Genetic and environmental influences on obsessional traits and symptoms

The genetic epidemiology of obsessive-compulsive disorder: a systematic review and meta-analysis

The first systematic review and meta-analysis of obsessive-compulsive disorder (OCD) genetic epidemiology was published approximately 20 years ago. Considering the relevance of all the studies published since 2001, the current study aimed to update the state-of-art knowledge on the field. All published data concerning the genetic epidemiology of OCD from the CENTRAL, MEDLINE, EMBASE, BVS, and OpenGrey databases were searched by two independent researchers until September 30, 2021. To be included, the articles had to fulfill the following criteria: OCD diagnosis provided by standardized and validated instruments; or medical records; inclusion of a control group for comparison and case-control, cohort or twin study designs. The analysis units were the first-degree relatives (FDRs) of OCD or control probands and the co-twins in twin pairs. The outcomes of interest were the familial recurrence rates of OCD and the correlations of OCS in monozygotic compared with dizygotic twins. Nineteen family, twenty-nine twin, and six population-based studies were included. The main findings were that OCD is a prevalent and highly familial disorder, especially among the relatives of children and adolescent probands, that OCD has a phenotypic heritability of around 50%; and that the higher OCS correlations between MZ twins were mainly due to additive genetic or to non-shared environmental components.

The Genetic Architecture of Obsessive-Compulsive Disorder: Contribution of Liability to OCD From Alleles Across the Frequency Spectrum

OBJECTIVE

Obsessive-compulsive disorder (OCD) is known to be substantially heritable; however, the contribution of genetic variation across the allele frequency spectrum to this heritability remains uncertain. The authors used two new homogeneous cohorts to estimate the heritability of OCD from inherited genetic variation and contrasted the results with those of previous studies.

METHODS

The sample consisted of 2,090 Swedish-born individuals diagnosed with OCD and 4,567 control subjects, all genotyped for common genetic variants, specifically >400,000 single-nucleotide polymorphisms (SNPs) with minor allele frequency (MAF) ≥0.01. Using genotypes of these SNPs to estimate distant familial relationships among individuals, the authors estimated the heritability of OCD, both overall and partitioned according to MAF bins.

RESULTS

Narrow-sense heritability of OCD was estimated at 29% (SE=4%). The estimate was robust, varying only modestly under different models. Contrary to an earlier study, however, SNPs with MAF between 0.01 and 0.05 accounted for 10% of heritability, and estimated heritability per MAF bin roughly followed expectations based on a simple model for SNP-based heritability.

CONCLUSIONS

These results indicate that common inherited risk variation (MAF ≥0.01) accounts for most of the heritable variation in OCD. SNPs with low MAF contribute meaningfully to the heritability of OCD, and the results are consistent with expectation under the "infinitesimal model" (also referred to as the "polygenic model"), where risk is influenced by a large number of loci across the genome and across MAF bins.

Genetics of obsessive-compulsive disorder

BACKGROUND

Obsessive-compulsive disorder (OCD) is a psychiatric disorder with multiple symptom dimensions (e.g. contamination, symmetry). OCD clusters in families and decades of twin studies clearly demonstrate an important role for genetics in the etiology of the disorder.

METHODS

In this review, we summarize the genetic epidemiology and molecular genetic studies of OCD and obsessive-compulsive symptoms.

RESULTS

OCD is a heritable, polygenic disorder with contributions from both common and rare variants, including de novo deleterious variations. Multiple studies have provided reliable support for a large additive genetic contribution to liability to OCD, with discrete OCD symptom dimensions having both shared and unique genetic risks. Genome-wide association studies have not produced significant results yet, likely because of small sample sizes, but larger meta-analyses are forthcoming. Both twin and genome-wide studies show that OCD shares genetic risk with its comorbid conditions (e.g. Tourette syndrome and anorexia nervosa).

CONCLUSIONS

Despite significant efforts to uncover the genetic basis of OCD, the mechanistic understanding of how genetic and environmental risk factors interact and converge at the molecular level to result in OCD's heterogeneous phenotype is still mostly unknown. Future investigations should increase ancestral genetic diversity, explore age and/or sex differences in genetic risk for OCD and expand the study of pharmacogenetics, gene expression, gene × environment interactions and epigenetic mechanisms for OCD.

A dimensional perspective on the genetics of obsessive-compulsive disorder

This review covers recent findings in the genomics of obsessive-compulsive disorder (OCD), obsessive-compulsive symptoms, and related traits from a dimensional perspective. We focus on discoveries stemming from technical and methodological advances of the past five years and present a synthesis of human genomics research on OCD. On balance, reviewed studies demonstrate that OCD is a dimensional trait with a highly polygenic architecture and genetic correlations to multiple, often comorbid psychiatric phenotypes. We discuss the phenotypic and genetic findings of these studies in the context of the dimensional framework, relying on a continuous phenotype definition, and contrast these observations with discoveries based on a categorical diagnostic framework, relying on a dichotomous case/control definition. Finally, we highlight gaps in knowledge and new directions for OCD genetics research.

Maternal Effects as Causes of Risk for Obsessive-Compulsive Disorder

BACKGROUND

While genetic variation has a known impact on the risk for obsessive-compulsive disorder (OCD), there is also evidence that there are maternal components to this risk. Here, we partitioned sources of variation, including direct genetic and maternal effects, on risk for OCD.

METHODS

The study population consisted of 822,843 individuals from the Swedish Medical Birth Register, born in Sweden between January 1, 1982, and December 31, 1990, and followed for a diagnosis of OCD through December 31, 2013. Diagnostic information about OCD was obtained using the Swedish National Patient Register.

RESULTS

A total of 7184 individuals in the birth cohort (0.87%) were diagnosed with OCD. After exploring various generalized linear mixed models to fit the diagnostic data, genetic maternal effects accounted for 7.6% (95% credible interval: 6.9%-8.3%) of the total variance in risk for OCD for the best model, and direct additive genetics accounted for 35% (95% credible interval: 32.3%-36.9%). These findings were robust under alternative models.

CONCLUSIONS

Our results establish genetic maternal effects as influencing risk for OCD in offspring. We also show that additive genetic effects in OCD are overestimated when maternal effects are not modeled.

Genetic susceptibility in obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is present in 1.5-2.5% of the population and can result in substantial lifelong disability. It is characterized by intrusive thoughts, sensations, and urges and by repetitive behaviors that are difficult to control despite, in most cases, preserved insight as to their excessive or irrational nature. The causes and underlying pathophysiology of OCD are not well understood, which has limited the development of new treatments and interventions. Despite evidence for a substantial genetic contribution to disease risk, identification and replication of genetic variants associated with OCD have been challenging. Decades of candidate gene association studies have provided little insight. They are now being supplanted by modern genomewide approaches to discover both common and rare sequence and structural variants. Studies to date suggest potential novel therapeutic avenues such as modulators of glutamatergic and immune pathways; however, individual genetic findings are not yet statistically robust or replicated. Further efforts are clearly needed to identify specific risk variants and to confirm vulnerable pathways by studying much larger cohorts of patients with comprehensive variant discovery approaches. Mouse knockout models have already made notable inroads into our understanding of OCD pathology; their utility will only increase as specific risk alleles are identified.

