The use of genetic epidemiology to guide classification in child and adult psychopathology

Primate Models as a Translational Tool for Understanding Prenatal Origins of Neurodevelopmental Disorders Associated With Maternal Infection

Pregnant women represent a uniquely vulnerable population during an infectious disease outbreak, such as the COVID-19 pandemic. Although we are at the early stages of understanding the specific impact of SARS-CoV-2 exposure during pregnancy, mounting epidemiological evidence strongly supports a link between exposure to a variety of maternal infections and an increased risk for offspring neurodevelopmental disorders. Inflammatory biomarkers identified from archived or prospectively collected maternal biospecimens suggest that the maternal immune response is the critical link between infection during pregnancy and altered offspring neurodevelopment. This maternal immune activation (MIA) hypothesis has been tested in animal models by artificially activating the immune system during pregnancy and evaluating the neurodevelopmental consequences in MIA-exposed offspring. Although the vast majority of MIA model research is carried out in rodents, the nonhuman primate model has emerged in recent years as an important translational tool. In this review, we briefly summarize human epidemiological studies that have prompted the development of translationally relevant MIA models. We then highlight notable similarities between humans and nonhuman primates, including placental structure, pregnancy physiology, gestational timelines, and offspring neurodevelopmental stages, that provide an opportunity to explore the MIA hypothesis in species more closely related to humans. Finally, we provide a comprehensive review of neurodevelopmental alterations reported in current nonhuman primate models of maternal infection and discuss future directions for this promising area of research.

Familial aggregation of anxiety disorder subtypes and anxious temperament in the NIMH Family Study of Affective Spectrum Disorders

BACKGROUND

Evidence from family and twin studies suggests that mood and anxiety disorders, and related temperamental factors may share common etiologic factors. We examine the familial aggregation and coaggregation of anxiety disorder subtypes and anxiety-related temperamental traits, and their association with mood disorders.

METHODS

A total of 477 probands and 549 first-degree adult relatives from a large community based family study of affective spectrum disorders completed semi-structured diagnostic interviews and self-reported assessments of temperamental traits including: negative affectivity on the 'Positive and Negative Affect Schedule' (PANAS), neuroticism anxiety on the 'Zuckerman-Kuhlman Personality Questionnaire' (ZKPQ), and anxiety sensitivity on the 'Anxiety Sensitivity Index' (ASI).

RESULTS

The anxiety-related temperamental traits of negative affectivity, neuroticism anxiety and anxiety sensitivity had significant familial specificity, even after controlling for comorbid mood and anxiety disorders in probands and relatives. Yet, these traits in probands did not predict anxiety disorders in relatives. Although some anxiety subtypes were familial, there were no longer familial links between anxiety disorder subtypes (generalized anxiety disorder, social anxiety or panic disorder) after controlling for mood disorder subtypes in probands and relatives.

LIMITATIONS

Cross-sectional interviews were used to estimate disorders, and self-report measures were used for temperamental traits.

CONCLUSIONS

These results confirm previous research regarding familial overlap between anxiety subtypes and mood disorders, however their shared liability cannot be fully explained by anxiety-related temperamental traits. These findings suggest that anxiety-related temperamental traits may indicate a vulnerability for mood and anxiety disorders or a potential consequence of these conditions.

Role of environmental factors and epigenetics in autism spectrum disorders

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder thought to be caused by predisposing high-risk genes that may be altered during the early development by environmental factors. The impact of maternal challenges during pregnancy on the prevalence of ASD has been widely studied in clinical and animal studies. Here, we review some clinical and pre-clinical evidence that links environmental factors (i.e., infection, air pollution, pesticides, valproic acid and folic acid) and the risk of ASD. Additionally, certain prenatal environmental challenges such as the valproate and folate prenatal exposures allow us to study mechanisms possibly linked to the etiology of ASD, for instance the epigenetic processes. These mechanistic pathways are also presented and discussed in this chapter.

