Risk of bipolar disorder and schizophrenia in relatives of people with attention-deficit hyperactivity disorder

Psychotic Symptoms in Attention-Deficit/Hyperactivity Disorder: An Analysis of the MTA Database

OBJECTIVE

To assess the prevalence of psychotic symptoms among youths (14-25 years of age) with a childhood diagnosis of attention-deficit/hyperactivity disorder (ADHD) combined type.

METHOD

Participants in the Multimodal Treatment Study of Children with ADHD (MTA) and a local normative comparison group (LNCG) were systematically assessed 6, 8, 10, 12, 14, and 16 years after the original enrollment at a mean age of 8.5 years. Trained research assistants administered a psychosis screener, and positive screens were referred to study clinicians to confirm or exclude psychosis. Possible associations between screening positive and alcohol or substance use were assessed.

RESULTS

Data were available from 509 MTA participants (88% of original MTA sample; mean age 25.1 years) and 276 LNCG participants (96% of original sample; mean age 24.6 years) at year 16. Twenty-six MTA participants (5%; 95% CI 3-7) and 11 LNCG participants (4%; 95% CI 2-6) screened positive for at least 1 psychotic symptom (p = .60). Most psychotic symptoms were transient. The prevalence of clinician-confirmed psychotic symptoms was 1.1% (95% CI 0.2-2.1) in the MTA group and 0.7% (0-1.7) in the LNCG (p = .72). Greater cannabis use was reported by those who screened positive (p < .05) and were confirmed positive (p < .01).

CONCLUSION

There was no evidence that ADHD increased the risk for psychotic symptoms. In the ADHD and normative comparison groups, more frequent cannabis use was associated with a greater likelihood of experiencing psychotic symptoms, thus supporting the recommendation that youth should not use cannabis.

Associations of attention-deficit/hyperactivity and other childhood disorders with psychotic experiences and disorders in adolescence

Prodromal symptoms of psychosis are associated with an increased risk of transition, functional impairment, poor mental health, and unfavorable developmental prospects. Existing interventions targeting the prodrome are non-satisfactory. It may thus be more promising to attempt to identify risk factors in the premorbid phase preceding the prodrome to increase the chances of successful preventive approaches. Here, we investigate whether childhood mental disorders in general and attention-deficit/hyperactivity disorder (ADHD) specifically indicate a risk for subsequent psychotic experiences and disorders. We used a sample from the prospective Avon Longitudinal Study of Parents and Children (N = 5528). When the participants were 7 years old, mental disorders were assigned according to the DSM-IV. In standardized interviews, psychotic experiences were assessed at age 12 and psychotic disorders at age 18. We examined the associations of each of the childhood mental disorders alone and in combination with psychotic experiences at age 12 and psychotic disorders at age 18 using logistic regression. Compared to participants without a disorder, participants with a mental disorder had a higher risk of psychotic experiences at age 12 (OR 1.70, 95 % CI 1.28-2.27) and of psychotic disorders at age 18 (OR 2.31, 95 % CI 1.03-5.15). Particularly, the ADHD combined subtype at age 7 was strongly associated with psychotic experiences at age 12 (OR 3.26, 95 % CI 1.74-6.10). As expected, childhood mental disorders are risk indicators of psychotic experiences and disorders. To improve prevention, health care professionals need to screen for psychotic experiences in children with non-psychotic disorders.

Familial aggregation of attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) aggregates in families. To date, the strength, pattern, and characteristics of the familial aggregation have not been thoroughly assessed in a population-based family sample.

METHODS

In this cohort study, we identified relative pairs of twins, full and half-siblings, and full and half cousins from 1,656,943 unique individuals born in Sweden between 1985 and 2006. The relatives of index persons were followed from their third birthday to 31 December 2009 for ADHD diagnosis. Birth year adjusted hazard ratio (HR), that is, the rate of ADHD in relatives of ADHD-affected index persons compared with the rate of ADHD in relatives of unaffected index persons, was estimated in the different types of relatives using Cox proportional hazards model.

RESULTS

During the follow-up, 31,865 individuals were diagnosed with ADHD (male to female ratio was 3.7). The birth year adjusted HRs were as follows: 70.45 for monozygotic twins; 8.44 for dizygotic twins; 8.27 for full siblings; 2.86 for maternal half-siblings; 2.31 for paternal half-siblings; 2.24 for full cousins; 1.47 for half cousins. Maternal half-siblings had significantly higher HR than in paternal half-siblings. The HR did not seem to be affected by index person's sex. Full siblings of index persons with ADHD diagnosis present at age 18 or older had a higher rate of ADHD (HR: 11.49) than full siblings of index persons with ADHD diagnosis only before age 18 (HR: 4.68).

CONCLUSIONS

Familial aggregation of ADHD increases with increasing genetic relatedness. The familial aggregation is driven by not only genetic factors but also a small amount of shared environmental factors. Persistence of ADHD into adulthood indexes stronger familial aggregation of ADHD.

The Familial Co-Aggregation of Attention-Deficit/Hyperactivity Disorder and Intellectual Disability: A Register-Based Family Study

OBJECTIVE

Although many studies document an association between attention-deficit/hyperactivity disorder (ADHD) and intellectual disability (ID), little is known about the etiology of this comorbidity and how it should be addressed in clinical settings. We sought to clarify this issue.

METHOD

All individuals born in Sweden between 1987 and 2006 (n = 2,049,587) were identified using the Medical Birth Register (MBR). From this we selected 7 cohorts of relatives: 1,899,654 parent-offspring pairs, 4,180 monozygotic twin pairs, 12,655 dizygotic twin pairs, 914,848 full sibling pairs, 136,962 maternal half-sibling pairs, 134,502 paternal half-sibling pairs, and 2,790,164 full cousin pairs. We used within-individual and within-family analyses to assess the association between ADHD and ID.

RESULTS

Individuals with ID were at increased risk for ADHD compared to those without ID, and relatives of participants with ID were at increased risk of ADHD compared with relatives of those without ID. The magnitude of this association was positively associated with the fraction of the genome shared by the relative pair and was lower for severe compared with mild and moderate ID. Model-fitting analyses demonstrated that 91% of the correlation between the liabilities of ADHD and ID was attributable to genetic factors.

CONCLUSION

These data provide evidence that nearly all of the comorbidity between ADHD and ID can be attributed to genetic factors, which has implications for diagnostic practice.

