Diagnostic accuracy and linkage analysis: how useful are schizophrenia spectrum phenotypes?

An integration of schizophrenia with schizotypy: identification of schizotaxia and implications for research on treatment and prevention

The liability to schizophrenia (schizotaxia) is associated with deficits in a variety of domains, including negative symptoms and neuropsychological deficits, even in the absence of psychosis or pre-psychotic prodromal symptoms. Conceptually, this view of schizotaxia is similar to negative schizotypy (i.e., schizotypal personality disorder minus the positive symptoms). It is broader than DSM-IV schizotypal personality disorder (SPD), however, in that more relatives of patients with schizophrenia show core symptoms of schizotaxia than meet the diagnostic criteria for SPD. Three lines of evidence support the validity of schizotaxia. First, evidence of concurrent validation was obtained by showing that schizotaxic subjects were more impaired than non-schizotaxic subjects on a variety of independent clinical scales. Second, schizotaxic subjects showed higher levels of negative symptoms on the Structured Interview for Schizotypy than non-schizotaxic subjects, but did not differ on positive symptoms. Third, subjects who met predetermined criteria for schizotaxia (i.e., negative symptoms and neuropsychological deficits) showed positive effects following treatment with low doses of risperidone (0.25-2.0 mg). Thus, clinical deficits in schizotaxia may be identifiable, and to a significant extent, reversible. Implications for the conception of schizotypy and the prevention of schizophrenia will be discussed.

Concurrent validation of schizotaxia: a pilot study

BACKGROUND

Many first-degree relatives of patients with schizophrenia show deficits in clinical, neuropsychological, neurobiological and social domains, in the absence of psychosis. We recently reformulated Meehl's concept of schizotaxia to conceptualize the liability to schizophrenia, and we proposed preliminary criteria based on the presence of negative symptoms and neuropsychological deficits. Here we investigate the concurrent validity of schizotaxia by comparing a group of subjects who met criteria for schizotaxia with a group who did not on independent measures of clinical function, and on lifetime rates of selected comorbid psychiatric disorders.

METHODS

Twenty-seven adults who were first-degree, biological relatives of patients with schizophrenia were evaluated for schizotaxia based on our predetermined criteria involving negative symptoms and neuropsychological deficits. Subjects also received portions of the Diagnostic Interview for Genetic Studies, the Structured Interview for Schizotypy, the Family Interview for Genetic Studies, the DSM-IV Global Assessment of Functioning, the Physical Anhedonia Scale, the Social Adjustment Scale and the Symptom Checklist-90-Revised. Subjects who met criteria for schizotaxia were compared with those who did not on each of the clinical measures, and on their rates of comorbid DSM-IV psychiatric diagnoses.

RESULTS

Eight subjects met criteria for schizotaxia, and 19 did not. Subjects with schizotaxia showed significantly lower levels of function on each of the clinical scales. Differences in comorbid psychiatric diagnoses were not significant, although the rate of lifetime substance abuse diagnoses in the schizotaxic group (50%) approached levels that are often seen in schizophrenia.

CONCLUSIONS

These findings provide the first evidence of concurrent validation for a proposed syndrome of schizotaxia. They are also consistent with the view that the vulnerability to schizophrenia may be defined, at least partially, although larger studies to assess both the concurrent and predictive validity of schizotaxia will be required to confirm these results.

Family and twin strategies as a head start in defining prodromes and endophenotypes for hypothetical early-interventions in schizophrenia

In an effort to share the experiences of 'genotype-hunters'-who have approached the difficult task of forecasting future schizophrenia in the young offspring or other relatives of index cases, in new samples guided by the prior probabilities of 15% in offspring or 50% in identical co-twins-with 'early-interventionists'-who focus on purported prodromal symptoms in children who would be treated pharmacologically to prevent the development of schizophrenia-we provide a focused review that emphasizes the hazards of false positives in both approaches. Despite the advantages prospective high-risk strategies have had from clinical and laboratory findings that implicate some prodromal signs and endophenotypes, e.g. attention, memory, and information processing evaluations, the yields are not sufficient for practical applications involving antipsychotic drugs for undiagnosed children. Even more caution than usual is required, given the suggestions that the developing neocortex is vulnerable to dopaminergic exposure.

