables.

METHODS

We systematically searched MEDLINE, EMBASE, PsycINFO, CINAHL, HMIC, ASSIA for articles published in English, from inception to November 23, 2020. We included randomized controlled trials examining interventions provided in community or outpatient settings for CEN. The primary outcome was 'personality disorder' symptoms, while secondary outcomes included anxiety symptoms, depressive symptoms, and global psychiatric symptoms. Random-effects meta-analysis was conducted for each outcome, and meta-regression analysis was performed to assess the moderating effects of treatment characteristics. The quality of the studies and the degree of publication bias was assessed.

RESULTS

We included 54 trials (n = 3716 participants) in the meta-analysis. We found a large effect size (g = 0.78, 95% CI: 0.56 to 1.01, p < 0.0001) favoring interventions for 'borderline personality disorder' (BPD) symptoms over Treatment as Usual or Waitlist (TAU/WL), and the efficacy was maintained at follow-up (g = 1.01, 95% CI: 0.37 to 1.65, p = 0.002). Interventions effectively reduced anxiety symptoms (g = 0.58, 95% CI: 0.21 to 0.95, p = 0.002), depressive symptoms (g = 0.57, 95% CI: 0.32 to 0.83, p < 0.0001), and global psychiatric symptoms (g = 0.50, 95% CI: 0.35 to 0.66, p < 0.0001) compared to TAU/WL. The intervention types were equally effective in treating all symptom categories assessed. Treatment duration and treatment intensity did not moderate the effectiveness of the interventions for any outcome.

CONCLUSIONS

People with a 'personality disorder' diagnosis benefited from psychological and psychosocial interventions delivered in community or outpatient settings, with all therapeutic approaches showing similar effectiveness. Mental health services should provide people with CEN with specialised treatments in accordance with the availability and the patients' preferences.

Individual placement and support and employment in personality disorders: a registry based cohort study

BACKGROUND

To explore the relative impact of Individual Placement and Support (IPS) in patients with personality disorders (PDs) as compared to patients with other mental disorders.

METHODS

Data from the Dutch Employee Insurance Agency of participants enrolled in a national IPS trajectory between 2008 and 2018 were linked to corresponding data on employment outcomes, diagnostic and sociodemographic information from Statistics Netherlands. This resulted in a sample of 335 participants with PDs who could be compared with 1073 participants with other mental disorders.

RESULTS

Participants with PD just as often found competitive employment as participants with other mental disorders (37.6% vs. 38.0%, OR_adjusted = 0.97, 95% confidence interval (CI) 0.74 to 1.27). The median time to gaining employment for those gaining employment (37.9%) was 195.5 days (mean number of days 252.5) in the PD group and 178.5 days (mean number of days 234.6) in the other mental disorders group (HR_adjusted = 0.95, 95% CI 0.77 to 1.18). Also, total number of hours paid for competitive employment did not differ significantly between groups (median hours 686.5 vs 781.5, IRR_adjusted = 0.85 95% CI 0.69 to 1.05).

CONCLUSIONS

Based on this study, which includes the largest sample of patients with PDs in any published IPS study, IPS seems to result in an equal percentage of patients with PDs and other mental disorders, gaining and maintaining employment. Although future studies should determine whether PD-specific adaptations to IPS are useful, our findings indicate that IPS could be an effective way to increase employment outcomes in PDs. This is important because the enormous societal costs of PDs are largely driven by loss of economic productivity, and because clinical recovery in PDs is suggested to be enhanced when patients are employed.

The role of borderline personality disorder symptoms on absenteeism & work performance in the Netherlands Study of Depression and Anxiety (NESDA)

BACKGROUND

Symptoms of borderline personality disorder (BPD) were previously found to be associated with decreased work performance, even after controlling for depressive and anxiety disorders. Furthermore, co-occurrence of BPD and affective disorders is common. Therefore, we examined the effect of BPD symptoms on occupational functioning in workers with affective disorders.

METHODS

Healthy workers (n = 287), workers with current depression/anxiety only (n = 195), workers with BPD symptoms only (n = 54), and workers with both depression/anxiety and BPD symptoms (n = 103) were selected from the Netherlands Study of Depression and Anxiety (NESDA). Both a categorical and dimensional approach were used to cross-sectionally study the effect of BPD symptoms on work performance and absenteeism.

