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The multidimensionality of schizotypy in nonpsychotic relatives of patients with schizophrenia and its applications in ordered subsets linkage analysis of schizophreniaYin-Ju Lien 1, Hui-Chun Tsuang 1 2, Abigail Chiang 1, Chih-Min Liu 3 4, Ming H. Hsieh 4, Tzung-Jeng Hwang 4, Shi K. Liu 4 5, Po-Chang Hsiao 6, Stephen V. Faraone 7 8, Ming T. Tsuang 9 10, Hai-Gwo Hwu 1 3 4 11, Wei J. Chen 1 3 4 6 *
1Institute of Epidemiology, College of Public Health, National Taiwan University, Taipei, Taiwan
2Center for General Education, College of Humanities and Social Sciences, Chang Jung Christian University, Tainan, Taiwan
3Department of Psychiatry, College of Medicine, National Taiwan University, Taipei, Taiwan
4Department of Psychiatry, National Taiwan University Hospital, Taipei, Taiwan
5Far Eastern Memorial Hospital, Taipei, Taiwan
6Genetic Epidemiology Core Laboratory, Research Center for Medical Excellence, National Taiwan University, Taipei, Taiwan
7Medical Genetics Research Center and Department of Psychiatry and Behavioral Sciences, SUNY Upstate Medical University, Syracuse, New York
8Department of Neuroscience and Physiology, SUNY Upstate Medical University, Syracuse, New York
9Department of Psychiatry, Center for Behavioral Genomics, University of California, San Diego, La Jolla, California
10Department of Epidemiology and Psychiatry, Harvard Institute of Psychiatric Epidemiology and Genetics, Harvard Medical Center, Boston, Massachusetts
11Department of Psychology, College of Science, National Taiwan University, Taipei, Taiwan
email: Wei J. Chen ()
*Correspondence to Wei J. Chen, Institute of Epidemiology, College of Public Health, NationalTaiwanUniversity, 17 Xu-Zhou Road, Taipei 100, Taiwan.
Lien and Tsuang contributed equally to this work.
How to cite this article: Lien Y-J, Tsuang H-C, Chiang A, Liu C-M, Hsieh MH, Hwang T-J, Liu SK, Hsiao P-C, Faraone SV, Tsuang MT, Hwu H-G, Chen WJ. 2009. The Multidimensionality of Schizotypy in Nonpsychotic Relatives of Patients With Schizophrenia and Its Applications in Ordered Subsets Linkage Analysis of Schizophrenia. Am J Med Genet Part B.
Funded by:
National Health Research Institutes, Taiwan; Grant Number: DOH 88-HR-825, NHRI-GT-EX89P825P, NHRI-EX90-8825PP, NHRI-EX91, NHRI-EX92, NHRI-EX93-9113PP, NHRI-EX95-9511PP
National Science Council, Taiwan; Grant Number: NSC83-0412-B-002-310, NSC84-2331-B-002-187, NSC95-3114-P002-005-Y
National Institute of Mental Health, USA; Grant Number: 1R01-MH-59624-01
NTU; Grant Number: 97HP0023
schizotypy ?schizophrenia ?factor analysis ?genome-wide linkage analysis ?ordered subset analysis
Abstract
This study aimed to examine the multidimensionality of schizotypy and validate the structure using ordered subset linkage analyses on information from both relatives' schizotypy and probands' schizophrenia symptoms. A total of 203 and 1,310 nonpsychotic first-degree relatives from simplex and multiplex schizophrenia families, respectively, were interviewed with the Diagnostic Interview for Genetic Studies, which contains a modified Structured Interview for Schizotypy. Using Mplus program with categorical factor indicators, a four-factor model (Negative Schizotypy, Positive Schizotypy, Interpersonal Sensitivity, and Social Isolation/Introversion) was extracted by exploratory factor analysis from relatives of simplex families and was confirmed in relatives of multiplex families. The validity of each factor was supported by distinct linkage findings resulting from ordered subset analysis based on different combinations of schizophrenia-schizotypy factors. Six chromosomal regions with significant increase in nonparametric linkage z score (NPL-Z) were found as follows: 15q21.1 (NPL-Z=3.60) for Negative Schizophrenia-Negative Schizotypy, 10q22.3 (NPL-Z=3.83) and 15q21.3 (NPL-Z=3.36) for Negative Schizophrenia-Social Isolation/Introversion, 5q14.2 (NPL-Z=3.20) and 11q23.3 (NPL-Z=3.31) for Positive Schizophrenia-Positive Schizotypy, and 4q32.1 (NPL-Z=3.31) for Positive Schizophrenia-Interpersonal Sensitivity. The greatest NPL-Z of 3.83 on 10q22.3 in the subset was significantly higher than the greatest one of 2.88 in the whole sample (empirical P-value=0.04). We concluded that a consistent four-factor model of schizotypy could be derived in nonpsychotic relatives across families of patients with different genetic loadings in schizophrenia. Their differential relations to linkage signals have etiological implications and provide further evidence for their validity. © 2009 Wiley-Liss, Inc.