Affected sibling pair linkage analysis of qualitative and quantitative traits for schizophrenia on chromosome 22 in a Chinese population

We performed nonparametric linkage analysis on 136 families with two or more siblings with schizophrenia from Sichuan, southwestern China. In addition to categorical diagnosis, we used quantitative trait information from the Positive and Negative Symptom Scale and the modified Overt Aggression Scale. Categorical analysis using the diagnosis of schizophrenia and a maximum likelihood identity-by-descent method produced scores of close to 0 throughout the whole region tested. Multipoint analysis allowed exclusion of most markers with a relative risk of > 2, but did not exclude the possibility of a relative risk of < 1.5 for four of the markers. Our results provide no significant evidence for a locus for schizophrenia on chromosome 22. Quantitative linkage analysis using the PANSS-G scale score produced a maximum LOD score of approximately 1.2 with the marker D22S310, using either the Haseman-Elston method or maximum likelihood variance estimation with or without dominance. PANSS-N produced a maximum LOD score of 1.2 at the D22S283 locus. LOD score of about 1 are easily produced by chance. Thus, we conclude that under quantitative trait we also find no evidence of linkage between schizophrenia and markers on chromosome 22 in our Chinese sibling pair sample.

Single or multiple familial cognitive risk factors in schizophrenia?

The fact that relatives of patients with schizophrenia display subtle cognitive abnormalities suggests genetic transmission of an underlying cognitive endophenotype. It was examined to what extent the cognitive abnormalities that discriminate patients and relatives from controls do so independently of each other, and independent of IQ. Neuropsychological measures were assessed in 50 patients with schizophrenia, 50 first-degree relatives of patients with schizophrenia, and 50 healthy controls. The assessment focused on episodic memory, attentional span, simple and complex speed of information, and semantic memory. Factor analysis of the cognitive test results yielded four factors reflecting speed, episodic memory, working memory, and semantic fluency. Performance of the relatives was intermediate to that of the patients and the controls after adjustment for age, sex, educational level, and IQ. For both patients and relatives, speed of information processing, working memory, and episodic memory independently discriminated from control performance, with a similar pattern in the order of the size of the effects. The results suggest the existence of more than one familial cognitive risk factor for schizophrenia. Independent familial cognitive risk factors may represent separate causal influences or separate indicators of risk related to the same genetic mechanism.

Early neurobehavioral deficits as phenotypic indicators of the schizophrenia genotype and predictors of later psychosis

Schizophrenia is a genetically complex disorder that requires sharper delineation of its phenotypic boundaries. Considerable attention has been devoted in recent family and high-risk studies to the identification of both subclinical and other phenotypes, such as neurobehavioral deficits, that may be indicators of the genetic liability to schizophrenia. In high-risk studies, candidate liability indicators that are evident by young ages are also evaluated for their ability to predict future schizophrenia or spectrum disorders. We report on assessments of verbal short-term memory, gross motor skills, and global attention administered in midchildhood to offspring of schizophrenic, affectively ill, and normal parents as predictors of adult psychoses and as possible indicators of schizophrenia-susceptibility genes.

Schizophrenia: family studies and treatment of spectrum disorders

A substantial part of the contribution of genetic studies to the treatment of schizophrenia involves its emphasis on reliable and valid diagnoses. One consequence of this focus is the recognition that schizophrenic illness is broader than the diagnostic entity of schizophrenia itself, and instead consists of a “spectrum” of related disorders. Because some of the symptoms in these disorders differ from each other, they provide an opportunity to determine which ones reflect a common etiology. To the extent that such symptoms are identifiable, they may provide a foundation for treatment and even prevention strategies. In this paper, we focus on a clinical condition - “schizotaxia” - that may reflect the liability for schizophrenia. To characterize the nature and extent of this proposed syndrome, we will review results from family studies in our laboratory, and consider conceptual foundations and criteria for assessment. A more general consideration of treatment strategies for schizophrenia spectrum disorders follows, along with suggestions for future research. Our initial attempts to treat and validate schizotaxia are encouraging, and raise the possibility that early treatment might eventually prevent or attenuate the development of other, more severe disorders in the schizophrenia spectrum, including schizophrenia itself.