RESULTS

Compared to healthy controls, all symptomatic groups had impaired occupational functioning. Workers with current depression/anxiety had higher long-term absenteeism (OR = 3.59; 95%CI:1.83-7.02) and impaired work performance (OR = 7.81; 95%CI:4.44-13.73), workers with BPD symptoms only had higher impaired work performance (OR = 6.02 95%CI:2.76-13.09), and workers with both depression/anxiety and BPD symptoms had higher long-term absenteeism (OR = 3.66 95%CI:1.69-7.91) and impaired work performance (OR = 10.41 95%CI:5.38-20.15). No difference was found between the (symptomatic) groups. In the dimensional analysis, all associations between BPD symptoms and occupational measures disappeared when depressive symptoms were added. Depressive and BPD symptoms were highly correlated (r = .67).

CONCLUSIONS

Our findings confirm that both affective disorders and BPD symptoms are associated with occupational dysfunction. The effect of BPD symptoms however, seems mediated by depressive symptoms. This would suggest that focusing on affective symptoms in occupational health may be effective to improve occupational functioning in persons with BPD.

INdividual Vocational and Educational Support Trial (INVEST) for young people with borderline personality disorder: study protocol for a randomised controlled trial

Background

The clinical onset of borderline personality disorder (BPD) usually occurs in young people (aged 12–25 years) and commonly leads to difficulty achieving and maintaining vocational (education and/or employment) engagement. While current psychosocial interventions lead to improvements in psychopathology, they have little effect upon functioning. Individual Placement and Support (IPS) is a client-driven model that assists individuals with severe mental illness to engage with education and/or employment appropriate to their personal goals, and that provides ongoing support to maintain this engagement. The objective of the INdividual Vocational and Educational Support Trial (INVEST) is to evaluate the effectiveness of adding IPS to an evidence-based early intervention programme for BPD, with the aim of improving vocational outcomes.

Methods/design

INVEST is a single-blind, parallel-groups, randomised controlled trial (RCT). The randomisation is stratified by gender and age and uses random permuted blocks. The interventions are 39 weeks of either IPS, or ‘usual vocational services’ (UVS). Participants will comprise 108 help-seeking young people (aged 15–25 years) with three or more DSM-5 BPD features and a desire to study or work, recruited from the Helping Young People Early (HYPE) early intervention programme for BPD at Orygen, in Melbourne, Australia. All participants will receive the HYPE intervention. After baseline assessment, staff who are blind to the intervention group allocation will conduct assessments at 13, 26, 39 and 52 weeks. At the 52-week primary endpoint, the primary outcome is the number of days in mainstream education/employment since baseline. Secondary outcomes include the cost-effectiveness of the intervention, quality of life, and BPD severity.

Discussion

Current treatments for BPD have little impact on vocational outcomes and enduring functional impairment is prevalent among this patient group. IPS is a targeted functional intervention, which has proven effective in improving vocational outcomes for adults and young people with psychotic disorders. This trial will investigate whether IPS is effective for improving vocational (employment and educational) outcomes among young people with subthreshold or full-syndrome BPD.

Trial registration

Australian New Zealand Clinical Trials Registry, ID: ACTRN12619001220156. 13 September 2019.

Employment in Personality Disorders and the Effectiveness of Individual Placement and Support: Outcomes from a Secondary Data Analysis

Purpose Personality disorders (PDs) are associated with severe functional impairment and subsequent high societal costs, increasing the need to improve occupational functioning in PD. Individual placement and support (IPS) is an effective, evidence-based method of supported employment, which so far has been tested in various mixed patient populations with severe mental illness (SMI, including PDs). However, the effectiveness of IPS for PDs per se remains uninvestigated. Methods Data from the SCION trial were used, including 31 SMI patients with PDs and 115 SMI patients with other primary diagnoses (primarily psychotic disorders). First, the interaction effect of diagnosis (PD vs other SMI) and intervention (IPS vs traditional vocational rehabilitation) was studied. Second, in the IPS condition, difference between diagnostic groups in time to first job was studied. Results We did not find evidence of a moderating effect of PD diagnosis on the primary effect of IPS (proportion who started in regular employment) (OR = 0.592, 95% CI 0.80-4.350, p = 0.606) after 30 months. Also, PD diagnosis did not moderate the effect of time until first job in IPS. Conclusions From the present explorative analysis we did not find evidence for a moderating effect of PD diagnosis on the effectiveness of IPS among PD participants. This indicates that IPS could be as effective in gaining employment in participants with PD as it is in participants with other SMI. Future studies, implementing larger numbers, should confirm whether IPS is equally effective in PDs and study whether augmentations or alterations to the standard IPS model might be beneficiary for PD.