Students with Anxiety: Implications for Professional School Counselors

Anxiety is one of the most pervasive mental health concerns affecting students, yet a significant number of students with anxiety disorders remain underserved. If left untreated, anxiety can hinder students’ personal/social, academic, and career development. The purpose of this article is to provide professional school counselors with helpful information about the etiology of anxiety disorders and brief, evidence-based prevention and intervention options. The authors discuss specific recommendations for the identification, assessment, and treatment of anxiety that fit within the unique school environment.

Revealing the complex genetic architecture of obsessive-compulsive disorder using meta-analysis

Two obsessive-compulsive disorder (OCD) genome-wide association studies (GWASs) have been published by independent OCD consortia, the International Obsessive-Compulsive Disorder Foundation Genetics Collaborative (IOCDF-GC) and the OCD Collaborative Genetics Association Study (OCGAS), but many of the top-ranked signals were supported in only one study. We therefore conducted a meta-analysis from the two consortia, investigating a total of 2688 individuals of European ancestry with OCD and 7037 genomically matched controls. No single-nucleotide polymorphisms (SNPs) reached genome-wide significance. However, in comparison with the two individual GWASs, the distribution of P-values shifted toward significance. The top haplotypic blocks were tagged with rs4733767 (P=7.1 × 10^-7; odds ratio (OR)=1.21; confidence interval (CI): 1.12-1.31, CASC8/CASC11), rs1030757 (P=1.1 × 10^-6; OR=1.18; CI: 1.10-1.26, GRID2) and rs12504244 (P=1.6 × 10^-6; OR=1.18; CI: 1.11-1.27, KIT). Variants located in or near the genes ASB13, RSPO4, DLGAP1, PTPRD, GRIK2, FAIM2 and CDH20, identified in linkage peaks and the original GWASs, were among the top signals. Polygenic risk scores for each individual study predicted case-control status in the other by explaining 0.9% (P=0.003) and 0.3% (P=0.0009) of the phenotypic variance in OCGAS and the European IOCDF-GC target samples, respectively. The common SNP heritability in the combined OCGAS and IOCDF-GC sample was estimated to be 0.28 (s.e.=0.04). Strikingly, ∼65% of the SNP-based heritability in the OCGAS sample was accounted for by SNPs with minor allele frequencies of ⩾40%. This joint analysis constituting the largest single OCD genome-wide study to date represents a major integrative step in elucidating the genetic causes of OCD.

Learning From Animal Models of Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) affects 2%-3% of the population worldwide and can cause significant distress and disability. Substantial challenges remain in the field of OCD research and therapeutics. Approved interventions alleviate symptoms only partially, with 30%-40% of patients being resistant to treatment. Although the etiology of OCD is still unknown, research evidence points toward the involvement of cortico-striato-thalamocortical circuitry. This review focuses on the most recent behavioral, genetics, and neurophysiologic findings from animal models of OCD. Based on evidence from these models and parallels with human studies, we discuss the circuit hyperactivity hypothesis for OCD, a potential circuitry dysfunction of action termination, and the involvement of candidate genes. Adding a more biologically valid framework to OCD will help researchers define and test new hypotheses and facilitate the development of targeted therapies based on disease-specific mechanisms.

Genetics of obsessive-compulsive disorder and related disorders

Twin and family studies support a significant genetic contribution to obsessive-compulsive disorder (OCD) and related disorders, such as chronic tic disorders, trichotillomania, skin-picking disorder, body dysmorphic disorder, and hoarding disorder. Recently, population-based studies and novel laboratory-based methods have confirmed substantial heritability in OCD. Genome-wide association studies and candidate gene association studies have provided information on specific gene variations that may be involved in the pathobiology of OCD, though a substantial portion of the genetic risk architecture remains unknown.

Differential Parental Influence in the Familial Aggregation of Obsessive Compulsive Disorder

The familial nature of OCD has been well established. Clinical characteristics such as early age of onset, comorbidity with tic disorders, and higher rates of symmetry symptoms have been associated with the familial aggregation of OCD, though little research has examined the differential impact of paternal and maternal OCD. The current study explored parental influence on the expression of these characteristics and reports on 310 probands diagnosed with OCD as well as 1,580 of their biological first-degree relatives. The probands were evaluated by trained clinical raters using semi-structured assessments, and relative diagnoses were obtained based on probands' reports. Similar to previous findings, 10.13% of the 1,580 relatives (n = 160) were reported to have significant OCD symptoms. Only probands who reported having a father with OCD, rather than any first-degree relative, were more likely to have an early age of onset, symmetry and exactness obsessions, and higher rates of comorbidity. No significant differences were found with respect to the probands who reported their mothers as having OCD. These findings suggest that paternal OCD, rather than simply any first-degree relative having OCD, may influence whether probands exhibit the clinical characteristics commonly associated with the familial subtype of OCD.

Prevalence and heritability of obsessive-compulsive spectrum and anxiety disorder symptoms: A survey of the Australian Twin Registry

While past twin studies indicate moderate levels of heritability of "obsessive-compulsive related" and anxiety disorder symptoms, no single study has reported such estimates in the same twin population nor examined potential genetic sex differences. We assessed symptoms of obsessive-compulsive disorder, body dysmorphic disorder, hoarding disorder, hypochondriasis, panic disorder, social phobia and generalized anxiety disorder in 2,495 adult twins (1,468 female). Prevalence estimates for the corresponding symptom measures were determined using empirically derived cut-off scores. Twin resemblance was assessed by Pearson correlations and biometrical model-fitting analyses, incorporating sex-specific effects, using OpenMx. Prevalence estimates ranged from 1.6% in the symptoms of generalized anxiety to 16.9% for social phobia. Female twins demonstrated significantly higher prevalence rates across all domains with the exception of obsessive-compulsive symptoms. Additive genetic factors accounted for a moderate proportion of the total liability to each symptom domain. Evidence suggesting qualitative genetic sex differences (i.e., distinct genetic influences between genders) was observed for body dysmorphic concern and panic symptoms, while quantitative differences were observed for hoarding and social phobia symptoms, indicating stronger heritability in females. Novel findings in this study include the observation of probable genetic sex differences in liability towards hoarding symptoms and dysmorphic concern, as well as the lack of such differences in hypochondriasis. The trend towards qualitative sex differences in panic symptoms has some intuitive appeal with regard to biological-experimental models of panic.

Brain activation during response interference in twins discordant or concordant for obsessive compulsive symptoms

One of the core behavioral features associated with obsessive compulsive symptomatology is the inability to inhibit thoughts and/or behaviors. Neuroimaging studies have indicated abnormalities in frontostriatal and dorsolateral prefrontal - anterior cingulate circuits during inhibitory control in patients with obsessive compulsive disorder compared with controls. In the present study, task performance and brain activation during Stroop color-word and Flanker interference were compared within monozygotic twin pairs discordant for obsessive compulsive symptoms and between groups of pairs scoring very low or very high on obsessive compulsive symptoms, in order to examine the differential impact of non-shared environmental versus genetic risk factors for obsessive compulsive symptomatology on inhibitory control related functional brain activation. Although performance was intact, brain activation during inhibition of distracting information differed between obsessive compulsive symptom high-scoring compared to low-scoring subjects. Regions affected in the discordant group (e.g., temporal and anterior cingulate gyrus) were partly different from those observed to be affected in the concordant groups (e.g., parietal gyrus and thalamus). A robust increase in dorsolateral prefrontal activity during response interference was observed in both the high-scoring twins of the discordant sample and the high-scoring twins of the concordant sample, marking this structure as a possible key region for disturbances in inhibitory control in obsessive compulsive disorder.