Risk factors for the existence of attention deficit hyperactivity disorder symptoms in children with autism spectrum disorders

Over the years, several authors have reported symptoms of attention deficit hyperactivity disorder (ADHD) in patients with autism spectrum disorders (ASD); however, studies on the risk factors of ADHD symptoms in children with ASD are lacking. The aim of this cross-sectional study was to identify the risk factors for the development of ADHD symptoms in children with ASD. The sample consisted of 67 children with ASD who were assessed with Conner's Parent Rating Scale-Revised (CPRS-R), and with a semi-structured detailed interview administered to parents, to collect a series of clinical data such as coexisting somatic and neuropsychiatric problems and familial and pre/peri/postpartum risk factors. We found that 55% of ASD children exceeded the cut-off of CPRS-R Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), total scale. The univariate analyses showed that children's age (P=0.048), motor delay (P=0.039), enuresis (P=0.014), allergies (P<0.01), comorbid oppositional defiant disorder (P=0.026) and intellectual disabilities comorbidities (P=0.034) were associated to the CPRS-R DSM-IV total score. Some familial predictors such as neuropsychiatric family history of intellectual disabilities (P=0.003) and psychosis (P=0.039) were related to the CPRS-R DSM-IV total score. In particular, a model including allergies (P=0.000) and family history of psychosis (P=0.03) explained 25% (corrected R²=0.25) of the variance of the DSM-IV ADHD score. In conclusion, we identified some risk factors associated with the development of ADHD symptoms in ASD children that need to be studied further.

Predictive validity of parent- and self-rated ADHD symptoms in adolescence on adverse socioeconomic and health outcomes

There is scarcity of research investigating the validity of self-report of attention deficit hyperactivity disorder (ADHD) symptoms compared to other informants, such as parents. This study aimed to compare the predictive associations of ADHD symptoms rated by parents and their children across adolescence on a range of adverse socioeconomic and health outcomes in early adulthood. Parent- and self-rated ADHD symptoms were assessed in 2960 individuals in early (13-14 years) and late adolescence (16-17 years). Logistic regression analyses were used to compare the associations between parent- and self-rated ADHD symptoms at both time points and adverse life outcomes in young adulthood obtained from Swedish national registries. Both parent- and self-ratings of ADHD symptoms were associated with increased risk for adverse outcomes, although associations of parent-ratings were more often statistically significant and were generally stronger (OR = 1.12-1.49, p < 0.05) than self-ratings (OR = 1.07-1.17, p < 0.05). After controlling for the other informant, parent-ratings of ADHD symptoms in both early and late adolescence significantly predicted academic and occupational failure, criminal convictions and traffic-related injuries, while self-ratings of ADHD symptoms only in late adolescence predicted substance use disorder and academic failure. Our findings suggest that both parent- and self-ratings of ADHD symptoms in adolescence provides valuable information on risk of future adverse socioeconomic and health outcomes, however, self-ratings are not valuable once parent-ratings have been taken into account in predicting most outcomes. Thus, clinicians and researchers should prioritize parent-ratings over self-ratings.

Medication for Attention-Deficit/Hyperactivity Disorder and Risk for Depression: A Nationwide Longitudinal Cohort Study

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is associated with high rates of psychiatric comorbidity, including depression. However, it is unclear whether ADHD medication increases or decreases the risk for depression.

METHODS

We studied all individuals with a diagnosis of ADHD born between 1960 and 1998 in Sweden (N = 38,752). We obtained data for prescription of ADHD medication, diagnosis of depression and other psychiatric disorders, and sociodemographic factors from population-based registers. The association between ADHD medication and depression was estimated with Cox proportional hazards regression.

RESULTS

After adjustment for sociodemographic and clinical confounders, ADHD medication was associated with a reduced long-term risk (i.e., 3 years later) for depression (hazard ratio = 0.58; 95% confidence interval, 0.51-0.67). The risk was lower for longer duration of ADHD medication. Also, ADHD medication was associated with reduced rates of concurrent depression; within-individual analysis suggested that occurrence of depression was 20% less common during periods when patients received ADHD medication compared with periods when they did not (hazard ratio = 0.80; 95% confidence interval, 0.70-0.92).

CONCLUSIONS

Our study suggests that ADHD medication does not increase the risk of later depression; rather, medication was associated with a reduced risk for subsequent and concurrent depression.

How to Move Beyond the Diagnostic and Statistical Manual of Mental Disorders/International Classification of Diseases

A new nosology for mental disorders is needed as a basis for effective scientific inquiry. Diagnostic and Statistical Manual of Mental Disorders and International Classification of Diseases diagnoses are not natural, biological categories, and these diagnostic systems do not address mental phenomena that exist on a spectrum. Advances in neuroscience offer the hope of breakthroughs for diagnosing and treating major mental illness in the future. At present, a neuroscience-based understanding of brain/behavior relationships can reshape clinical thinking. Neuroscience literacy allows psychiatrists to formulate biologically informed psychological theories, to follow neuroscientific literature pertinent to psychiatry, and to embark on a path toward neurologically informed clinical thinking that can help move the field away from Diagnostic and Statistical Manual of Mental Disorders and International Classification of Diseases conceptualizations. Psychiatrists are urged to work toward attaining neuroscience literacy to prepare for and contribute to the development of a new nosology.

Prenatal smoking exposure and neuropsychiatric comorbidity of ADHD: a finnish nationwide population-based cohort study

BACKGROUND

Prenatal smoking exposure has been associated with attention-deficit/hyperactivity disorder (ADHD). ADHD is commonly associated with a wide spectrum of psychiatric comorbidity. The association between smoking and neuropsychiatric comorbidity of ADHD has remained understudied. The aim of this study is to examine the association between prenatal exposure to maternal smoking and offspring ADHD, and test whether the smoking-ADHD associations are stronger when ADHD is accompanied by other lifetime neuropsychiatric comorbidities.

METHODS

The study is based on a nested case-control design and includes all Finnish singletons born between 1991 and 2005 and diagnosed with ADHD by 2011 (n = 10,132), matched with four controls (n = 38,811) on date of birth, sex and residence in Finland.

RESULTS

The risk for ADHD with or without comorbidity was significantly increased among offspring exposed to maternal smoking on adjusting for potential confounders (OR = 1.75, CI 95 % = 1.65-1.86). Compared to the only ADHD cases, subjects with comorbid conduct disorder or oppositional defiant disorder had a significantly stronger association with smoking exposure (OR = 1.80, CI 95 % = 1.55-2.11).

CONCLUSIONS

Prenatal smoking represents an important risk factor for the ADHD comorbid with CD/ODD. Further research on the association between prenatal smoking exposure and neuropsychiatric comorbidity of ADHD is needed considering the increased risk among these subjects of an overall poor health outcome as compared to only ADHD. In particular, studies utilizing biomarkers or including subjects with neuropsychiatric conditions with and without comorbid ADHD are needed.

