Informative phenotypes for genetic studies of psychiatric disorders

Cumulative genetic score of KIAA0319 affects reading ability in Chinese children: moderation by parental education and mediation by rapid automatized naming

KIAA0319, a well-studied candidate gene, has been shown to be associated with reading ability and developmental dyslexia. In the present study, we investigated whether KIAA0319 affects reading ability by interacting with the parental education level and whether rapid automatized naming (RAN), phonological awareness and morphological awareness mediate the relationship between KIAA0319 and reading ability. A total of 2284 Chinese children from primary school grades 3 and 6 participated in this study. Chinese character reading accuracy and word reading fluency were used as measures of reading abilities. The cumulative genetic risk score (CGS) of 13 SNPs in KIAA0319 was calculated. Results revealed interaction effect between CGS of KIAA0319 and parental education level on reading fluency. The interaction effect suggested that individuals with a low CGS of KIAA0319 were better at reading fluency in a positive environment (higher parental educational level) than individuals with a high CGS. Moreover, the interaction effect coincided with the differential susceptibility model. The results of the multiple mediator model revealed that RAN mediates the impact of the genetic cumulative effect of KIAA0319 on reading abilities. These findings provide evidence that KIAA0319 is a risk vulnerability gene that interacts with environmental factor to impact reading abilities and demonstrate the reliability of RAN as an endophenotype between genes and reading associations.

Does the severity of autism symptoms change over time? A review of the evidence, impacts, and gaps in current knowledge

Studies evaluating change in autism symptom severity across the lifespan have yielded inconsistent results, making it difficult to assess the prevalence of meaningful change in autism symptom severity, and what characterizes it. Better understanding the ways in which autism symptoms change over time is crucial, with important implications for intervention. Synthesizing information across past studies, autism symptom severity change (especially decreases) appears common, though stability of symptoms is also frequent. Symptom severity change is characterized by variability in patterns of change between different individuals (between-person), variability in change within a person's trajectory across time (within-person), and variability in change patterns across symptom domains (i.e., social-communication, restricted/repetitive behaviors). Variability in severity change is likely impacted by differences in person-level characteristics (e.g., sex, IQ, sociodemographic factors) as well as developmental processes across time. Numerous methodological issues may impact our ability to understand how common change in symptom severity is, including varying measurement tools, analytic approaches, and change patterns between symptom domains across time. Potential implications of better understanding and characterizing symptom severity change include incorporation of severity change patterns and predictors of change into research on biomarkers, and consideration of such predictors as moderators or mediators of change in clinical practice.

Animal models of developmental dyslexia: Where we are and what we are missing

Developmental dyslexia (DD) is a complex neurodevelopmental disorder and the most common learning disability among both school-aged children and across languages. Recently, sensory and cognitive mechanisms have been reported to be potential endophenotypes (EPs) for DD, and nine DD-candidate genes have been identified. Animal models have been used to investigate the etiopathological pathways that underlie the development of complex traits, as they enable the effects of genetic and/or environmental manipulations to be evaluated. Animal research designs have also been linked to cutting-edge clinical research questions by capitalizing on the use of EPs. For the present scoping review, we reviewed previous studies of murine models investigating the effects of DD-candidate genes. Moreover, we highlighted the use of animal models as an innovative way to unravel new insights behind the pathophysiology of reading (dis)ability and to assess cutting-edge preclinical models.

The Mediation Role of Dynamic Multisensory Processing Using Molecular Genetic Data in Dyslexia

Although substantial heritability has been reported and candidate genes have been identified, we are far from understanding the etiopathogenetic pathways underlying developmental dyslexia (DD). Reading-related endophenotypes (EPs) have been established. Until now it was unknown whether they mediated the pathway from gene to reading (dis)ability. Thus, in a sample of 223 siblings from nuclear families with DD and 79 unrelated typical readers, we tested four EPs (i.e., rapid auditory processing, rapid automatized naming, multisensory nonspatial attention and visual motion processing) and 20 markers spanning five DD-candidate genes (i.e., DYX1C1, DCDC2, KIAA0319, ROBO1 and GRIN2B) using a multiple-predictor/multiple-mediator framework. Our results show that rapid auditory and visual motion processing are mediators in the pathway from ROBO1-rs9853895 to reading. Specifically, the T/T genotype group predicts impairments in rapid auditory and visual motion processing which, in turn, predict poorer reading skills. Our results suggest that ROBO1 is related to reading via multisensory temporal processing. These findings support the use of EPs as an effective approach to disentangling the complex pathways between candidate genes and behavior.

From BDNF to reading: Neural activation and phonological processing as multiple mediators

The BDNF gene is a prominent promoter of neuronal development, maturation and plasticity. Its Val⁶⁶Met polymorphism affects brain morphology and function within several areas and is associated with several cognitive functions and neurodevelopmental disorder susceptibility. Recently, it has been associated with reading, reading-related traits and altered neural activation in reading-related brain regions. However, it remains unknown if the intermediate phenotypes (IPs, such as brain activation and phonological skills) mediate the pathway from gene to reading or reading disability. By conducting a serial multiple mediation model in a sample of 94 children (age 5-13), our findings revealed no direct effects of genotype on reading. Instead, we found that genotype is associated with brain activation in reading-related and more domain general regions which in turn is associated with phonological processing which is associated with reading. These findings suggest that the BDNF-Val⁶⁶Met polymorphism is related to reading via phonological processing and functional activation. These results support brain imaging data and neurocognitive traits as viable IPs for complex behaviors.

Impressions of Humanness for Android Robot may Represent an Endophenotype for Autism Spectrum Disorders

Identification of meaningful endophenotypes may be critical to unraveling the etiology and pathophysiology of autism spectrum disorders (ASD). We investigated whether impressions of "humanness" for android robot might represent a candidate characteristic of an ASD endophenotype. We used a female type of android robot with an appearance similar to that of a real person. Significant differences in overall impressions of 'humanness' for android robot were found between adolescents with ASD and typical development (TD) controls, as well as parents of children with ASD and parents of TD controls. Our current work does suggest robotic systems could potentially play an intelligent role in dissecting ASD heterogeneity.

Persistent primary reflexes affect motor acts: Potential implications for autism spectrum disorder

In typical motor development progress in use of goal-directed actions and communicative gestures depends on the inhibition of several primitive reflexes, especially those that involve the hand or mouth. This study explored the relationship between the persistence of primitive reflexes that involve the hand or mouth and the motor repertoire in a sample of 12- to 17-month-old infants. Moreover, since children with Autism Spectrum Disorders (ASD) often have difficulty in performing skilled movements and show poor gesture repertoire, and since ASD represents the upper extreme of a constellation of traits that may be continuously distributed in the general population, we investigated the relationship between the persistence of primitive reflexes in the same sample of infants and the subclinical autistic traits measured in their parents. Results revealed that the persistence of the primitive reflexes correlated with motor repertoire irrespective of infant's age, and it was greater among infants whose parents had more subclinical autistic traits. Our findings suggest that the persistence of primitive reflexes might alter the developmental trajectory of future motor ability and therefore their evaluation might be an early indicator of atypical development.

Phenotypic Features of Central Sensitization

PURPOSE

The current manuscript reviews approaches for phenotyping central sensitization (CS).

METHODS

The manuscript covers the concept of diagnostic phenotyping, use of endophenotypes, biomarkers, and symptom clusters. Specifically, the components of CS that include general sensory sensitivity (assessed by quantitative sensory testing) and a symptom cluster denoting sleep difficulties, pain, affect, cognitive difficulties, and low energy (S.P.A.C.E.).

