Research in Spectrum Disorders 6 (2012) 717–725

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Research in Disorders

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Do the traits of autism-spectrum overlap with those of schizophrenia or obsessive-compulsive disorder in the general population?

Akio Wakabayashi a,b,*, Simon Baron-Cohen b, Chris Ashwin b,c a Department of Psychology, Chiba University, Chiba 263-8522, Japan b Autism Research Centre, Department of Experimental Psychology and Psychiatry, , Douglas House, 18b Trumpington Road, Cambridge CB2 2AH, UK c Department of Psychology, University of Bath, Bath BA2 7AY, UK

ARTICLE INFO ABSTRACT

Article history: Social and communicative deficits, restricted interests and repetitive behaviors are Received 25 August 2011 diagnostic features of autism spectrum disorders (ASD). The present study examined the Received in revised form 18 September 2011 relationship between autistic characteristics and schizophrenia-spectrum traits as well Accepted 20 September 2011 as between autistic characteristics and obsessive-compulsive traits in typically developed young adults. The Autism-Spectrum Quotient (AQ) was given separately to Keywords: two large samples. In addition, one sample (N = 662) was given the Schizotypal Autism-spectrum Personality Questionnaire (SPQ) to assess schizophrenia-spectrum traits, whereas the Schizophrenia othersample(N =347) was given the Padua Inventory (PI) to assess obsessive- Obsessive-compulsive disorder (OCD) compulsive disorder (OCD) traits. The results revealed a moderate correlation between Autism-Spectrum Quotient (AQ) Schizotypal Personality Questionnaire (SPQ) the AQ and the SPQ total scores; however, multiple regression analyses showed that the Padua Inventory (PI) ‘‘Cognitive-Perceptual’’ factor did not predict the autism-spectrum degree, although autistic characteristics and schizophrenia-spectrum traits had common social–emo- tional difficulties. Similarly, there was a moderate correlation between the AQ and PI total scores, which suggests that they had common problems in cognitive aspects; however, autism-spectrum and OCD traits differed with regard to other behavioral characteristics including repetitive or impulsive behaviors. Therefore, there was not a large overlap of the autism-spectrum and either the schizophrenia- or obsessive- compulsive spectrums, although certain traits were correlated with each other. ß 2011 Elsevier Ltd. All rights reserved.

1. Introduction

1.1. Autism and schizophrenia

Autism (or autism spectrum disorders; ASD) is defined as abnormalities in social development and communication as well as strong displays of restricted interests and repetitive behaviors (American Psychological Association, 2000; World Health Organization, 1992). Although autism is an independent diagnostic category, some researchers have suggested that there is some resemblance between autism and schizophrenia (Petty, Ornitz, Michelman, & Zimmerman, 1984; Volkmar & Cohen, 1991), including recent work by Hurst, Nelson-Gray, Mitchell, and Kwapil (2007) and Konstantareas and Hewitt (2001). In the past, autism was considered to be an early form of schizophrenia. This belief reflected an awareness of the behavioral characteristics common to both conditions. Kanner’s (1943) use of the term ‘autism’ was applied to connect

* Corresponding author at: Department of Psychology, Chiba University, Chiba 263-8522, Japan. Tel.: +81 43 290 2282. E-mail address: [email protected] (A. Wakabayashi).

1750-9467/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.rasd.2011.09.008 718 A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725 autism to schizophrenia. Bleuler (1911) coined ‘autism’ to describe the thought processes of people with schizophrenia such as self-centered thinking, rather than the absence of social relatedness. However, because both autism and schizophrenia show types of social impairment and their non-social, detached symptoms are obvious, it is not surprising that the label ‘schizophrenic’ was also formerly used to refer to people with autism. Although some people become psychotic in early childhood, their symptoms do not resemble those of autism. Furthermore, children with autism are easily distinguished from those with psychotic conditions in most cases. Autism and schizophrenia are readily distinguishable diagnostic entities; however, the surface behaviors of some adults with autism resemble those of people with negative symptoms of schizophrenia. Specifically, these people have little or no social communication ability or facial/emotional expression and have a tendency to withdraw from social situations. They also often exhibit simple stereotypic or repetitive movements. On the other hand, people with positive symptoms of schizophrenia obviously differ from individuals with autism, including in their surface behaviors. The most common positive symptoms of schizophrenia are illusions such as hearing voices and delusions such as believing an unrelated event is connected to them in some important way. There have been few reports of these unusual experiences in people with autism; more importantly, most positive symptoms of schizophrenia require theory of mind (Corcoran, Mercer, & Frith, 1995), which people with autism profoundly lack (for example, paranoid delusions often contain attributions of others’ mental states). Consequently, interest in the relationship between autism and schizophrenia declined decades ago. However, some behavioral characteristics suggest that there is a link between autism and schizophrenia (Hurst et al., 2007; Konstantareas & Hewitt, 2001); moreover, this suggestion is based on a biological– neurological perspective (Cade et al., 1999; Sun & Cade, 1999).

