Early expression of a pathophysiological feature of schizophrenia: saccadic intrusions into smooth-pursuit eye movements in school-age children vulnerable to schizophrenia

The Clinical Presentation of Childhood-Onset Schizophrenia: A Literature Review

This literature review explores the research on the clinical presentation of childhood-onset schizophrenia (COS) that was conducted in the period 1994–2004. A literature search was done using Internet search engines and psychological databases to collect English-language journal articles from 1994 onwards. Research indicates that COS is a stable diagnosis. Generally, there is a clear history of premorbid abnormalities, an insidious onset and a deteriorating course. For the majority of cases there seems to be a poor outcome. Despite the limitations in the research conducted thus far, findings provide important insights into COS and several possibilities for future research.

Psychophysiological markers of vulnerability to psychopathology in men with an extra X chromosome (XXY)

Studying genetically defined syndromes associated with increased risk for psychopathology may help in understanding neurodevelopmental mechanisms related to risk for psychopathology. Klinefelter syndrome (47,XXY) is one of the most common sex chromosomal aneuploidies (1 in 650 male births) and associated with increased vulnerability for psychopathology, including psychotic symptoms. Yet, it remains unknown whether this increased risk is associated with underlying psychophysiological mechanisms that are typically deficient in individuals with psychotic disorders. The present study assessed three “classic” psychophysiological markers of psychosis in Klinefelter syndrome (KS): smooth pursuit eye movements (SPEM), prepulse inhibition (PPI) and P50 suppression. Fourteen adults with KS and 15 non-clinical adults participated in the study. Data on SPEM (reflecting visuo-motor control) as well as PPI and P50 suppression (reflecting sensory gating) were collected. Dysfunctions in SPEM were observed in individuals with KS, with less smooth pursuit as expressed in lower position gain. Also, reduced sensory gating in individuals with KS was suggested by significantly reduced prepulse inhibition of the startle response (PPI) (effect size 1.6). No abnormalities were found in suppression of the P50 (effect size 0.6). We speculate that impairments in these psychophysiological mechanisms may reflect core brain dysfunctions that may also mediate the described increased vulnerability for psychotic symptoms in KS. Although speculative, such deficit specific, rather than disorder specific, psychophysiological dysfunctions in KS might convey vulnerability to other types of psychopathology as well. As KS already can be diagnosed prenatally, the predictive value of childhood impairments in prepulse inhibition and smooth pursuit for development of psychopathology later in life could be assessed. In sum, studying individuals with KS may prove to be an avenue of research leading to new hypotheses and insights into “at risk” pathways to psychopathology.

Smooth pursuit eye movement (SPEM) in patients with multiple complex developmental disorder (MCDD), a subtype of the pervasive developmental disorder

OBJECTIVE

Multiple complex developmental disorder (MCDD) is a well-defined and validated behavioural subtype of pervasive developmental disorder-not otherwise specified (PDD-NOS) and is thought to be associated with a higher risk of developing a schizophrenic spectrum disorder. The question was addressed whether patients with MCDD show the same psychophysiological abnormalities as seen in patients with schizophrenia.

METHOD

Smooth pursuit eye movement (pursuit gain and saccadic parameters) was measured in children with either MCDD (n=18) or autism (n=18), and in age- and IQ-matched controls (n=36), as well as in a group of adult patients with schizophrenia (n=14) and a group of adult controls (n=17).

RESULTS

We found the expected effect of lower velocity gain and increased number of saccades in schizophrenic patients. Children with MCDD also showed a lower velocity gain compared to controls children. In contrast, velocity gain was similar in autistic subjects and controls. No differences for velocity gain were found in a direct comparison between MCDD and autism. Saccadic parameters were not significantly different from controls in either MCDD or autistic subjects.

CONCLUSION

Children with MCDD, like schizophrenic adults, show a reduced velocity gain, which could indicate that schizophrenia spectrum disorders and MCDD share (at least to some degree) a common neurobiological background.