RESULTS

Each of the assessment domains are described with reference to CS and their presence in chronic overlapping pain conditions (COPCs) - conditions likely influenced by CS.

CONCLUSIONS

COPCs likely represent clinical diagnostic phenotypes of CS. Components of CS can also be assessed using QST or self-report instruments designed to assess single elements of CS or more general composite indices.

Executive functioning and local-global visual processing: candidate endophenotypes for autism spectrum disorder?

BACKGROUND

Heterogeneity within autism spectrum disorder (ASD) hampers insight in the etiology and stimulates the search for endophenotypes. Endophenotypes should meet several criteria, the most important being the association with ASD and the higher occurrence rate in unaffected ASD relatives than in the general population. We evaluated these criteria for executive functioning (EF) and local-global (L-G) visual processing.

METHODS

By administering an extensive cognitive battery which increases the validity of the measures, we examined which of the cognitive anomalies shown by ASD probands also occur in their unaffected relatives (n = 113) compared to typically developing (TD) controls (n = 100). Microarrays were performed, so we could exclude relatives from probands with a de novo mutation in a known ASD susceptibility copy number variant, thus increasing the probability that genetic risk variants are shared by the ASD relatives. An overview of studies investigating EF and L-G processing in ASD relatives was also provided.

RESULTS

For EF, ASD relatives - like ASD probands - showed impairments in response inhibition, cognitive flexibility and generativity (specifically, ideational fluency), and EF impairments in daily life. For L-G visual processing, the ASD relatives showed no anomalies on the tasks, but they reported more attention to detail in daily life. Group differences were similar for siblings and for parents of ASD probands, and yielded larger effect sizes in a multiplex subsample. The group effect sizes for the comparison between ASD probands and TD individuals were generally larger than those of the ASD relatives compared to TD individuals.

CONCLUSIONS

Impaired cognitive flexibility, ideational fluency and response inhibition are strong candidate endophenotypes for ASD. They could help to delineate etiologically more homogeneous subgroups, which is clinically important to allow assigning ASD probands to different, more targeted, interventions.

When Is an Endophenotype Useful to Detect Association to a Disease? Exploring the Relationships between Disease Status, Endophenotype and Genetic Polymorphisms

OBJECTIVES

To investigate the conditions and analysis strategies required so that endophenotypes related to a disease help discover genetic variants involved in the disease.

METHODS

The association with disease susceptibility variants is examined as a function of the relationships between disease status, endophenotype values and the genotype at another disease or endophenotype susceptibility locus assumed to be previously known, using approximate linear models of allele frequencies as a function of these variables and simulations in the context of family studies when the endophenotype is dichotomous.

RESULTS

Under genetic mechanisms where the risk allele of the tested locus has an effect exclusively in subjects with the endophenotype, the risk allele frequency differences between affected and unaffected subjects are much greater in the subset of subjects with an endophenotype impairment than in those without such an impairment, and power gains are obtained when testing the association under a joint disease-endophenotype model, both with two-locus or single-locus tests. However, with moderate main effect on the risk of disease or endophenotype impairment, testing directly the association between risk allele and disease or endophenotype is more powerful than testing under a joint disease-endophenotype model.

CONCLUSIONS

Joint modeling of disease and endophenotype should be used only in parallel with standard disease association testing.

A genome-wide association study of kynurenic acid in cerebrospinal fluid: implications for psychosis and cognitive impairment in bipolar disorder

Elevated cerebrospinal fluid (CSF) levels of the glia-derived N-methyl-D-aspartic acid receptor antagonist kynurenic acid (KYNA) have consistently been implicated in schizophrenia and bipolar disorder. Here, we conducted a genome-wide association study based on CSF KYNA in bipolar disorder and found support for an association with a common variant within 1p21.3. After replication in an independent cohort, we linked this genetic variant-associated with reduced SNX7 expression-to positive psychotic symptoms and executive function deficits in bipolar disorder. A series of post-mortem brain tissue and in vitro experiments suggested SNX7 downregulation to result in a caspase-8-driven activation of interleukin-1β and a subsequent induction of the brain kynurenine pathway. The current study demonstrates the potential of using biomarkers in genetic studies of psychiatric disorders, and may help to identify novel drug targets in bipolar disorder.

Clinical and Neurobiological Relevance of Current Animal Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social and communication impairments, as well as repetitive and restrictive behaviors. The phenotypic heterogeneity of ASD has made it overwhelmingly difficult to determine the exact etiology and pathophysiology underlying the core symptoms, which are often accompanied by comorbidities such as hyperactivity, seizures, and sensorimotor abnormalities. To our benefit, the advent of animal models has allowed us to assess and test diverse risk factors of ASD, both genetic and environmental, and measure their contribution to the manifestation of autistic symptoms. At a broader scale, rodent models have helped consolidate molecular pathways and unify the neurophysiological mechanisms underlying each one of the various etiologies. This approach will potentially enable the stratification of ASD into clinical, molecular, and neurophenotypic subgroups, further proving their translational utility. It is henceforth paramount to establish a common ground of mechanistic theories from complementing results in preclinical research. In this review, we cluster the ASD animal models into lesion and genetic models and further classify them based on the corresponding environmental, epigenetic and genetic factors. Finally, we summarize the symptoms and neuropathological highlights for each model and make critical comparisons that elucidate their clinical and neurobiological relevance.

Neuropsychological performance measures as intermediate phenotypes for attention-deficit/hyperactivity disorder: A multiple mediation analysis

Genetic influences on dopaminergic neurotransmission have been implicated in attention-deficit hyperactivity disorder (ADHD) and are theorized to impact cognitive functioning via alterations in frontal-striatal circuitry. Neuropsychological functioning has been proposed to account for the potential associations between dopamine candidate genes and ADHD. However, to date, this mediation hypothesis has not been directly tested. Participants were 498 youth ages 6-17 years (mean M = 10.8 years, SD = 2.4 years, 55.0% male). All youth completed a multistage, multiple-informant assessment procedure to identify ADHD and non-ADHD cases, as well as a comprehensive neuropsychological battery. Youth provided a saliva sample for DNA analyses; the 480 base pair variable number of tandem repeat polymorphism of the dopamine active transporter 1 gene (DAT1) and the 120 base pair promoter polymorphism of the dopamine receptor D4 gene (DRD4) were genotyped. Multiple mediation analysis revealed significant indirect associations between DAT1 genotype and inattention, hyperactivity-impulsivity, and oppositionality, with specific indirect effects through response inhibition. The results highlight the role of neurocognitive task performance, particularly response inhibition, as a potential intermediate phenotype for ADHD, further elucidating the relationship between genetic polymorphisms and externalizing psychopathology.

Breast Milk Protects Against Gastrointestinal Symptoms in Infants at High Risk for Autism During Early Development

OBJECTIVES

Parents of children with autism spectrum disorders (ASDs) often report gastrointestinal (GI) dysfunction in their children. The objectives of the present study were to determine whether infants at high risk for developing ASD (ie, siblings of children diagnosed as having ASD) show greater prevalence of GI problems and whether this prevalence is associated with diet and age at weaning from breast milk.

METHODS

Using questionnaires, diet history and GI problems were tracked prospectively and retrospectively in 57 high-risk infants and for comparison in 114 low-risk infants (infants from families without ASD history).