1.2. Autism and obsessive-compulsive disorder

As well as a lack of, or profound deficits in, social interactive skills, obsessional interests, and engaging in repetitive behaviors are also core features of ASD. These characteristics of ASD resemble not only those of schizophrenia but also those of obsessive-compulsive disorder (OCD). With regard to the latter relationship, although both ASD and OCD have common features such as repetitive or stereotypic behaviors, there has been little research on this subject. However, two studies have reported the experiences of obsessions and compulsions in people with ASD and OCD (McDougle et al., 1995; McDougle,Kresch,&Posey,2000;Russell,Mataix-Cols,Anson,&Murphy,2005). Both studies found that, although there were also some similarities, there were certain differences between people with autism and those with OCD with regard to their obsessions and compulsions. However, because the autistic sample in McDougle et al.’s study (1995) included 50% of people with autism with below-average IQs, it was unclear as to whether these patients were able to report their symptoms correctly. Russell et al. (2005) compared the frequency and severity of repetitive ‘obsessional’ thoughts and compulsive behaviors in 40 high-functioning adults with ASD and 45 gender-matched adults with OCD. The severity and types of obsessive- compulsive symptoms were assessed using the 10-item Yale-Brown Obsessive-Compulsive Scale (Y-BOCS; Goodman, Price, Rasmussen, & Mazure, 1989) and its ancillary Symptom Checklist (Y-BOCS-SC), respectively. The results revealed a similar frequency of obsessions and compulsions across the two groups; however, the OCD group reported significantly higher frequencies of somatic obsessions and repeating/checking compulsions. A discrimination analysis revealed that a single type of obsession, somatic, and a single type of compulsion, repeating, predicted group membership because both symptoms were more frequent in the OCD group than the ASD group. The number of reported symptoms showed that the OCD group had more obsessions and compulsions than the ASD group.

1.3. Autism spectrum disorders and the analogue approach

Regarding the research described above, determining whether the behavior of people with ASD resemble those with schizophrenia or OCD is difficult. Clarifying the similarities and differences between ASD and the other disorders is important. The present study uses an analogue approach to examine this problem. This approach assumes that people with a clinical diagnosis of psychological/psychopathological disorder are at one extreme of a continuum of related and normative individual differences or characteristics. ‘Abnormal’ behavior and experiences are assumed to be different from those in the general population only in terms of their frequency and severity. As an example of the analogue approach’s point of view regarding autistic psychological difficulties, autism and (AS) are thought to exist on a continuum of social communication (dis)ability in which AS serves as the bridge between autism and normality (Baron-Cohen, 1995; Frith, 1991; Wing, 1981, 1988). Consistent with this idea, research has shown that autistic behaviors are observed in the normal population to some degree (Baron-Cohen, Wheelwright, Skinner, Martin, & Clubley, 2001; Wakabayashi, Baron-Cohen, Wheelwright, & Tojo, 2006). Relatives of people with autism also show some of the behavioral characteristics of autism (i.e., the broader phenotype; Bailey et al., 1995). Based on this view, the Autism-Spectrum Quotient (AQ) was developed to measure the degree of autistic traits in both typical developed and clinically diagnosed people (Baron-Cohen et al., 2001). The AQ has been used to screen high- functioning people with autism and AS with a high degree of accuracy (Baron-Cohen et al., 2001) and cross-cultural consistency (Wakabayashi et al., 2006). The results of research using the AQ have also revealed that the degree of autistic A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725 719 traits is normally distributed in the general population, with some individuals displaying a certain number of autistic traits (Baron-Cohen et al., 2001; Wakabayashi et al., 2006). This result suggests that conducting an analogue study of ASD with typically developed participants is possible, because the AQ allows for measuring individual differences in the number of autistic traits in general population. Our reasons for adopting an analogue approach are as follows: (1) due to subtle theory- of-mind-related problems, AS or high-functioning autism might impair a participant’s ability to judge their own social or communicative behaviors and thoughts (Baron-Cohen, 1995; Baron-Cohen, Jolliffe, Mortimore, & Robertson, 1997), thereby increasing the likelihood that individuals will inaccurately report these characteristics. Also most schizophrenic and obsessive-compulsive traits are related to people’s thought processes and behavior; therefore, these participants need certain meta-representative abilities to assess themselves. (2) There are some reliable measures of schizophrenic (schizophrenia-spectrum) traits (for example, the Schizotypal Personality Questionnaire, Raine, 1991) and obsessive- compulsive traits (for example, the Padua Inventory, Sanavio, 1988) for both clinically diagnosed people and those who are not. Both measures have been frequently used in analogue research on clinical/psychopathological issues, and their usefulness and reliability have been widely confirmed (for example, Daneluzzo, Bustini, Stratta, Casacchia, & Rossi, 1998; Sternberger & Burns, 1990). Hurst et al. (2007) recently studied the relationship between autistic and schizotypal traits in a large, non-clinical sample. However, some questions remain regarding their results because their sample consisted of approximately 80% females; however, ASD occurs in four times as many males as females (Newschaffer et al., 2007), and schizophrenia occurs in males and females equally (Castle, Wessely, Der, & Murray, 1991). Therefore, these diagnostic relationships should be re-examined in a large gender-matched sample. This paper examines the similarities and differences between the degrees of autistic traits and schizophrenic traits and obsessive-compulsive traits in typically developed participants. We expect to find that there may be some correlations or overlap between the numbers or degrees of autistic traits and schizophrenic traits and OCD traits; however, autistic traits would be independent of schizophrenic traits and obsessive-compulsive traits as a whole.