Received: 22 November 2008; Accepted: 18 February 2009
Digital Object Identifier (DOI)10.1002/ajmg.b.30948About DOI
Article TextINTRODUCTION
The existence of schizotypy [Meehl, [1962]], the latent construct that underlies genetic susceptibility to schizophrenia, was postulated to describe the continuum between disease states and normal traits [Fanous et al., [2001]]. Using such phenotypes may increase statistical power and help clarify the complex etiology of schizophrenia [Fanous and Kendler, [2005]]. One unsolved issue is the structure and content of schizotypy. More than 20 self-report scales have been developed to assess schizotypy and most studies investigating the structure of schizotypy used such scales [Vollema and van den Bosch, [1995]]. Compared with psychiatric interviews, self-report questionnaires were less likely to differentiate relatives of schizophrenia from control probands [Kendler et al., [1996]] and could not collect information about schizotypal signs [Kendler et al., [1989], [1995]]. Therefore, it is critical to investigate the dimensionality of schizotypy in this population with a structured interview such as the Structured Interview for Schizotypy (SIS) [Kendler et al., [1989]]. The SIS measures both schizotypal symptoms, from the interviewee's self-report, and schizotypal signs, from the interviewer's observations of behavior.
Most studies have investigated the structure of schizotypy in unrelated subjects [Raine et al., [1994]; Chen et al., [1997]; Venables and Rector, [2000]; Vollema and Hoijtink, [2000]]. Only five studies conducted factor analyses on schizotypy in relatives of patients with schizophrenia [Kendler et al., [1995]; Fogelson et al., [1999]; Bergman et al., [2000]; Miller et al., [2002]; Mata et al., [2003]]. Although two out of the five studies used the SIS to assess schizotypy [Kendler et al., [1995]; Miller et al., [2002]], a common limitation of these studies was that the statistical methods used assumed normality for items entered into the factor analysis, which was questionable. Studies among both unrelated subjects and relatives identified positive and negative dimensions [Raine et al., [1994]; Kendler et al., [1995]; Vollema and van den Bosch, [1995]; Chen et al., [1997]; Fogelson et al., [1999]; Bergman et al., [2000]; Venables and Rector, [2000]; Vollema and Hoijtink, [2000]; Mata et al., [2003]]. Although they agreed on the content of the positive dimension, the findings for the negative dimension were not consistent [Kendler et al., [1995]; Vollema and van den Bosch, [1995]; Venables and Rector, [2000]]. It is unclear whether the inconsistent finding resulted from sample or assessment tool differences.
A challenging issue in assessing the validity of the structure of schizotypy is how to incorporate relatives' schizotypy with probands' schizophrenia. Several studies reported potential associations between certain candidate genes for schizophrenia and dimensions of schizotypy [Stefanis et al., [2004], [2007]; Lin et al., [2005]]. However, candidate gene studies provide poor coverage of the genome [Drago et al., [2007]]. The genome-wide scan is an attractive alternative for exploring genomic regions influencing different dimensions of schizotypy. Thus far, only one genome-wide linkage analysis of schizotypy has been published [Fanous et al., [2007]], in which a genome-wide genetic correlation between schizophrenia and schizotypy was indicated. Recently, a new approach called ordered subset analysis (OSA) [Scott et al., [2003]; Hauser et al., [2004]] has been developed to seek subsets of schizophrenia families with etiological homogeneity in a genetic linkage analysis. If the subsetting is based not only on proband's schizophrenia symptoms but also on schizotypy in nonpsychotic relatives, it may help increase linkage signals as well as assess the validity of different dimensions of schizotypy.