Borderline Personality Disorder Features Are Associated with Concurrent Pain-Related Disability in a Chronic Pain Sample

OBJECTIVE

To determine whether core features of borderline personality disorder are associated with increased rates of being on disability benefits due to chronic pain conditions.

SUBJECTS

A total of 147 patients currently in treatment for chronic pain at a multimodal chronic pain clinic.

METHODS

We tested for a concurrent relationship between borderline personality disorder features and employment status using self-report measures.

RESULTS

Borderline personality disorder features were associated with increased likelihood of currently being on disability due to pain conditions (odds ratio [OR] = 23.13, 95% confidence interval [CI] = 1.68-318.73), on disability due to other conditions (OR = 33.65, 95% CI = 2.15-526.13), and unemployed (OR = 20.14, 95% CI = 1.38-294.93), even while controlling for pain severity and interference, depression, and trait anxiety. A follow-up analysis revealed that these associations were due to the negative relationships facet of borderline personality disorder features.

CONCLUSIONS

Borderline personality disorder features, particularly negative relationships, are associated with increased rates of pain disability, general disability, and unemployment in a chronic pain sample. Future research should examine mechanisms by which the maladaptive interpersonal behaviors and cognitions of borderline personality disorder might result in worse long-term employment outcomes of chronic pain.

Unemployment and the Relationship between Borderline Personality Pathology and Health

Evidence suggests that employment may buffer against the negative health outcomes associated with borderline personality disorder (BPD). The purpose of the current analyses was to examine unemployment and the BPD-health relationship prospectively. Participants were 1,536 older adults in a longitudinal study of health and aging, with repeated measures of physical health, depressive symptoms, and life satisfaction. We measured BPD features using multiple sources at baseline, and used principal components analysis to obtain latent scores. Multilevel models indicated that unemployment experiences did not moderate the prospective relationship between BPD features and physical health or life satisfaction, but did strengthen the positive relationship between BPD features and depressive symptoms. These findings provide insight into mechanisms of recovery for individuals with BPD.

Barriers and facilitators to employment in borderline personality disorder: A qualitative study among patients, mental health practitioners and insurance physicians

Background

Borderline personality disorder (BPD) is associated with unemployment and impaired functioning. However, a comprehensive understanding of barriers and facilitators to employment from a multidisciplinary perspective is currently lacking. Therefore, the aim of this qualitative study was to explore barriers and facilitators in gaining and maintaining employment in BPD from the perspectives of patients, mental health practitioners (MHPs) and insurance physicians (IPs).

Methods

Fifteen semi-structured interviews were conducted in patients with BPD and two focus groups were carried out among MHPs (n = 7) and IPs (n = 6) following a thematic content analysis approach.

Results

All participants described barriers and facilitators relating to three overall themes: characteristics of BPD, stigma, and support to employment. Barriers to employment mainly related to characteristics of BPD, such as low self-image, difficulty posing personal boundaries, difficulty regulating emotions, and lack of structure. MHPs and IPs additionally mentioned externalization and overestimation of competencies on the part of patients. Enhancing emotion regulation and self-reflection by successful treatment was suggested as a facilitator to enhance employment. Increasing collaboration between mental health and vocational rehabilitation services, and increasing knowledge about BPD, were suggested to increase sustainable employment and decrease stigma.

Conclusions

The present findings revealed that both facilitators and barriers are important in gaining and maintaining employment in BPD in which diminishing symptoms, examining stigma and increasing support to employment are key. As a next step, supported employment strategies that follow patient preferences and integrate employment and mental health services, should be studied in the context of BPD.