2. Materials and methods

2.1. Instruments

AQ. The AQ (Japanese version; Wakabayashi, Tojo, Baron-Cohen, & Wheelwright, 2004) is a 50-item, self-administered questionnaire that assesses the degree to which an adult with normal intelligence has traits associated with the autism- spectrum. Research has shown that the Japanese version of the AQ is equivalent to the original UK version (Baron-Cohen et al., 2001; Wakabayashi et al., 2006). AQ scores range from 0 to 50. Schizotypal Personality Questionnaire (SPQ; Raine, 1991). The SPQ assesses the degree of schizotypal personality (or schizophrenia-spectrum) traits in both normal and pathological populations. This inventory is composed of 74 items that comprise nine subscales based on the DSM-IV-TR schizotypal personality disorder diagnostic criteria (American Psychological Association, 2000). The nine subscales include ‘Ideas of reference’, ‘Excessive social anxiety’, ‘Odd beliefs or magical thinking’, ‘Unusual perceptual experiences’, ‘Odd or eccentric behavior’, ‘No close friends’, ‘Odd speech’, ‘Constricted affect’, and ‘Suspiciousness’. These subscales are classified into three factors: ‘Cognitive-Perceptual’, ‘Interpersonal’, and ‘Disorganized’. We used the Japanese adaptation of the SPQ to measure schizotypal personality traits. This version is administered in the same format as the original American version and has similar psychometric properties and reliability (Wakabayashi, submitted for publication). SPQ scores range from 0 to 74. The Padua Inventory (PI; Sanavio, 1988). The PI was used to measure the degree of obsessive-compulsive traits in participants. This measure has been widely used to assess obsessive-compulsive traits in both clinical and non-clinical samples (for example, Sternberger & Burns, 1990), and much research supports its reliability and validity not only in the western world (Kyrios, Bhar, & Wade, 1996; Macdonald & de Silva, 1999; Sternberger & Burns, 1990; Van Oppen, Hoekstra, & Emmelkamp, 1995) but also in other cultures (Goodarzi & Firoozabadi, 2005; Min, 1999). In addition, research has revealed that the PI has a relatively stable four-factor structure, although slight differences have been observed across different countries. The PI is a self-administered, 60-item questionnaire that assesses the number and severity of OCD symptoms in normal and clinical populations. Each item is rated on a 0–4 scale in which 0 indicates that the item is ‘‘not at all’’ disturbing and 4 indicates that it is ‘‘very much’’ disturbing. We used the Japanese version of the PI; a previous study standardized this measure and reported its psychometric properties and reliability (Wakabayashi & Aobayashi, 2007). The Japanese version of the PI is composed of a total score and four subscale scores including which consists of ‘Impaired control of mental activities’, ‘Checking behavior’, ‘Being contaminated’, and ‘Impulsiveness’.

2.2. Participants

One group of 662 students (328 males and 334 females) and another group of 347 students (189 males and 158 females) from introductory psychology courses at Chiba University were recruited to examine the relationship between ASD and schizophrenia and the relationship between ASD and OCD, respectively, from 2007 to 2009. The mean age of participants was 18.9 years (SD = 1.41), with a range from 18 to 27 years. No people participated in both groups. All participants provided informed consent and agreed to participate in the study. 720 A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725

2.3. Procedure

The questionnaires were administered to participants in classes. Half of the former group of participants (N = 662) completed the AQ first and the SPQ between one and two months later. The remaining participants completed the questionnaires in the reverse order. Similarly, in the latter group (N = 347), half the participants completed the AQ first and the PI one to two months later. The other half of the participants completed questionnaires in the reverse order. Questionnaires with missing data or more than one response on the same item were rejected. The participants described above are those who completed every item; only the data from these participants were included in the analyses.