Psychiatric neuroimaging: Joining forces with epidemiology

Severe mental illnesses such as schizophrenia and mood disorders have a major impact on public health. Disease prevalence and phenotypic expression are the products of environment and gene interactions. However, our incomplete understanding of their aetiology and pathophysiology thwarts primary prevention and early diagnosis and limits the effective application of currently available treatments as well as the development of novel therapeutic approaches. Neuroimaging can provide detailed in vivo information about the biological mechanisms underpinning the relationship between genetic variation and clinical phenotypes or response to treatment. However, the biological complexity of severe mental illness results from unknown or unpredictable interactions between multiple genetic and environmental factors, many of which have only been partially identified. We propose that the use of epidemiological principles to neuroimaging research is a necessary next step in psychiatric research. Because of the complexity of mental disorders and the multiple risk factors involved only the use of large epidemiologically defined samples will allow us to study the broader spectrum of psychopathology, including sub-threshold presentation and explore pathophysiological processes and the functional impact of genetic and non-genetic factors on the onset and persistence of psychopathology.

Translational opportunities in the prenatal immune environment: Promises and limitations of the maternal immune activation model

The prenatal environment, and in particular, the maternal-fetal immune environment, has emerged as a targeted area of research for central nervous system (CNS) diseases with neurodevelopmental origins. Converging evidence from both clinical and preclinical research indicates that changes in the maternal gestational immune environment can alter fetal brain development and increase the risk for certain neurodevelopmental disorders. Here we focus on the translational potential of one prenatal animal model - the maternal immune activation (MIA) model. This model stems from the observation that a subset of pregnant women who are exposed to infection during pregnancy have an increased risk of giving birth to a child who will later be diagnosed with a neurodevelopmental disorder, such as autism spectrum disorder (ASD) or schizophrenia (SZ). The preclinical MIA model provides a system in which to explore causal relationships, identify underlying neurobiological mechanisms, and, ultimately, develop novel therapeutic interventions and preventative strategies. In this review, we will highlight converging evidence from clinical and preclinical research that links changes in the maternal-fetal immune environment with lasting changes in offspring brain and behavioral development. We will then explore the promises and limitations of the MIA model as a translational tool to develop novel therapeutic interventions. As the translational potential of the MIA model has been the focus of several excellent review articles, here we will focus on what is perhaps the least well developed area of MIA model research - novel preventative strategies and therapeutic interventions.

Antenatal nutritional supplementation and autism spectrum disorders in the Stockholm youth cohort: population based cohort study

Objective To determine whether nutritional supplementation during pregnancy is associated with a reduced risk of autism spectrum disorder (ASD) with and without intellectual disability in offspring.Design Observational prospective cohort study using multivariable logistic regression, sibling controls, and propensity score matching.Setting Stockholm County, Sweden.Participants 273 107 mother-child pairs identified through population registers. The study sample was restricted to children who were aged 4 to 15 years by the end of follow-up on 31 December 2011 and were born between 1996 and 2007.Exposures Multivitamin, iron, and folic acid supplement use was reported at the first antenatal visit.Main outcome measure Diagnosis of ASD with and without intellectual disability in children determined from register data up to 31 December 2011.Results Prevalence of ASD with intellectual disability was 0.26% (158 cases in 61 934) in the maternal multivitamin use group and 0.48% (430 cases in 90 480) in the no nutritional supplementation use group. Maternal multivitamin use with or without additional iron or folic acid, or both was associated with lower odds of ASD with intellectual disability in the child compared with mothers who did not use multivitamins, iron, and folic acid (odds ratio 0.69, 95% confidence interval 0.57 to 0.84). Similar estimates were found in propensity score matched (0.68, 0.54 to 0.86) and sibling control (0.77, 0.52 to 1.15) matched analyses, though the confidence interval for the latter association included 1.0 and was therefore not statistically significant. There was no consistent evidence that either iron or folic acid use were inversely associated with ASD prevalence.Conclusions Maternal multivitamin supplementation during pregnancy may be inversely associated with ASD with intellectual disability in offspring. Further scrutiny of maternal nutrition and its role in the cause of autism is recommended.