Evidence for a genetic overlap between body dysmorphic concerns and obsessive-compulsive symptoms in an adult female community twin sample

Body dysmorphic disorder (BDD) is thought to be etiologically related to obsessive-compulsive disorder (OCD) but the available evidence is incomplete. The current study examined the genetic and environmental sources of covariance between body dysmorphic and obsessive-compulsive symptoms in a community sample of adult twins. A total of 2,148 female twins (1,074 pairs) completed valid and reliable measures of body dysmorphic concerns and obsessive-compulsive symptoms. The data were analyzed using bivariate twin modeling methods and the statistical programme Mx. In the best-fitting model, the covariation between body dysmorphic and obsessive-compulsive traits was largely accounted for by genetic influences common to both phenotypes (64%; 95% CI: 0.50-0.80). This genetic overlap was even higher when specific obsessive-compulsive symptom dimensions were considered, with up to 82% of the phenotypic correlation between the obsessing and symmetry/ordering symptom dimensions and dysmorphic concerns being attributable to common genetic factors. Unique environmental factors, although influencing these traits individually, did not substantially contribute to their covariation. The results remained unchanged when excluding individuals reporting an objective medical condition/injury accounting for their concern in physical appearance. The association between body dysmorphic concerns and obsessive-compulsive symptoms is largely explained by shared genetic factors. Environmental risk factors were largely unique to each phenotype. These results support current recommendations to group BDD together with OCD in the same DSM-5 chapter, although comparison with other phenotypes such as somatoform disorders and social phobia is needed.

Twin Studies on Obsessive–Compulsive Disorder: A Review

Genetic factors have historically been thought of as important in the development of obsessive–compulsive disorder (OCD). For the estimation of the relative importance of genetic and environmental factors, twin studies are an obvious approach. Twin studies of OCD have a long history, starting in 1929. In this review, over 70 years of twin research of OCD is presented, using four different approaches that represent the steps in the twin research of OCD from past to present. These steps include (1) case-studies of twins with OCD from the old literature; (2) twin studies of OCD using Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria; (3) twin studies of OCD using a dimensional approach, comparing resemblances in monozygotic and dizygotic twins; and (4) twin studies of OCD using a dimensional approach, analyzing the data with Structural Equation Modeling. It is concluded that only the studies using the last method have convincingly shown that, in children, obsessive–compulsive (OC) symptoms are heritable, with genetic influences in the range of 45% to 65%. In adults, studies are suggestive for a genetic influence on OC symptoms, ranging from 27% to 47%, but a large twin study using a bio- metrical approach with continuous data is still needed to provide conclusive evidence. Strategies for future twin studies of OCD are discussed.

White matter differences in monozygotic twins discordant or concordant for obsessive-compulsive symptoms: a combined diffusion tensor imaging/voxel-based morphometry study

BACKGROUND

Neuroimaging studies of obsessive-compulsive disorder (OCD) patients point to deficits in cortico-striato-thalamo-cortical circuits that might include changes in white matter. The contribution of environmental and genetic factors to the various OCD-related changes in brain structures remains to be established.

METHODS

White matter structures were analyzed in 140 subjects with both diffusion tensor imaging and voxel-based morphometry. We studied 20 monozygotic twin pairs discordant for obsessive-compulsive symptoms (OCS) to detect the effects of environmental risk factors for obsessive-compulsive (OC) symptomatology. Furthermore, we compared 28 monozygotic twin pairs concordant for low OCS scores with 23 twin pairs concordant for high OCS scores to detect the effects of genetic risk factors for OC symptomatology.

RESULTS

Discordant pair analysis showed that the environmental risk was associated with an increase in dorsolateral-prefrontal white matter. Analysis of concordant pairs showed that the genetic risk was associated with a decrease in inferior frontal white matter. Various white matter tracts showed opposite effects of environmental and genetic risk factors (e.g., right medial frontal, left parietal, and right middle temporal), illustrating the need for designs that separate these classes of risk factors.

CONCLUSIONS

Different white matter regions were affected by environmental and genetic risk factors for OC symptomatology, but both classes of risk factors might, in aggregate, create an imbalance between the indirect loop of the cortico-striato-thalamo-cortical network (to the dorsolateral-prefrontal region)-important for inhibition and switching between behaviors-and the direct loop (involving the inferior frontal region) that contributes to the initiation and continuation of behaviors.

Etiology of obsessions and compulsions: a meta-analysis and narrative review of twin studies

The relative importance of genetic and environmental factors in the etiology of obsessive-compulsive (OC) symptoms is unclear. Cognitive-behavioral models propose that shared environment (e.g., parenting style) is important. Family segregation studies suggest that nonadditive genetic factors may be involved. To investigate the etiology of OC symptoms, a meta-analysis was conducted of 37 twin samples from 14 studies, supplemented by a narrative review. Results indicated that in terms of mean effect sizes, (a) additive genetic effects and nonshared environment accounted for most of the variance in OC symptoms, (b) shared environment and nonadditive genetic effects made little or no contribution; (c) these findings did not vary with sex or symptom severity; (d) variance due to nonshared environment increased with age; (e) gene-environment interactions play an etiologic role; (f) OC symptoms are shaped by etiologic factors common to all types of OC symptoms but also have symptom-specific etiologies; and (g) OC symptoms are also shaped by very general etiologic factors (e.g., those influencing negative emotionality). Overall, the findings indicate that OC symptoms have a complex etiologic architecture that is not adequately explained by contemporary etiological models.

Genetic and environmental factors in complex neurodevelopmental disorders

Complex neurodevelopmental disorders, such as schizophrenia, autism, attention deficit (hyperactivity) disorder, (manic) depressive illness and addiction, are thought to result from an interaction between genetic and environmental factors. Association studies on candidate genes and genome-wide linkage analyses have identified many susceptibility chromosomal regions and genes, but considerable efforts to replicate association have been surprisingly often disappointing. Here, we summarize the current knowledge of the genetic contribution to complex neurodevelopmental disorders, focusing on the findings from association and linkage studies. Furthermore, the contribution of the interaction of the genetic with environmental and epigenetic factors to the aetiology of complex neurodevelopmental disorders as well as suggestions for future research are discussed.