3. Theory and calculations

Because the AQ (Baron-Cohen et al., 2001) was based on the autism-spectrum hypothesis, it was used to assess the degree of autistic (autism-spectrum) traits in each participant. With regard to the measure of schizophrenic traits, various instruments exist. The continuum on which schizophrenia is an extreme condition (schizophrenia-spectrum) has been conceptualized in terms of schizotypal personality characteristics (Meehl, 1962). This quantitative trait approach is compatible with the genetic theory of schizophrenia. Although many first- degree relatives of patients with schizophrenia do not have schizophrenia, they nevertheless show schizotypal personality characteristics (Katy, Rosenthal, Wender, Schulsinger, & Jacobsen, 1975). The SPQ (Raine, 1991) was used to assess the degree of schizotypal personality traits observed in each participant in this study. Many people believe that schizotypal personality disorder (SPD) is a mild form of schizophrenia (American Psychiatric Association, 2000). Odd forms of thinking and perceiving characterize SPD; individuals with this disorder often seek isolation from others. In addition, the SPQ assesses the degree of schizotypal traits in the normal population as well as in people with schizophrenia (Raine, 1991). Schizotypal personality traits and schizophrenic (or schizophrenia-spectrum) traits are the same (Meehl, 1962; Venables & Bailes, 1994). If there is some overlap or a relationship between the traits of autism-spectrum and schizophrenia-spectrum, then there should be a correlation between the AQ and SPQ the total scores. In addition, the correlations between the AQ and SPQ subscale scores should identify which schizophrenic trait is related to autism-spectrum. In addition to the overlap between ASD and schizophrenia or the overlap between autism-spectrum and schizophrenic traits, we are also interested in the connection between ASD and OCD. To investigate this connection, we examined the relationship between autistic traits and obsessive-compulsive traits. Most people with ASD show strong interests in specific topics and display stereotyped/repetitive behaviors; these behavioral characteristics are also observed in people with OCD. It is suggested that ASD and OCD might share a common genetic vulnerability (Buxbaum, Ramoz, Sakurai, Silverman, & Hollander, 2007). Similar to the schizophrenia-spectrum, a continuum between normal personality dimensions and psychopathological conditions of OCD has been proposed (Rachman & De Silva, 1978; Rachman and de Silva, 1978; Salkovskis & Harrison, 1984). This continuum is often referred to as the ‘Obsessive-Compulsive Disorder Spectrum’ (Hollander et al., 2005). The Padua Inventory (PI) was used to assess the degree of OCD traits in each participant. If autism-spectrum is related with OCD traits, we should find a correlation between the AQ and PI scores. Furthermore, differences among the correlations on the AQ and PI subscales should suggest which OCD traits are related to which autistic traits. Furthermore, we examined the profile of the ASD analogue model on the SPQ and PI scales. There is a cut-off point on the AQ that discriminates groups with as many true positives and as few false negatives as possible. In the Japanese AQ sample, that cut-off is a score of 33+ because approximately 90% of the ASD group scored at this level, whereas only 3% of controls did so in a standardized study (Wakabayashi et al., 2006). Therefore, participants who scored 33 and above are considered to constitute an analogue model of ASD because they have a similar amount of autistic traits and are homogeneous with people with ASD on the autism-spectrum dimension. In this study, the diagnostic status of participants is unknown; there might have been some people with ASD in the samples (assuming an approximate ASD rate of 1 in 200).

4. Results

4.1. The relationship between autism-spectrum and schizophrenic traits

Firstly, AQ scores and SPQ scores of the participants in this study were examined to see if they were equivalent to those in standardized data. T-tests revealed that both mean scores were not statistically different from those of the standardized data respectively (M = 20.9, SD = 6.58 vs. M = 20.7, SD = 6.38, t = 0.624, p = 0.53 for the AQ; M = 32.5, SD = 10.09 vs. M = 31.8, SD = 10.33, t = 1.370, p = 0.17 for the SPQ).

4.1.1. The correlations between the AQ and SPQ Table 1 shows the Pearson’s product-moment correlation coefficients among the AQ score and the SPQ total score as well as its nine sub-scale scores. The AQ score was moderately correlated with the SPQ total score; furthermore, it was also correlated with three sub-scales: ‘Excessive social anxiety’, ‘No close friends’ and ‘Constricted affect’. With regard to SPQ factors, the AQ score was highly correlated with the ‘Interpersonal’ factor; however, there was almost no correlation with the ‘Cognitive-Perceptual’ factor. Although most of the other subscales revealed correlations to some extent, the size of the A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725 721

Table 1 Correlations between the AQ score and the SPQ total score and its subscale scores.

Participants Total Ideas of Social Odd Unusual Odd No close Odd Constricted Suspiciousness SPQ reference anxiety beliefs perception behavior friends speech affect

All (N = 662) 0.483* 0.145* 0.453* À0.173* 0.135* 0.233* 0.512* 0.238* 0.495* 0.277* Males (N = 328) 0.526* 0.201* 0.491* À0.065* 0.194* 0.244* 0.484* 0.319* 0.476* 0.262* Females (N = 334) 0.447* 0.111 0.443* À0.224* 0.049 0.224* 0.521* 0.220* 0.492* 0.269* * p < 0.001.

correlation coefficients were rather low, around r = 0.2 and below. There was a slightly negative but significant correlation between the AQ score and ‘Odd beliefs or magical thinking’ (r = À0.17, p < .001).

4.1.2. Multiple regression analysis of the AQ score by the SPQ To examine the extent to which the SPQ explains the AQ score, we applied a regression analysis to our data. A standard multiple regression analysis was performed using the AQ score as the outcome and the eight SPQ subscales as predictors but excluding ‘Odd beliefs or magical thinking’ because it was negatively correlated with the AQ score. The results showed that the SPQ scales explained 40% of the variability in the autism-spectrum. Another multiple regression analysis was performed using the AQ score as the outcome and the three factors from the SPQ as predictors. The results showed that the three SPQ factors explained 37% of the variability in the autism-spectrum.

4.2. The relationship between autism-spectrum and obsessive-compulsive traits

Similar to the analyses on the relationships between the AQ and SPQ, we first examined whether participant AQ and PI scores were equivalent to standardized data. T-tests showed that neither dataset was statistically different from the standardized data (M = 20.4, SD = 6.08 vs. M = 20.7, SD = 6.38, t = 0.768, p = 0.44 for the AQ; M = 76.2, SD = 30.97 vs. M = 72.7, SD = 34.76, t = 1.579, p = 0.12 for the PI).

4.2.1. The correlation between the AQ and PI Table 2 shows the Pearson’s product-moment correlation coefficients among the AQ score and the PI total score as well as its four subscales. The AQ score was moderately correlated with the PI total score. Among the subscales, although ‘Impaired control of mental activities’ had the highest correlation, it was not highly correlated with the AQ score. The other three subscales had low correlations coefficients, from r = 0.20 to 0.30.