Phenotypic markers as risk factors in schizophrenia: neurocognitive functions

OBJECTIVE

To review the literature on neurocognitive measures as risk markers for schizophrenia and to present data from the Perth family study of schizophrenia. Of all the risk markers that have been identified, the most promising are deficits in sustained attention.

METHOD

Inclusion in the review was determined by whether the research addressed a number of key questions: methods of assessing sustained attention; evidence of sustained attention deficits in patients and first-degree relatives including children; the importance of attentional dysfunction in the schizophrenic process and functional outcome; and the biological basis of sustained attention deficits.

RESULTS

Sustained attention deficits are evident in both patients and a proportion of their first-degree relatives, a finding replicated in preliminary data from the Perth family study. The literature suggests that the attention deficit is a stable enduring trait that is independent of clinical state. The neural basis of the deficit may be a functional disconnection between prefrontal and parietal cortex. Attention impairment is an important predictor of functional outcome in patients and the development of social dysfunction in adulthood in the at-risk offspring of patients. However, sustained attention deficits that are measured in childhood results in an unacceptable high false-positive rate (21%) when predicting which at-risk offspring of parents with schizophrenia will develop a schizophrenia spectrum disorder, although the overall classification accuracy (78%) is impressive.

CONCLUSIONS

The main findings are that sustained attention deficits are important risk markers for schizophrenia but need to be supplemented by other neurocognitive risk markers to improve predictive accuracy.

Schizotypy: phenotypic marker as risk factor

OBJECTIVE

To evaluate measures of schizotypy as familial risk factors for schizophrenia with the aim of making recommendations for assessing schizotypy as part of screening procedures for identifying people at risk of schizophrenia.

METHOD

Published studies using self-report and interview-based measures of schizotypy to assess relatives of patients with schizophrenia are reviewed. A parent study is reported evaluating the diagnostic accuracy of parental schizotypy as assessed by three questionnaire-based measures: the Chapman Perceptual Aberration and Physical Anhedonia Scales, and the Eysenck Psychoticism Scale. Group scores for these self-report ratings of 23 parent-pairs of patients with schizophrenia, 20 parent-pairs of patients with chronic nonpsychotic psychiatric disorder, and 19 parent-pairs of healthy comparison subjects are compared.

RESULTS

Consistent with published evidence that self-report measures of psychosis-proneness and schizotypy do not consistently reflect familial risk factors that are specific for schizophrenia, scores on questionnaire measures of schizotypy did not distinguish the parents of patients with schizophrenia from the parents in the other two groups.

CONCLUSIONS

Interview-based assessments of schizotypy better assess familial risk factors than self-report measures of schizotypy. Questionnaire measures of schizotypy should be supplemented by interview-based assessments when screening for individuals at risk of schizophrenia.

Saccadic eye movement abnormalities in relatives of patients with schizophrenia

Recent studies note abnormalities in saccadic eye movements of relatives of patients with schizophrenia. The current study examined which aspects of the saccadic system are affected, whether these saccadic abnormalities are associated with schizophrenia spectrum personality symptoms (SSP), and whether such an association is dependent on a family history of schizophrenia. Furthermore, the study examined what proportion of relatives have the saccadic abnormality(ies). Fifty-five first-degree relatives with no DSM-III-R Axis I diagnosis participated in the study. Twenty-one of these relatives experienced SSP symptoms and 34 had no Axis II diagnosis. Sixty-two subjects with no Axis I diagnosis were recruited from the community. Twenty-five experienced SSP symptoms and 37 had no Axis II diagnosis. Prosaccades (saccades toward the target) and antisaccades (saccades made in the opposite direction of the target jump) were examined. Relatives, particularly those with SSP, had difficulties with the antisaccade task as suggested by higher error rates and longer antisaccade latency. Prosaccades were not different in relatives compared to the community subjects, although the effects of field were different in the two groups on some measures. The antisaccade latency was 'abnormal' in only a small proportion (1.6%) of community subjects compared to 14.9% of all relatives (35.3% of SSP relatives and 3.3% of non-SSP relatives). Relatives of patients with schizophrenia have deficits in aspects of the saccadic system involved in generating internally driven saccades and inhibition of unwanted saccades. These deficits implicate frontal ocular motor neuronal circuitry involving frontal cortical and basal ganglia areas. These deficits are associated with SSP symptoms, but not in the absence of a blood relationship to schizophrenia. The relatively high prevalence rate of the abnormality in at-risk subjects may have relevance for use of these measures in linkage analysis.