Reading problems and major mental disorders - co-occurrences and familial overlaps in a Swedish nationwide cohort

Reading problems often co-occur with ADHD and conduct disorder. However, the patterns of co-occurrence and familial overlap between reading problems and other psychiatric disorders have not been systematically explored. We conducted a register-based cohort study including 8719 individuals with reading problems and their siblings, along with matched comparison individuals. Conditional logistic regressions estimated risks for ADHD, autism, obsessive-compulsive disorder, anorexia nervosa, schizophrenia, bipolar disorder, depression, substance use disorder, and violent/non-violent criminality in individuals with reading problems and their siblings. Diagnoses of psychiatric disorders were physician-assigned and ascertained from the Swedish National Patient Register, and crime convictions from the Swedish National Crime Register. We found that individuals with reading problems had excess risks for all psychiatric disorders (except anorexia nervosa) and criminality, with risk ratios between 1.34 and 4.91. Siblings of individuals with reading problems showed excess risks for ADHD, autism, schizophrenia, bipolar disorder, depression, substance use disorder, and non-violent criminality, with risk ratios between 1.14 and 1.70. In summary, individuals with reading problems had increased risks of virtually all psychiatric disorders, and criminality. The origin of most of these overlaps was familial, in that siblings of individuals with reading problems also had elevated risks of ADHD, autism, schizophrenia, bipolar disorder, depression, substance use disorder, and non-violent criminality. These findings have implications for gene-searching efforts, and suggest that health care practitioners should be alert for signs of psychiatric disorders in families where reading problems exist.

Acute intermittent porphyria: comorbidity and shared familial risks with schizophrenia and bipolar disorder in Sweden

Acute intermittent porphyria (AIP) has been associated with schizophrenia in some studies, but prior research is limited by the absence of comparison populations. Here, we linked Swedish registers to examine the risk of schizophrenia and bipolar disorder in 717 individuals diagnosed with AIP and their first-degree relatives, compared with matched individuals without AIP and their first-degree relatives. Individuals with AIP had a fourfold increased risk of schizophrenia or bipolar disorder. Similarly, relatives of individuals with AIP had double the risk of schizophrenia or bipolar disorder, suggesting that these associations may be as a result of common genetic influences.

Advancing parental age and autism: multifactorial pathways

Converging evidence from epidemiological, genetic, and animal studies supports the hypothesis that advancing parental age, both of the father and mother, increases the risk of autism spectrum disorders (ASD) in offspring. Paternal age has received considerable attention, with whole-genome sequencing studies linking older fathers to higher rates of de novo mutations and increased risk of ASD. The current evidence suggests that the increased risk of ASD in the offspring of older mothers may be related to mechanisms different from those operating in older fathers. Causal pathways probably involve the interaction of multiple risk factors. Although the etiology of ASD is still poorly understood, studies of parental age provide clues into the genetic and environ-mental mechanisms that mediate the risk of ASD.

Etiological overlap between obsessive-compulsive disorder and anorexia nervosa: a longitudinal cohort, multigenerational family and twin study

Obsessive-compulsive disorder (OCD) often co-occurs with anorexia nervosa (AN), a comorbid profile that complicates the clinical management of both conditions. This population-based study aimed to examine patterns of comorbidity, longitudinal risks, shared familial risks and shared genetic factors between OCD and AN at the population level. Participants were individuals with a diagnosis of OCD (N=19,814) or AN (N=8,462) in the Swedish National Patient Register between January 1992 and December 2009; their first-, second- and third-degree relatives; and population-matched (1:10 ratio) unaffected comparison individuals and their relatives. Female twins from the population-based Swedish Twin Register (N=8,550) were also included. Females with OCD had a 16-fold increased risk of having a comorbid diagnosis of AN, whereas males with OCD had a 37-fold increased risk. Longitudinal analyses showed that individuals first diagnosed with OCD had an increased risk for a later diagnosis of AN (risk ratio, RR=3.6), whereas individuals first diagnosed with AN had an even greater risk for a later diagnosis of OCD (RR=9.6). These longitudinal risks were about twice as high for males than for females. First- and second-degree relatives of probands with OCD had an increased risk for AN, and the magnitude of this risk tended to increase with the degree of genetic relatedness. Bivariate twin models revealed a moderate but significant degree of genetic overlap between self-reported OCD and AN diagnoses (ra =0.52, 95% CI: 0.26-0.81), but most of the genetic variance was disorder-specific. The moderately high genetic correlation supports the idea that this frequently observed comorbid pattern is at least in part due to shared genetic factors, though disorder-specific factors are more important. These results have implications for current gene-searching efforts and for clinical practice.