4.2.2. Multiple regression analysis of the AQ score by the PI score To examine the extent to which the PI subscale scores explained the AQ score, we applied a regression analysis to our data. A standard multiple regression analysis was performed with the AQ score as the outcome and the four PI subscales as predictors. The four PI subscales explained 16% of the variability in the autism-spectrum. Only two subscales (‘Impaired control of mental activities’ and ‘Impulsiveness’) predicted the degree of autistic traits.

4.3. The profile of analogue model of autism spectrum disorders on the SPQ and PI scores

4.3.1. Participants who fit the ASD analogue model Fifty-six participants with SPQ fit the ASD analogue model; 18 participants with PI also fit this condition. Their mean AQ scores were 34.1 (SD = 1.48, ranging from 33 to 38) and 33.9 (SD = 1.47, ranging from 33 to 38), respectively. We compared this analogue group with the whole sample with regard to their SPQ and PI scores. Additionally, we also calculated the number of participants who fit the analogue models of schizotypal personality disorder and obsessive- compulsive disorder based on their SPQ and PI scores respectively. In these cases, each cut-off point was the mean score plus 2 SD because this score corresponds to a standard T score of 70, and the probability that a participant scored at this level or above is 2.3%. This likelihood almost corresponds with the statistical value of the cut-off point. That is, the cut-off point of the AQ was 33, which was based on the diagnostic discrimination between people with or without ASD. This score corresponds with the mean score plus 2 SD (i.e., 20.7 + 2 Â 6.38 = 33.5).

Table 2 Correlations between the AQ score and the Padua Inventory scores.

Participants PI total Impaired control Checking behavior Being contaminated Impulsive thought

All (N = 347) 0.411* 0.378* 0.289* 0.227* 0.314* Males (N = 189) 0.406* 0.377* 0.305* 0.248* 0.285* Females (N = 158) 0.409* 0.419* 0.256 0.179 0.350* * p < 0.001. 722 A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725

4.3.2. The profile of the analogue model of ASD on the SPQ Table 3 shows the SPQ total score and its nine subscale scores for the analogue ASD group and all participants. As expected, the analogue ASD group scored higher than the whole sample with regard to the total SPQ score. The analogue ASD group scored significantly higher than the whole sample on most of the subscales but not except ‘Ideas of reference’ (no correlation) and ‘Odd beliefs or magical thinking’ (negatively correlated). The analogue ASD group did not show any differences from the whole sample with regard to ‘Ideas of reference’; moreover, their ‘Odd beliefs or magical thinking’ scores were significantly lower than those of the whole sample (p < 0.01).

4.3.3. The profile of analogue model of ASD on the PI Table 4 shows the PI total score and its four subscale scores. The analogue ASD group scored higher on the PI total score than the whole sample. The analogue ASD group also scored higher than the whole sample on two subscales: ‘Impaired control’ and ‘Impulsive thoughts’ (ps < 0.05). However, there were no between-group differences on two aspects that characterize OCD: ‘Being contaminated’ (to avoid dirty things) and ‘Checking behavior (repetitive confirmation of own behaviors)’.

4.3.4. The coexistence of ASD and SPD as well as ASD and OCD Finally, six participants fit the analogue model of SPD (10.7%), and three participants fit the analogue model of OCD (16.7%) in each ASD analogue sample.

5. Discussion

In this paper, we examined the relationship between autism-spectrum and schizophrenic traits as well as between autism-spectrum and obsessive-compulsive traits in university students using an analogue approach. The results obtained from the correlations between the AQ and SPQ suggest that there is a relationship between the autism-spectrum and some schizophrenic traits: in particular, ‘Excessive social anxiety’ and ‘No close friends’. This result is consistent with the clinical characteristics of people with ASD and people with schizophrenic disorder (American Psychiatric Association, 2000). Although those features showed the highest correlations with the AQ, these relationships were not strong. On the whole, these results suggest that the autism-spectrum has more differences to rather than similarities with the schizophrenia-spectrum. The correlations between the AQ score and the three SPQ factors also supported this result. Although the ‘Interpersonal’ subscale had a high correlation with the AQ score, the other factors had low correlations. These correlations correspond to the results of a former study that investigated the relationship between the AQ and the SPQ (Hurst et al., 2007). The multiple regression analysis result also supported this view. Specifically, this result showed that the SPQ explained only 40% of the variability of the AQ. This result suggests that the nine diagnostic criteria of schizotypal personality disorder, which consist of schizophrenia-spectrum traits, cannot sufficiently explain the individual differences in AQ scores. Perhaps not all schizophrenic traits are associated with the autism-spectrum; however, specific traits might show more of a relationship. The characteristics common to both autistic traits and schizophrenic traits include strong anxiety of social interaction and isolation from others. These behavioral characteristics are core features of both ASD and schizophrenia, and the term ‘autism’ often represents such non-social behaviors in general. However, the two disorders differ from each other in many aspects.

Table 3 Comparisons of the SPQ scores between analogue ASD group and all sample.

Group Total Ideas of Social Odd Unusual Odd No close Odd Constricted Suspiciousness SPQ reference anxiety beliefs perception behavior friends speech affect

ASD (N = 56) 41.9 4.3 6.4 1.2 4.3 3.9 5.6 6.1 4.7 5.3 All (N = 662) 32.5 4.1 4.8 1.9 3.6 2.5 3.5 5.2 2.7 4.3 t 6.749** 0.699 5.429** 3.298** 2.669** 4.726** 8.095** 3.279** 7.555** 3.377**

*p < 0.05, **p < 0.01.