Defining the schizophrenia phenotype

Schizophrenia is a complex disease with multifactorial etiology. The schizophrenia phenotype has been traditionally defined by chronic psychosis and functional deterioration. However, the boundary of the phenotype is likely to be more extensive than the one defined by chronic psychosis. This is highlighted by the findings of subtle, schizophrenia- like deficits in the nonschizophrenic, first-degree relatives of schizophrenic patients. Subtle clinical signs and symptoms, cognitive impairment particularly in attention and memory, and neurophysiologic deficits such as in sensory gating and smooth-pursuit eye movements all define aspects of the schizophrenia phenotype.

Schizophrenia: vulnerability versus disease

One of the most important trends in the treatment of schizophrenia involves its early diagnosis and intervention. The ultimate goal of research is the prevention of the disorder, A major impediment to the development of prevention strategies, however, is that we do not yet know what the liability for schizophrenia is before the onset of psychosis. Consequently, early treatment attempts are focused on the “prodrome,” which involves the early symptoms of psychosis. In a companion paper, we recently suggested that prevention work should focus not only on the prodrome, but also on “schizotaxia,” which is a clinically meaningful condition that may reflect the vulnerability to schizophrenia in the absence of psychosis. Because schizotaxia can be assessed prior to the prodrome, studies of schizotaxia might lead to more effective prevention programs. We continue the characterization of schizotaxia in this paper by focusing on the etiological roots of schizotaxia, plus its likely neurodevelopmental course, clinical expression, and treatment. Finally, the importance of including neurobiological variables in the conceptualization and eventual diagnosis of schizotaxia is reviewed.

Towards the prevention of schizophrenia

There is a growing emphasis on attempts to identify the early signs and symptoms of schizophrenia, largely because early detection and treatment of psychosis (i.e., secondary prevention) are associated with relatively favorable clinical outcomes. This raises the issue of whether prevention of psychosis itself is possible. The achievement of this goal will require the identification of a premorbid state that could serve as the foundation for treatment strategies aimed ultimately at the prevention of schizophrenia. Fortunately, evidence for such a state is emerging, in part because schizophrenia may result from a neurodevelopmental disorder that is associated with a variety of clinical, neurobiological, and neuropsychologic features occurring well before the onset of psychosis. These features may serve as both indicators of risk for subsequent deterioration and the foundation of treatment efforts. We reformulated Meehl's term schizotaxia to describe this liability and discuss here how its study could form the basis for future strategies of prevention. We also include a description of our initial attempts to devise treatment protocols for schizotaxia. It is concluded that schizotaxia is a feasible concept on which to base prevention efforts, and that treatment of adult schizotaxia may be among the next steps in the process.

Neuropsychologic functioning among the nonpsychotic relatives of schizophrenic patients: the effect of genetic loading

BACKGROUND

We previously reported that the nonpsychotic relatives of schizophrenic patients exhibited disturbances in executive functioning, verbal and visual memory, auditory attention, mental control, and verbal ability. In a 4-year follow-up, we showed that the discriminating power of most of these tests was stable over time.

METHODS

In this report we compare 41 nonpsychotic persons who have only one schizophrenic first-degree relative (simplex families) with 36 nonpsychotic persons who have two schizophrenic first-degree relatives (multiplex families). Our goal was to test a hypothesis that neuropsychologic deficits would be worse among the latter.