Demographic Characteristics and Psychiatric Comorbidity of Children and Adolescents Diagnosed with ADHD in Specialized Healthcare

Recent studies have shown an increasing incidence of attention-deficit/hyperactivity disorder (ADHD) among children diagnosed in specialized services. This study aims to describe children with ADHD in Finnish specialized healthcare by reporting the demographic characteristics, time trends in diagnosis, psychiatric comorbidity, and the validity of register-based diagnoses. All the singletons born in Finland between 1991 and 2005 and diagnosed with ADHD by 2011 were identified and their psychiatric comorbidity data was obtained from the Finnish Hospital Discharge Register (FHDR). Parents of 69 patients were interviewed via telephone for a diagnostic validation. A total of 10,409 children were identified with ADHD, with a male: female ratio of 5.3:1 and a psychiatric comorbidity rate of 76.7 %. Of the validation sample 88 % met the diagnostic criteria of ADHD for DSM-IV. There is an increasing trend of ADHD diagnosis among both males and females. Psychiatric comorbidity is common and includes a wide range of disorders among children with ADHD. There was an increase of ADHD diagnoses especially among boys. More attention is needed to detect ADHD among girls in health services. Diagnoses in the FHDR show diagnostic validity and their sociodemographic patterns are in line with previous studies.

Obstetric mode of delivery and attention-deficit/hyperactivity disorder: a sibling-matched study

BACKGROUND

It has been suggested that birth by caesarean section (CS) may affect psychological development through changes in microbiota or stress response. We assessed the impact of mode of delivery, specifically CS, on the development of attention-deficit/hyperactivity disorder (ADHD), using a large, population-based cohort.

METHODS

The study cohort consisted of all singleton live births in Sweden from 1990 to 2008 using data from Swedish national registers. Mode of delivery included: unassisted vaginal delivery(VD), assisted VD, elective CS or emergency CS. ADHD was determined using International Classification of Diseases version 10 (F90 or F98.8), or prescription for ADHD medication. We used Cox regression to assess the association between birth by CS and ADHD in the total study population, adjusting for perinatal and sociodemographic factors, then stratified Cox regression analysis on maternal identification number to assess the association among siblings.

RESULTS

Our cohort consisted of 1 722 548 children, and among these 47 778 cases of ADHD. The hazard ratio (HR) of the association between elective CS, compared with unassisted VD, and ADHD was 1.15 [95% confidence interval (CI): 1.11-1.20] in the cohort, and 1.05 (95% CI: 0.93-1.18) in the stratified analysis. The HR of the association between emergency CS and ADHD was 1.16 (95% CI: 1.12-1.20])in the cohort and 1.13 (95% CI: 1.01-1.26) in the stratified analysis.

CONCLUSION

Birth by CS is associated with a small increased risk of ADHD. However among siblings the association only remained for emergency CS. If this were a causal effect by CS, the association would be expected to persist for both types of CS, suggesting the observed association is due to confounding.

Patterns of Nonrandom Mating Within and Across 11 Major Psychiatric Disorders

IMPORTANCE

Psychiatric disorders are heritable, polygenic traits, which often share risk alleles and for which nonrandom mating has been suggested. However, despite the potential etiological implications, the scale of nonrandom mating within and across major psychiatric conditions remains unclear.

OBJECTIVE

To quantify the nature and extent of nonrandom mating within and across a broad range of psychiatric conditions at the population level.

DESIGN, SETTING, AND PARTICIPANTS

Population-based cohort using Swedish population registers. Participants were all Swedish residents with a psychiatric diagnosis of interest (attention-deficit/hyperactivity disorder, autism spectrum disorder, schizophrenia, bipolar disorder, major depression, generalized anxiety disorder, agoraphobia, social phobia, obsessive-compulsive disorder, anorexia, or substance abuse), along with their mates. Individuals with select nonpsychiatric disorders (Crohn's disease, type 1 and type 2 diabetes mellitus, multiple sclerosis, or rheumatoid arthritis) were included for comparison. General population samples were also derived and matched 1:5 with each case proband. Inpatient and outpatient diagnostic data were derived from the Swedish National Patient Register (1973-2009), with analyses conducted between June 2014 and May 2015.

MAIN OUTCOMES AND MEASURES

Correlation in the diagnostic status of mates both within and across disorders. Conditional logistic regression was used to quantify the odds of each diagnosis in the mates of cases relative to matched population controls.

RESULTS

Across cohorts, data corresponded to 707 263 unique case individuals, with women constituting 45.7% of the full population. Positive correlations in diagnostic status were evident between mates. Within-disorder correlations were marginally higher (range, 0.11-0.48) than cross-disorder correlations (range, 0.01-0.42). Relative to matched populations, the odds of psychiatric case probands having an affected mate were significantly elevated. Differences in the magnitude of observed relationships were apparent by disorder (odds ratio range, 0.8-11.4). The number of comorbidities in a case proband was associated with the proportion of affected mates. These relationships were not apparent or weaker in magnitude among nonpsychiatric conditions (correlation range, -0.03 to 0.17).

CONCLUSIONS AND RELEVANCE

Nonrandom mating is evident in psychiatric populations both within specific disorders and across the spectrum of psychiatric conditions. This phenomenon may hold important implications for how we understand the familial transmission of these disorders and for psychiatric genetic research.

Delineating ADHD and bipolar disorder: A comparison of clinical profiles in adult women

OBJECTIVE

Overlapping symptoms can make the diagnostic differentiation of attention-deficit/hyperactivity disorder (ADHD) and bipolar disorder (BD) challenging in adults using current clinical assessments. This study sought to determine if current clinical measures delineate ADHD from BD in adults, comparing relative levels of ADHD, BD and emotional lability (EL) symptoms.

METHODS

Sixty adult women with ADHD, BD or controls were compared on self-report and interview measures for ADHD symptoms, mania, depression, EL, and impairment.

RESULTS

ADHD interview measures and self-ratings of ADHD symptoms best discriminated between ADHD and BD. Self-report measures of EL and depression showed non-specific enhancement in both clinical groups. BD-specific items may distinguish BD from ADHD if a retrospective time-frame is adopted.

CONCLUSIONS

Using measures which capture specific symptoms of ADHD and chronicity/episodicity of symptoms facilitates the delineation of ADHD from BD in adult women.

Prescription Stimulant Use and Hospitalization for Psychosis or Mania: A Population-Based Study

Small studies suggest that prescription stimulants can precipitate psychosis and mania. We conducted a population-based case-crossover study to examine whether hospitalization for psychosis or mania was associated with initiation of stimulant therapy. Between October 1, 1999 and March 31, 2013, we studied 12,856 young people who received a stimulant prescription and were subsequently hospitalized for psychosis or mania. Of these, 183 commenced treatment during 1 of 2 prespecified 60-day intervals (defined as the "risk interval" and "control interval," respectively) prior to admission. We found that stimulant initiation was associated with an increased risk of hospitalization for psychosis or mania in the subsequent 60 days (odds ratio, 1.86; 95% confidence interval, 1.39-2.56). The risk was marginally higher in patients treated with antipsychotic drugs (odds ratio, 2.06; 95% confidence interval, 1.38-3.28), but remained in patients with no such history (odds ratio, 1.66; 95% confidence interval, 1.09-2.66). One third of subjects received another stimulant prescription after hospital discharge. Of these, 45% were readmitted with psychosis or mania shortly thereafter. We conclude that initiation of prescription stimulants is associated with an increased risk of hospitalization for psychosis or mania. Resumption of therapy is common, which may reflect a lack of awareness of the potential causative role of these drugs.