The current study aimed to examine the structure of schizotypy in nonpsychotic first-degree relatives of schizophrenia patients and validate the multidimensionality of schizotypy by means of ordered subset linkage analyses. Our goals were (1) to examine the structure of schizotypy and (2) to test if incorporating schizotypy factors with schizophrenia factors in OSA would identify different susceptibility gene regions.
METHODS
Subjects
First-degree relatives of schizophrenia patients were recruited from three family studies in Taiwan: the Multidimensional Psychopathology Group Research Project, the Multidimensional Psychopathological Study on Schizophrenia, and the Taiwan Schizophrenia Linkage Study. These studies have been described in greater detail in previous articles [Hwu et al., [2005]; Tsuang et al., [2006]]. The first study invited patients consecutively admitted to acute inpatient wards of NationalTaiwanUniversityHospital, TaipeiCityPsychiatricCenter, and ProvincialTao-YuanPsychiatricCenter from 1993 to 1998, if they met DSM-III-R criteria for schizophrenic disorders. During the study period, the diagnostic criteria shifted to DSM-IV and earlier subjects were re-diagnosed with the updated criteria. The second and third studies aimed to collect sib-pairs who were co-affected with schizophrenia and had at least two living first-degree relatives. The affected sib-pair probands, who met DSM-IV criteria for schizophrenia or schizoaffective disorder, depressed type, were identified from either inpatient wards or outpatient clinics of NationalTaiwanUniversityHospital and ProvincialTao-YuanPsychiatricCenter from 1998 to 2001 for the second study and from 78 psychiatric hospitals or health centers throughout Taiwan from 1998 to 2002 for the third study. Written informed consent was obtained from all subjects after complete description of the study. The first and second studies were approved by the institutional review boards of the participating hospitals. The third study was approved by both the US Department of Health and Human Services and the NationalTaiwanUniversityHospital's Internal Review Board of Human Studies.
A total of 234, 142, and 1,276 first-degree relatives (from 94, 70, and 607 families) were directly interviewed in the three studies, respectively. The simplex group, those families with only one member affected with schizophrenia, mainly comprised subjects from the first study. Among 94 participating families in the first study, 5 families had one parent affected with schizophrenia or schizophreniform disorders and were excluded. Six other families had an affected sibling, one of which had also been included in the second study. The multiplex group, those from families with a sib-pair co-affected with schizophrenia, comprised subjects from the second and third studies as well as the five families with co-affected sib-pairs in the first study.
For the schizotypy analyses, subjects with schizophrenia, schizophreniform disorder, or mental retardation were excluded. The remaining study population comprised 1,513 nonpsychotic first-degree relatives, with 203 and 1,310 from the simplex and multiplex groups, respectively. The subjects from simplex and multiplex families were comparable in terms of gender (44% vs. 48% were male). The relatives from multiplex families were older (56.3?nbsp;15.1 years vs. 46.7?nbsp;15.5 years) and had a lower education level (6.7?nbsp;4.9 years vs. 9.6?nbsp;4.7 years).
Interview Instruments and Diagnostic Procedures
All participating probands and first-degree relatives were interviewed with the Diagnostic Interview for Genetic Studies (DIGS) [Nurnberger et al., [1994]], which contains the modified SIS [Kendler et al., [1989]]. The Chinese version of the DIGS and its reliability has been described previously [Chen et al., [1998]]. Interviews with the Chinese version of the DIGS were carried out by research assistants who had received standardized training. In addition to the DIGS, interviewers used the Chinese version of the Family Interview for Genetic Studies (FIGS) [NIMH Genetics Initiative, [1992]] to collect relevant information on relatives. Two psychiatrists independently reviewed all available information including the DIGS, the FIGS, hospital records, and the interviewer's notes. Best estimate lifetime psychiatric diagnosis according to the DSM-IV criteria were determined independently; if both disagreed about a diagnosis, a third one was sought, and a consensus diagnosis was reached after discussion.