RESULTS

In low-risk infants, prevalence of GI symptoms, in aggregate, did not vary with diet or age of weaning. By contrast, high-risk infants with GI symptoms were weaned earlier than those without symptoms (P < 0.04), and high-risk infants showed greater prevalence of GI symptoms, in aggregate, on a no breast milk diet than on an exclusive breast milk diet (P < 0.017). Constipation, in particular, was more prevalent in high-risk infants compared with low-risk infants (P = 0.01), especially on a no breast milk diet (P = 0.002). High-risk infants who completed weaning earlier than 6 months showed greater prevalence of constipation (P = 0.001) and abdominal distress (P = 0.004) than those fully weaned after 6 months.

CONCLUSIONS

The greater prevalence of GI symptoms in high-risk infants suggests that GI dysfunction during early infant development may be a part of the ASD endophenotype. Late weaning and exclusive breast milk were associated with protection against GI symptoms in high-risk infants.

Estimating genetic effect sizes under joint disease-endophenotype models in presence of gene-environment interactions

Effects of genetic variants on the risk of complex diseases estimated from association studies are typically small. Nonetheless, variants may have important effects in presence of specific levels of environmental exposures, and when a trait related to the disease (endophenotype) is either normal or impaired. We propose polytomous and transition models to represent the relationship between disease, endophenotype, genotype and environmental exposure in family studies. Model coefficients were estimated using generalized estimating equations and were used to derive gene-environment interaction effects and genotype effects at specific levels of exposure. In a simulation study, estimates of the effect of a genetic variant were substantially higher when both an endophenotype and an environmental exposure modifying the variant effect were taken into account, particularly under transition models, compared to the alternative of ignoring the endophenotype. Illustration of the proposed modeling with the metabolic syndrome, abdominal obesity, physical activity and polymorphisms in the NOX3 gene in the Quebec Family Study revealed that the positive association of the A allele of rs1375713 with the metabolic syndrome at high levels of physical activity was only detectable in subjects without abdominal obesity, illustrating the importance of taking into account the abdominal obesity endophenotype in this analysis.

Repetitive behavior in 12-month-olds later classified with autism spectrum disorder

OBJECTIVE

As compared to the utility of early emerging social communicative risk markers for predicting a later diagnosis of autism spectrum disorder (ASD), less is known about the relevance of early patterns of restricted and repetitive behaviors. We examined patterns of stereotyped motor mannerisms and repetitive manipulation of objects in 12-month-olds at high and low risk for developing ASD, all of whom were assessed for ASD at 24 months.

METHOD

Observational coding of repetitive object manipulation and stereotyped motor behaviors in digital recordings of the Communication and Symbolic Behavior Scales was conducted using the Repetitive and Stereotyped Movement Scales for 3 groups of 12-month-olds: low-risk infants (LR, n = 53); high-familial-risk infants who did not meet diagnostic criteria for ASD at 24 months (HR-negative, n = 75); and high-familial-risk infants who met diagnostic criteria for ASD at 24 months (HR-ASD, n = 30).

RESULTS

The HR-ASD group showed significantly more stereotyped motor mannerisms than both the HR-negative group (p = .025) and the LR group (p = .001). The HR-ASD and HR-negative groups demonstrated statistically equivalent repetitive object manipulation scores (p = .431), and both groups showed significantly more repetitive object manipulation than the LR group (p < .040). Combining the motor and object stereotypy scores into a Repetitive and Stereotyped Movement Scales (RSMS) composite yielded a disorder-continuum effect such that each group was significantly different from one another (LR < HR-negative < HR-ASD).

CONCLUSION

These results suggest that targeted assessment of repetitive behavior during infancy may augment early ASD identification efforts.

Limited fine motor and grasping skills in 6-month-old infants at high risk for autism

Atypical motor behaviors are common among children with autism spectrum disorders (ASD). However, little is known about onset and functional implications of differences in early motor development among infants later diagnosed with ASD. Two prospective experiments were conducted to investigate motor skills among 6-month-olds at increased risk (high risk) for ASD (N1  = 129; N2  = 46). Infants were assessed using the Mullen Scales of Early Learning (MSEL) and during toy play. Across both experiments, high-risk infants exhibited less mature object manipulation in a highly structured (MSEL) context and reduced grasping activity in an unstructured (free-play) context than infants with no family history of ASD. Longitudinal assessments suggest that between 6 and 10 months, grasping activity increases in high-risk infants.

Early head growth in infants at risk of autism: a baby siblings research consortium study

OBJECTIVE

Although early brain overgrowth is frequently reported in autism spectrum disorder (ASD), the relationship between ASD and head circumference (HC) is less clear, with inconsistent findings from longitudinal studies that include community controls. Our aim was to examine whether head growth in the first 3 years differed between children with ASD from a high-risk (HR) sample of infant siblings of children with ASD (by definition, multiplex), HR siblings not diagnosed with ASD, and low-risk (LR) controls.

METHOD

Participants included 442 HR and 253 LR infants from 12 sites of the international Baby Siblings Research Consortium. Longitudinal HC data were obtained prospectively, supplemented by growth records. Random effects nonlinear growth models were used to compare HC in HR infants and LR infants. Additional comparisons were conducted with the HR group stratified by diagnostic status at age 3: ASD (n = 77), developmental delay (DD; n = 32), and typical development (TD; n = 333). Nonlinear growth models were also developed for height to assess general overgrowth associated with ASD.

RESULTS

There was no overall difference in head circumference growth over the first 3 years between HR and LR infants, although secondary analyses suggested possible increased total growth in HR infants, reflected by the model asymptote. Analyses stratifying the HR group by 3-year outcomes did not detect differences in head growth or height between HR infants who developed ASD and those who did not, nor between infants with ASD and LR controls.

CONCLUSION

Head growth was uninformative as an ASD risk marker within this HR cohort.

Longitudinal patterns of repetitive behavior in toddlers with autism

BACKGROUND

Recent evidence suggests that restricted and repetitive behaviors may differentiate children who develop autism spectrum disorder (ASD) by late infancy. How these core symptoms manifest early in life, particularly among infants at high risk for the disorder, is not well characterized.

METHODS

Prospective, longitudinal parent-report data (Repetitive Behavior Scales-Revised) were collected for 190 high-risk toddlers and 60 low-risk controls from 12 to 24 months of age. Forty-one high-risk children were classified with ASD at age 2. Profiles of repetitive behavior were compared between groups using generalized estimating equations.

RESULTS

Longitudinal profiles for children diagnosed with ASD differed significantly from high- and low-risk children without the disorder on all measures of repetitive behavior. High-risk toddlers without ASD were intermediate to low risk and ASD positive counterparts. Toddlers with ASD showed significantly higher rates of repetitive behavior across subtypes at the 12-month time point. Repetitive behaviors were significantly correlated with adaptive behavior and socialization scores among children with ASD at 24 months of age, but were largely unrelated to measures of general cognitive ability.

CONCLUSIONS

These findings suggest that as early as 12 months of age, a broad range of repetitive behaviors are highly elevated in children who go on to develop ASD. While some degree of repetitive behavior is elemental to typical early development, the extent of these behaviors among children who develop ASD appears highly atypical.

The persistence of cognitive deficits in remitted and unremitted ADHD: a case for the state-independence of response inhibition

BACKGROUND

Response inhibition, working memory, and response variability are possible endophenotypes of ADHD based on their association with the disorder and evidence of heritability. One of the critical although rarely studied criteria for a valid endophenotype is that it persists despite waxing and waning of the overt manifestations of the disorder, a criterion known as state-independence. This study examined whether these aspects of cognition exhibit state-independence in ADHD.