Psychiatric disorders in child and adolescent offspring of patients with schizophrenia and bipolar disorder: A controlled study

BACKGROUND

Early clinical manifestations predating schizophrenia (SZ) and bipolar disorder (BP) have not been fully characterized. Child offspring studies are a valuable opportunity to study the natural history of the illness from its earliest stages. However, there is limited evidence assessing young offspring of SZ and BP simultaneously. We set out to assess rates of psychiatric disorders in child and adolescent offspring of SZ and BP, relative to offspring of community controls, so as to characterize the early phenotype of the disorders comparatively.

METHODS

SZ and BP parents with offspring aged 7-17years were recruited through adult mental health services of two tertiary hospitals. Community control (CC) parents were recruited from the same geographical area. Ninety BP-offspring, 41 SZ-offspring and 107 CC-offspring were assessed using the K-SADS-PL by child psychiatrists blinded to parental status. Differences in prevalence of psychiatric disorders between groups were adjusted for confounders and for sibling correlation using generalised estimating equations.

RESULTS

We found a gradient of clinical severity and social disadvantage between SZ, BP and CC-offspring. After adjusting for socio-demographic confounders, SZ and BP-offspring presented higher rates of attention deficit hyperactivity disorder (ADHD) than CC-offspring. ADHD was more prevalent in SZ-offspring than BP-offspring, and BP-offspring presented a higher prevalence of depression than CC-offspring.

CONCLUSIONS

The higher rates of ADHD in SZ-offspring suggest that abnormal neurodevelopmental processes may exert a stronger influence in SZ than BP. Follow-up of these children will help elucidate the role of ADHD and depression phenotypes in predicting future transition to SZ or BP.

Attention-deficit/hyperactivity disorder, methylphenidate use and the risk of developing schizophrenia spectrum disorders: A nationwide population-based study in Taiwan

This study estimated the risk of developing psychotic disorders by comparing children with ADHD to non-ADHD controls, and to examine whether methylphenidate (MPH) treatment influences the risks of psychotic disorders. A nationwide cohort of patients who were newly diagnosed with ADHD (n=73,049) and age- and gender-matched controls (n=73,049) were selected from Taiwan's National Health Insurance database from January 2000 to December 2011. All participants were observed until December 31, 2011. Cox regression models were used to estimate the effects of ADHD diagnosis and MPH use on subsequent outcomes. Having a diagnosis of any psychotic disorder and of schizophrenia were set as two different outcomes and were analyzed separately. Compared to the control group, the ADHD group showed significantly increased risk of developing any psychotic disorder (adjusted hazard ratio [aHR], 5.20; 95% confidence interval [CI], 4.30-6.30) and schizophrenia (aHR, 4.65; 95% CI, 3.59-6.04). Compared to ADHD patients without psychosis, patients with ADHD who developed psychosis had significantly older age at first diagnosis of ADHD (9.4±3.3years vs. 10.6±4.0years). Among patients with ADHD, MPH use significantly increased the risk of developing any psychotic disorder (aHR, 1.20; 95% CI, 1.04-1.40), but did not increase the risk of developing schizophrenia (aHR, 1.16; 95% CI, 0.94-1.42). The results indicated that previous diagnoses of ADHD are a powerful indicator of developing psychotic disorders. Nevertheless, the specific mechanisms of the relationships between ADHD, MPH use and psychotic disorders need further elucidation in future clinical studies.

The aetiology of schizophrenia: what have the Swedish Medical Registers taught us?

OBJECTIVE

To review the last thirty years of studies that, using Swedish population registers, have added to our understanding of the aetiology of schizophrenia SAMPLE INCLUDED/METHODS: A literature search was performed to systematically review all studies that using Swedish Population based registers have investigated the aetiology of schizophrenia. Key authors in the field, predominately from Swedish institutions, were additionally contacted and key journals hand searched, for missing references. A quality assessment methodological review was then conducted on each study. Data was extracted and tabulated on identified aetiological themes

RESULTS

61 articles were included corresponding to 10 identified aetiological themes. Although the majority of included studies were retrospective cohort studies, case control studies were also included where they used population based registers. Confirming previous research, schizophrenia was found to have a multi-factorial aetiological basis with pregnancy and birth factors, parental age, social adversity, genetics, substance misuse, migration and ethnicity, personality, non-psychiatric co-morbidity, psychiatric history and poor cognitive performance all found to be significantly associated with an increased risk of later schizophrenia.

CONCLUSIONS

Although some difficulties exist in analysing the interplay between each of these factors, the Swedish population registers have added considerably to our understanding of each of the presented individual aetiological themes. The ability to study the whole population over several decades has been particularly useful in determining the timing of exposures.

Behavioral and Genetic Evidence for GIRK Channels in the CNS: Role in Physiology, Pathophysiology, and Drug Addiction

G protein-coupled inwardly rectifying potassium (GIRK) channels are widely expressed throughout the brain and mediate the inhibitory effects of many neurotransmitters. As a result, these channels are important for normal CNS function and have also been implicated in Down syndrome, Parkinson's disease, psychiatric disorders, epilepsy, and drug addiction. Knockout mouse models have provided extensive insight into the significance of GIRK channels under these conditions. This review examines the behavioral and genetic evidence from animal models and genetic association studies in humans linking GIRK channels with CNS disorders. We further explore the possibility that subunit-selective modulators and other advanced research tools will be instrumental in establishing the role of individual GIRK subunits in drug addiction and other relevant CNS diseases and in potentially advancing treatment options for these disorders.

Genetics in child and adolescent psychiatry: methodological advances and conceptual issues

Discovering the genetic basis of early-onset psychiatric disorders has been the aim of intensive research during the last decade. We will first selectively summarize results of genetic research in child and adolescent psychiatry by using examples from different disorders and discuss methodological issues, emerging questions and future directions. In the second part of this review, we will focus on how to link genetic causes of disorders with physiological pathways, discuss the impact of genetic findings on diagnostic systems, prevention and therapeutic interventions. Finally we will highlight some ethical aspects connected to genetic research in child and adolescent psychiatry. Advances in molecular genetic methods have led to insights into the genetic architecture of psychiatric disorders, but not yet provided definite pathways to pathophysiology. If replicated, promising findings from genetic studies might in some cases lead to personalized treatments. On the one hand, knowledge of the genetic basis of disorders may influence diagnostic categories. On the other hand, models also suggest studying the genetic architecture of psychiatric disorders across diagnoses and clinical groups.