Brain activation during cognitive planning in twins discordant or concordant for obsessive-compulsive symptoms

Neuroimaging studies have indicated abnormalities in cortico-striatal-thalamo-cortical circuits in patients with obsessive–compulsive disorder compared with controls. However, there are inconsistencies between studies regarding the exact set of brain structures involved and the direction of anatomical and functional changes. These inconsistencies may reflect the differential impact of environmental and genetic risk factors for obsessive–compulsive disorder on different parts of the brain. To distinguish between functional brain changes underlying environmentally and genetically mediated obsessive–compulsive disorder, we compared task performance and brain activation during a Tower of London planning paradigm in monozygotic twins discordant (n = 38) or concordant (n = 100) for obsessive–compulsive symptoms. Twins who score high on obsessive–compulsive symptoms can be considered at high risk for obsessive–compulsive disorder. We found that subjects at high risk for obsessive–compulsive disorder did not differ from the low-risk subjects behaviourally, but we obtained evidence that the high-risk subjects differed from the low-risk subjects in the patterns of brain activation accompanying task execution. These regions can be separated into those that were affected by mainly environmental risk (dorsolateral prefrontal cortex and lingual cortex), genetic risk (frontopolar cortex, inferior frontal cortex, globus pallidus and caudate nucleus) and regions affected by both environmental and genetic risk factors (cingulate cortex, premotor cortex and parts of the parietal cortex). Our results suggest that neurobiological changes related to obsessive–compulsive symptoms induced by environmental factors involve primarily the dorsolateral prefrontal cortex, whereas neurobiological changes induced by genetic factors involve orbitofrontal–basal ganglia structures. Regions showing similar changes in high-risk twins from discordant and concordant pairs may be part of compensatory networks that keep planning performance intact, in spite of cortico-striatal-thalamo-cortical deficits.

The genetics of obsessive-compulsive disorder: a review

Obsessive-compulsive disorder (OCD) is a serious psychiatric disorder that affects approximately 2% of the populations of children and adults. Family aggregation studies have demonstrated that OCD is familial, and results from twin studies demonstrate that the familiality is due in part to genetic factors. Only three genome-wide linkage studies have been completed to date, with suggestive but not definitive results. In addition, over 80 candidate gene studies have been published. Most of these studies have focused on genes in the serotonergic and dopaminergic pathways. Unfortunately, none have achieved genome-wide significance, and, with the exception of the glutamate transporter gene, none have been replicated. Future research will require the collaboration of multidisciplinary teams of investigators to (i) achieve sufficiently large samples of individuals with OCD; (ii) apply the state-of-the-art laboratory techniques; and (iii) perform the bioinformatic analyses essential to the identification of risk loci.

Slitrk5 deficiency impairs corticostriatal circuitry and leads to obsessive-compulsive-like behaviors in mice

Obsessive-compulsive disorder (OCD) is a common psychiatric disorder defined by the presence of obsessive thoughts and repetitive compulsive actions, and it often encompasses anxiety and depressive symptoms. Recently, the corticostriatal circuitry has been implicated in the pathogenesis of OCD. However, the etiology, pathophysiology and molecular basis of OCD remain unknown. Several studies indicate that the pathogenesis of OCD has a genetic component. Here we demonstrate that loss of a neuron-specific transmembrane protein, SLIT and NTRK-like protein-5 (Slitrk5), leads to OCD-like behaviors in mice, which manifests as excessive self-grooming and increased anxiety-like behaviors, and is alleviated by the selective serotonin reuptake inhibitor fluoxetine. Slitrk5(-/-) mice show selective overactivation of the orbitofrontal cortex, abnormalities in striatal anatomy and cell morphology and alterations in glutamate receptor composition, which contribute to deficient corticostriatal neurotransmission. Thus, our studies identify Slitrk5 as an essential molecule at corticostriatal synapses and provide a new mouse model of OCD-like behaviors.

Child and adolescent psychiatric genetics

The current status of child and adolescent psychiatric genetics appears promising in light of the initiation of genome-wide association studies (GWAS) for diverse polygenic disorders and the molecular elucidation of monogenic Rett syndrome, for which recent functional studies provide hope for pharmacological treatment strategies. Within the last 50 years, tremendous progress has been made in linking genetic variation to behavioral phenotypes and psychiatric disorders. We summarize the major findings of the Human Genome Project and dwell on largely unsuccessful candidate gene and linkage studies. GWAS for the first time offer the possibility to detect single nucleotide polymorphisms and copy number variants without a priori hypotheses as to their molecular etiology. At the same time it is becoming increasingly clear that very large sample sizes are required in order to enable genome wide significant findings, thus necessitating further large-scaled ascertainment schemes for the successful elucidation of the molecular genetics of childhood and adolescent psychiatric disorders. We conclude by reflecting on different scenarios for future research into the molecular basis of early onset psychiatric disorders. This review represents the introductory article of this special issue of the European Child and Adolescent Psychiatry.

Are obsessive-compulsive symptom dimensions familial in nonclinical individuals?

BACKGROUND

Obsessive-compulsive disorder (OCD) is a heterogeneous condition, which can be expressed as various potentially overlapping symptom dimensions. In clinical samples, some of these dimensions are associated with increased familial risk for OCD and appear to be familial (intercorrelated within pairs of affected family members), whereas others are not. The goal of this study was to determine whether obsessive-compulsive (OC) symptom dimensions are familial in a nonclinical sample.

METHODS

OC symptom dimensions and negative affect were assessed in 184 female undergraduate students and their parents using the Obsessive-Compulsive Inventory-Revised (OCI-R) and the Positive and Negative Affect Scales, respectively. Bivariate correlations and multiple regression models controlling for age and negative affect were employed to examine the familiarity of OC symptom dimensions.

RESULTS

The OCI-R total scores were significantly correlated in both mother-daughter and father-daughter dyads but the magnitude of these correlations tended to be greater for the mother-daughter dyads. Multiple regression models showed that the Ordering and Hoarding subscales of the OCI-R breed true in mother-daughter dyads. Ordering scores in mothers were also predictive of other symptoms in the daughters (Washing and Checking).

CONCLUSIONS

These results are broadly consistent with the findings in clinical samples and suggest that Ordering and Hoarding are more strongly familial than other symptom dimensions and that high Ordering scores in mothers are associated with increased levels of symptoms in daughters in a less specific manner.

Emotional disorders: cluster 4 of the proposed meta-structure for DSM-V and ICD-11

BACKGROUND

The extant major psychiatric classifications DSM-IV, and ICD-10, are atheoretical and largely descriptive. Although this achieves good reliability, the validity of a medical diagnosis would be greatly enhanced by an understanding of risk factors and clinical manifestations. In an effort to group mental disorders on the basis of aetiology, five clusters have been proposed. This paper considers the validity of the fourth cluster, emotional disorders, within that proposal.

METHOD

We reviewed the literature in relation to 11 validating criteria proposed by a Study Group of the DSM-V Task Force, as applied to the cluster of emotional disorders.

RESULTS

An emotional cluster of disorders identified using the 11 validators is feasible. Negative affectivity is the defining feature of the emotional cluster. Although there are differences between disorders in the remaining validating criteria, there are similarities that support the feasibility of an emotional cluster. Strong intra-cluster co-morbidity may reflect the action of common risk factors and also shared higher-order symptom dimensions in these emotional disorders.

CONCLUSION

Emotional disorders meet many of the salient criteria proposed by the Study Group of the DSM-V Task Force to suggest a classification cluster.