SPEM dysfunction and general schizotypy as measured by the SSQ: a controlled study

Background

SPEM dysfunction is a well-known phenomenon in schizophrenia. The principal aim of the present study was to examine whether SPEM dysfunction is already observable in subjects scoring high on a specific measure of schizotypy (SSQ General Schizotypy) that was selected because of its intimate relationship with schizophrenic prodromal unfolding.

Methods

Applying ANOVAs, we determined the relationship of subjects' scores on SSQ General Schizotypy and eye movements elicited by targets of different speed. We also examined whether there exists an association between our schizotypy measure and pupil size.

Results

We found more SPEM dysfunction in subjects scoring high on SSQ General Schizotypy than in subjects scoring average on that factor, irrespective of the speed of the target. No relationship was found between baseline pupil size and General Schizotypy.

Conclusion

The present study provides additional evidence that SPEM dysfunction is associated with schizotypic features that precede the onset of schizophrenia and is already observable in general population subjects that show these features.

Eye movement dysfunction in first-degree relatives of patients with schizophrenia: a meta-analytic evaluation of candidate endophenotypes

Several forms of eye movement dysfunction (EMD) are regarded as promising candidate endophenotypes of schizophrenia. Discrepancies in individual study results have led to inconsistent conclusions regarding particular aspects of EMD in relatives of schizophrenia patients. To quantitatively evaluate and compare the candidacy of smooth pursuit, saccade and fixation deficits in first-degree biological relatives, we conducted a set of meta-analytic investigations. Among 18 measures of EMD, memory-guided saccade accuracy and error rate, global smooth pursuit dysfunction, intrusive saccades during fixation, antisaccade error rate and smooth pursuit closed-loop gain emerged as best differentiating relatives from controls (standardized mean differences ranged from .46 to .66), with no significant differences among these measures. Anticipatory saccades, but no other smooth pursuit component measures were also increased in relatives. Visually-guided reflexive saccades were largely normal. Moderator analyses examining design characteristics revealed few variables affecting the magnitude of the meta-analytically observed effects. Moderate effect sizes of relatives v. controls in selective aspects of EMD supports their endophenotype potential. Future work should focus on facilitating endophenotype utility through attention to heterogeneity of EMD performance, relationships among forms of EMD, and application in molecular genetics studies.

A review on eye movement studies in childhood and adolescent psychiatry

The neural substrates of eye movement measures are largely known. Therefore, measurement of eye movements in psychiatric disorders may provide insight into the underlying neuropathology of these disorders. Visually guided saccades, antisaccades, memory guided saccades, and smooth pursuit eye movements will be reviewed in various childhood psychiatric disorders. The four aims of this review are (1) to give a thorough overview of eye movement studies in a wide array of psychiatric disorders occurring during childhood and adolescence (attention-deficit/hyperactivity disorder, oppositional deviant disorder and conduct disorder, autism spectrum disorders, reading disorder, childhood-onset schizophrenia, Tourette's syndrome, obsessive compulsive disorder, and anxiety and depression), (2) to discuss the specificity and overlap of eye movement findings across disorders and paradigms, (3) to discuss the developmental aspects of eye movement abnormalities in childhood and adolescence psychiatric disorders, and (4) to present suggestions for future research. In order to make this review of interest to a broad audience, attention will be given to the clinical manifestation of the disorders and the theoretical background of the eye movement paradigms.