Attention-deficit/hyperactivity disorder and risk for substance use disorders in relatives

BACKGROUND

Previous research indicates that attention-deficit/hyperactivity disorder (ADHD) is highly associated with substance use disorders (SUD). However, these studies have failed to clarify the nature of the overlap. The main aim of this study was to explore whether the overlap between ADHD and SUD could be explained by shared genetic and environmental factors or by harmful effects of ADHD medication.

METHODS

We employed a matched cohort design across different levels of family relatedness recorded from 1973-2009. By linking longitudinal Swedish national registers, 62,015 ADHD probands and first-degree and second-degree relatives were identified and matched 1:10 with control subjects without ADHD and their corresponding relatives. Any record of SUD was defined by discharge diagnoses of the International Classification of Diseases or a purchase of any drug used in the treatment of SUD.

RESULTS

First-degree relatives of ADHD probands were at elevated risk for SUD (odds ratios 2.2 and 1.8) compared with relatives of control subjects. The corresponding relative risk in second-degree relatives was substantially lower (odd ratios 1.4 and 1.4). The familial aggregation patterns remained similar for first-degree and second-degree relatives after excluding individuals with coexisting disorders such as schizophrenia, bipolar disorder, depression, and conduct disorder.

CONCLUSIONS

Our findings suggest that the co-occurrence of ADHD and SUD is due to genetic factors shared between the two disorders, rather than to a general propensity for psychiatric disorders or harmful effects of ADHD medication.

Raising attention to attention deficit hyperactivity disorder in schizophrenia

Schizophrenia and attention deficit hyperactivity disorder (ADHD) are two psychiatric disorders with a negative impact on quality of life of individuals affected. Although they are classified into distinct disorders categories, attentional dysfunction is considered as a core feature in both conditions, either at the clinical then pathophysiological level. Beyond the obvious clinical overlap between these disorders, the Research Domain Criteria approach might offer an interesting perspective for disentangling common circuits underpinning both disorders. Hence, we review evidences regarding the overlap between schizophrenia and ADHD, at the clinical level, and at the level of underlying brain mechanisms. The evidence regarding the influence of environmental risk factors in the emergence of both disorders, and their developmental trajectories is also reviewed. Among these, we will try to elucidate the complex relationship between stimulants use and psychotic symptoms, discussing the potential role of ADHD medication in inducing psychosis or in exacerbating it. We aim that, taken together, these findings may promote further investigation with important implications both for clinicians and research. In fact, considering the amounting evidence on the overlap between schizophrenia and ADHD, the delineation of their boundaries might help in the decision for diagnosis and treatment. Moreover, it may help to promote interventions focused on the prevention of both schizophrenia and ADHD, by the reduction of recognized environmental risk factors.

Bipolar disorder and its relation to major psychiatric disorders: a family-based study in the Swedish population

OBJECTIVES

Bipolar disorder (BPD) shares genetic components with other psychiatric disorders; however, uncertainty remains about where in the psychiatric spectra BPD falls. To understand the etiology of BPD, we studied the familial aggregation of BPD and co-aggregation between BPD and schizophrenia, depression, anxiety disorders, attention-deficit hyperactivity disorder, drug abuse, personality disorders, and autism spectrum disorders.

METHODS

A population-based cohort was created by linking several Swedish national registers. A total of 54,723 individuals with BPD were identified among 8,141,033 offspring from 4,149,748 nuclear families. The relative risk of BPD in relatives and the co-occurrence of other psychiatric disorders in patients with BPD and their relatives were compared to those of matched-population controls. Structural equation modeling was used to estimate the heritability and tetrachoric correlation.

RESULTS

The familial risks for relatives of BPD probands were 5.8-7.9 in first-degree relatives, and decreased with genetic distance. Co-occurrence risks for other psychiatric disorders were 9.7-22.9 in individuals with BPD and 1.7-2.8 in full siblings of BPD probands. Heritability for BPD was estimated at 58%. The correlations between BPD and other psychiatric disorders were considerable (0.37-0.62) and primarily due to genetic effects. The correlation with depression was the highest (0.62), and was 0.44 for schizophrenia.

CONCLUSIONS

The high familial risks provide evidence that genetic factors play an important role in the etiology of BPD, and the shared genetic determinants suggest pleiotropic effects across different psychiatric disorders. Results also indicate that BPD is in both the mood and psychotic spectra, but possibly more closely related to mood disorders.

Psychotic disorders comorbid with attention-deficit hyperactivity disorder: an important knowledge gap

Psychotic disorders (PDs) and attention-deficit hyperactivity disorder (ADHD) are frequently comorbid. Clinicians are often reticent to treat ADHD in patients with psychosis, fearing that psychostimulants will worsen psychotic symptoms. Advances in neurobiology have challenged the simplistic dichotomy where PD is considered a disorder of high dopamine (DA), treated by DA antagonists, and ADHD a disorder of low DA, treated by DA agonists. In our paper, we review the literature on comorbid ADHD and psychosis. Treating ADHD with psychostimulants may be considered in patients with PD who have been stabilized with antipsychotics (APs). Not treating ADHD may have consequences because ADHD may predispose patients to drug abuse, which further increases the risk of PD. Nevertheless, more systematic studies are needed as there remains some uncertainty on the combined use of APs and psychostimulants in comorbid PD and ADHD.

Early stages of pediatric bipolar disorder: retrospective analysis of a Czech inpatient sample

BACKGROUND

Approximately 30%-60% of adults diagnosed with bipolar disorder (BD) report onset between the ages 15 and 19 years; however, a correct diagnosis is often delayed by several years. Therefore, investigations of the early features of BD are important for adequately understanding the prodromal stages of the illness.

METHODS

A complete review of the medical records of 46 children and adolescents who were hospitalized for BD at two psychiatric teaching centers in Prague, Czech Republic was performed. Frequency of BD in all inpatients, age of symptom onset, phenomenology of mood episodes, lifetime psychiatric comorbidity, differences between very-early-onset (<13 years of age) and early-onset patients (13-18 years), and differences between the offspring of parents with and without BD were analyzed.

RESULTS

The sample represents 0.83% of the total number of inpatients (n=5,483) admitted during the study period at both centers. BD often started with depression (56%), followed by hypomania (24%) and mixed episodes (20%). The average age during the first mood episode was 14.9 years (14.6 years for depression and 15.6 years for hypomania). Seven children (15%) experienced their first mood episode before age 13 years (very early onset). Traumatic events, first-degree relatives with mood disorders, and attention deficit hyperactivity disorder were significantly more frequent in the very-early-onset group vs the early-onset group (13-18 years) (P≤0.05). The offspring of bipolar parents were significantly younger at the onset of the first mood episode (13.2 vs 15.4 years; P=0.02) and when experiencing the first mania compared to the offspring of non-BD parents (14.3 vs 15.9 years; P=0.03). Anxiety disorders, substance abuse, specific learning disabilities, and attention deficit hyperactivity disorder were the most frequent lifetime comorbid conditions.