METHODS

One hundred and seventy-nine children diagnosed with ADHD in a rigorous baseline assessment were contacted for follow-up assessment in adolescence. Of this sample, 130 (73%) were reascertained. At follow-up, children previously diagnosed with ADHD were identified as remittent (n = 24), persistent (n = 64), or in partial remission (n = 42) based on symptoms and impairment of the disorder. Response inhibition, working memory, and response variability were assessed both in childhood (baseline) and adolescence (follow-up) and were compared with age-matched controls (40 children and 28 adolescents) seen at either time point.

RESULTS

Relative to controls, ADHD children showed baseline deficits in response inhibition, working memory, and response variability. Only the group difference in response inhibition remained significant in adolescence. In general, cognitive performance among ADHD participants improved with age and did so regardless of changes in ADHD symptoms and impairment. Within the ADHD group, however, cognitive performance in childhood and in adolescence did not differ amongst those with persistent, remittent, and partially remittent forms of the disorder.

CONCLUSIONS

Results demonstrate that response inhibition not only distinguishes ADHD children from their unaffected peers but is also state-independent, such that deficits remain present irrespective of changes in the disease phenotype. In other words, inhibitory deficits measured in childhood persist into adolescence even when the ADHD phenotype remits. These findings provide further evidence that the ability to stop prepotent actions is an endophenotype of ADHD.

The KMO allele encoding Arg452 is associated with psychotic features in bipolar disorder type 1, and with increased CSF KYNA level and reduced KMO expression

The kynurenine pathway metabolite kynurenic acid (KYNA), modulating glutamatergic and cholinergic neurotransmission, is increased in cerebrospinal fluid (CSF) of patients with schizophrenia or bipolar disorder type 1 with psychotic features. KYNA production is critically dependent on kynurenine 3-monooxygenase (KMO). KMO mRNA levels and activity in prefrontal cortex (PFC) are reduced in schizophrenia. We hypothesized that KMO expression in PFC would be reduced in bipolar disorder with psychotic features and that a functional genetic variant of KMO would associate with this disease, CSF KYNA level and KMO expression. KMO mRNA levels were reduced in PFC of bipolar disorder patients with lifetime psychotic features (P=0.005, n=19) or schizophrenia (P=0.02, n=36) compared with nonpsychotic patients and controls. KMO genetic association to psychotic features in bipolar disorder type 1 was studied in 493 patients and 1044 controls from Sweden. The KMO Arg(452) allele was associated with psychotic features during manic episodes (P=0.003). KMO Arg(452) was studied for association to CSF KYNA levels in an independent sample of 55 Swedish patients, and to KMO expression in 717 lymphoblastoid cell lines and 138 hippocampal biopsies. KMO Arg(452) associated with increased levels of CSF KYNA (P=0.03) and reduced lymphoblastoid and hippocampal KMO expression (P≤0.05). Thus, findings from five independent cohorts suggest that genetic variation in KMO influences the risk for psychotic features in mania of bipolar disorder patients. This provides a possible mechanism for the previous findings of elevated CSF KYNA levels in those bipolar patients with lifetime psychotic features and positive association between KYNA levels and number of manic episodes.

Kainate receptors in health and disease

Our understanding of the molecular properties of kainate receptors and their involvement in synaptic physiology has progressed significantly over the last 30 years. A plethora of studies indicate that kainate receptors are important mediators of the pre- and postsynaptic actions of glutamate, although the mechanisms underlying such effects are still often a topic for discussion. Three clear fields related to their behavior have emerged: there are a number of interacting proteins that pace the properties of kainate receptors; their activity is unconventional since they can also signal through G proteins, behaving like metabotropic receptors; they seem to be linked to some devastating brain diseases. Despite the significant progress in their importance in brain function, kainate receptors remain somewhat puzzling. Here we examine discoveries linking these receptors to physiology and their probable implications in disease, in particular mood disorders, and propose some ideas to obtain a deeper understanding of these intriguing proteins.

Evaluation of the relationship between the ZNF804A single nucleotide polymorphism rs1344706 A/C variant and schizophrenia subtype in Han Chinese patients

OBJECTIVE

Recent genome wide association studies (GWASs) assessing the relationship between schizophrenia (SZ) and the ZNF804A gene, particularly the single nucleotide polymorphism (SNP) rs1344706, have yielded conflicting results. Schizophrenia is a heterogeneous disorder, so it is possible that an association may be restricted to specific SZ subtypes and that population heterogeneity may obscure a contribution of ZNF804A allelic variation to SZ risk. We thus evaluated the association between rs1344706 and different clinical SZ subtypes in a large Han Chinese patient population.

METHOD

The rs1344706 genotype was determined in 1,025 SZ patients and 977 healthy controls using polymerase chain reaction restriction fragment length polymorphisms (PCR-RFLPs). The clinical SZ subtypes included paranoid, catatonic, disintegrated, and undifferentiated, diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition IV (DSM-IV).

RESULTS

No significant differences in genotype and allele frequencies were found between controls and either the total SZ population (A > C, chi2 = 4.339, 2.994; p = 0.227, 0.087, respectively) or paranoid SZ patients (chi2 = 2.053, 0.002; p = 0.562, 0.973, respectively). However, there was a significant association between genotype frequency and SZ subtype (chi2 = 12.632, p = 0.049).

CONCLUSIONS

We found no evidence that the ZNF804A SNP rs1344706 is a susceptibility locus for SZ. However, conflicting results from previous association studies may be due to genetic heterogeneity between different patient SZ subtypes.

Response inhibition and ADHD traits: correlates and heritability in a community sample

Endophenotypes or intermediate phenotypes are of great interest in neuropsychiatric genetics because of their potential for facilitating gene discovery. We evaluated response inhibition, latency and variability measures derived from the stop task as endophenotypes of ADHD by testing whether they were related to ADHD traits in the general population, heritable and shared genetic risk with ADHD traits. Participants were 16,099 children and adolescents, ages 6 to 18 years who visited a local science center. We measured ADHD traits using the Strengths and Weaknesses of ADHD-symptoms and Normal-Behavior (SWAN) rating scale and performance on the stop signal task (SST)-response inhibition (SSRT), response latency (GoRT), and response variability (GoRTSD). Regression analysis was used to assess the relationship of cognitive measures and ADHD traits while controlling for family, age, sex, ethnicity, socioeconomic status and treatment status. Heritability of ADHD and cognitive traits was estimated using SOLAR in 7,483 siblings from 3,507 families that included multiple siblings. Bivariate relationships between pairs of variables were examined. Individuals with greater ADHD trait scores had worse response inhibition, slower response latency, and greater variability. Younger participants and girls had inferior performance although the gender effects were minimal and evident in youngest participants. Inhibition, latency, variability, total ADHD traits, inattention and hyperactivity-impulsivity scores were significantly heritable. ADHD traits and inhibition, but not latency or variability were coheritable. In the largest study in the general population, we found support for the validity of response inhibition as an endophenotype of ADHD.