GPs' views and experiences of managing patients with personality disorder: a qualitative interview study

OBJECTIVE

The aim of this study was to explore GPs' views and experiences of managing patients with personality disorder (PD), and their views on the role of the Improving Access to Psychological Therapies (IAPT) programme as a support service.

DESIGN

In-depth interviews, analysed thematically.

PARTICIPANTS

Fifteen GPs (7 women and 8 men) of varying age and clinical experience, working in practices that differed in terms of the socio-demographic characteristics of their patient populations.

SETTING

Twelve general practices based in the West of England, UK.

RESULTS

GPs described patients with PD as being challenging to work with and that this work required dedicated time and care. They described experiencing particular difficulty with monitoring their patient's mental health, as well as having little knowledge about the efficacy or availability of treatments for their attenders with PD. They were aware that this patient population often experienced poor mental health and reported a propensity for them to fall into the gap between primary and secondary mental health services, leaving GPs with little choice but to improvise their own management plans, which occasionally involved funding third-sector treatment options. In terms of IAPT services' role in managing these patients, GPs wanted shorter waiting times, better inter-agency communication, more highly trained therapists and more treatment options for patients with PD. They also wanted the service to be able to 'hold' patients with PD in treatment over a longer period than currently offered.

CONCLUSIONS

Findings suggest that, overall, GPs did not consider National Health Service mental health services to offer an effective treatment for patients with PD. While they considered the IAPT programme to be a valuable service for patients with less complex mental health needs, such as depression and anxiety; they felt that the current service provision struggled to meet the needs of patients with more complex mental health needs, as exemplified by people with PD.

Personality disorder: a disease in disguise

Personality disorders (PDs) can be described as the manifestation of extreme personality traits that interfere with everyday life and contribute to significant suffering, functional limitations, or both. They are common and are frequently encountered in virtually all forms of health care. PDs are associated with an inferior quality of life (QoL), poor health, and premature mortality. The aetiology of PDs is complex and is influenced by genetic and environmental factors. The clinical expression varies between different PD types; the most common and core aspect is related to an inability to build and maintain healthy interpersonal relationships. This aspect has a negative impact on the interaction between health-care professionals and patients with a PD. From being discrete and categorical disease entities in previous classification systems, the current concept of PD, reflected in the newly proposed ICD-11, is a dimensional description based on the severity of the disturbed functioning rather than on the type of clinical presentation. Insight about the characteristics of PDs among medical practitioners is limited, which is partly because persons do not seek health care for their PD, but instead for other medical issues which are obscured by their underlying personality problems. What needs to be emphasized is that PDs affect both the clinical presentation of other medical problems, and the outcome of these, in a negative manner and that the integrated effects of having a PD are a shortened life expectancy. Accordingly, PDs need to be recognized in clinical practice to a greater extent than previously.

A hierarchical causal taxonomy of psychopathology across the life span

We propose a taxonomy of psychopathology based on patterns of shared causal influences identified in a review of multivariate behavior genetic studies that distinguish genetic and environmental influences that are either common to multiple dimensions of psychopathology or unique to each dimension. At the phenotypic level, first-order dimensions are defined by correlations among symptoms; correlations among first-order dimensions similarly define higher-order domains (e.g., internalizing or externalizing psychopathology). We hypothesize that the robust phenotypic correlations among first-order dimensions reflect a hierarchy of increasingly specific etiologic influences. Some nonspecific etiologic factors increase risk for all first-order dimensions of psychopathology to varying degrees through a general factor of psychopathology. Other nonspecific etiologic factors increase risk only for all first-order dimensions within a more specific higher-order domain. Furthermore, each first-order dimension has its own unique causal influences. Genetic and environmental influences common to family members tend to be nonspecific, whereas environmental influences unique to each individual are more dimension-specific. We posit that these causal influences on psychopathology are moderated by sex and developmental processes. This causal taxonomy also provides a novel framework for understanding the heterogeneity of each first-order dimension: Different persons exhibiting similar symptoms may be influenced by different combinations of etiologic influences from each of the 3 levels of the etiologic hierarchy. Furthermore, we relate the proposed causal taxonomy to transdimensional psychobiological processes, which also impact the heterogeneity of each psychopathology dimension. This causal taxonomy implies the need for changes in strategies for studying the etiology, psychobiology, prevention, and treatment of psychopathology. (PsycINFO Database Record