CONCLUSION

Clinicians must be aware of the potential for childhood BD onset in patients who suffer from recurrent depression, who have first-degree relatives with BD, and who have experienced severe psychosocial stressors.

Psychosis in adulthood is associated with high rates of ADHD and CD problems during childhood

BACKGROUND

Patients diagnosed with schizophrenia display poor premorbid adjustment (PPA) in half of the cases. Attention deficit/hyperactivity disorder (ADHD) and conduct disorder (CD) are common child psychiatric disorders. These two facts have not previously been linked in the literature.

AIMS

To determine the prevalence of ADHD/CD problems retrospectively among patients with psychoses, and whether and to what extent the high frequency of substance abuse problems among such patients may be linked to ADHD/CD problems.

METHOD

ADHD and CD problems/diagnoses were retrospectively recorded in one forensic (n = 149) and two non-forensic samples (n = 98 and n = 231) of patients with a psychotic illness: schizophrenia, bipolar or other, excluding drug-induced psychoses.

RESULTS

ADHD and CD were much more common among the patients than in the general population-the odds ratio was estimated to be greater than 5. There was no significant difference in this respect between forensic and non-forensic patients. Substance abuse was common, but substantially more common among patients with premorbid ADHD/CD problems.

CONCLUSIONS

Previous views regarding PPA among patients with a psychotic illness may reflect an association between childhood ADHD/CD and later psychosis. The nature of this association remains uncertain: two disorders sharing some generative mechanisms or one disorder with two main clinical manifestations. Childhood ADHD and particularly CD problems contribute to the high frequency of substance abuse in such groups.

Maternal age at childbirth and risk for ADHD in offspring: a population-based cohort study

BACKGROUND

Women who give birth at younger ages (e.g. teenage mothers) are more likely to have children who exhibit behaviour problems, such as attention-deficit/hyperactivity disorder (ADHD). However, it is not clear whether young maternal age is causally associated with poor offspring outcomes or confounded by familial factors.

METHODS

The association between early maternal age at childbirth and offspring ADHD was studied using data from Swedish national registers. The sample included all children born in Sweden between 1988 and 2003 (N = 1 495 543), including 30 674 children with ADHD. We used sibling- and cousin-comparisons to control for unmeasured genetic and environmental confounding. Further, we used a children-of-siblings model to quantify the genetic and environmental contribution to the association between maternal age and offspring ADHD.

RESULTS

Maternal age at first birth (MAFB) was associated with offspring ADHD. Teenage childbirth (<20 years) was associated with 78% increased risk of ADHD. The association attenuated in cousin-comparison, suggesting unmeasured familial confounding. The children-of-siblings model indicated that the association between MAFB and ADHD was mainly explained by genetic confounding.

CONCLUSIONS

All children born to mothers who bore their first child early in their reproductive lives were at increased risk of ADHD. The association was mainly explained by genetic factors transmitted from mothers to their offspring that contribute to both age at childbirth and ADHD in offspring. Our results highlight the importance of using family-based designs to understand how early life circumstances affect child development.

Research review: Polygenic methods and their application to psychiatric traits

BACKGROUND

Despite evidence from twin and family studies for an important contribution of genetic factors to both childhood and adult onset psychiatric disorders, identifying robustly associated specific DNA variants has proved challenging. In the pregenomics era the genetic architecture (number, frequency and effect size of risk variants) of complex genetic disorders was unknown. Empirical evidence for the genetic architecture of psychiatric disorders is emerging from the genetic studies of the last 5 years.

METHODS AND SCOPE

We review the methods investigating the polygenic nature of complex disorders. We provide mini-guides to genomic profile (or polygenic) risk scoring and to estimation of variance (or heritability) from common SNPs; a glossary of key terms is also provided. We review results of applications of the methods to psychiatric disorders and related traits and consider how these methods inform on missing heritability, hidden heritability and still-missing heritability.

FINDINGS

Genome-wide genotyping and sequencing studies are providing evidence that psychiatric disorders are truly polygenic, that is they have a genetic architecture of many genetic variants, including risk variants that are both common and rare in the population. Sample sizes published to date are mostly underpowered to detect effect sizes of the magnitude presented by nature, and these effect sizes may be constrained by the biological validity of the diagnostic constructs.

CONCLUSIONS

Increasing the sample size for genome wide association studies of psychiatric disorders will lead to the identification of more associated genetic variants, as already found for schizophrenia. These loci provide the starting point of functional analyses that might eventually lead to new prevention and treatment options and to improved biological validity of diagnostic constructs. Polygenic analyses will contribute further to our understanding of complex genetic traits as sample sizes increase and as sample resources become richer in phenotypic descriptors, both in terms of clinical symptoms and of nongenetic risk factors.

Differential diagnosis, comorbidity, and treatment of attention-deficit/hyperactivity disorder in relation to bipolar disorder or borderline personality disorder in adults

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) in adults can resemble, and often co-occurs with, bipolar disorder (BD) and borderline personality disorder (BPD). This can lead to mistaken diagnoses and ineffective treatment, resulting in potentially serious adverse consequences. All three conditions can substantially impair well-being and functioning, while BD and BPD are associated with suicidality.

OBJECTIVES

To update clinicians on the overlap and differences in the symptomatology of ADHD versus BD and BPD in adults; differential diagnosis of ADHD from BD and BPD in adults; and diagnosis and treatment of adults with comorbid ADHD-BD or ADHD-BPD.

METHODS

We searched four databases, referred to the new Diagnostic and Statistical Manual of Mental Disorders, 5th edition, used other relevant literature, and referred to our own clinical experience.

RESULTS

ADHD coexists in ∼20% of adults with BD or BPD. BD is episodic, with periods of normal mood although not necessarily function. In patients with comorbid ADHD-BD, ADHD symptoms are apparent between BD episodes. BPD and ADHD are associated with chronic trait-like symptoms and impairments. Overlapping symptoms of BPD and ADHD include impulsivity and emotional dysregulation. Symptoms of BPD but not ADHD include frantically avoiding real/imagined abandonment, suicidal behavior, self-harm, chronic feelings of emptiness, and stress-related paranoia/severe dissociation. Consensus expert opinion recommends that BD episodes should be treated first in patients with comorbid ADHD, and these patients may need treatment in stages (e.g. mood stabilizer[s], then a stimulant/atomoxetine). Data is scarce and mixed about whether stimulants or atomoxetine exacerbate mania in comorbid ADHD-BD. BPD is primarily treated with psychotherapy. Principles of dialectical behavioral treatment for BPD may successfully treat ADHD in adults, as an adjunct to medication. No fully evidence-based pharmacotherapy exists for core BPD symptoms, although some medications may be effective for individual symptom domains, e.g. impulsivity (shared by ADHD and BPD). In our experience, treatment of ADHD should be considered when treating comorbid personality disorders.