Investigating phenotypic heterogeneity in children with autism spectrum disorder: a factor mixture modeling approach

BACKGROUND

Autism spectrum disorder (ASD) is characterized by notable phenotypic heterogeneity, which is often viewed as an obstacle to the study of its etiology, diagnosis, treatment, and prognosis. On the basis of empirical evidence, instead of three binary categories, the upcoming edition of the DSM 5 will use two dimensions - social communication deficits (SCD) and fixated interests and repetitive behaviors (FIRB) - for the ASD diagnostic criteria. Building on this proposed DSM 5 model, it would be useful to consider whether empirical data on the SCD and FIRB dimensions can be used within the novel methodological framework of Factor Mixture Modeling (FMM) to stratify children with ASD into more homogeneous subgroups.

METHODS

The study sample consisted of 391 newly diagnosed children (mean age 38.3 months; 330 males) with ASD. To derive subgroups, data from the Autism Diagnostic Interview-Revised indexing SCD and FIRB were used in FMM; FMM allows the examination of continuous dimensions and latent classes (i.e., categories) using both factor analysis (FA) and latent class analysis (LCA) as part of a single analytic framework.

RESULTS

Competing LCA, FA, and FMM models were fit to the data. On the basis of a set of goodness-of-fit criteria, a 'two-factor/three-class' factor mixture model provided the overall best fit to the data. This model describes ASD using three subgroups/classes (Class 1: 34%, Class 2: 10%, Class 3: 56% of the sample) based on differential severity gradients on the SCD and FIRB symptom dimensions. In addition to having different symptom severity levels, children from these subgroups were diagnosed at different ages and were functioning at different adaptive, language, and cognitive levels.

CONCLUSIONS

Study findings suggest that the two symptom dimensions of SCD and FIRB proposed for the DSM 5 can be used in FMM to stratify children with ASD empirically into three relatively homogeneous subgroups.

Association between the GRM7 rs3792452 polymorphism and attention deficit hyperacitiveity disorder in a Korean sample

Background

The purpose of this study was to investigate the association between the ionotropic and glutamate receptors, N-methyl D-asparate 2A (GRIN2A) and 2B (GRIN2B), and the metabotropic glutamate receptor mGluR7 (GRM7) gene polymorphisms and attention-deficit hyperactivity disorder (ADHD) in Korean population.

Methods

We conducted a case–control analysis of 202 ADHD subjects and 159 controls, performed a transmission disequilibrium test (TDT) on 149 trios, and compared scores from the continuous performance test (CPT), the Children’s Depression Inventory (CDI), and the State-Trait Anxiety Inventory for Children (STAIC) according to the genotype of the glutamate receptor genes.

Results

There were no significant differences in the genotype or allele frequencies of the GRIN2A rs8049651, GRIN2B rs2284411, or GRM7 rs37952452 polymorphisms between the ADHD and control groups. For 148 ADHD trios, the TDT analysis also showed no preferential transmission of the GRIN2A rs8049651 or GRIN2B rs2284411 polymorphisms. However, the TDT analysis of the GRM7 rs3792452 polymorphism showed biased transmission of the G allele (χ2 = 4.67, p = 0.031). In the ADHD probands, the subjects with GG genotype in the GRM7 rs37952452 polymorphism had higher mean T-scores for omission errors on the CPT than did those with the GA or AA genotype (t = 3.38, p = 0.001). In addition, the ADHD subjects who were homozygous for the G allele in the GRM7 rs37952452 polymorphism had higher STAIC-T (t = 5.52, p < 0.001) and STAIC-S (t = 2.74, p = 0.007) scores than did those with the GA or AA genotype.

Conclusions

These results provide preliminary evidence of an association between the GRM7 rs37952452 polymorphism and selective attention deficit and anxiety found within the Korean ADHD population.

Phenotype refinement for comorbid attention deficit hyperactivity disorder and reading disability

Comorbidity between Attention Deficit Hyperactivity Disorder (ADHD) and reading disability (RD) is common; however, the heritability of this comorbidity is not well understood. This may be due to the complexity and heterogeneity of ADHD and RD phenotypes. Using alternative ADHD-RD sub-phenotypes instead of those arising from the DSM-IV may lead to greater success in the search for comorbid ADHD-RD susceptibility genes. Therefore, this study aims to refine ADHD-RD phenotypes into homogenous informative sub-phenotypes using latent class analysis (LCA). LCA was performed on 2,610 Australian twin families (6,535 individuals) in order to generate probabilistic genetically distinct classes that define ADHD-RD subtypes, including comorbidity, based on related symptom clusters. The LCA separated the phenotypes for ADHD and RD into nine classes. One class was unaffected; three classes demonstrated the three DSM-IV subtypes of ADHD, three subtypes showed different severities of RD, and two classes expressed a combination of RD and ADHD subtypes. LCA proved effective in refining the phenotypes of ADHD alone, RD alone, and ADHD-RD comorbidity, and its ability to classify them into homogenous groups based on clusters of symptoms, suggesting that the latent classes may be robust enough to use in molecular genetic studies.

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.

The genetics of attention deficit/hyperactivity disorder in adults, a review

The adult form of attention deficit/hyperactivity disorder (aADHD) has a prevalence of up to 5% and is the most severe long-term outcome of this common neurodevelopmental disorder. Family studies in clinical samples suggest an increased familial liability for aADHD compared with childhood ADHD (cADHD), whereas twin studies based on self-rated symptoms in adult population samples show moderate heritability estimates of 30-40%. However, using multiple sources of information, the heritability of clinically diagnosed aADHD and cADHD is very similar. Results of candidate gene as well as genome-wide molecular genetic studies in aADHD samples implicate some of the same genes involved in ADHD in children, although in some cases different alleles and different genes may be responsible for adult versus childhood ADHD. Linkage studies have been successful in identifying loci for aADHD and led to the identification of LPHN3 and CDH13 as novel genes associated with ADHD across the lifespan. In addition, studies of rare genetic variants have identified probable causative mutations for aADHD. Use of endophenotypes based on neuropsychology and neuroimaging, as well as next-generation genome analysis and improved statistical and bioinformatic analysis methods hold the promise of identifying additional genetic variants involved in disease etiology. Large, international collaborations have paved the way for well-powered studies. Progress in identifying aADHD risk genes may provide us with tools for the prediction of disease progression in the clinic and better treatment, and ultimately may help to prevent persistence of ADHD into adulthood.

Symptom dimensions as alternative phenotypes to address genetic heterogeneity in schizophrenia and bipolar disorder

This study introduces a novel way to use the lifetime ratings of symptoms of psychosis, mania and depression in genetic linkage analysis of schizophrenia (SZ) and bipolar disorder (BP). It suggests using a latent class model developed for family data to define more homogeneous symptom subtypes that are influenced by a smaller number of genes that will thus be more easily detectable. In a two-step approach, we proposed: (i) to form homogeneous clusters of subjects based on the symptom dimensions and (ii) to use the information from these homogeneous clusters in linkage analysis. This framework was applied to a unique SZ and BP sample composed of 1278 subjects from 48 large kindreds from the Eastern Quebec population. The results suggest that our strategy has the power to increase linkage signals previously obtained using the diagnosis as phenotype and allows for a better characterization of the linkage signals. This is the case for a linkage signal, which we formerly obtained in chromosome 13q and enhanced using the dimension mania. The analysis also suggests that the methods may detect new linkage signals not previously uncovered by using diagnosis alone, as in chromosomes 2q (delusion), 15q (bizarre behavior), 7p (anhedonia) and 9q (delusion). In the case of the 15q and 2q region, the results coincide with linkage signals detected in other studies. Our results support the view that dissecting phenotypic heterogeneity by modeling symptom dimensions may provide new insights into the genetics of SZ and BP.