Obsessive-Compulsive Disorder, Psychosis, and Bipolarity: A Longitudinal Cohort and Multigenerational Family Study

Obsessive-compulsive disorder (OCD) often co-occurs with psychotic and bipolar disorders; this comorbidity complicates the clinical management of these conditions. In this population-based longitudinal and multigenerational family study, we examined the patterns of comorbidity, longitudinal risks, and shared familial risks between these disorders. Participants were individuals with a diagnosis of OCD (n = 19,814), schizophrenia (n = 58,336), bipolar disorder (n = 48,180), and schizoaffective disorder (n = 14,904) included in the Swedish Patient Register between January 1969 and December 2009; their first-, second-, and third-degree relatives; and population-matched (1:10 ratio) unaffected comparison individuals and their relatives. The Swedish Prescribed Drug Register was used to control for the potential effect of medication in the longitudinal analyses. Individuals with OCD had a 12-fold increased risk of having a comorbid diagnosis of schizophrenia and a 13-fold increased risk of bipolar disorder and schizoaffective disorder. Longitudinal analyses showed that individuals first diagnosed with OCD had an increased risk for later diagnosis of all other disorders, and vice versa. The risk of bipolar disorder was reduced, but not eliminated, when the use of selective serotonin reuptake inhibitors was adjusted for. OCD-unaffected first-, second-, and third-degree relatives of probands with OCD had a significantly increased risk for all 3 disorders; the magnitude of this risk decreased as the genetic distance increased. We conclude that OCD is etiologically related to both schizophrenia spectrum and bipolar disorders. The results have implications for current gene-searching efforts and for clinical practice.

The association between Darier disease, bipolar disorder, and schizophrenia revisited: a population-based family study

OBJECTIVES

Darier disease is an autosomal dominant skin disorder caused by mutations in the ATPase, Ca++ transporting, cardiac muscle, slow twitch 2 (ATP2A2) gene and previously reported to cosegregate with bipolar disorder and schizophrenia in occasional pedigrees. It is, however, unknown whether these associations exist also in the general population, and the objective of this study was to examine this question.

METHODS

We compared a national sample of individuals with Darier disease and their first-degree relatives with matched unexposed individuals from the general population and their first-degree relatives, respectively. To examine risks for bipolar disorder and schizophrenia, risk ratios and 95% confidence intervals (CIs) were estimated using conditional logistic regressions.

RESULTS

Individuals with Darier disease had a 4.3 times higher risk of being diagnosed with bipolar disorder (95% CI: 2.6-7.3) and a 2.3 times higher risk of being diagnosed with schizophrenia (95% CI: 1.1-5.2) than matched individuals from the general population. Relatives of individuals with Darier disease had a 1.6 times higher risk of having bipolar disorder (95% CI: 1.1-2.5) than relatives of matched individuals from the general population, but no increased risk of schizophrenia (risk ratio = 0.8, 95% CI: 0.4-1.8).

CONCLUSIONS

The association between Darier disease and bipolar disorder is manifest also in the population, and our data suggest that genetic variability within the ATP2A2 gene that causes Darier disease also confers susceptibility for bipolar disorder. The Darier-causing mutations merit additional attention in molecular genetic research on bipolar disorder.

Maternal hospitalization with infection during pregnancy and risk of autism spectrum disorders

Animal models indicate that maternal infection during pregnancy can result in behavioral abnormalities and neuropathologies in offspring. We examined the association between maternal inpatient diagnosis with infection during pregnancy and risk of ASD in a Swedish nationwide register-based birth cohort born 1984-2007 with follow-up through 2011. In total, the sample consisted of 2,371,403 persons with 24,414 ASD cases. Infection during pregnancy was defined from ICD codes. In the sample, 903 mothers of ASD cases (3.7%) had an inpatient diagnosis of infection during pregnancy. Logistic regression models adjusted for a number of covariates yielded odds ratios indicating approximately a 30% increase in ASD risk associated with any inpatient diagnosis of infection. Timing of infection did not appear to influence risk in the total Swedish population, since elevated risk of ASD was associated with infection in all trimesters. In a subsample analysis, infections were associated with greater risk of ASD with intellectual disability than for ASD without intellectual disability. The present study adds to the growing body of evidence, encompassing both animal and human studies, that supports possible immune-mediated mechanisms underlying the etiology of ASD.