CONCLUSIONS

It is important to accurately diagnose ADHD, BD, and BPD to ensure correct targeting of treatments and improvements in patient outcomes. However, there is a shortage of data about treatment of adults with ADHD and comorbid BD or BPD.

The heritability of clinically diagnosed attention deficit hyperactivity disorder across the lifespan

BACKGROUND

No prior twin study has explored the heritability of clinically diagnosed attention deficit hyperactivity disorder (ADHD). Such studies are needed to resolve conflicting results regarding the importance of genetic effects for ADHD in adults. We aimed to estimate the relative contribution of genetic and environmental influences for clinically diagnosed ADHD across the lifespan with a specific focus on ADHD in adults.

METHOD

Information on zygosity and sex was obtained from 59514 twins born between 1959 and 2001 included in the nationwide population-based Swedish Twin Registry. Clinical data for ADHD diagnoses (i.e. stimulant or non-stimulant medication for ADHD) were obtained from the Swedish Prescribed Drug Register (PDR) and from the National Patient Register (i.e. ICD-10 diagnosis of ADHD). Twin methods were applied to clinical data of ADHD diagnoses using structural equation modeling with monozygotic (MZ) and dizygotic (DZ) twins.

RESULTS

The best-fitting model revealed a high heritability of ADHD [0.88, 95% confidence interval (CI) 0.83-0.92] for the entire sample. However, shared environmental effects were non-significant and of minimal importance. The heritability of ADHD in adults was also substantial (0.72, 95% CI 0.56-0.84).

CONCLUSIONS

This study shows that the heritability of clinically diagnosed ADHD is high across the lifespan. Our finding of high heritability for clinically diagnosed ADHD in adults indicates that the previous reports of low heritability are best explained by rater effects, and that gene-identification studies of ADHD in adults need to consider pervasiveness (e.g. multiple raters) and developmentally (e.g. childhood-onset criteria) informative data.

Mediators of the association between parental severe mental illness and offspring neurodevelopmental problems

PURPOSE

Parental severe mental illness (SMI) is associated with an increased risk of offspring autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). We conducted a study to examine the extent to which risk of preterm birth, low birth weight, and small for gestational age mediated this association.

METHODS

We obtained data on offspring born 1992-2001 in Sweden (n = 870,017) through the linkage of multiple population-based registers. We used logistic and Cox regression to assess the associations between parental SMI, adverse pregnancy outcomes, and offspring ASD and ADHD, as well as tested whether adverse pregnancy outcomes served as mediators.

RESULTS

After controlling for measured covariates, maternal and paternal SMI were associated with an increased risk for preterm birth, low birth weight, and gestational age, and for offspring ASD and ADHD. These pregnancy outcomes were also associated with an increased risk of ASD and ADHD. We found that pregnancy outcomes did not mediate the association between parental SMI and offspring ASD and ADHD, as there was no substantial change in magnitude of the risk estimates after controlling for pregnancy outcomes.

CONCLUSIONS

Parental SMI and adverse pregnancy outcomes appear to be independent risk factors for offspring ASD and ADHD.

Genomic insights into the overlap between psychiatric disorders: implications for research and clinical practice

Psychiatric disorders such as schizophrenia, bipolar disorder, major depressive disorder, attention-deficit/hyperactivity disorder and autism spectrum disorder are common and result in significant morbidity and mortality. Although currently classified into distinct disorder categories, they show clinical overlap and familial co-aggregation, and share genetic risk factors. Recent advances in psychiatric genomics have provided insight into the potential mechanisms underlying the overlap between these disorders, implicating genes involved in neurodevelopment, synaptic plasticity, learning and memory. Furthermore, evidence from copy number variant, exome sequencing and genome-wide association studies supports a gradient of neurodevelopmental psychopathology indexed by mutational load or mutational severity, and cognitive impairment. These findings have important implications for psychiatric research, highlighting the need for new approaches to stratifying patients for research. They also point the way for work aiming to advance our understanding of the pathways from genotype to clinical phenotype, which will be required in order to inform new classification systems and to develop novel therapeutic strategies.

Genetic variation associated with euphorigenic effects of d-amphetamine is associated with diminished risk for schizophrenia and attention deficit hyperactivity disorder

Here, we extended our findings from a genome-wide association study of the euphoric response to d-amphetamine in healthy human volunteers by identifying enrichment between SNPs associated with response to d-amphetamine and SNPs associated with psychiatric disorders. We found that SNPs nominally associated (P ≤ 0.05 and P ≤ 0.01) with schizophrenia and attention deficit hyperactivity disorder were also nominally associated with d-amphetamine response. Furthermore, we found that the source of this enrichment was an excess of alleles that increased sensitivity to the euphoric effects of d-amphetamine and decreased susceptibility to schizophrenia and attention deficit hyperactivity disorder. In contrast, three negative control phenotypes (height, inflammatory bowel disease, and Parkinson disease) did not show this enrichment. Taken together, our results suggest that alleles identified using an acute challenge with a dopaminergic drug in healthy individuals can be used to identify alleles that confer risk for psychiatric disorders commonly treated with dopaminergic agonists and antagonists. More importantly, our results show the use of the enrichment approach as an alternative to stringent standards for genome-wide significance and suggest a relatively novel approach to the analysis of small cohorts in which intermediate phenotypes have been measured.

Serious transport accidents in adults with attention-deficit/hyperactivity disorder and the effect of medication: a population-based study

IMPORTANCE

Studies have shown that attention-deficit/hyperactivity disorder (ADHD) is associated with transport accidents, but the magnitude of the association remains unclear. Most important, it is also unclear whether ADHD medication reduces this risk.

OBJECTIVES

To estimate the association between ADHD and the risk of serious transport accidents and to explore the extent to which ADHD medication influences this risk among patients with ADHD.

DESIGN, SETTING, AND PARTICIPANTS

In total, 17,408 patients with a diagnosis of ADHD were observed from January 1, 2006, through December 31, 2009, for serious transport accidents documented in Swedish national registers. The association between ADHD and accidents was estimated with Cox proportional hazards regression. To study the effect of ADHD medication, we used stratified Cox regression to compare the risk of accidents during the medication period with the risk during the nonmedication period within the same patients.

MAIN OUTCOMES AND MEASURES

Serious transport accident, identified as an emergency hospital visit or death due to transport accident.

RESULTS

Compared with individuals without ADHD, male patients with ADHD (adjusted hazard ratio, 1.47; 95% CI, 1.32-1.63) and female patients with ADHD (1.45; 1.24-1.71) had an increased risk of serious transport accidents. In male patients with ADHD, medication was associated with a 58% risk reduction (hazard ratio, 0.42; 95% CI, 0.23-0.75), but there was no statistically significant association in female patients. Estimates of the population-attributable fractions suggested that 41% to 49% of the accidents in male patients with ADHD could have been avoided if they had been receiving treatment during the entire follow-up.