Sex differences in repetitive stereotyped behaviors in autism: implications for genetic liability

The implications of the well known sex differences in the prevalence of autism spectrum disorder (ASD) are not well understood. The aim of this paper was to investigate whether these differences might be associated with differences in genetic liability. Individuals with ASD (970 families, 2,028 individuals) were recruited as part of the Autism Genome Project (AGP). The families were differentiated into families containing a female (either female-female or male-female) and those with only males. If the sex with the lower prevalence is associated with a greater genetic liability necessary to cross sex-specific thresholds, the males from female containing families should be more severely affected than males from male only families. Affected subjects from the different types of families with ASD were sampled and compared on the social reciprocity and repetitive behavior scores from the Autism Diagnostic Interview-Revised (ADI-R). In general, females had lower repetitive behavior scores than males. More importantly, males from female containing families had higher repetitive behavior scores than males from male-male families. No such differences were apparent on the social reciprocity scores. These results support the hypothesis of a multiple threshold model of genetic liability of ASD with females having a higher liability for affectation status, at least on the repetitive behavior dimension of the disorder. These data also support the dissociation of the different phenotypic dimensions of ASD in terms of its genetic architecture. The implications of these results for linkage and association studies are discussed.

Neuropsychological endophenotypes in attention-deficit/hyperactivity disorder: a review of genetic association studies

As a relatively large body of research has been published up to now, it may be informative to explore whether the use of endophenotypes has produced consistent findings in attention-deficit hyperactivity disorder (ADHD). We reviewed the results of genetic studies investigating associations between putative susceptibility genes for ADHD and neuropsychological traits relevant for this disorder. A PubMed database search identified 47 studies. Most of them (n = 36) examined a single candidate gene, while seven studies examined two or three genes and only four studies examined 10 genes or more. The most investigated genes were DRD4, DAT1, COMT, MAOA, and DBH. Regarding DRD4, association of high reaction time variability with the 7-R allele absence appears to be the most consistent result. Speed of processing, set shifting, and cognitive impulsiveness were less frequently investigated, but seem to be altered in the 7-R allele carriers. Regarding DAT1, majority of studies reported negative results indicating that this gene may have a modulating effect rather than direct influence on cognitive functioning. The other genes were investigated in fewer studies, and the reported findings need to be replicated. The principal methodological issues that could represent confounding factors and may explain conflicting results are discussed.

Verbal and visual memory impairments among young offspring and healthy adult relatives of patients with schizophrenia and bipolar disorder: selective generational patterns indicate different developmental trajectories

OBJECTIVE

Memory deficits have been shown in patients affected by schizophrenia (SZ) and bipolar (BP)/mood disorder. We recently reported that young high-risk offspring of an affected parent were impaired in both verbal episodic memory (VEM) and visual episodic memory (VisEM). Understanding better the trajectory of memory impairments from childhood to adult clinical status in risk populations is crucial for early detection and prevention. In multigenerational families densely affected by SZ or BP, our aim was to compare the memory impairments observed in young nonaffected offspring with memory functioning in nonaffected adult relatives and patients.

METHODS

For 20 years, we followed up numerous kindreds in the Eastern Québec population. After having characterized the Diagnostic and Statistical Manual of Mental Disorders phenotypes, we assessed cognition (N = 381) in 3 subsamples in these kindreds and in controls: 60 young offspring of a parent affected by SZ or BP, and in the adult generations, 92 nonaffected adult relatives and 40 patients affected by SZ or BP. VEM was assessed with the California Verbal Learning Test and VisEM with the Rey figures.

RESULTS

The VEM deficits observed in the offspring were also found in adult relatives and patients. In contrast, the VisEM impairments observed in the young offspring were present only in patients, not in the adult relatives.

CONCLUSION

Implications for prevention and genetic mechanisms can be drawn from the observation that VEM and VisEM would show distinct generational trajectories and that the trajectory associated with VisEM may offer a better potential than VEM to predict future risk of developing the disease.

A genome-wide linkage scan for distinct subsets of schizophrenia characterized by age at onset and neurocognitive deficits

BACKGROUND

As schizophrenia is genetically and phenotypically heterogeneous, targeting genetically informative phenotypes may help identify greater linkage signals. The aim of the study is to evaluate the genetic linkage evidence for schizophrenia in subsets of families with earlier age at onset or greater neurocognitive deficits.

METHODS

Patients with schizophrenia (n  =  1,207) and their first-degree relatives (n  =  1,035) from 557 families with schizophrenia were recruited from six data collection field research centers throughout Taiwan. Subjects completed a face-to-face semi-structured interview, the Continuous Performance Test (CPT), the Wisconsin Card Sorting Test, and were genotyped with 386 microsatellite markers across the genome.

RESULTS

A maximum nonparametric logarithm of odds (LOD) score of 4.17 at 2q22.1 was found in 295 families ranked by increasing age at onset, which had significant increases in the maximum LOD score compared with those obtained in initial linkage analyses using all available families. Based on this subset, a further subsetting by false alarm rate on the undegraded and degraded CPT obtained further increase in the nested subset-based LOD on 2q22.1, with a score of 7.36 in 228 families and 7.71 in 243 families, respectively.

CONCLUSION

We found possible evidence of linkage on chromosome 2q22.1 in families of schizophrenia patients with more CPT false alarm rates nested within the families with younger age at onset. These results highlight the importance of incorporating genetically informative phenotypes in unraveling the complex genetics of schizophrenia.

Zebrafish behavioural assays of translational relevance for the study of psychiatric disease

Understanding the pathogenesis of the complex behavioural disorders that constitute psychiatric disease is a major challenge for biomedical research. Assays in rodents have contributed significantly to our understanding of the neural basis of behavioural disorders and continue to be one of the main focuses for the development of novel therapeutics. Now, owing to their genetic tractability and optical transparency (allowing in vivo imaging of circuit function) and the rapid expansion of genetic tools, zebrafish are becoming increasingly popular for behavioural genetic research. The increased development of behavioural assays in zebrafish raises the possibility of exploiting the advantages of this system to identify molecular mechanisms contributing to behavioural phenotypes associated with psychiatric disorders as well as potential therapeutics. This mini-review describes behavioural paradigms in zebrafish that can be used to address endophenotypes associated with psychiatric disease. The content reflects the interests of the author and covers tests of cognitive functions, response choice and inhibition, social interaction and executive function.

Young offspring at genetic risk of adult psychoses: the form of the trajectory of IQ or memory may orient to the right dysfunction at the right time

Objective

Neurocognitive dysfunctions analogous to those of adult patients have been detected in children at risk of schizophrenia and bipolar disorder. This led to the following developmental question: Do IQ and memory impairments exhibit different developmental courses from childhood to young adulthood in terms of stability or fluctuations?

Methods

In a high risk sample, we used a step by step sampling approach to narrow-down the early disease mechanisms. Upstream, we started with a 20-year follow-up of 48 densely affected multigenerational kindreds, including 1500 clinically characterized adult members. We then identified 400 adult members affected by a DSM-IV schizophrenia or bipolar disorder. Downstream, we finally focused on 65 offspring (of an affected parent) aged 7 to 22, who were administered a neuropsychological battery. We then constructed cross-sectional trajectories that were compared to those of controls.

Results

The childhood IQ deficit displayed a stability until young adulthood. The delay in visual memory exhibited a non-linear two-stage trajectory: a lagging period during childhood followed by a recuperation period from adolescence until adulthood, as supported by a significant Group x Age Periods interaction. No data suggested deterioration between 7 and 22.