Neurophysiological endophenotypes across bipolar and schizophrenia psychosis

The search for liability genes of the world's 2 major psychotic disorders, schizophrenia and bipolar disorder I (BP-I), has been extremely difficult even though evidence suggests that both are highly heritable. This difficulty is due to the complex and multifactorial nature of these disorders. They encompass several intermediate phenotypes, some overlapping across the 2 psychotic disorders that jointly and/or interactively produce the clinical manifestations. Research of the past few decades has identified several neurophysiological deficits in schizophrenia that frequently occur before the onset of psychosis. These include abnormalities in smooth pursuit eye movements, P50 sensory gating, prepulse inhibition, P300, mismatch negativity, and neural synchrony. Evidence suggests that many of these physiological deficits are distinct from each other. They are stable, mostly independent of symptom state and medications (with some exceptions) and are also observed in non-ill relatives. This suggests a familial and perhaps genetic nature. Some deficits are also observed in the BP-I probands and to a lesser extent their relatives. These deficits in physiological measures may represent the intermediate phenotypes that index small effects of genes (and/or environmental factors). The use of these measures in genetic studies may help the hunt for psychosis liability genes and clarify the extent to which the 2 major psychotic disorders share etio-pathophysiology. In spite of the rich body of work describing these neurophysiological measures in psychotic disorders, challenges remain: Many of the neurophysiological phenotypes are still relatively complex and are associated with low heritability estimates. Further refinement of these physiological phenotypes is needed that could identify specific underlying physiological deficits and thereby improve their heritability estimates. The extent to which these neurophysiological deficits are unique or overlap across BP-I and schizophrenia is unclear. And finally, the clinical and functional consequences of the neurophysiological deficits both in the probands and their relatives are not well described.

A brief taxometrics primer

Taxometric procedures provide an empirical means of determining which psychiatric disorders are typologically distinct from normal behavioral functioning. Although most disorders reflect extremes along continuously distributed behavioral traits, identifying those that are discrete has important implications for accurate diagnosis, effective treatment, early identification of risk, and improved understanding of etiology. This article provides (a) brief descriptions of the conceptual bases of several taxometric procedures, (b) example analyses using simulated data, and (c) strategies for avoiding common pitfalls that are often observed in taxometrics research. To date, most taxometrics studies have appeared in the adult psychopathology literature. It is hoped that this primer will encourage interested readers to extend taxometrics research to child and adolescent populations.

Neurophysiological biomarkers for drug development in schizophrenia

Schizophrenia represents a pervasive deficit in brain function, leading to hallucinations and delusions, social withdrawal and a decline in cognitive performance. As the underlying genetic and neuronal abnormalities in schizophrenia are largely unknown, it is challenging to measure the severity of its symptoms objectively, or to design and evaluate psychotherapeutic interventions. Recent advances in neurophysiological techniques provide new opportunities to measure abnormal brain functions in patients with schizophrenia and to compare these with drug-induced alterations. Moreover, many of these neurophysiological processes are phylogenetically conserved and can be modelled in preclinical studies, offering unique opportunities for use as translational biomarkers in schizophrenia drug discovery.

Use of the ADOS and ADI-R in children with psychosis: importance of clinical judgment

The Autism Diagnostic Observation Schedule (ADOS) and the Autism Diagnostic Interview - Revised (ADI-R) are considered to be the 'gold standard' in diagnostic evaluations for autism. Developed as research tools and now gaining wide clinical use, the ADOS/ADI-R assessment package has been demonstrated to differentiate children with autism from those with other developmental disabilities; however, little work concerning the reliability and validity of the tools in children with a known history of psychosis has been undertaken. We report on the administration of the ADOS, ADI-R and clinical judgment in three cases of Childhood-Onset Schizophrenia. All 3 children met both ADOS and ADI-R criteria for an autism spectrum diagnosis, even though none of them received a clinical diagnosis of autism from either a research child psychiatrist or an experienced clinically trained, research psychologist with expertise in autism. Issues concerning overlap of symptom presentation and implications for research and clinical use of these assessment tools are discussed.

The stability of inhibitory and working memory deficits in children and adolescents who are children of parents with schizophrenia

Cognitive deficits are a central feature of schizophrenia and occur in first-degree relatives of schizophrenic probands, even in the absence of psychotic symptoms. A number of cognitive domains have been implicated including measures of response inhibition and working memory. While the stability of cognitive deficits has been demonstrated in individuals with schizophrenia, stability of deficits has not been explored in first-degree relatives. This report focuses on 25 children (ages 6-15 years), all with at least one schizophrenic parent. The children were assessed twice, utilizing inhibitory and working memory tasks, with a mean 2.6 years between visits. Stop reaction time (a measure of motor inhibition) and performance on a counting span task (a measure of verbal working memory) were borderline to mildly impaired (compared with a typically developing comparison group) at both visits with similar effect sizes (stopping task time 1, effect size = 0.46, time 2 effect size = 0.50; counting span time 1 effect size = 0.53, time 2 effect size = 0.42). For these 2 tasks, individual age-adjusted scores also correlated across both time points (r = 0.41-0.76) suggesting that individual children maintained deficits across time. As etiologically driven strategies are developed for the cognitive deficits of schizophrenia, expansion of these treatments to relatives who share the cognitive but not the psychotic symptoms may be worth exploring.