Parental age and the risk of autism spectrum disorders: findings from a Swedish population-based cohort

BACKGROUND

The objectives of this study were to examine the independent and dependent associations of maternal and paternal age and risk of offspring autism spectrum disorders (ASD), with and without intellectual disability (ID).

METHODS

The sample consisted of 417 303 Swedish children born 1984-2003. ASD case status (N = 4746) was ascertained using national and regional registers. Smoothing splines in generalized additive models were used to estimate associations of parental age with ASD.

RESULTS

Whereas advancing parental age increased the risk of child ASD, maternal age effects were non-linear and paternal age effects were linear. Compared with mothers at the median age 29 years, those <29 had similar risk, whereas risk increased after age 30, with an odds ratio (OR) of 1.75 [95% (CI): 1.63-1.89] at ages 40-45. For fathers, compared with the median age of 32 years, the OR for ages 55-59 was 1.39 (1.29-1.50). The risk of ASD was greater for older mothers as compared with older fathers. For example, mothers aged 40-45 (≥97.2th percentile) had an estimated 18.63 (95% CI: 17.25-20.01) ASD cases per 1000 births, whereas fathers aged 55-59 (≥99.7th percentile) had 16.35 (95% CI: 15.11-17.58) ASD cases per 1000 births. In analyses stratified by co-parental age, increased risk due to advancing paternal age was evident only with mothers ≤35 years. In contrast, advancing maternal age increased risk regardless of paternal age. Advancing parental age was more strongly associated with ASD with ID, compared with ASD without ID.

CONCLUSIONS

We confirm prior findings that advancing parental age increases risk of ASD, particularly for ASD with ID, in a manner dependent on co-parental age. Although recent attention has emphasized the effects of older fathers on ASD risk, an increase of n years in maternal age has greater implications for ASD risk than a similar increase in paternal age.

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

BACKGROUND

Attention-deficit hyperactivity disorder (ADHD) is associated with bipolar disorder and schizophrenia, and it has been suggested that combined bipolar disorder and ADHD is aetiologically distinct from the pure disorders.

AIMS

To clarify whether ADHD shares genetic and environmental factors with bipolar disorder and schizophrenia.

METHOD

By linking longitudinal Swedish national registers, we identified 61 187 persons with ADHD (the proband group) and their first- and second-degree relatives, and matched them with a control group of people without ADHD and their corresponding relatives. Conditional logistic regression was used to determine the risks of bipolar disorder and schizophrenia in the relatives of the two groups.

RESULTS

First-degree relatives of the ADHD proband group were at increased risk of both bipolar disorder (odds ratio (OR) = 1.84-2.54 for parents, offspring and full siblings) and schizophrenia (OR = 1.71-2.22 for parents, offspring and full siblings). The risks of bipolar disorder and schizophrenia among second-degree relatives were substantially lower than among full siblings.

CONCLUSIONS

These findings suggest that the co-occurrence of ADHD and bipolar disorder as well as ADHD and schizophrenia is due to shared genetic factors, rather than representing completely aetiologically distinct subsyndromes.

Brief report: maternal smoking during pregnancy and autism spectrum disorders

Prenatal exposure to tobacco smoke is suggested as a potential risk factor for autism spectrum disorders (ASD). Previous epidemiological studies of this topic have yielded mixed findings. We performed a case-control study of 3,958 ASD cases and 38,983 controls nested in a large register-based cohort in Sweden. ASD case status was measured using a multisource case ascertainment system. In adjusted results, we found that maternal smoking during pregnancy is not associated with increased risk of ASD regardless of presence or absence of comorbid intellectual disability. Apparent associations were attributable to confounding by sociodemographic characteristics of parents such as education, income, and occupation.

Molecular genetics research in ADHD: ethical considerations concerning patients' benefit and resource allocation