An investigation of temperament endophenotype candidates for early emergence of the core cognitive component of eating disorders

BACKGROUND

This study was designed to investigate potential temperament endophenotypes for clinically significant importance of shape and weight.

METHOD

Seven temperament risk factors for eating disorders and the Eating Disorder Examination were assessed in 699 female twins aged 12-15 years. Each variable was evaluated against the following endophenotype criteria: associated with illness in the general population; found in non-affected family members at a higher rate than in the general population; and, heritable.

RESULTS

All seven variables were significantly associated with clinically significant importance of shape and weight, while thin-ideal internalization, ineffectiveness, body dissatisfaction and sensitivity to punishment were found at significantly elevated levels in non-affected twins, when controlling for sister's temperament score. These four variables had genetic correlations with importance of shape and weight, ranging from 0.48 to 0.95.

CONCLUSIONS

Future research should evaluate the stability of the identified endophenotypes and their utility for predicting significant growth in importance of shape and weight, and also whether different endophenotypes emerge when the importance of weight and shape reaches its peak in adolescents, around 15 to 16 years of age.

Marital resemblance for obsessive-compulsive, anxious and depressive symptoms in a population-based sample

BACKGROUND

Resemblance between spouses can be due to phenotypic assortment, social homogamy and/or marital interaction. A significant degree of assortment can have consequences for the genetic architecture of a population. We examined the existence and cause(s) of assortment for obsessive-compulsive (OC), anxious and depressive symptoms in a population-based twin-family sample.

METHOD

OC, anxious and depressive symptoms were measured in around 1400 twin-spouse pairs and >850 parent pairs. Correlations of twins and their spouse, twin and co-twin's spouse, spouses of both twins and parents of twins were obtained to consider phenotypic assortment versus social homogamy as possible causes of marital resemblance. The association of length of relationship with marital resemblance was also investigated. Finally, we examined whether within-trait or cross-trait processes play a primarily role in marital resemblance.

RESULTS

Small but significant within-trait correlations of between 0.1 and 0.2 were seen for spouse similarity in OC, anxious and depressive symptoms. Cross-correlations were significant but lower. There was no correlation between length of relationship and marital resemblance. From the pattern of correlations for twin-spouse, co-twin-spouse and spouses of both twins, phenotypic assortment could not be distinguished from social homogamy. Both within- and cross-assortment processes play a role in marital resemblance.

CONCLUSIONS

Small within- and across-trait correlations exist for OC, anxious and depressive symptoms. No evidence for marital interaction was found. Spouse correlations are small, which makes it difficult to distinguish between social homogamy and phenotypic assortment. It is unlikely that correlations of this size will have a large impact on genetic studies.

The association between parental bonding and obsessive compulsive disorder in offspring at high familial risk

BACKGROUND

The aim of the current study is to estimate the association between parenting factors derived from the Parental Bonding Instrument (PBI) and a lifetime DSM-IV diagnosis of OCD.

METHOD

Data were from approximately 1200 adults from 465 families assessed as part of a large family and genetic study of OCD. The association of three parenting factors, for fathers and mothers, with offspring OCD status were examined; analyses were stratified by parental OCD status and family loading for OCD (multiplex versus sporadic).

RESULTS

Three factors were derived by principal components factor analysis of the PBI (maternal and paternal care, overprotection and control). Maternal overprotection was associated with OCD in offspring with familial OCD (familial cases) but only if neither parent was affected with OCD, which suggests independent but additive environmental and genetic risk (OR = 5.9, 95% CI 1.2, 29.9, p = 0.031). Paternal care was a protective factor in those not at high genetic risk (sporadic cases) (OR = 0.2, 95% CI 0.0, 0.8, p = 0.027). Maternal overprotection was also associated with offspring OCD in sporadic families (OR = 2.9, 95% CI 1.3, 6.6, p = 0.012). The finding that parental overprotection and care were not associated with offspring OCD when at least one parent had OCD addressed directly the hypothesis of maternal or paternal OCD adversely impacting parenting.

CONCLUSIONS

This study provides evidence that aspects of parenting may contribute to the development of OCD among offspring. Prospective studies of children at risk for OCD are needed to explore the direction of causality.

Genetic and environmental contributions to self-report obsessive-compulsive symptoms in Dutch adolescents at ages 12, 14, and 16

OBJECTIVE

To determine the contributions of genetic and environmental influences to variation in self-report of obsessive-compulsive (OC) symptoms in a population-based twin sample of adolescent boys and girls.

METHOD

Self-report ratings on the eight-item Youth Self-Report Obsessive-Compulsive Scale were collected in Dutch mono- and dizygotic twin pairs who participated at age 12 (N = 746 twin pairs), 14 (N = 963 pairs), or 16 years (N = 1,070 pairs). Structural equation modeling was used to break down the variation in liability to OC symptoms into genetic and environmental components.

RESULTS

At age 12, no difference in prevalence was found for OC symptoms in boys and girls. At ages 14 and 16, the prevalence was higher in girls. At all ages, genetic factors contributed significantly to variation on OC symptom liability; 27% at the age of 12,57% at the age of 14, and 54% at the age of 16. There were no sex differences in heritability. Only at age 12, environmental factors shared by children from the same family contributed significantly (16%) to individual differences in OC symptom scores.

CONCLUSIONS

During adolescence, OC symptoms are influenced by genetic and nonshared environmental factors. Sex differences in prevalence, but not heritability, emerge in adolescence. At age 12, shared environmental factors are of importance, but their influence disappears at later ages. This is in line with earlier research at age 12 that used parental ratings of OC symptoms. Thus, between-family factors play a significant role in explaining individual differences in OC symptoms at this age.

Evidence for a heritable unidimensional symptom factor underlying obsessionality

The division of obsessive-compulsive symptoms (OCS) into specific factors is now widely accepted. However, the utility of these categories for genetic studies remains unclear, as studies examining their heritability have been inconsistent. Less attention has been paid to the possibility that clinically significant obsessionality is primarily determined by a "core" group of OCS that crosses the boundaries between symptom subgroups. The aim of this study is to determine whether such a core group exists, and to compare its heritability to that of the more traditionally derived symptom factors. We examined the properties and heritability of obsessive-compulsive symptoms in college students, medical students, and obsessive-compulsive disorder (OCD) families using the Leyton Obsessional Inventory. In each of the three samples, we identified a core group of symptoms that comprised a single unique construct and accounted for over 90% of the variation of the four more traditional symptom factors. This core construct was highly correlated with OCD in our families and had a heritability estimate of 0.19 when OCD was not included as a covariate and 0.49 when OCD was included as a covariate. In contrast, the four symptom factors were not heritable. There appears to be an underlying unidimensional component to obsessionality, both in non-clinical and clinical samples. This component, which is heritable, accounts for the majority of the variation of the more traditionally derived symptom factors in our sample, and is composed of OCS that are not specific to any of the symptom subgroups.