Ten good reasons to consider biological processes in prevention and intervention research

Most contemporary accounts of psychopathology acknowledge the importance of both biological and environmental influences on behavior. In developmental psychopathology, multiple etiological mechanisms for psychiatric disturbance are well recognized, including those operating at genetic, neurobiological, and environmental levels of analysis. However, neuroscientific principles are rarely considered in current approaches to prevention or intervention. In this article, we explain why a deeper understanding of the genetic and neural substrates of behavior is essential for the next generation of preventive interventions, and we outline 10 specific reasons why considering biological processes can improve treatment efficacy. Among these, we discuss (a) the role of biomarkers and endophenotypes in identifying those most in need of prevention; (b) implications for treatment of genetic and neural mechanisms of homotypic comorbidity, heterotypic comorbidity, and heterotypic continuity; (c) ways in which biological vulnerabilities moderate the effects of environmental experience; (d) situations in which Biology x Environment interactions account for more variance in key outcomes than main effects; and (e) sensitivity of neural systems, via epigenesis, programming, and neural plasticity, to environmental moderation across the life span. For each of the 10 reasons outlined we present an example from current literature and discuss critical implications for prevention.

High rates of comorbidity are found in childhood-onset schizophrenia

BACKGROUND

For adults with schizophrenia, comorbidity is common and contributes to impairment. Thus, there has been an increasing effort to identify and treat comorbid symptoms. This report extends that work by examining comorbidity in children and young adolescents with childhood-onset schizophrenia.

METHODS

Eighty-two children, ages 4-15 years, with schizophrenia or schizoaffective disorder received structured diagnostic instruments for symptoms and pharmacological treatment history. DSM-IV diagnoses were identified using a non-hierarchical approach.

RESULTS

Eighty-one (99%) of the children with schizophrenia or schizoaffective disorder had at least one comorbid psychiatric illness: attention deficit hyperactivity disorder (84%), oppositional defiant disorder (43%), depression (30%), and separation anxiety disorder (25%) were the most common comorbid conditions identified. Pharmacological treatment of the comorbid conditions was uncommon.

DISCUSSION

Comorbid syndromes are common in children and young adolescents with schizophrenia or schizoaffective disorder. Pharmacological treatment of the comorbid conditions is rare; however it is unclear if this is due to DSM-IVs hierarchical diagnostic system or to a lack of empirically driven guidelines for appropriate treatment. Additional efforts focused on comorbidity in very-early-onset schizophrenia are warranted.

Endophenotypes in the Genetic Analyses of Mental Disorders

Common mental disorders such as schizophrenia, bipolar disorder, and severe major depression are highly heritable, but differ from single-gene (Mendelian) diseases in that they are the end products of multiple causes. Although this fact may help explain their prevalence from an evolutionary perspective, the complexity of the causes of these disorders makes identification of disease-promoting genes much more difficult. The "endophenotype" approach is an alternative method for measuring phenotypic variation that may facilitate the identification of susceptibility genes for complexly inherited traits. Here we examine the endophenotype construct in context of psychiatric genetics. We first develop an evolutionary theoretical framework for common mental disorders and differentiate them from simpler, single-gene disorders. We then provide a definition and description of endophenotypes, elucidating several features that will make a proposed endophenotype useful in psychiatric genetic research and evaluating the methods for detecting and validating such endophenotypes. We conclude with a review of recent results in the schizophrenia literature that illustrate the usefulness of endophenotypes in genetic analyses of mental disorders, and discuss implications of these findings for models of disease causation and nosology. Given that in mental disorders as in behavior generally, the pathways from genotypes to phenotypes are circuitous at best, discernment of endophenotypes more proximal to the effects of genetic variation will aid attempts to link genes to disorders.