Conclusion

In these offspring at genetic risk, the developmental trajectory of global IQ impairment may not apply to specific domains of cognition such as episodic memory. Different cognitive dysfunctions would mark different developmental courses. The shape of the trajectories might itself have a meaning and provide empirical leads for targeting the right dysfunction at the right time in future prevention research.

Genome-wide association scan of korean autism spectrum disorders with language delay: a preliminary study

OBJECTIVE

Communication problems are a prevalent symptom of autism spectrum disorders (ASDs), which have a genetic background. Although several genome-wide studies on ASD have suggested a number of candidate genes, few studies have reported the association or linkage of specific endophenotypes to ASDs.

METHODS

Forty-two Korean ASD patients who showed a language delay were enrolled in this study with their parents. We performed a genome-wide scan by using the Affymetrix SNP Array 5.0 platform to identify candidate genes responsible for language delay in ASDs.

RESULTS

We detected candidate single-nucleotide polymorphisms (SNPs) in chromosome 11, rs11212733 (p-value=9.76×10(-6)) and rs7125479 (p-value=1.48×10(-4)), as a marker of language delay in ASD using the transmission disequilibrium test and multifactor dimensionality reduction test.

CONCLUSION

Although our results suggest that several SNPs are associated with language delay in ASD, rs11212733 we were not able to observe any significant results after correction of multiple comparisons. This may imply that more samples may be required to identify genes associated with language delay in ASD.

Latent class model with familial dependence to address heterogeneity in complex diseases: adapting the approach to family-based association studies

Clinical diagnoses of complex diseases may often encompass multiple genetically heterogeneous disorders. One way of dissecting this heterogeneity is to apply latent class (LC) analysis to measurements related to the diagnosis, such as detailed symptoms, to define more homogeneous disease sub-types, influenced by a smaller number of genes that will thus be more easily detectable. We have previously developed a LC model allowing dependence between the latent disease class status of relatives within families. We have also proposed a strategy to incorporate the posterior probability of class membership of each subject in parametric linkage analysis, which is not directly transferable to genetic association methods. Under the framework of family-based association tests (FBAT), we now propose to make the contribution of an affected subject to the FBAT statistic proportional to his or her posterior class membership probability. Simulations showed a modest but robust power advantage compared to simply assigning each subject to his or her most probable class, and important power gains over the analysis of the disease diagnosis without LC modeling under certain scenarios. The use of LC analysis with FBAT is illustrated using autism spectrum disorder (ASD) symptoms on families from the Autism Genetics Research Exchange, where we examined eight regions previously associated to autism in this sample. The analysis using the posterior probability of membership to an LC detected an association in the JARID2 gene as significant as that for ASD (P = 3 × 10(-5)) but with a larger effect size (odds ratio = 2.17 vs. 1.55).

Contrast sensitivity for motion detection and direction discrimination in adolescents with autism spectrum disorders and their siblings

The magnocellular (M) pathway hypothesis proposes that impaired visual motion perception observed in individuals with Autism Spectrum Disorders (ASD) might be mediated by atypical functioning of the subcortical M pathway, as this pathway provides the bulk of visual input to cortical motion detectors. To test this hypothesis, we measured luminance and chromatic contrast sensitivity, thought to tap M and Parvocellular (P) pathway processing, respectively. We also tested the hypothesis that motion processing is impaired in ASD using a novel paradigm that measures motion processing while controlling for detectabilty. Specifically, this paradigm compares contrast sensitivity for detection of a moving grating with contrast sensitivity for direction-of-motion discrimination of that same moving grating. Contrast sensitivities from adolescents with ASD were compared to typically-developing adolescents, and also unaffected siblings of individuals with ASD (SIBS). The results revealed significant group differences on P, but not M, pathway processing, with SIBS showing higher chromatic contrast sensitivity than both participants with ASD and TD participants. This atypicality, unique to SIBS, suggests the possible existence of a protective factor in these individuals against developing ASD. The results also revealed impairments in motion perception in both participants with ASD and SIBS, which may be an endophenotype of ASD. This impairment may be driven by impairments in motion detectors and/or by reduced input from neural areas that project to motion detectors, the latter possibility being consistent with the notion of reduced connectivity between neural areas in ASD.

General and social anxiety in the BTBR T+ tf/J mouse strain

BTBR T+ tf/J (BTBR) is an inbred mouse strain that shows behavioral traits with analogies to the three diagnostic symptoms of autism spectrum disorder (ASD); deficits in social interaction, impaired communication, and repetitive behaviors with restricted interests. Previous findings reveal that when compared to C57BL/6J (B6) and other inbred strains, BTBR exhibit normal to low anxiety-like traits in paradigms designed to assess anxiety-related behaviors. The current study assessed the generality of these anxiety findings. In experiment 1, B6 and BTBR mice were tested in the elevated plus maze (EPM), mouse defense test battery (MDTB) and elevated zero-maze. BTBR mice exhibited an anxiogenic profile in the EPM, with a reduction in open arm time and an increase in risk assessment behaviors, as compared to B6. In the MDTB, BTBR showed enhanced vocalization to the predator, and significantly less locomotor activity than B6 in the pre-threat situation, but significantly more locomotion than B6 following exposure to a predator threat, suggesting enhanced defensiveness to the predator. In the zero-maze, BTBR mice showed a significantly higher number of entries and time spent in the open segments of the apparatus, when compared to B6. In experiment 2, a three-chambered social preference test was used to evaluate effects of the systemic administration of an anxiolytic compound, diazepam, on B6 and BTBR social approach. Diazepam consistently increased time in the compartment containing the social stimulus, for both B6 and BTBR mice. However, in the vehicle treated groups, B6 mice spent significantly more time while BTBR mice spent significantly less time in the social stimulus compartment; after diazepam administration both B6 and BTBR strains significantly preferred the social stimulus chamber. These results suggest that while the anxiety responses of BTBR mice to novel situations (EPM and zero-maze) are inconsistent, BTBR mice appear to be more defensive to animate threat stimuli (predator or another mouse). Reduction of anxiety by diazepam normalized the social preference of BTBR for a mouse stimulus in the three-chambered test.

Neurotrophin-3 gene, intelligence, and selective attention deficit in a Korean sample with attention-deficit/hyperactivity disorder

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) is a complex neurodevelopmental disorder with a strong genetic component. Neurotrophin-3 (NTF3), which participates in the differentiation and survival of dopaminergic and noradrenergic neurons, has been identified as a factor in the development of ADHD. We investigated the relationships between ADHD and NTF3 gene polymorphism.

METHODS

We conducted a case-control analysis of 202 ADHD subjects and 159 controls, performed a transmission disequilibrium test (TDT) on 151 trios, and compared the intelligence quotient (IQ) and a continuous performance test (CPT) according to the genotype of two single-nucleotide polymorphisms (SNPs) (rs6332 and rs6489630) in the NTF3 gene.

RESULTS

In the case-control and family-based analyses, NTF3 was not significantly associated with ADHD. However, in the ADHD probands, the subjects with AA genotype in the rs6332 SNP had significantly higher mean T-scores for commission errors on the CPT than did those with the AG genotypes (p=0.045). The mean IQ of the ADHD probands who had the CC genotype of the rs6489630 SNP were higher compared with those who had the CT or TT genotype (p=0.035). The mean T-score for response time on the CPT was higher in the subjects with TT genotype in the rs6489630 SNP compared to those with the CC or CT genotype, even after adjusting for the effect of IQ (p=0.021).