CONCLUSIONS AND RELEVANCE

Attention-deficit/hyperactivity disorder is associated with an increased risk of serious transport accidents, and this risk seems to be possibly reduced by ADHD medication, at least among male patients. This should lead to increased awareness among clinicians and patients of the association between serious transport accidents and ADHD medication.

Maternal pre-pregnancy body mass index and offspring attention deficit hyperactivity disorder: a population-based cohort study using a sibling-comparison design

BACKGROUND

High maternal pre-pregnancy body mass index (BMI) is associated with increased risk of offspring attention deficit hyperactivity disorder (ADHD). However, the role of unmeasured familial confounding for this association remains unclear.

METHODS

We conducted a population-based cohort study via linkage of Swedish national and regional registers to investigate maternal pre-pregnancy BMI (underweight: BMI <18.5; overweight: 25≤ BMI <30; obesity: BMI ≥30) in relation to offspring ADHD. We followed 673 632 individuals born in Sweden between 1992 and 2000, with prospectively collected information on maternal pre-pregnancy BMI, until they received an ADHD diagnosis or ADHD medication, death, emigration or 31 December 2009. Hazard ratios (HRs) were estimated by Cox proportional hazards models. Stratified Cox proportional hazards models were applied to data on full siblings to control for unmeasured familial confounding.

RESULTS

At the population level, pre-pregnancy overweight/obesity was associated with increased risk of offspring ADHD (HR(overweight) = 1.23, 95% CI = 1.18-1.27, P = 0.01; HR(obesity) = 1.64, 95% CI = 1.57-1.73, P = 0.01), after adjustment for measured covariates. In full sibling comparisons, however, previously observed associations no longer remained (HR(overweight) = 0.98, 95% CI = 0.83-1.16, P = 0.82; HR(obesity) = 1.15, 95% CI = 0.85-1.56, P = 0.38).

CONCLUSIONS

The results suggested that the association between maternal pre-pregnancy overweight/obesity and offspring ADHD could be ascribed to unmeasured familial confounding.

Familial confounding of the association between maternal smoking during pregnancy and ADHD in offspring

BACKGROUND

Maternal Smoking During Pregnancy (SDP) has consistently been associated with increased risk of attention-deficit/hyperactivity disorder (ADHD) in offspring, but recent studies indicate that this association might be due to unmeasured familial confounding.

METHODS

A total of 813,030 individuals born in Sweden between 1992 and 2000 were included in this nationwide population-based cohort study. Data on maternal SDP and ADHD diagnosis were obtained from national registers and patients were followed up from the age of 3 to the end of 2009. Hazard Ratios (HRs) were estimated using stratified Cox regression models. Cousin and sibling data were used to control for unmeasured familial confounding.

RESULTS

At the population level maternal SDP predicted ADHD in offspring (HR(ModerateSDP) = 1.89; HR(HighSDP)= 2.50). This estimate gradually attenuated toward the null when adjusting for measured confounders (HR(ModerateSDP)= 1.62; HR(HighSDP)= 2.04), unmeasured confounders shared within the extended family (i.e., cousin comparison) (HR(ModerateSDP)= 1.45; HR(HighSDP)= 1.69), and unmeasured confounders within the nuclear family (i.e., sibling comparison) (HR(ModerateSDP)= 0.88; HR(HighSDP)= 0.84).

CONCLUSIONS

Our results suggest that the association between maternal SDP and offspring ADHD are due to unmeasured familial confounding.

Preterm birth and mortality and morbidity: a population-based quasi-experimental study

IMPORTANCE

Preterm birth is associated with increased mortality and morbidity. However, previous studies have been unable to rigorously examine whether confounding factors cause these associations rather than the harmful effects of being born preterm.

OBJECTIVE

To estimate the extent to which the associations between early gestational age and offspring mortality and morbidity are the result of confounding factors by using a quasi-experimental design, the sibling-comparison approach, and by controlling for statistical covariates that varied within families.

DESIGN, SETTING, AND PARTICIPANTS

A population-based cohort study, combining Swedish registries to identify all individuals born in Sweden from 1973 to 2008 (3,300,708 offspring of 1,736,735 mothers) and link them with multiple outcomes.

MAIN OUTCOMES AND MEASURES

Offspring mortality (during infancy and throughout young adulthood) and psychiatric (psychotic or bipolar disorder, autism, attention-deficit/hyperactivity disorder, suicide attempts, substance use, and criminality), academic (failing grades and educational attainment), and social (partnering, parenthood, low income, and social welfare benefits) outcomes through 2009.

RESULTS

In the population, there was a dose-response relationship between early gestation and the outcome measures. For example, extreme preterm birth (23-27 weeks of gestation) was associated with infant mortality (odds ratio, 288.1; 95% CI, 271.7-305.5), autism (hazard ratio [HR], 3.2; 95% CI, 2.6-4.0), low educational attainment (HR, 1.7; 1.5-2.0), and social welfare benefits (HR, 1.3; 1.2-1.5) compared with offspring born at term. The associations between early gestation and mortality and psychiatric morbidity generally were robust when comparing differentially exposed siblings and controlling for statistical covariates, whereas the associations with academic and some social problems were greatly or completely attenuated in the fixed-effects models.

CONCLUSIONS AND RELEVANCE

The mechanisms responsible for the associations between preterm birth and mortality and morbidity are outcome-specific. Associations between preterm birth and mortality and psychiatric morbidity are largely independent of shared familial confounds and measured covariates, consistent with a causal inference. However, some associations, particularly predicting suicide attempt, educational attainment, and social welfare benefits, are the result of confounding factors. The findings emphasize the importance of both reducing preterm birth and providing wraparound services to all siblings in families with an offspring born preterm.

Genomics and the classification of mental illness: focus on broader categories

Coinciding with the release of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, two recently published molecular genetics analyses suggest large overlaps in genetic liability to schizophrenia, bipolar disorder and major depressive disorder. This indicates that a broader category of severe mental illness may be an important target for future large-scale etiological and therapeutic investigations. Studies of patient groups not restricted to current diagnostic categories may lead to a genetically informed nosology.

Attention-deficit hyperactivity disorder and the shifting sands of psychiatric nosology

Larsson et al provide epidemiological evidence for a genetic association between attention-deficit hyperactivity disorder (ADHD) and both bipolar disorder and schizophrenia and Hamshere and colleagues confirm the latter association with genome-wide data. Although a genetic link between ADHD and bipolar disorder has been hypothesised for over a decade, the association with schizophrenia fills a notable gap in the literature. This editorial discusses the implications of these findings for clinicians, who must address psychiatric comorbidity in their treatment formulations, and researchers who are learning that the discrete categorical diagnoses of our diagnostic systems may not be up to the task of clarifying the causes and cures of psychopathology.