Early biomarkers of psychosis

Biological traits that are predictive of the later development of psychosis have not yet been identified. The complex, multidetermined nature of schizophrenia and other psychoses makes it unlikely that any single biomarker will be both sensitive and specific enough to unambiguously identify individuals who will later become psychotic. However, current genetic research has begun to identify genes associated with schizophrenia, some of which have phenotypes that appear early in life. While these phenotypes have low predictive power for identifying individuals who will become psychotic, they do serve as biomarkers for pathophysiological processes that can become the targets of prevention strategies. Examples are given from work on the role of the alpha(T)nicotinic receptor and its gene CHRNA7 on chromosome 15 in the neurobiology and genetic transmission of schizophrenia.

Saccadic eye movement task identifies cognitive deficits in children with schizophrenia, but not in unaffected child relatives

BACKGROUND

The delayed oculomotor response (DOR) task requires response inhibition followed by movement of gaze towards a known spatial location without a current stimulus. Abnormalities in response inhibition and in the spatial accuracy of the eye movement are found in individuals with schizophrenia and in many of their relatives, supporting the use of these saccadic abnormalities as endophenotypes in genetic studies. It is unknown whether school-age children, either with psychosis or as relatives of a schizophrenic proband, can be included.

METHOD

One hundred eighty-seven children, ages 5.8-16.0 years - 45 children with childhood-onset schizophrenia, 64 children with a first-degree relative with schizophrenia, and 84 typically developing children - completed DOR tasks with 1 and 3 second delays.

RESULTS

Children with childhood-onset schizophrenia demonstrated impaired response inhibition and impaired spatial accuracy compared to both relatives and typicals; however, relatives and typicals did not differ from each other.

CONCLUSIONS

Children with childhood-onset schizophrenia have saccadic abnormalities similar to those found in adults with schizophrenia, supporting the continuity of executive function deficits in childhood-onset with adolescent and adult-onset schizophrenia. However, saccadic tasks are not sensitive to genetic risk in non-psychotic children and 6-15-year-old children should not be included in genetic studies utilizing this endophenotype.

Premorbid indicators and risk for schizophrenia: a selective review and update

Prospective studies of young relatives at risk for schizophrenia (high-risk studies, HR) can shed light on premorbid precursors of schizophrenia. Early HR studies pointed to a wide prevalence of schizophrenia spectrum psychopathology among young relatives at increased genetic risk. Recent studies suggest that young HR relatives have neurobehavioral deficits and structural, physiological, and neurochemical brain abnormalities that may date back to childhood or earlier. In this paper, we provide a selected overview of the lessons and limitations of early "first generation" studies and the beginning insights from recent "second generation" studies. We also provide an interim summary of data from the ongoing studies of young relatives at risk for schizophrenia in Pittsburgh. Collectively, such data may help us to predict the eventual emergence of schizophrenia, and schizophrenia spectrum or non-spectrum psychopathology.

Childhood-onset schizophrenia: smooth pursuit eye-tracking dysfunction in family members

BACKGROUND

Childhood-onset schizophrenia (COS), a severe form of the disorder, is of interest for etiologic studies. Smooth pursuit eye-tracking dysfunction (ETD) is a biological marker for schizophrenia.

AIMS

To compare familial eye-tracking abnormalities for COS and adult-onset schizophrenia (AOS).

METHOD

Eye-tracking performance for 70 COS parents, 64 AOS parents and 20 COS siblings was compared to their respective age-matched control groups.

RESULTS

COS and AOS parents had higher rate of dichotomously rated eye-tracking dysfunction than their respective controls (16% vs. 1% and 22% vs. 4%, respectively). COS parents and siblings also differed from controls on several continuous measures. However, scores for COS, AOS and control groups overlapped extensively.

CONCLUSIONS

Genetic factors underlying eye-tracking dysfunction appear more salient for COS. However, eye-tracking measures have to be used with caution for endophenotypic definition due to low predictive power.