Table 4 Comparisons of the PI scores between analogue ASD group and all sample.

Participants PI total Impaired control Checking behavior Being contaminated Impulsive thought

ASD (N = 18) 110.1 37.4 26.2 13.4 10.2 All (N = 347) 78.2 30.9 23.1 10.9 5.9 t 4.248** 2.397* 1.485 1.440 3.170**

*p < 0.05, **p < 0.01. A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725 723

This study revealed the differences between ASD and schizophrenia via an analogue study on the relationship between autism-spectrum and schizophrenic traits. Specifically, there was a negative correlation between the AQ score and the ‘Odd beliefs and magical thinking’ subscale. This result corresponds with the diagnostic criteria that discriminates ASD from schizophrenia; that is, people with schizophrenia often have positive symptoms such as delusions that require some form of mental attribution, whereas people with ASD hardly show this type of symptom. Similarly, the results obtained from the correlations between the AQ and PI suggest that there is a relationship between autism-spectrum and obsessive-compulsive traits. In particular, the ‘Impaired control of mental activities’ subscale (a cognitive impairment) is related to autism-spectrum, which suggests that this relationship falls into the executive (mal) function theory of autism. This theory is the best for predicting the repetitive and restricted behaviors of people with autism (Russell, 1998). However, there was only a small correlation between the AQ score and the PI subscale ‘Checking behavior’. This subscale is closely connected with the repetitive behaviors that are observed in people with ASD. In general, these results suggest that the relationship between the autism-spectrum and the OCD is less similar than the relationship between the autism-spectrum and the schizophrenia. The multiple regression analysis result also supported this view. The result showed that the PI subscales explained only 16% of the variability of the AQ scores. This result suggests that the four characteristics of obsessive-compulsive disorder are insufficient to explain the individual differences in the autism-spectrum. This results means that ASD has only a partial similarity to OCD. Although people with ASD often show some obsessive behavior (for example, they usually have a strong obsession with specific things or acts), they do not have content-free obsessions (Baron-Cohen & Wheelwright, 1999), whereas people with OCD tend to have less specific obsessions and compulsions. These aspects clearly differentiate ASD from OCD. The only trait common to both autism-spectrum and obsessive-compulsive traits was a tendency toward executive dysfunction as measured by the ‘Impaired control of mental activity’ subscale. This feature is a core characteristic of OCD, and it was observed in people who had higher autism-spectrum scores; however, other OCD characteristics had almost no relationship with autism-spectrum traits. The results of the ASD analogue model profile on the SPQ as well as the one on the PI suggest that people with ASD resemble partly those with schizophrenia and those with OCD, respectively, but are not that similar to either. These results also suggest that the proportion of people with ASD who show SPD or OCD is small. The suggestion that the autism bears a resemblance to schizophrenia or OCD is not reasonable, despite some of the behavioral similarities that are observed in people with ASD and those with schizophrenia or OCD. This finding suggests that a neurocognitive mechanism underlies the differences that exist between ASD and the other disorders. However, the present study cannot comment on this issue because it only examined the behavioral and cognitive aspects that are related to ASD, schizophrenia, and OCD. The data reported in this paper are exclusively from university students; different results might be obtained from people with ASD. Some personality questionnaires require that participants have metacognitive abilities to reflect on their own thoughts and behaviors, and these measures present difficulties for people with ASD, even if they had normal or high intelligence. The questionnaires used in this study reliably measure individual differences in the traits of autism spectrum, schizophrenia-spectrum, and obsessive-compulsive spectrum, even in a non-clinical sample. Therefore, although our participants were from a non-clinical sample, we feel that our results provide important insights into the similarities and differences between ASD and schizophrenia as well as between ASD and OCD. High levels of general anxiety are typical in people with ASD and most people with schizophrenia; this condition might cause some people to observe similarities between these disorders. The schizophrenia-spectrum condition that includes only negative symptoms, schizoid personality disorder, might have a greater similarity to ASD than schizotypal personality disorder. However, losing pleasure in social and leisure activities is a symptom of schizoid personality disorder. On the surface, this symptom might appear similar to people with autism who lack interest in communication; however, most people with autism find pleasure in their obsessive or repetitive activities and do not lose interest in them. Thus, this aspect is different from schizoid personality disorder. Some types of obsessive-compulsive-like behaviors are seen in people with ASD. Adults with high-functioning ASD reported experiencing a high frequency of obsessions and compulsions as intrusive, distressing and time-consuming (Russell et al., 2005). The results of this study suggested that people who have much autism-spectrum traits tend to have an impaired control of mental activities, which is a core feature in those with OCD. Executive function deficits and preferences for local rather than global information processing have been reported in people with ASD and those with OCD (Ozonoff, Pennington, & Rogers, 1991; Savage, Baer, & Keuthen, 1999). However, repeating and checking rituals were not more frequent in people who had many ASD traits. It is not known whether obsessive-compulsive behaviors in people with OCD and those with ASD share a common neurocognitive basis. The continuum (analogue) approach could assist researchers in psychiatric genetics in that, because psychopathological conditions might result from complex genetic traits, a subset of the susceptibility genes that cause individuals to have psychiatric conditions are present in people at moderate or low levels on the postulated dimension. For this reason, characterizing the relevant psychological spectrum relevant to a given psychiatric diagnosis is important because this dimension might define a quantitative phenotype. Our results could have important implications for clinical practice and research. From a therapeutic perspective, clinicians should consider the possibility that significant schizophrenic symptoms, obsessive-compulsive symptoms, or both 724 A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725 exist in people with ASD, rather than classifying their phenomenology as a characteristic of ASD. The proper assessment to distinguish ASD from these two phenomena is important.