Workplace interventions for common mental disorders: a systematic meta-review

Depression and anxiety disorders are the leading cause of sickness absence and long-term work incapacity in most developed countries. The present study aimed to carry out a systematic meta-review examining the effectiveness of workplace mental health interventions, defined as any intervention that a workplace may either initiate or facilitate that aims to prevent, treat or rehabilitate a worker with a diagnosis of depression, anxiety or both. Relevant reviews were identified via a detailed systematic search of academic and grey literature databases. All articles were subjected to a rigorous quality appraisal using the AMSTAR assessment. Of the 5179 articles identified, 140 studies met the inclusion criteria, of which 20 were deemed to be of moderate or high quality. Together, these reviews analysed 481 primary research studies. Moderate evidence was identified for two primary prevention interventions; enhancing employee control and promoting physical activity. Stronger evidence was found for CBT-based stress management although less evidence was found for other secondary prevention interventions, such as counselling. Strong evidence was also found against the routine use of debriefing following trauma. Tertiary interventions with a specific focus on work, such as exposure therapy and CBT-based and problem-focused return-to-work programmes, had a strong evidence base for improving symptomology and a moderate evidence base for improving occupational outcomes. Overall, these findings demonstrate there are empirically supported interventions that workplaces can utilize to aid in the prevention of common mental illness as well as facilitating the recovery of employees diagnosed with depression and/or anxiety.

Sickness allowance histories among disability retirees due to mental disorders: A retrospective case-control study

OBJECTIVES

The aim was to describe sickness allowance histories before disability retirement due to mental disorders and to examine whether receiving sickness allowance due to mental disorders and somatic conditions predicts future disability retirement.

METHOD

Pre-retirement sickness allowance histories were traced backwards for 7 years among Finnish residents aged 25-64 years who had retired due to mental disorders in 2011 (n=5.544). For each retiree, five sex- and age-matched controls were drawn from the non-retired population. Conditional logistic regression was used to calculate the risk for disability retirement by sickness allowance history and to control for the effects of educational level, social class, marital status and the urbanisation level of the municipality.

RESULTS

The proportion of sickness allowance recipients increased steadily during the years preceding disability retirement, and was highest among those who retired due to bipolar disorders or depression. Those who had received sickness allowance due to mental disorders 6-7 years earlier had 6.5 times higher risk and those with sickness allowance 1-2 years earlier 11.7 times higher risk for disability retirement. Sickness allowance due to somatic conditions increased the risk for disability retirement 1.6-1.9 times. Sickness allowance most strongly predicted retirement due to bipolar disorders and depression. Adjustment for covariates had little effect.

CONCLUSION

Those who retired due to mental disorders more often had sickness allowance due to both mental disorders and somatic conditions, but in particular sickness allowance due to mental disorders predicted disability retirement due to mental disorders.

Borderline Personality Disorder in Young People: Are We There Yet?

Although borderline personality disorder (BPD) usually has its onset in young people, its diagnosis and treatment is often delayed. The past 2 decades have seen a rapid increase in evidence establishing that BPD can be diagnosed before 18 years of age and that BPD in young people is both continuous with BPD in adults and more notable for its similarities than for any differences. This knowledge has led to the first wave of controlled treatment trials, which have established that early intervention through appropriate BPD diagnosis and treatment leads to clinically meaningful improvements for patients. However, there is still much work to do in terms of treatment development and innovation and overcoming challenges to successful translation of evidence into practice. To advance early intervention for BPD, access to evidence-based treatments needs to improve, the variety of available treatments (including novel pharmacotherapies) needs to increase, treatments need to be matched to individual development and to the phase and stage of disorder, and workforce development strategies need to update knowledge, culture, and practice in relation to BPD in young people.

Personality disorders are important risk factors for disability pensioning

PURPOSE

To determine whether personality disorders (PDs) are associated with increased risk of disability pensioning in young adults, independent of other common mental disorders.