DECLARATION OF INTEREST

The study was done at the National Institutes of Health.

The inheritance of intermediate phenotypes for schizophrenia

PURPOSE OF REVIEW

While schizophrenia is substantially heritable, the mode of inheritance is complex, involving numerous genes of small effect and a non-trivial environmental component. The 'endophenotype' approach is an alternative method for measuring phenotypic variation that may facilitate the identification of susceptibility genes in the context of complexly inherited traits. Here we review recent studies applying this method to measures of brain structure, physiology, and function in samples of schizophrenia patients and their non-ill first-degree relatives (siblings and co-twins).

RECENT FINDINGS

The results suggest that there are multiple heritable dimensions of central nervous system pathology in schizophrenia, including disturbances in the structure and functioning of frontal lobe systems involved in working memory and executive processes, temporal lobe systems involved in episodic memory, auditory perception, and language processing, and cortical and sub-cortical systems mediating smooth pursuit eye movements and sensorimotor gating. A number of genetic loci that are suspected to play a role in predisposing to schizophrenia, including the DISC1, COMT, neuregulin, dysbindin, and alpha-7 nicotinic receptor genes, appear to affect quantitative variation on one or more of these indicators.

SUMMARY

Future work is encouraged to address whether each of these neural system dysfunctions are under the influence of a partially distinct set of genes, to elucidate the manner in which multiple genes may coalesce in determining schizophrenia-promoting dysfunction in each neurobehavioral domain, and to clarify the degree of overlap in these quantitative trait loci-endophenotype relationships with other forms of psychosis, particularly bipolar disorder.

Approaches for adolescents with an affected family member with schizophrenia

Prospective studies of adolescents at risk for schizophrenia (high-risk studies) can shed light on the possible premorbid precursors of schizophrenia. Recent studies have provided evidence of neurobehavioral, brain structural, physiologic, and neurochemical deficits in adolescent nonpsychotic high-risk relatives that may date back to childhood or earlier. These results are collectively providing a critical window into the inter-relationships between genetic predisposition, neurodevelopment, and premorbid indicators of risk in schizophrenia. Convergent approaches are inherently powerful in mutually informing each other in enriching the knowledge of the risk factors that predict the eventual onset of schizophrenia. Defining such reliable predictors of the onset of schizophrenia may provide us with the tools to better understand the etiology and pathophysiology of the illness, and may pave the way for innovative methods of treatment and possibly prevention. The authors review the relevant literature in this promising field of inquiry and summarize recent findings from high-risk studies.

Eye movements and psychiatric disease

PURPOSE OF REVIEW

During the past year a number of studies have been published on eye movement dysfunction in patients with psychiatric disease. According to the mainstream of modern neuropsychiatric research, these studies cover either genetic aspects or the results of pharmacological manipulation.

RECENT FINDINGS

A few studies addressed impaired smooth pursuit eye movements (eye tracking dysfunction) in unaffected relatives of psychiatric patients, and were important in excluding non-specific effects (e.g. medication) and isolating genetic predisposition to the disease. This predisposition could be demonstrated in families of schizophrenic patients irrespective of whether the index case was sporadic or familial. One large study demonstrated pathological distributions of various parameters of smooth pursuit eye movement performance in groups of schizophrenic patients and their relatives. However, another study challenged the specificity of eye tracking dysfunction as a trait marker for schizophrenia by showing that its prevalence was identical among relatives of patients with affective disorder and schizophrenia. Eye tracking dysfunction was associated with two gene polymorphisms that interfere with dopamine metabolism and are thus reasonable candidate genes for the predisposition to schizophrenia. The influence of nicotine and neuroleptic drugs on eye movement performance was studied in schizophrenic patients. Nicotine improved smooth pursuit performance in three studies, one of which attributed this finding to enhanced attention. Two groups of schizophrenic patients treated with two different atypical neuroleptic drugs, risperidone and olanzapine, did not differ in a battery of saccadic tasks.

SUMMARY

Eye movements provide an important tool to measure pharmacological effects in patients and unravel genetic traits in psychiatric disease.