The modified SIS in the DIGS 2.0 contains 13 global ratings on a 7-point scale for schizotypal symptoms and 6 global ratings on a 5-point scale for schizotypal signs, with higher scores representing more severe schizotypal features. According to the DIGS training manual, the major modifications in the SIS section were a newly added section on anger to perceived slights to meet DSM-III-R criterion A.6 for paranoid personality disorder. Due to the conservativeness of discussing about sex in Taiwan culture, particular in adults, the global rating on sexual anhedonia was not included in the study for the concern of its validity. To evaluate the consistency of the global ratings, those of the first study were re-evaluated independently by three investigators on the basis of the individual items; then a consensus rating was reached and calibration was done if needed. To increase the comparability in SIS global ratings between the three studies, the consensus rating rules derived from the first study were written in computer algorithms using SAS to perform global ratings. The intraclass correlation coefficient between the SAS algorithm and the consensus rating of the first study ranged from 0.70 (for jealousy) to 1.00 (for odd behavior) with a mean (崆D) of 0.83?nbsp;0.09 (Table I).
TableI. Factors Loadings From a VARIMAX Factor Analysis of 18 Schizotypal Symptoms and Signs in 203 Nonpsychotic First-Degree Relatives of the Simplex FamiliesSchizotypal symptoms or signs / Intraclass correlation coefficient / Negative schizotypy / Positive schizotypy / Interpersonal Sensitivity / Social Isolation/Introversion
Irritabilitya / -b / 88 / -7 / -4 / -12
Aloofness/coldnessa / 0.89 / 79 / 2 / 4 / 30
Guardednessa / 0.98 / 78 / -15 / 31 / 6
Poor rapporta / 0.88 / 70 / -22 / 9 / 22
Suspiciousness / 0.76 / 52 / 41 / 24 / 19
Odd speecha / 0.87 / 49 / 14 / -44 / 21
Illusions / 0.81 / -14 / 82 / 13 / -0.1
Psychotic-like phenomena / 0.80 / -3 / 46 / -26 / 30
Magical thinking / 0.79 / -2 / 44 / 9 / -5
Ideas of reference / 0.84 / 10 / 42 / 25 / 3
Social anxiety / 0.95 / -11 / 5 / 65 / 8
Sensitivity / 0.84 / 7 / 17 / 55 / 5
Anger to perceived slights / 0.81 / 26 / 21 / 45 / -11
Introversion / 0.79 / -3 / -16 / 31 / 95
Social isolation / 0.72 / 7 / 1 / 1 / 45
Jealousy / 0.70 / 9 / 2 / 38 / 3
Restricted emotion / 0.73 / 12 / 16 / -11 / 27
Odd behaviora / 1.00 / 37 / 19 / -0.4 / -10
Variance, % / 21.5 / 13.8 / 10.7 / 9.6
aSchizotypal sign; a self-report symptom if no superscript was assigned.
bOnly one item corresponding to irritability.
Bold values represent factor loadings greater than 0.4.
Symptoms of probands were assessed using the Scales for Positive and Negative Symptoms (SANS and SAPS) [Andreasen, [1983], [1984]] in the Taiwan Schizophrenia Linkage Study [Hwu et al., [2005]].
Factor Analysis
Factor analyses of both schizotypal and schizophrenic symptoms were conducted using Mplus version 3.13 [Muthen and Muthen, [2004]]. We first conducted exploratory factor analyses with VARIMAX rotation of the 18 global ratings of schizotypal symptoms and signs in the relatives from simplex schizophrenia families. Then this factor structure was evaluated with confirmatory factor analysis among the relatives from multiplex schizophrenia families.