METHODS

2,770 young adults from the general population were assessed for PDs by the Structured Interview for DSM-IV Personality, and for common mental disorders by the Composite of International Diagnostic Interview. These data were linked to the Norwegian National Insurance Administration's recordings of disability benefits for a 10-year period. Logistic regression analyses were applied to investigate the association between PDs and disability pensioning. The analyses were conducted for three types of PD measures: categorical diagnoses (any PD), dimensional scores of individual PDs and higher order components retrieved by principal component analyses.

RESULTS

Having any PD was strongly associated with disability pensioning, regardless of disability diagnosis. The estimated odds ratio (OR) was substantially higher for PDs [OR 4.69 (95% confidence interval (CI) 2.6-8.5)] than for mood disorders [OR 1.3 (CI 0.7-2.3)] and anxiety disorders [OR 2.3 (CI 1.3-4.3)]. Measured dimensionally, all PD traits except antisocial traits were significantly associated with disability pensioning. After adjusting for co-occurring traits of other PDs, only schizoid, dependent and borderline PD traits showed a significant positive association with disability pension, while antisocial traits showed a significant negative association. The principal component analyses showed that negative affectivity, psychoticism, and detachment was associated with an increased risk of disability pensioning, while antagonism/disinhibition and obsessivity were not.

CONCLUSIONS

PDs are strongly associated with disability pensioning in young adults, and might be more important predictors of work disability than anxiety and depressive disorders. Certain aspects of pathologic personalities are particularly important predictors of disability.

Common mental disorders and cause-specific disability retirement

OBJECTIVES

Common mental disorders are prevalent among employees and may cause work disability. We aimed to examine the association between common mental disorders and disability retirement, with an emphasis on the severity of disorders and diagnostic causes for retirement.

METHODS

Our data were derived from the Helsinki Health Study cohort on the staff of the City of Helsinki, Finland. The baseline mail surveys were made in 2000-2002 among employees reaching ages 40, 45, 50, 55 and 60 in each year (n=8960, response rate 67%, 80% women). Disability retirement events from national registers (n=628) were followed up by the end of 2010 and linked to the baseline data. After exclusions, the number of participants was 6525. Common mental disorders were measured by the General Health Questionnaire 12-item version (GHQ-12). Covariates at baseline included sociodemographic, work-related and health-related factors. Hazard ratios (HR) and 95% CIs were calculated using Cox proportional hazards models.

RESULTS

Common mental disorders showed a graded association with disability retirement. For disability retirement due to any diagnostic cause, the fully adjusted HR for the GHQ-12 score 7-12 was 2.16, 95% CI 1.63 to 2.85. For disability retirement due to mental disorders the corresponding HR was 7.46, 95% CI 4.46 to 12.49. For disability retirement due to musculoskeletal diseases, the association was weaker and did not survive all adjustments.

CONCLUSIONS

Common mental disorders are an important antecedent of disability retirement in general and due to mental disorders in particular. Successful measures against common mental disorders may prevent disability retirement due to mental disorders.

Personality disorders and long-term sick leave: a population-based study of young adult Norwegian twins

Personality disorders (PDs) reduce global functioning, are associated with high levels of work disability, and are thus also likely to influence long-term sick leave (LTSL). Previous research has indicated significant genetic influence on both DSM-IV PDs and LTSL. To what degree genes contributing to PDs also influence LTSL has not been investigated. The aims of the current study were to investigate which PDs were significantly associated with LTSL, to what extent the genetic contributions to these PDs account for the heritability of LTSL, and to explore the hypothesis of a causal association between PDs and LTSL. The sample consisted of 2,771 young, adult Norwegian twins, born 1967-1979. PDs were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV). The age range for the interview was 20-32. The data were subsequently linked to public records of LTSL (sick leave >16 days) up to 11 years later. The odds ratio for being in the highest LTSL category (>15% sick leave) when fulfilling the DSM-IV criteria for any PD diagnosis was 2.6 (1.8-3.8, 95% CI). Dimensional representations of schizotypal, paranoid, and borderline PD were independently and significantly associated with LTSL. The heritability of LTSL was 0.50. Genetic factors shared with the PDs accounted for 20% of this. The association between PDs and LTSL was due to shared genetic and not environmental influences, and was mainly explained by one common genetic factor. The hypothesis of a causal association was not supported, indicating that the association is explained by overlapping genetic liability between PDs and LTSL.