Immense resource allocations have led to great data output in genetic research. Concerning ADHD resources spent on genetic research are less than those spent on clinical research. But there are successful efforts made to increase support for molecular genetics research in ADHD. Concerning genetics no evidence based conclusive results have significant impact on prevention, diagnosis or treatment yet. With regard to ethical aspects like the patients' benefit and limited resources the question arises if it is indicated to think about a new balance of resource allocation between molecular genetics and non-genetics research in ADHD. An ethical reflection was performed focusing on recent genetic studies and reviews based on a selective literature search. There are plausible reasons why genetic research results in ADHD are somehow disappointing for clinical practice so far. Researchers try to overcome these gaps systematically, without knowing what the potential future benefits for the patients might be. Non-genetic diagnostic/therapeutic research may lead to clinically relevant findings within a shorter period of time. On the other hand, non-genetic research in ADHD may be nurtured by genetic approaches. But, with the latter there exist significant risks of harm like stigmatization and concerns regarding data protection. Isolated speeding up resources of genetic research in ADHD seems questionable from an ethical point of view. There is a need to find a new balance of resource allocation between genetic and non-genetic research in ADHD, probably by integrating genetics more systematically into clinical research. A transdisciplinary debate is recommended.

Family history of schizophrenia and bipolar disorder as risk factors for autism

CONTEXT

The clinical and etiologic relation between autism spectrum disorders (ASDs) and schizophrenia is unclear. The degree to which these disorders share a basis in etiology has important implications for clinicians, researchers, and those affected by the disorders.

OBJECTIVE

To determine whether a family history of schizophrenia and/or bipolar disorder is a risk factor for ASD.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a case-control evaluation of histories of schizophrenia or bipolar disorder in first-degree relatives of probands in 3 samples—population registers in Sweden, Stockholm County (in Sweden), and Israel. Probands met criteria for ASD, and affection status of parents and siblings for schizophrenia and bipolar disorder were established.

RESULTS

The presence of schizophrenia in parents was associated with an increased risk for ASD in a Swedish national cohort (odds ratio [OR], 2.9; 95% CI, 2.5-3.4) and a Stockholm County cohort (OR, 2.9; 95% CI, 2.0-4.1). Similarly, schizophrenia in a sibling was associated with an increased risk for ASD in a Swedish national cohort (OR, 2.6; 95% CI, 2.0-3.2) and an Israeli conscription cohort (OR, 12.1; 95% CI, 4.5-32.0). Bipolar disorder showed a similar pattern of associations but of lesser magnitude.

CONCLUSIONS

Findings from these 3 registers along with consistent findings from a similar study in Denmark suggest that ASD, schizophrenia, and bipolar disorder share common etiologic factors.

The structure of autism symptoms as measured by the autism diagnostic observation schedule

The current study tested several competing models of the autism phenotype using data from modules 1 and 3 of the ADOS. Participants included individuals with ASDs aged 3-18 years (N = 1,409) from the AGRE database. Confirmatory factor analyses were performed on total samples and subsamples based on age and level of functioning. Three primary models were tested, including a one-factor model, the DSM-IV model, and the anticipated DSM-V model. Results indicated all models fit similarly. Module 1 ratings yielded better indices of fit across all models and higher inter-factor correlations than Model 3. Model fits were impacted by age and level of functioning. The lack of differentiation between models suggests that the structure of ASD symptoms is complex to measure statistically.

Migration and autism spectrum disorder: population-based study

BACKGROUND

Migration has been implicated as a risk factor for autism, but evidence is limited and inconsistent.

AIMS

To investigate the relationship between parental migration status and risk of autism spectrum disorder, taking into consideration the importance of region of origin, timing of migration and possible discrepancies in associations between autism subtypes.

METHOD

Record-linkage study within the total child population of Stockholm County between 2001 and 2007. Individuals with high- and low-functioning autism were defined as having autism spectrum disorder with and without comorbid intellectual disability, and ascertained via health and habilitation service registers.

RESULTS

In total, 4952 individuals with autism spectrum disorder were identified, comprising 2855 children with high-functioning autism and 2097 children with low-functioning autism. Children of migrant parents were at increased risk of low-functioning autism (odds ratio (OR) = 1.5, 95% CI 1.3-1.7); this risk was highest when parents migrated from regions with a low human development index, and peaked when migration occurred around pregnancy (OR = 2.3, 95% CI 1.7-3.0). A decreased risk of high-functioning autism was observed in children of migrant parents, regardless of area of origin or timing of migration. Parental age, income or obstetric complications did not fully explain any of these associations.

CONCLUSIONS

Environmental factors associated with migration may contribute to the development of autism presenting with comorbid intellectual disability, especially when acting in utero. High- and low-functioning autism may have partly different aetiologies, and should be studied separately.