Heritability of obsessive-compulsive symptom dimensions

Recent research has shown that obsessive-compulsive symptoms (OCS) differ remarkably among patients and can be divided into several symptom dimensions. OCS are influenced by genetic components, but it is unknown to what extent these symptom dimensions are heritable. The phenotypic heterogeneity also raises the question to what extent the symptom dimensions are influenced by specific or shared genetic factors. We studied a population sample of 1,383 female twins from the Virginia Twin Registry. OCS was measured by a questionnaire with 20 items from the Padua Inventory. After factor analysis, three reliable OC symptom dimensions were retained: Rumination, Contamination, and Checking. These OC dimensions were analyzed with multivariate genetic models to investigate both the overlap and uniqueness of genetic and environmental contributions underlying OC symptom dimensions. The multivariate common pathway model provided the best description of the data. All symptom dimensions share variation with a latent common factor, that is, OC behavior. Variation in this common factor was explained by both genes (36%) and environmental factors (64%). Only the Contamination dimension was influenced by specific genes and seemed to be a relatively independent dimension. The results suggest that a broad OC behavioral phenotype exists, influenced by both genes and nonshared environment. In addition, we found evidence for specific genetic and environmental factors underlying the Contamination dimension. Use of the Contamination dimension could therefore provide a powerful approach for the detection of genetic susceptibility loci that contribute to OCS.

The genetics of obsessive compulsive disorder: a review of the evidence

Obsessive compulsive disorder (OCD) is a common psychiatric disorder that can have disabling effects on both adults and children. Twin, family, segregation, and linkage studies have demonstrated that OCD is familial, that the familiality is due in part to genetic factors and there are regions of the genome which very likely harbor susceptibility loci for OCD. Over 60 candidate gene studies have been conducted. Most studies have focused on genes in the serotonergic and dopaminergic pathways. Unfortunately, none have achieved genome-wide significance and with the exception of the glutamate transporter gene, none have been reliably replicated. Future research will requite much larger samples and the collaboration of researchers to be able to identify susceptibility loci for OCD.

The genetics of anorexia nervosa collaborative study: methods and sample description

OBJECTIVE

Supported by National Institute of Mental Health (NIMH), this 12-site international collaboration seeks to identify genetic variants that affect risk for anorexia nervosa (AN).

METHOD

Four hundred families will be ascertained with two or more individuals affected with AN. The assessment battery produces a rich set of phenotypes comprising eating disorder diagnoses and psychological and personality features known to be associated with vulnerability to eating disorders.

RESULTS

We report attributes of the first 200 families, comprising 200 probands and 232 affected relatives.

CONCLUSION

These results provide context for the genotyping of the first 200 families by the Center for Inherited Disease Research. We will analyze our first 200 families for linkage, complete recruitment of roughly 400 families, and then perform final linkage analyses on the complete cohort. DNA, genotypes, and phenotypes will form a national eating disorder repository maintained by NIMH and available to qualified investigators.

Environmental factors in obsessive-compulsive behavior: evidence from discordant and concordant monozygotic twins

To investigate environmental factors that protect against or exacerbate obsessive-compulsive (OC) symptoms, we selected 25 monozygotic (MZ) twin pairs discordant, 17 MZ twin pairs concordant high and 34 MZ pairs concordant low on OC symptoms from a large longitudinal Dutch sample of adult twin pairs and their family members, applying stringent criteria for OC symptomatology. Data were collected on psychopathology, family structure, health, lifestyle, birth complications and life events. Unique environmental factors were studied using within-discordant MZ pair comparisons, whereas between-concordant MZ pair comparisons were used to study environmental factors that are shared by the twins of an MZ pair. The high-scoring MZ twins of the discordant group reported more life events (especially sexual abuse) than their low-scoring twin-siblings. The between-pair comparisons showed lower birth weight in the discordant MZ pairs than in the concordant MZ pairs. Further, the concordant high MZ pairs as well as their spouses had a lower educational level than the two other groups. On scale scores of anxious-depression, neuroticism, and somatic complaints, concordant high MZ pairs showed highest scores, and the discordant MZ pairs scored intermediate, except for neuroticism, on which the high-scoring twins of discordant MZ pairs were equal to the concordant high pairs. Discordance on psychological scale scores between the concordant MZ pairs was evident from 1991 onward, and within the discordant MZ pairs from 1997 onward, confirming previous reports of an association of early-onset OC symptoms with higher genetic load. Parent scores of OC symptoms and anxious-depression suggested intermediate genetic load in the discordant MZ group. In conclusion, this study reports on both unique and shared environmental factors associated with OC symptomatology. Whether these factors operate in addition to or in interaction with genetic disposition is to be elucidated in future studies.

The analytical epidemiology of obsessive-compulsive disorder: risk factors and correlates

In this qualitative systematic review, we evaluate studies of the demographic, innate, and environmental risk factors and correlates associated with the development of Obsessive-Compulsive Disorder (OCD) in epidemiological samples. We found that a significant proportion of the studies indicate that late adolescence is a period of increased vulnerability for the development of OCD; that OCD affects predominantly female adults and male children and adolescents; that those who are unmarried or abusing drugs are more likely to present with OCD; that OCD is a familial and genetic disorder, particularly when one considers symptom dimensions instead of categorical diagnosis and when the disorder begins at an early age; and that individuals with OCD from the community, like those seen in clinical settings, may be especially prone to present psychiatric conditions such as mood and anxiety disorders. Although there are plenty of data on the correlates and risk factors of OCD in epidemiological samples, more research is needed on other potential risk factors, including obstetrical and pregnancy problems, pre-morbid neurocognitive functioning, and streptococcal infections, among others.

Genetic and environmental influences on obsessive-compulsive symptoms in adults: a population-based twin-family study

BACKGROUND

The contribution of genetic factors to obsessive-compulsive (OC) symptoms has not been examined using a large population-based sample of adults. Furthermore, the extent to which there are qualitative and quantitative differences in genetic architecture between men and women with OC symptoms has not been elucidated.

METHOD

We obtained the Young Adult Self Report Obsessive-Compulsive Scale (YASR-OCS) from a group of 5893 monozygotic (MZ) and dizygotic (DZ) twins, and 1304 additional siblings from the population-based Netherlands Twin Register. Structural equation modelling was used to decompose the variation in OC behaviour into genetic and environmental components and analyse quantitative and qualitative sex differences.

RESULTS

Familial resemblance was the same for DZ twins and non-twin siblings, which means that there was no evidence for a special twin environment. The same genetic risk factors for OC behaviour were expressed in men and women. Depending on the choice of fit index, we found small (39% for men and 50% for women) or no sex differences (47% for both men and women) in heritability. The remaining variance in liability was due to individual-specific environment.

CONCLUSIONS

OC behaviour showed a moderate heritability. At most, small quantitative sex differences were found in the genetic architecture of OC behaviour, and no qualitative sex differences.