RESULTS

Relatives from multiplex families differed significantly from controls on estimated intelligence, immediate and delayed logical memories, and immediate visual reproductions. In contrast, in comparisons with controls, relatives from simplex families only differed on immediate logical memories. Comparisons between relatives from multiplex and simplex families showed that the former group had significantly worse scores for estimated intelligence, immediate and delayed logical memories, and immediate visual reproductions. We also found group x gender interactions: the worse performance of the multiplex group was seen for females.

CONCLUSIONS

These results are consistent with the idea that neuropsychologic deficits in relatives of schizophrenic patients reflect their degree of genetic predisposition to schizophrenia. They also suggest hypotheses about gender differences in the familial transmission of the disorder.

Department of Veterans Affairs Cooperative Studies Program genetic linkage study of schizophrenia: ascertainment methods and sample description

To help clarify the genetics of schizophrenia, the Department of Veterans Affairs Cooperative Studies Program has completed data collection for a genetic linkage study of schizophrenia. This article describes the methodological details of the data collection. Subsequent articles will describe the results of our genome scan, which is now in progress. The data collection protocol included the Diagnostic Interview for Genetic Studies, the Family Interview for Genetic Studies, a review of medical records, and the collection of blood for transformation into lymphoblast cell lines. Among relatives of schizophrenic probands, we assessed auditory attention and verbal memory with neuropsychological tests. Among the 166 families ascertained for the study, 143 had a single affected sib-pair, 17 had three affected siblings, one had five affected siblings and five had two sets of affected siblings. There was a total of 216 affected sib-pairs in these families. Using the n-1 rule, these families contain 188 independent affected sib-pairs.

Toward guidelines for pedigree selection in genetic studies of attention deficit hyperactivity disorder

Converging evidence from family, twin, and adoption studies points to a substantial genetic component of the etiology of attention deficit hyperactivity disorder (ADHD). These data about ADHD have motivated molecular genetic studies of the disorder, which have produced intriguing but somewhat conflicting results. Some studies have reported associations with candidate genes and others not. Our review of the literature shows that one problem facing molecular genetic studies of ADHD is that its recurrence risk to first-degree relatives is only about five times higher than the population prevalence. This suggests that, to produce consistently replicated results, molecular genetic studies should either use much larger samples or should select those families in which genes exert the largest effect. Risch [(1990a) Am J Hum Genet 46:222-228; (1990b) Am J Hum Genet 46:229-241] proved that the statistical power of a linkage study increases with the magnitude of risk ratios (lambda's) computed by dividing the affection rate among each relative type to the rate of affection in the population. Our prior work suggests two dimensions of genetic heterogeneity that might be useful for selecting ADHD subjects for molecular genetic studies: comorbidity with conduct disorder and persistence of ADHD into adolescence. This paper shows that these sub-phenotypes are useful for molecular genetic studies because (1) they have much higher empirical lambda values and (2) they affect a substantial minority of ADHD patients.

Poor perception of nonverbal social-emotional cues in relatives of schizophrenic patients

The present study compared nonverbal social perception in relatives of schizophrenic patients (n = 21) with that of normal controls (n= 19). We hypothesized that relatives would display deficits in social perception and we sought to determine the skills that are associated with this deficit. Relatives performed significantly worse than controls on the Profile of Nonverbal Sensitivity Test (PONS), despite comparable performance on skills hypothesized to be related to nonverbal social perception: visual perception, nonverbal problem solving, facial recognition, facial affect recognition, naming, social judgment, and vigilance. To further explore the relationships among these skills, we calculated correlations between the PONS score and associated skills separately within both the relative and control groups and assessed whether the values of these correlations differed between groups. Correlations that differed significantly indicated a greater association, within relatives, between slower reaction times on vigilance tasks and poor PONS performance. Further research is needed to clarify the nature of this relationship, to better characterize social perception deficits in relatives, and to determine whether these perceptual deficits are part of the genetic diathesis to schizophrenia.