6. Conclusion

The autism-spectrum partly resembles the schizophrenia-spectrum and the obsessive-compulsive spectrum because there are some behavioral similarities in people with ASD compared with those with schizophrenia and those with OCD. However, there was not a large overlap of the autism-spectrum and either the schizophrenia- or obsessive-compulsive spectrums. The proportion of people with ASD who show some SPD or OCD traits at a diagnostic level is very small.

References

American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text revision). Washington, DC: American Psychiatric Association. Bailey, A., Le Courteur, A., Gottesman, I., Bolton, P., Simonoff, E., Yuzda, E., et al. (1995). Autism as a strongly genetic disorder: Evidence from a British Twin Study. Psychological Medicine, 25, 63–77. Baron-Cohen, S. (1995). Mindblindness: An essay on autism and theory of mind. Cambridge, MA: MIT Press/Bradford Books. Baron-Cohen, S., & Wheelwright, S. (1999). ‘Obsessions’ in children with autism or Asperger syndrome. British Journal of Psychiatry, 175, 484–490. Baron-Cohen, S., Jolliffe, T., Mortimore, C., & Robertson, M. (1997). Another advanced test of theory of mind: Evidence from high functioning adults with autism or Asperger syndrome. Journal of Child Psychology and Psychiatry, 38, 813–822. Baron-Cohen, S., Wheelwright, S., Skinner, R., Martin, J., & Clubley, E. (2001). The Autism-Spectrum Quotient (AQ): Evidence from Asperger syndrome or high- functioning autism, males and females, scientists and mathematicians. Journal of Autism and Developmental Disorders, 31, 5–17. Bleuler, E. (1911). Dementia praecox or the group of schizophrenias. New York: International Universities Book. (translated by Zinkin, J., 1950). Buxbaum, J. D., Ramoz, N., Sakurai, T., Silverman, J., & Hollander, E. (2007). Do autism and OCD have shared genetic vulnerability? Abstracts for European Psychiatry, 22, S32–S33. Cade, R. J., Privette, R. M., Fregly, M., Rowland, N., Sun, Z., Zele, V., et al. (1999). Autism and schizophrenia: Intestinal disorders. Nutritional Neuroscience, 2, 57–72. Castle, D., Wessely, S., Der, G., & Murray, R. M. (1991). The incidence of operationally defined schizophrenia in Camberwell 1965-84. British Journal of Psychiatry, 159, 790–794. Corcoran, R., Mercer, G., & Frith, C. D. (1995). Schizophrenia, symptomatology and social inference; Investigating ‘‘theory of mind’’ in people with schizophrenia. Schizophrenia Research, 17, 5–13. Daneluzzo, E., Bustini, M., Stratta, P., Casacchia, M., & Rossi, A. (1998). Schizotypal Personality Questionnaire and Wisconsin Card Sorting Test in a population of DSM-III-R schizophrenic patients and control subjects. Comprehensive Psychiatry, 39, 143–148. Frith, U. (1991). Autism and Asperger’s syndrome. Cambridge: Cambridge University Press. Goodarzi, M. A., & Firoozabadi, A. (2005). Reliability and validity of the Padua Inventory in an Iranian population. Behaviour Research and Therapy, 43, 43–54. Goodman, W. K., Price, L. H., Rasmussen, S. A., & Mazure, C. (1989). The Yale-Brown Obsessive Compulsive Scale I: Development, use and reliability. Archives of General Psychiatry, 46, 1006–1011. Hollander, E., Freidberg, J. P., Wasserman, S., Yeh, C.-C., & Iyengar, R. (2005). The case for the OCD spectrum. In J. S. Abramowitz & A. C. Houts (Eds.), Concepts and controversies in obsessive-compulsive disorder (pp. 95–118). Hurst, R. M., Nelson-Gray, R. O., Mitchell, J. T., & Kwapil, T. R. (2007). The relationship of Asperger’s characteristics and schizotypal personality traits in a non- clinical adult sample. Journal of Autism and Developmental Disorders, 37, 1711–1720. Kanner, L. (1943). Autistic disturbances of affective contact. Nervous Child, 2, 217–250. Katy, S., Rosenthal, D., Wender, P. H., Schulsinger, F., & Jacobsen, B. (1975). Mental illness in the biological and adoptive families of adopted individual who have become schizophrenic: A preliminary report base on psychiatric interviews. In R. Fieve, D. Rosenthal, & H. Brill (Eds.), Genetic research in psychiatry. Baltimore, MD: John Hopkins University Press. Konstantareas, M. M., & Hewitt, T. (2001). Autistic disorder and schizophrenia: Diagnostic overlaps. Autism and Developmental Disorders, 31, 19–28. Kyrios, M., Bhar, S., & Wade, D. (1996). The assessment of obsessive-compulsive phenomena: Psychometric and normative data on the Padua Inventory from as Australian non-clinical student sample. Behaviour Research and Therapy, 34, 85–95. Macdonald, A. M., & de Silva, P. (1999). The assessment of obsessionality using the Padua Inventory: Its validity in a British non-clinical sample. Personality and Individual Differences, 27, 1027–1048. McDougle, C. J, Kresch, L. E., Goodman, W. K., Naylor, S. T., Volkmar, F. R., Cohen, D. J., et al. (1995). A case-controlled study of repetitive thoughts and behaviour in adults with autistic disorder and obsessive-compulsive disorder. American Journal of Psychiatry, 152, 772–777. McDougle, C. J., Kresch, L. E., & Posey, D. J. (2000). Repetitive thoughts and behaviour in pervasive developmental disorders: Treatment with serotonin reuptake inhibitors. Journal of Autism and Developmental Disorders, 30, 427–435. Meehl, P. (1962). Schizotaxia, schizotypia, schizophrenia. American Psychologist, 17, 827–838. Min, B. B. (1999). Reliability and validity of the Korean translation of Maudsley obsessive-compulsive inventory and Padua inventory. Korean Journal of Clinical Psychology, 18, 163–182. Newschaffer, C. J., Croen, L. A., Daniel, J., Giarelli, E., Grether, J. K., Levy, S. E., et al. (2007). The spectrum disorders. Annual Review of Public Health, 28, 235–258. Ozonoff, S., Pennington, B. F., & Rogers, S. J. (1991). Executive function deficits in high-functioning autistic individuals: Relationship to theory of mind. Journal of Child Psychology and Psychiatry, 32, 1107–1122. Petty, L., Ornitz, E. M., Michelman, J. D., & Zimmerman, E. G. (1984). Autistic children who became schizophrenic. Archives of General Psychiatry, 41, 129–135. Rachman, S., & De Silva, P. (1978). Abnormal and normal obsessions. Behaviour Research and Therapy, 16, 233–238. Raine, A. (1991). The SPQ: A scale for the assessment of schizotypal personality based on DSM-III-R criteria. Schizophrenia Bulletin, 17, 556–564. Russell, J. (1998). How executive disorders can bring about an inadequate ‘theory of mind’. In J. Russell (Ed.), Autism as an executive disorder (pp. 256–299). Oxford: Oxford University Press. Russell, A. J., Mataix-Cols, D., Anson, M., & Murphy, D. G. M. (2005). Obsessions and compulsions in Asperger syndrome and high-functioning autism. British Journal of Psychiatry, 186, 525–528. Salkovskis, P., & Harrison, J. (1984). Abnormal and normal obsessions—A replication. Behavioural Research and Therapy, 22, 549–552. Sanavio, E. (1988). Obsessions and compulsions: The Padua Inventory. Behaviour Research and Therapy, 26, 169–177. Savage, C. R., Baer, L., & Keuthen, N. J. (1999). Organizational strategies mediate nonverbal memory impairment in obsessive-compulsive disorder. Biological Psychiatry, 45, 905–916. Sternberger, L. G., & Burns, G. L. (1990). Obsessions and compulsions: Psychometric properties of the Padua Inventory with an American college population. Behaviour Research and Therapy, 28, 341–345. Sun, Z., & Cade, J. R. (1999). A peptide found in schizophrenia and autism causes behavioral changes in rat. Autism, 3, 85–95. Van Oppen, P., Hoekstra, R. J., & Emmelkamp, P. M. G. (1995). The structure of obsessive-compulsive symptoms. Behaviour Research and Therapy, 33, 15–23. A. Wakabayashi et al. / Research in Autism Spectrum Disorders 6 (2012) 717–725 725