Heritability and clinical features of multigenerational families with obsessive-compulsive disorder and hoarding

To date, only one complete genome screen for obsessive-compulsive disorder (OCD) has been published. That study identified a region of suggestive linkage (maximum lod score of 2.25) with a relatively small sample size (N = 56; 27 with OCD). Additional complete genome screens are needed to confirm this finding and identify other regions of linkage. We present the clinical characteristics and power to detect linkage of 11 multigenerational families with OCD and hoarding (N = 92; 44 with OCD), as well as heritability estimates for several quantitative traits. Families with at least two individuals with OCD were identified through probands with childhood-onset OCD. Expected lod scores were calculated for simulated genetic marker data under an additive and two dominant models assuming a dense SNP marker map. All affected individuals had an early age of onset (18 or younger). Hoarding was present in 46% of subjects. Obsessive-compulsive symptoms and hoarding were highly heritable. The maximum mean expected lod score was 3.31 for OCD and 1.39 for hoarding. We found reasonable power to detect regions of interest (lod = 2) for OCD in these families, but will need to expand our family collection to have adequate power to detect regions of interest for hoarding.

Familiality of factor analysis-derived YBOCS dimensions in OCD-affected sibling pairs from the OCD Collaborative Genetics Study

BACKGROUND

Identification of familial, more homogenous characteristics of obsessive-compulsive disorder (OCD) may help to define relevant subtypes and increase the power of genetic and neurobiological studies of OCD. While factor-analytic studies have found consistent, clinically meaningful OCD symptom dimensions, there have been only limited attempts to evaluate the familiality and potential genetic basis of such dimensions.

METHODS

Four hundred eighteen sibling pairs with OCD were evaluated using the Structured Clinical Interview for DSM-IV and the Yale-Brown Obsessive Compulsive Scale (YBOCS) Symptom Checklist and Severity scales.

RESULTS

After controlling for sex, age, and age of onset, robust sib-sib intraclass correlations were found for two of the four YBOCS factors: Factor IV (hoarding obsessions and compulsions (p = .001) and Factor I (aggressive, sexual, and religious obsessions, and checking compulsions; p = .002). Smaller, but still significant, familiality was found for Factor III (contamination/cleaning; p = .02) and Factor II (symmetry/ordering/arranging; p = .04). Limiting the sample to female subjects more than doubled the familiality estimates for Factor II (p = .003). Among potentially relevant comorbid conditions for genetic studies, bipolar I/II and major depressive disorder were strongly associated with Factor I (p < .001), whereas ADHD, alcohol dependence, and bulimia were associated with Factor II (p < .01).

CONCLUSIONS

Factor-analyzed OCD symptom dimensions in sibling pairs with OCD are familial with some gender-dependence, exhibit relatively specific relationships to comorbid psychiatric disorders and thus may be useful as refined phenotypes for molecular genetic studies of OCD.

Prenatal, perinatal, and postnatal risk factors in obsessive-compulsive disorder

BACKGROUND

The etiology of obsessive-compulsive disorder (OCD) remains unknown, although it is thought to involve an interaction of genetic and environmental factors. This study aimed to identify prenatal, perinatal, and postnatal risk factors in OCD.

METHODS

We compared retrospectively 68 OCD patients to 70 control subjects based on responses given on a standardized questionnaire. The questionnaire was designed to evaluate environmental factors, with a special focus on gestation, labor, birth, and early infancy aspects.

RESULTS

The group of OCD patients had risk factors with greater frequency than the control group. Notable among the significant findings (p < or = 0.001) were edema of the hands, feet, or face and excessive weight gain during gestation; hyperemesis gravidarum; prolonged labor; preterm birth; and jaundice. When socioeconomic class was used as a covariable in the logistic regression analysis, prolonged labor and edema during pregnancy remained statistically significant.

CONCLUSIONS

Some early risk factors may be associated with the expression of OCD later in life such as edema during pregnancy and prolonged labor. If our findings are confirmed in future studies, greater attention should be given to such factors in predisposed individuals, especially in prenatal care and delivery.

Genetic counselling for psychiatric disorders

Family, adoption and twin studies demonstrate that many adult psychiatric disorders, including schizophrenia, major depression and bipolar disorder, have a clear genetic component. The aetiology of psychiatric disorders is a complex combination of both genetic and environmental components. While potential susceptibility genes for psychiatric disorders have been identified, interaction with the environment is a crucial component in disease development. Pharmacogenetics and genetic testing have the potential to play key roles in the future of clinical psychiatry. At present, an increased risk of psychiatric disorders can be identified through a detailed family history. The empirical risk of developing a disorder has been determined for many psychiatric disorders and can be used as a general guide. Genetic counselling can extend and enhance patient care by providing information to patients about the complexities of inheriting psychiatric disorders and the associated risks of recurrence. The genetic counselling process can facilitate informed decision making, alleviate misconceptions and reduce stigma through an improved understanding of the genetic cause of psychiatric disorders, and offer support to patients and their families.

The role of clinical phenotypes in understanding the genetics of obsessive-compulsive disorder

Studies have shown that genetic factors are significant in predisposing individuals to obsessive-compulsive disorder (OCD). Family studies have demonstrated significantly higher rates of OCD in parents and siblings of OCD probands with an age-corrected morbid risk ranging from approximately 10% to 35% in first-degree relatives. Twin studies suggest that this familiality is, in part, due to genetic factors, and results from complex segregation analyses imply the existence of genes that have major effects on the transmission of OCD. However, not all cases of OCD seem to be familial. Furthermore, it appears that even in the familial form, there are clinical and genetic heterogeneities. Thus, future studies should either adjust the prevalence rates used in genetic analyses to account for nonfamilial cases or perform separate analyses of those families with a demonstrably familial form of OCD. Furthermore, in complex psychiatric disorders such as OCD, a single genetic locus may influence only a small part of phenotypic variance, and other genetic and environmental factors may interact in determining clinical phenotype. The implications of this finding on clinical and genetic heterogeneity in OCD are discussed.

The current status of association studies in obsessive-compulsive disorder

During the last 2 decades, a large number of association studies have been dedicated to disentangling the genetic components that may be involved in the etiology of OCD. The preliminary and frequently in consistent nature of the data represented in the majority of OCD psychiatric genetic-association studies may seem discouraging. Failure to replicate, and thus to confirm, previously identified susceptibility loci could result from a number of reasons, including the potential for population admixture, the clinical heterogeneity of OCD, small sample sizes (and subsequent lack of power),publication bias, epistasis, or failure to account for multiple testing. Various methods of accounting for these confounders do exist and should be implemented in any genetic-association study that is to be regarded as robust and replicable. Discrepancy between results, however, might be ascribed to the underlying genetic differences between the populations in the respective studies (ie, the investigated variant may be in linkage disequilibrium with the causal variant in one population but not in another). Such discrepancies are difficult to reconcile in single-locus association studies; haplotype analyses(in which a number of variants, usually single-nucleotide polymorphisms occurring on the same gene, are analyzed as a unit) may be able to resolve these uncertainties. Investigating epistatic interactions between variants in other genes that might be involved in the same physiologic pathways would be an alternative means of deciphering the reason for discrepant genetic association results.A valid means of increasing the power (by reducing background noise)would be to stratify the patient sample according to clinically defined sub-types, such as obsession and compulsion subtypes, age at onset of the disorder, and severity of the disorder. Although many of the OCD genetics studies have incorporated investigations of these subtypes [65,66,68,77,84-86,89,107,118,132,133,145,148,149], the number of subjects decreases after stratification, thereby limiting the power of the studies. It may therefore be useful to employ other quantitative approaches in the design of the investigation: the possibility should be considered that OCD symptoms can be broken down into multiple dimensions that are continuous with the normal population [150]. This division would represent an important route to disentangling the complex inheritance of OCD. The results obtained from genetic investigations should be incorporated with clinical and epidemiologic parameters to elucidate correctly the cause of OCD. Future studies should also be extended to incorporate the screening of more polymorphisms, because high-resolution mapping within specific chromosomes will improve knowledge regarding the impact of genetic diversity within the genes or linked chromosomal regions in OCD. The advantages ofa gene-based over a single-nucleotide polymorphism based approach are becoming ever more apparent [151]. Therefore, a more complete assessment of candidate genes, possibly using haplotype blocks that span larger regions,is proposed. In addition, increasing the amount of information on human genome sequences and polymorphisms will make it possible to characterize the amount of sequence variation expressed in the brain and to delineate the potential effects that these variations may have on the development of OCD. Knowledge of new functional variants will emerge as researchers gain an understanding of the potential for genetic variants in the coding and regulatory regions to impact gene expression.