Thalamic and amygdala-hippocampal volume reductions in first-degree relatives of patients with schizophrenia: an MRI-based morphometric analysis

BACKGROUND

Schizophrenia is characterized by subcortical and cortical brain abnormalities. Evidence indicates that some nonpsychotic relatives of schizophrenic patients manifest biobehavioral abnormalities, including brain abnormalities. The goal of this study was to determine whether amygdala-hippocampal and thalamic abnormalities are present in relatives of schizophrenic patients.

METHODS

Subjects were 28 nonpsychotic, and nonschizotypal, first-degree adult relatives of schizophrenics and 26 normal control subjects. Sixty contiguous 3 mm coronal, T1-weighted 3D magnetic resonance images of the brain were acquired on a 1.5 Tesla magnet. Cortical and subcortical gray and white matter and cerebrospinal fluid (CSF) were segmented using a semi-automated intensity contour mapping algorithm. Analyses of covariance of the volumes of brain regions, controlling for expected intellectual (i.e., reading) ability and diagnosis, were used to compare groups.

RESULTS

The main findings were that relatives had significant volume reductions bilaterally in the amygdala-hippocampal region and thalamus compared to control subjects. Marginal differences were noted in the pallidum, putamen, cerebellum, and third and fourth ventricles.

CONCLUSIONS

Results support the hypothesis that core components of the vulnerability to schizophrenia include structural abnormalities in the thalamus and amygdala-hippocampus. These findings require further work to determine if the abnormalities are an expression of the genetic liability to schizophrenia.

Neuropsychiatric dynamics: the study of mental illness using functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) is poised to make significant contributions to the study of neuropsychiatric illnesses. Whatever neural pathology attends such illnesses has proven subtle at best. By identifying predictable, regionally specific deficits in brain function, fMRI can suggest brain regions for detailed cellular analyses, provide valuable in vivo data regarding effective connectivity, provide a means to model the effects of various drug challenge paradigms, and characterize intermediate phenotypes in the search for the genes underlying mental illness. Nonetheless, as promising as fMRI appears to be in terms of its relative safety, repeatability, ability to generate individual brain maps and widespread availability, it is still subject to a number of unresolved conceptual conundrums inherited from earlier neuroimaging work. For example, functional neuroimaging has not generated any pathognomic findings in mental illness, has not established a clear link between neurophysiology and observable behavior, and has not resolved the potential confounds of medication. In this article, we will review the relevant historical background preceding fMRI, address methodological considerations in fMRI, and summarize recent fMRI findings in psychiatry. Finally, fMRI is being used to simplify the complex genetics of neuropsychiatric illness by generating quantitative and qualitative brain phenotypes.

No evidence for linkage between schizophrenia and markers at chromosome 15q13-14

Freedman et al. [1997: Proc Natl Acad Sci USA 94:587-592] reported linkage in nine multiplex schizophrenia families to markers on chromosome 15, using impaired neuronal inhibition to repeated auditory stimuli (P50), a neurophysiological deficit associated with schizophrenia, as the phenotype. The highest LOD score obtained (5.3 at theta = 0) was for marker D15S1360 mapped to chromosome 15q13-14, less than 120 kb from the alpha7-nicotinic receptor (CHRNA7) gene. The study also reported a small positive LOD score for D15S1360 when examined for linkage to the schizophrenia phenotype. Following these findings, we examined three polymorphic markers (D15S1360, L76630, and ACTC) on chromosome 15q13-14 near the CHRNA7 gene for linkage to schizophrenia, using 54 pedigrees from an independent study. Alleles for these three markers were genotyped and analyzed using parametric and nonparametric methods. No LOD score above 1.00 was obtained for any marker, and affected sib-pair analysis likewise showed no evidence for linkage. We conclude that in our families the region around the CHRNA7 locus does not contain a major locus for susceptibility to schizophrenia.