CONCLUSIONS

These results provide preliminary evidence of an association between NTF3 and the intelligence and selective attention deficit in the Korean population.

Complexity and accountability: the witches' brew of psychiatric genetics

This paper examines the role of complexity in descriptions of the aetiology of common psychiatric disorders. While scientists attest to the discovery of an underlying reality of complex inheritance--the so-called 'witches' brew' of genetic and non-genetic factors--we argue that 'complexity' also performs rhetorical work. In our analysis of scientific review papers (1999-2008), we find a relatively stable genre of accountability in which descriptions of complexity appear to neutralize past failures by incorporating different and sometimes competing methodological perspectives. We identify two temporal strategies: retrospective accounting, which reconstructs a history of psychiatric genetics that deals with the recent failures, citing earlier twin studies as proof of the heritability of common psychiatric disorders; and prospective accounting, which engages in the careful reconstruction of expectations by balancing methodological limitations with moderated optimism. Together, these strategies produce a simple-to-complex narrative that belies the ambivalent nature of complexity. We show that the rhetorical construction of complexity in scientific review papers is oriented to bridging disciplinary boundaries, marshalling new resources and reconstructing expectations that justify delays in gene discovery and risk prediction.

Pharmacogenetics of drug dependence: role of gene variations in susceptibility and treatment

Drug dependency is a highly prevalent mental health disorder that imposes a significant burden on those directly affected, health care systems, and society in general. There is substantial heritability in the susceptibility to drug addiction, which indicates that there are genetic risk factors. Variation in the human genome is abundant and can directly affect drug dependency phenotypes, for example, by altering the function of a gene product or by altering gene expression. Pharmacogenetic studies can assess the effects of genetic variation on the risk for a particular phenotype (e.g., being an alcoholic). In addition, pharmacogenetic variability in treatment efficacy and adverse reactions can be investigated to identify particular genetic variants associated with altered responses. This review highlights examples of genetic variations that are important in the development and maintenance of specific drug dependencies as well as those that affect the response to treatment.

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.

Systems Factorial Technology provides new insights on global-local information processing in autism spectrum disorders

Previous studies of global-local processing in autism spectrum disorders (ASDs) have indicated mixed findings, with some evidence of a local processing bias, or preference for detail-level information, and other results suggesting typical global advantage, or preference for the whole or gestalt. Findings resulting from this paradigm have been used to argue for or against a detail focused processing bias in ASDs, and thus have important theoretical implications. We applied Systems Factorial Technology, and the associated Double Factorial Paradigm (both defined in the text), to examine information processing characteristics during a divided attention global-local task in high-functioning individuals with an ASD and typically developing controls. Group data revealed global advantage for both groups, contrary to some current theories of ASDs. Information processing models applied to each participant revealed that task performance, although showing no differences at the group level, was supported by different cognitive mechanisms in ASD participants compared to controls. All control participants demonstrated inhibitory parallel processing and the majority demonstrated a minimum-time stopping rule. In contrast, ASD participants showed exhaustive parallel processing with mild facilitatory interactions between global and local information. Thus our results indicate fundamental differences in the stopping rules and channel dependencies in individuals with an ASD.

Retinal response to light in young nonaffected offspring at high genetic risk of neuropsychiatric brain disorders

BACKGROUND

In neuropsychiatric brain disorders, such as schizophrenia (SZ) and bipolar disorder (BD), the biased effect of chronic drug therapy and the toxic effect of illness once installed constitute obstacles to the identification of valid biomarkers. Such biomarkers could lie at the level of retinal function where anomalies have already been reported in adults suffering from neuropsychiatric disorders. Here, we report a specific electroretinographic (ERG) anomaly in young nonaffected and nonmedicated offspring at high genetic risk (HR) of these disorders.

METHODS

Electroretinography was performed in 29 HR offspring having one parent affected by DSM-IV SZ or BD (mean age: 20.8 years, SD 4.4) and 29 healthy control subjects (mean age: 20.6 years, SD 4.2). The HRs' parents descended from multigenerational families affected by SZ or BD.

RESULTS

Rod ERG (b-wave amplitude at V(max)) in HRs was significantly lower than control subjects (p < .0001; effect size of -1.47), whereas the cone ERG V(max) showed no difference (p = .27). No effects of gender, age, and seasons of testing were observed. The anomaly in retinal response (rod V(max) b-wave amplitude) was observed independently of parents' diagnosis (SZ; p = .007, effect size of -1.09; BD: p < .0001, effect size of -1.88) and was present in both the younger and older HRs (effect size of -1.6 and -1.8, respectively).

CONCLUSIONS

A rod retinal response anomaly before the age of the disease incidence may represent an early and specific biomarker of risk with meaning for further genetic and prevention research.

Anxiety in boys with attention-deficit/hyperactivity disorder with and without chronic multiple tic disorder

OBJECTIVE

This study examined the psychosocial and behavioral concomitants of anxiety in clinic-referred boys with attention-deficit/hyperactivity disorder (ADHD) with and without chronic multiple tic disorder (CMTD).

METHOD

ADHD boys with (n = 65) and without (n = 94) CMTD were evaluated with measures of psychiatric symptoms, mental health risk factors, and academic and social performance.

RESULTS

Boys with CMTD evidenced more severe anxiety and less social competence and were more likely to be living with only one biological parent than the ADHD Only group, but the magnitude of group differences was generally small. The severity of generalized anxiety, separation anxiety, social phobia, and obsessive-compulsive symptoms were uniquely associated with a different pattern of risk factors, and there was some evidence that these patterns differed for the two groups of boys.

CONCLUSION

Boys with CMTD had a relatively more severe and complex pattern of anxiety that was associated with different clinical features, all of which suggests that ADHD plus CMTD might better be conceptualized as a distinct clinical entity from ADHD Only. However, findings from the extant literature are mixed, and therefore this remains a topic for further study.

Systematic genotype-phenotype analysis of autism susceptibility loci implicates additional symptoms to co-occur with autism

Many genetic studies in autism have been performed, resulting in the identification of multiple linkage regions and cytogenetic aberrations, but little unequivocal evidence for the involvement of specific genes exists. By identifying novel symptoms in these patients, enhanced phenotyping of autistic individuals not only improves understanding and diagnosis but also helps to define biologically more homogeneous groups of patients, improving the potential to detect causative genes. Supported by recent copy number variation findings in autism, we hypothesized that for some susceptibility loci, autism resembles a contiguous gene syndrome, caused by aberrations within multiple (contiguous) genes, which jointly increases autism susceptibility. This would result in various different clinical manifestations that might be rather atypical, but that also co-occur with autism. To test this hypothesis, 13 susceptibility loci, identified through genetic linkage and cytogenetic analyses, were systematically analyzed. The Online Mendelian Inheritance in Man database was used to identify syndromes caused by mutations in the genes residing in each of these loci. Subsequent analysis of the symptoms expressed within these disorders allowed us to identify 33 symptoms (significantly more than expected, P=0.037) that were over-represented in previous reports mapping to these loci. Some of these symptoms, including seizures and craniofacial abnormalities, support our hypothesis as they are already known to co-occur with autism. These symptoms, together with ones that have not previously been described to co-occur with autism, might be considered for use as inclusion or exclusion criteria toward defining etiologically more homogeneous groups for molecular genetic studies of autism.