Autism spectrum disorders in the Stockholm Youth Cohort: design, prevalence and validity

OBJECTIVE

Reports of rising prevalence of autism spectrum disorders (ASD), along with their profound personal and societal burden, emphasize the need of methodologically sound studies to explore their causes and consequences. We here present the design of a large intergenerational resource for ASD research, along with population-based prevalence estimates of ASD and their diagnostic validity.

METHOD

The Stockholm Youth Cohort is a record-linkage study comprising all individuals aged 0-17 years, ever resident in Stockholm County in 2001-2007 (N = 589,114). ASD cases (N = 5,100) were identified using a multisource approach, involving registers covering all pathways to ASD diagnosis and care, and categorized according to co-morbid intellectual disability. Prospectively recorded information on potential determinants and consequences of ASD were retrieved from national and regional health and administrative registers. Case ascertainment was validated through case-note review, and cross validation with co-existing cases in a national twin study.

RESULTS

The 2007 year prevalence of ASD in all children and young people was 11.5 per 1,000 (95% confidence interval 11.2-11.8), with a co-morbid intellectual disability recorded in 42.6% (41.0-44.2) of cases. We found 96.0% (92.0-98.4) of reviewed case-notes being consistent with a diagnosis of ASD, and confirmed ASD in 85.2% (66.2-95.8) of affected twins.

CONCLUSIONS

Findings from this contemporary study accords with recently reported prevalence estimates from Western countries at around 1%, based on valid case ascertainment. The Stockholm Youth Cohort, in light of the availability of extensive information from Sweden's registers, constitutes an important resource for ASD research. On-going work, including collection of biological samples, will enrich the study further.

Maternal smoking during pregnancy and the prevalence of autism spectrum disorders, using data from the autism and developmental disabilities monitoring network

BACKGROUND

Reported associations between gestational tobacco exposure and autism spectrum disorders (ASDs) have been inconsistent.

OBJECTIVE

We estimated the association between maternal smoking during pregnancy and ASDs among children 8 years of age.

METHODS

This population-based case-cohort study included 633,989 children, identified using publicly available birth certificate data, born in 1992, 1994, 1996, and 1998 from parts of 11 U.S. states subsequently under ASD surveillance. Of these children, 3,315 were identified as having an ASD by the active, records-based surveillance of the Autism and Developmental Disabilities Monitoring Network. We estimated prevalence ratios (PRs) of maternal smoking from birth certificate report and ASDs using logistic regression, adjusting for maternal education, race/ethnicity, marital status, and maternal age; separately examining higher- and lower-functioning case subgroups; and correcting for assumed under-ascertainment of autism by level of maternal education.

RESULTS

About 13% of the source population and 11% of children with an ASD had a report of maternal smoking in pregnancy: adjusted PR (95% confidence interval) of 0.90 (0.80, 1.01). The association for the case subgroup autistic disorder (1,310 cases) was similar: 0.88 (0.72, 1.08), whereas that for ASD not otherwise specified (ASD-NOS) (375 cases) was positive, albeit including the null: 1.26 (0.91, 1.75). Unadjusted associations corrected for assumed under-ascertainment were 1.06 (0.98, 1.14) for all ASDs, 1.12 (0.97, 1.30) for autistic disorder, and 1.63 (1.30, 2.04) for ASD-NOS.

CONCLUSIONS

After accounting for the potential of under-ascertainment bias, we found a null association between maternal smoking in pregnancy and ASDs, generally. The possibility of an association with a higher-functioning ASD subgroup was suggested, and warrants further study.

Parental socioeconomic status and risk of offspring autism spectrum disorders in a Swedish population-based study

OBJECTIVE

Epidemiological studies in the United States consistently find autism spectrum disorders (ASD) to be overrepresented in high socioeconomic status (SES) families. These findings starkly contrast with SES gradients of many health conditions, and may result from SES inequalities in access to services. We hypothesized that prenatal measures of low, not high, parental SES would be associated with an increased risk of offspring ASD, once biases in case ascertainment are minimized.

METHOD

We tested this hypothesis in a population-based study in Sweden, a country that has free universal healthcare, routine screening for developmental problems, and thorough protocols for diagnoses of ASD. In a case-control study nested in a total population cohort of children aged 0 to 17 years living in Stockholm County between 2001 and 2007 (N = 589,114), we matched ASD cases (n = 4,709) by age and sex to 10 randomly selected controls. We retrieved parental SES measures collected at time of birth by record linkage.