Psychopathology: description and classification

DSM-IV's strong empirical base has yielded an instrument with good to excellent reliability and improved validity. Diagnostic reliability depends on both the clarity and validity of diagnostic criteria and the changeability of disorders over time: The reliability of schizophrenic spectrum disorders, personality disorders, and some childhood and adolescent disorders remains problematic. Findings on diagnostic validity appear paradoxical: Attempts to validate schizophrenic spectrum disorders with neurobiological and genetic-familial validators have been only modestly successful, whereas the tripartite personality trait model has differentiated a range of depressive and anxiety disorders. Research on comorbidity has identified several highly comorbid disorders (substance-related disorders, personality disorders, depression, and anxiety) as well as some adverse consequences of comorbidity. The advantages of dimensional approaches to diagnosis have largely been demonstrated conceptually; ultimate conclusions about the strengths and weaknesses of dimensional and syndromal methods await substantial additional empirical research.

Hippocampal N-acetyl aspartate in unaffected siblings of patients with schizophrenia: a possible intermediate neurobiological phenotype

BACKGROUND

Shared neurobiological characteristics of patients with schizophrenia and their siblings may represent "intermediate phenotypes" that may more closely reflect the genetic susceptibility underlying this illness. We sought evidence of such phenotypes using magnetic resonance spectroscopy based on previously described regional abnormalities in levels of the neuronal marker N-acetyl-aspartate (NAA) in the hippocampal area and dorsolateral prefrontal cortex of patients with schizophrenia.

METHODS

We studied 47 schizophrenics, 60 unaffected siblings, and 66 healthy control subjects with long echo time multislice proton magnetic resonance spectroscopic imaging, primarily measuring NAA, creatine plus phosphocreatine (CRE), and choline-containing compounds.

RESULTS

Both patients and their unaffected siblings had significant reductions in hippocampal area NAA/CRE as compared with control subjects. As exploratory analyses, estimates of heritability were performed. Although quantitative correlation of hippocampal NAA between patients and sibs was low (likely reflecting measurement noise), qualitatively defined "low hippocampal NAA/CRE phenotypes" yielded relative risk estimates (lambda s) of between 3.8 and 8.8, suggesting this characteristic is heritable.

CONCLUSIONS

Our finding adds to the evidence that hippocampal abnormalities are associated with schizophrenia and may represent a novel biological phenotype for genetic studies of schizophrenia.

Association of neuropsychological vulnerability markers in relatives of schizophrenic patients

We investigated the association of neuropsychological risk indicators in a matched sample of first-degree relatives of schizophrenic patients (n = 54) and normal controls (n = 72). We focussed on three functions previously identified in a smaller, initial sample as putative risk indicators of the schizophrenia genotype: abstraction, verbal memory and auditory attention. The expanded sample of relatives displayed significantly lower scores than controls on abstraction, verbal memory and auditory attention. The relatives demonstrated significant intercorrelations among these three functions. The significant correlations among relatives between attention and verbal memory and between attention and abstraction differed significantly from these correlations among controls. We discuss how the use of multiple risk indicators may help us better identify those relatives that carry the schizophrenia genotype.

Use of a quantitative trait to map a locus associated with severity of positive symptoms in familial schizophrenia to chromosome 6p

A number of recent linkage studies have suggested the presence of a schizophrenia susceptibility locus on chromosome 6p. We evaluated 28 genetic markers, spanning chromosome 6, for linkage to schizophrenia in 10 moderately large Canadian families of Celtic ancestry. Parametric analyses of these families under autosomal dominant and recessive models, using broad and narrow definitions of schizophrenia, produced no significant evidence for linkage. A sib-pair analysis using categorical disease definitions also failed to produce significant evidence for linkage. We then conducted a separate sibpair analysis using scores on positive-symptom (psychotic), negative-symptom (deficit), and general psychopathology-symptom scales as quantitative traits. With the positive symptom-scale scores, the marker D6S1960 produced P = 1.2 x 10(-5) under two-point and P = 5.4 x 10(-6) under multipoint analyses. Using simulation studies, we determined that these nominal P values correspond to empirical P values of .034 and .0085, respectively. These results suggest that a schizophrenia susceptibility locus on chromosome 6p may be related to the severity of psychotic symptoms. Assessment of behavioral quantitative traits may provide increased power over categorical phenotype assignment for detection of linkage in complex psychiatric disorders.