For the analyses of schizotypy, categorical factor indicators were used with unweighted and weighted least-squares estimation to implement exploratory and confirmatory analyses, respectively. These methods use polychoric correlations, which are more suitable than the usual Pearson's product-moment correlations for non-normal items. Model fit was assessed using comparative fit index (CFI), non-normed fit index (NNFI), and root mean square error of approximation (RMSEA) [Bentler, [1990]]. Values of the CFI and NNFI greater than 0.9 and values of the RMSEA less than 0.1 indicated a good fit. Factor scores were calculated by re-performing the confirmatory factor analysis on the whole data set (including both simplex and multiplex families).
For the analyses of clinical symptoms of schizophrenia, a three-factor model containing negative, positive, and disorganization dimensions was examined using the 7 global ratings from the SANS and SAPS following previous studies [Emsley et al., [2001]; Niehaus et al., [2005]].
Ordered Subset Linkage Analysis
The linkage sample included a total of 2,242 genotyped individuals, comprising 1,207 affected individuals and 1,035 unaffected individuals from 557 families with sib-pairs co-affected with schizophrenia, as previously described [Faraone et al., [2006]]. Genotyping was completed by the Center for Inherited Disease Research, using 386 microsatellite markers spaced at an average of 9-cM intervals. Non-Mendelian inheritance and excessive recombination events were checked, and erroneous genotypes were removed accordingly.
Based on this sample, a series of OSAs [Scott et al., [2003]; Hauser et al., [2004]] was conducted using nonparametric linkage z (NPL-Z) scores derived from software Merlin [Abecasis et al., [2002]] as input. The ordering of subsets was according to each family's covariate defined as the average scores of a schizophrenia factor from affected individuals and its corresponding schizotypy factor from nonpsychotic relatives within a family. Since the rating of schizophrenia symptoms (a 5-point scale) and schizotypy (a 7-point scale for schizotypal symptoms and a 6-point scale for schizotypal signs) was based on different scales, the summation of a schizophrenia factor and its corresponding schizotypy factor scores in each family was conducted on their standardized scores.
At the beginning, all the families were ranked according to the magnitude of family covariate in descending order, with those having the same covariate given the same rank. The genome-wide linkage analysis was then conducted in a series of subsets incrementally, starting with the rank that had the greatest family covariate. The procedure was repeated until all families were included in the final subset. The statistical significance of the difference between the greatest NPL-Z scores in a subset of families identified by OSA and the NPL-Z scores at the same position in the full set of families was evaluated via permutations. Under the null hypothesis that the ranking of the covariate is independent of the family's NPL-Z scores on the target chromosome, the families were randomly permuted with respect to the covariate ranking and a chromosome-wide P-value for each chromosome was yielded. A P-value of <0.05 was considered significant, suggesting that a particular subset of individuals in the sample is more strongly linked to the specified chromosomal region than the whole sample.
RESULTS
Factor Analysis of Relatives' Schizotypy
Examination of the scree plot from the exploratory factor analysis revealed a moderate break between factors four and five, which can be seen in Figure 1 of the data supplement in the online version of this article. The four-factor model (Table I) containing items with loadings larger than 0.4 was readily interpretable. The model extracted using the Promax oblique rotation method was the same. The three items of the SIS that did not load on any factor were jealousy, restricted emotion, and odd behavior. Of the other 15 items, only two (suspiciousness and odd speech) loaded simultaneously on two factors.
/ Figure 1. Factor loadings for a four-factor model of schizotypy.[Normal View 40K | Magnified View 77K]
The four-factor model was subsequently tested with confirmatory factor analysis in multiplex families, in which 64 out of 1,310 relatives were excluded due to missing more than one-third of the global ratings. Of the remaining 1,246 subjects, only six persons had missing global rating and each missed only one rating. The CFI, NNFI, and RMSEA for the confirmatory factor analysis were 0.924, 0.930, and 0.061, respectively, indicating a good fit to the data. The structure of the model and the resulting loadings are shown in Figure 2. Negative Schizotypy and Social Isolation/Introversion were moderately correlated (r=0.43, 95% confidence interval 0.33-0.53), whereas the Positive Schizotypy and Interpersonal Sensitivity were highly correlated (r=0.81, 95% confidence interval 0.73-0.89).