Venables, P. H., & Bailes, K. (1994). The structure of schizotypy, its relation to sub-diagnoses of schizophrenia and to sex and age. British Journal of Clinical Psychology, 33, 277–294. Volkmar, F. R., & Cohen, D. J. (1991). Comorbid association of autism and schizophrenia. American Journal of Psychiatry, 148, 1705–1707. Wakabayashi, A. Schizotypal personality traits in the Japanese general population: Schizophrenia-spectrum hypothesis and factor structure of the Schizotypal personality, submitted for publication. Wakabayashi, A., & Aobayashi, T. (2007). Psychometric properties of the Padua Inventory in a sample of Japanese university students. Personality and Individual Differences, 43, 1113–1123. Wakabayashi, A., Tojo, Y., Baron-Cohen, S., & Wheelwright, S. (2004). The Autism-Spectrum Quotient (AQ) Japanese version: Evidence from high-functioning clinical group and normal adults. The Japanese Journal of Psychology, 75, 78–84 (in Japanese with English abstract). Wakabayashi, A., Baron-Cohen, S., Wheelwright, S., & Tojo, Y. (2006). The Autism-Spectrum Quotient (AQ) in Japan: A cross-cultural comparison. Journal of Autism and Developmental Disorders, 36, 263–270. Wing, L. (1981). Asperger syndrome: A clinical account. Psychological Medicine, 11, 115–130. Wing, L. (1988). The autistic continuum. In L. Wing (Ed.), Aspects of autism: Biological research. London: Gaskell/Royal College of Psychiatrists. World Health Organization. (1992). International classification of diseases (10th ed.). Geneva: World Health Organization.