Reduced subcortical brain volumes in nonpsychotic siblings of schizophrenic patients: a pilot magnetic resonance imaging study

Substantial evidence suggests that nonpsychotic relatives of schizophrenia patients manifest subtle abnormalities in communication, eye movements, event-related potentials, and neuropsychological processes of attention, reasoning, and memory. We sought to determine whether adult relatives without psychosis or schizophrenia spectrum diagnoses might also have structural brain abnormalities, particularly in subcortical regions found to be impaired in patients with schizophrenia itself. Subjects were six sisters of schizophrenic patients and eleven normal female controls. Sixty contiguous 3 mm coronal, T1-weighted 3D magnetic resonance images (MRI) of the entire brain were acquired on a 1.5 Tesla magnet. Cortical and subcortical gray and white matter was segmented using a semiautomated intensity contour mapping algorithm. Volumes were adjusted for total brain volumes. Adjusted gray matter subcortical volumes were significantly smaller in relatives than in controls in total hippocampus, right amygdala, right putamen, left thalamus, and brainstem. Relatives had significantly enlarged left and total inferior lateral ventricles. These results, though preliminary, suggest that some never-psychotic relatives of schizophrenic patients have abnormal brain structure. If replicated in a larger sample including both sexes, these results would suggest that the genetic liability to schizophrenia is also expressed as structural brain abnormalities.

Schizotypal disorder: at the crossroads of genetics and nosology

The aim of this paper is to review the available evidence in support of the correctness of including the DSM-III/III-R schizotypal personality disorder (SPD) in the schizophrenia spectrum, to discuss the components that may account for the familial segregation of SPD, and to consider the implications for research and clinical use of this diagnostic category. The majority of the available data from genetic epidemiology studies, starting from probands with schizophrenia or with SPD, suggest that SPD is one of several phenotypes of liability for the schizophrenia spectrum. Recent twin studies suggest that the affect-constricted and eccentric aspects of SPD are the features that truly belong to the spectrum of schizophrenia, sharing important genetic influences. However, other components are more useful for the identification of SPD in clinical settings, and these may be the specific focus of treatment. The present categorization appears to be a reasonable trade-off for the purposes of both the investigator and the clinician, even though different components within SPD may have different origins and can be selectively emphasized according to the different aims involved.

Unipolar relatives in bipolar pedigrees: a search for elusive indicators of underlying bipolarity

In an effort to identify features indicative of underlying bipolarity within the unipolar relatives of bipolar probands, we compared unipolar relatives of bipolars with unipolar relatives of controls. Using data from the Yale-NIMH Collaborative Study of Depression, we compared a number of demographic and clinical features individually, and then developed a logistic regression model for the differences found. Unipolar relatives of bipolars were generally similar to relatives of controls, but they were older and more likely to suffer from more severe, even psychotic, depression, and somewhat less likely to report a brief transition into their illness. A multiple logistic regression model for observed differences was highly statistically significant, but had limited ability to discriminate effectively between the two groups. These findings suggest that more stringent diagnostic criteria might be beneficial if unipolar relatives are counted as affected in linkage studies of bipolar disorder. The ability of this strategy to improve the "clinical phenotype" is limited, however, and other approaches may be needed to identify features of underlying bipolarity and thus to define "caseness" for unipolar relatives in linkage analyses of bipolar disorder.

Neuropsychological functioning among the elderly nonpsychotic relatives of schizophrenic patients

In our prior work with a young sample (age < 60), we showed that three neuropsychological functions were impaired among relatives of schizophrenic patients: abstraction, verbal memory, and auditory attention. In the present work we show that these results do not generalize to an older sample aged 60 years and greater. Thus, although we and others have put forth measures of neuropsychological function as indicators of the schizophrenia genotype, the present study suggests that conclusions may be limited to non-elderly samples. Further work is needed to address this issue definitively.