RESULTS

Children of families with lower income, and of parents with manual occupations (OR = 1.4, 95% CI = 1.3-1.6) were at higher risk of ASD. No important relationships with parental education were observed. These associations were present after accounting for parental ages, migration status, parity, psychiatric service use, maternal smoking during pregnancy, and birth characteristics; and regardless of comorbid intellectual disability.

CONCLUSIONS

Lower, not higher, socioeconomic status was associated with an increased risk of ASD. Studies finding the opposite may be underestimating the burden of ASD in lower SES groups.

Glucocorticoids and stress‐related depression: an evaluation of biological mechanisms and the potential for new therapeutics

Purpose

Principles of epigenesis that provide a foundation for research into chronic medical disorders are increasingly being applied in the context of mental health. The purpose of this paper is to consider recent research evidence for epigenetic influences in the pathogenesis of depression, and the putative links with stress biology during exposure to chronic stress, with the aim of placing this into a context of potential new therapeutics.

Design/methodology/approach

Substantive reviews published during the last ten years were identified in a search of the Pubmed database in September 2010 using the terms “epigenetics” or “epigenesis” with “mental health”, “mood disorder”, “depression”, stress', “chronic stress” or “environment”, supplemented by hand‐searching of citations in the reviews.

Findings

Epigenetic mechanisms are both heritable and acquired, and their impact on the underlying genome helps explain individual vulnerability and patterns of occurrence of depression.

Originality/value

The paper shows that this relatively new field of research is in its infancy, and the influence of adverse environments (i.e. stressors) on genetic/epigenetic predisposition has promise for the advent of novel therapeutics based on epigenetic manipulation.

The cognitive genetics of neuropsychiatric disorders

Classification in psychiatry is heavily dependent on clinical symptoms and illness course. This ignores the critical role that cognitive problems play in neuropsychiatric disorders affecting different domains across the lifespan, from ADHD and autism to schizophrenia and Alzheimers disease. At this point, it is unclear whether cognitive mechanisms are specific to disorders, whether multiple processes can contribute to the same disorder, or whether aberrant neural processing can result in many different phenotypic outcomes. Understanding this would allow us to better grasp normal as well as pathological brain function. This could inform diagnostics based on understanding of neurophysiological processes and the consequent development of new therapeutics. Genetics, and the development of genomic research, offers real opportunities to understand the molecular mechanisms relevant to cognition. This chapter defines and describes the main cognitive phenotypes, which are investigated in psychiatric disorders. We review evidence for their heritability and early progress in the field using cytogenetic, linkage and candidate gene-based research methodologies. With high-throughput genomics it is now possible to explore novel common and rare risk variants for psychiatric disorders and their role in cognitive function at a genome-wide level. We review the results of early genomic studies and discuss the novel insights that they are starting to provide. Finally, we review the analysis of whole-genome DNA sequence data and the challenges that this will bring for cognitive genomics research.

Molecular genetics of attention-deficit/hyperactivity disorder: an overview

As heritability is high in attention-deficit/hyperactivity disorder (ADHD), genetic factors must play a significant role in the development and course of this disorder. In recent years a large number of studies on different candidate genes for ADHD have been published, most have focused on genes involved in the dopaminergic neurotransmission system, such as DRD4, DRD5, DAT1/SLC6A3, DBH, DDC. Genes associated with the noradrenergic (such as NET1/SLC6A2, ADRA2A, ADRA2C) and serotonergic systems (such as 5-HTT/SLC6A4, HTR1B, HTR2A, TPH2) have also received considerable interest. Additional candidate genes related to neurotransmission and neuronal plasticity that have been studied less intensively include SNAP25, CHRNA4, NMDA, BDNF, NGF, NTF3, NTF4/5, GDNF. This review article provides an overview of these candidate gene studies, and summarizes findings from recently published genome-wide association studies (GWAS). GWAS is a relatively new tool that enables the identification of new ADHD genes in a hypothesis-free manner. Although these latter studies could be improved and need to be replicated they are starting to implicate processes like neuronal migration and cell adhesion and cell division as potentially important in the aetiology of ADHD and have suggested several new directions for future ADHD genetics studies.