Complex segregation analysis of obsessive-compulsive disorder in families with pediatric probands

OBJECTIVE

The purpose of this study was to assess the mode of inheritance for obsessive-compulsive disorder (OCD) in families ascertained through pediatric probands.

METHODS

We ascertained 52 families (35 case and 17 control families) through probands between the ages of 10 and 17 years. Direct interviews were completed with 215 individuals. Family informant data were collected on another 450 individuals without direct interviews, forming two data sets with one contained within the other. Complex segregation analyses were performed using regressive models as programmed in REGTL in the S.A.G.E. package. All models used in the analyses included sex-specific age and type parameters.

RESULTS

All models that excluded a residual effect of an affected parent were rejected. With that parameter included, the environmental and sporadic models were rejected in comparisons with the most general model in both data sets (all p < 0.005). With the direct interview data, the general codominant Mendelian model was not rejected when compared with the most general model (p = 0.140). We could not distinguish between any of the simple Mendelian models using either data set. However, the dominant Mendelian model provided a somewhat better fit than the other Mendelian models to the direct interview data.

CONCLUSIONS

The results provide evidence for a major susceptibility locus in families with OCD when age at onset is incorporated into the model. Mendelian factors at most partially explained the familial aggregation of the phenotype, and residual familial effects were necessary to fit the data adequately. The results support the importance of linkage efforts by suggesting that a major locus is segregating within a proportion of families with OCD ascertained through pediatric probands.

A family study of early-onset obsessive-compulsive disorder

Results from family studies have suggested that obsessive-compulsive disorder (OCD) is a genetically heterogeneous disorder and have emphasized the importance of identifying valid subgroups of patients. The current study focused on early-onset OCD probands and examined the recurrence risks of OCD and tics among first-degree family members. One hundred six children and adolescents with OCD were recruited from a specialty clinic for OCD and 44 control individuals without OCD were identified by random-digit dialing. These 150 probands and their 465 first-degree relatives were assessed by trained interviewers, using standardized semi-structured interviews. Diagnoses were assigned according to DSM-IV criteria by two experts blind to the proband's diagnosis, through the best-estimate process. These data were analyzed using chi(2) tests, t-tests, logistic regression, and generalized estimating equations (GEE). Case probands had a mean age of onset of OC symptoms of 6.7 years (SD = 2.8), and high comorbid rates with Tourette syndrome (33%) and chronic tics (13.2%). Compared to control relatives, case relatives had higher age-corrected recurrence risks of OCD (22.7% vs. 0.9%, odds ratio (OR) = 32.5, 95% confidence interval (CI) = 4.5-230.8, P = 0.0005), and chronic tics (11.6% vs. 1.7%, OR = 7.9, 95% CI = 1.9-33.1, P = 0.005). A comorbid diagnosis of tics in the relatives was the best predictor of their diagnosis of OCD (OR = 7.35, 95% CI = 3.79-14.25, P < 0.0001). There was a significant correlation between the ages of onset of OCD in probands and their affected relatives. Childhood onset OCD is a highly familial disorder. Some early-onset cases may represent a valid subgroup, with higher genetic loading and shared vulnerability with chronic tic disorders.

A family study of obsessive-compulsive disorder with pediatric probands

Obsessive-compulsive disorder (OCD) is a heterogeneous disorder of unknown etiology. We examined the lifetime history of obsessions, compulsions, and OCD in the first- and second-degree relatives of 35 pediatric probands with OCD and 17 controls with no psychiatric diagnosis. All available first-degree relatives were directly interviewed blind to proband status with two semi-structured interviews. Parents were also interviewed to systematically assess the family psychiatric history of first- and second-degree relatives. Best-estimate lifetime diagnoses were made using all available sources of information. Data were analyzed with logistic regression by the generalized estimating equation method and with robust Cox regression models. The lifetime prevalence of definite OCD was significantly higher in case than control first-degree relatives (22.5% vs. 2.6%, P < 0.05). Compared to controls, case first-degree relatives also had significantly higher lifetime rates of obsessions and compulsions (both P < 0.05). There was no significant difference between case and control second-degree relatives in lifetime rates of OCD. First-degree relatives of case probands with ordering compulsions had a significantly higher lifetime rate of definite and subthreshold OCD than relatives of case probands without ordering compulsions (45.4% vs. 18.8%, P < 0.05). The lifetime prevalence of definite OCD was significantly higher in case first-degree relatives with a history of tics than in case first-degree relatives without a tic history (57.1% vs. 20.9%, P < 0.01). The results provide further evidence that early-onset OCD is highly familial and suggest that two clinical variables are associated with its familial aggregation.

A review of the evidence from family, twin and adoption studies for a genetic contribution to adult psychiatric disorders

Family, twin and adoption studies have provided major evidence for the role of genetics in numerous psychiatric disorders including obsessive-compulsive disorder, panic disorder, major depressive disorder, bipolar disorder, schizophrenia and Alzheimer's disease. As the search for patterns of inheritance and candidate genes of these complex disorders continues, we review relevant findings from quantitative genetic studies and outline the main challenges for the field of psychiatric genetics to focus on in order to more definitively establish the underpinnings of genetic and environmental influences of adult psychopathology.

Use of factor analysis to detect potential phenotypes in obsessive-compulsive disorder

This study aimed to identify symptom dimensions in obsessive-compulsive disorder (OCD) in order to reveal distinct clinical phenotypes. Factor analysis of the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) checklist on item level was performed on data from 335 outpatients with primary OCD. The relationship of demographic and clinical characteristics to the resulting factor scores was examined. A principal component analysis identified the following five consistent symptom dimensions: (1) contamination and cleaning, (2) aggressive, sexual and religious obsessions, (3) somatic obsessions and checking, (4) symmetry and counting/arranging compulsions and (5) high-risk assessment and checking. We observed significant differences in sex distribution, age of onset, Y-BOCS scores and familial prevalence of OCD in relation to the symptom dimensions. These findings provide further evidence for distinct clinical phenotypes in OCD.