Autism and schizophrenia in high functioning adults: Behavioral differences and overlap

Abstract

Several recent studies have demonstrated a genetical overlap between autism and schizophrenia. However, at a behavioral level it remains unclear which features can validly distinguish adults with autism from an adult schizophrenia group. To this end, the present study compared 21 individuals with the autistic disorder and 21 individuals with schizophrenia in self-reported features of autism and schizophrenia, as measured by the Autism-Spectrum Quotient (AQ) and the Schizotypal Personality Questionnaire (SPQ).

The schizophrenia group was more likely to report positive symptoms and the adults with autism were more likely to report impairments in social skill. Overlap was found between the two groups in negative symptoms, disorganization, attention to detail and imagination.

Thus, when discriminating between the two disorders, especially social skill and the presence of positive symptoms are relevant, whereas the presence of negative symptoms is not indicative.

Introduction

Recently, research demonstrated that autism and schizophrenia are genetically linked (Burbach & van der Zwaag, 2009). Apparently, the two disorders share common genotypical features, therefore phenotypical (cognitive) and endophenotypical (behavioral) overlap can be expected (Braff et al., 2007, Happé and Frith, 1996). In order to classify the two disorders correctly in adults and to choose appropriate interventions, it is important to know their precise behavioral overlap and differences. The present study aims to examine this.

Originally, autism and schizophrenia were thought to be closely linked and the DSM-II made no distinction between the two disorders (APA, 1968). However, research in the 1970s demonstrated that the two disorders could be reliably differentiated (Kolvin, 1971, Rutter, 1972). Throughout the years, various differences have been reported between the two disorders, for example in age of onset, sex distribution, family history and long-term outcome (Konstantareas and Hewitt, 2001, Tantam, 1991, Watkins et al., 1988, Werry, 1992). Furthermore, Volkmar and Cohen (1991) reported that the prevalence of schizophrenia in an autistic sample is not higher than in the general population, which at that time confirmed the hypothesis that autism and schizophrenia should be regarded as separate disorders.

However, research continued to report some degree of overlap between autism and schizophrenia (Dykens et al., 1991, Konstantareas and Hewitt, 2001). Currently, the growing body of genetic studies in autism and schizophrenia enabled a more fundamental examination of the overlap and differences between the two disorders. Results indicated that similar chromosomal rearrangements and several single genes emerge as genetic risks both in autism and schizophrenia (Burbach and van der Zwaag, 2009, Rapoport et al., 2009, Tabares-Seisdedos and Rubenstein, 2009). These findings gave rise to the hypothesis that the two disorders may arise from similar neurodevelopmental vulnerability, or actually share defects in biological pathways of brain development (Burbach and van der Zwaag, 2009, Rapoport et al., 2009). This confirms previous ideas that autism and schizophrenia are related (APA, 1968), although the overlap may be smaller than originally thought. Genotypical overlap between autism and schizophrenia is expected to reflect in similarities on neurocognitive (phenotypic) and behavioral (endophenotypic) levels (Nylander, Lugnegard, & Hallerback, 2008).

At the cognitive level, research indicated various similarities between autism and schizophrenia. For example, impairment in theory of mind (Baron-Cohen et al., 1985, Corcoran, 2000, Pilowsky et al., 2000), central coherence (Happé and Frith, 2006, John and Hemsley, 1992, Uhlhaas and Silverstein, 2005) and executive function (Kerns et al., 2008, Ozonoff et al., 2005) have been found both in autism and schizophrenia. However, only cognitive flexibility and theory of mind have been actually compared between the two groups. Individuals with autism appeared more impaired in cognitive flexibility (Schneider & Asarnow, 1987), for theory of mind, results are mixed, whereas children with autism were found more impaired than children with schizophrenia (Pilowsky et al., 2000), no differences have been reported for adult groups (Craig, Hatton, Craig, & Bentall, 2004). In other cognitive areas, the two groups have not yet been compared.

At the behavioral level, research showed which features that are associated with negative symptoms, as described in schizophrenia, are also present in autism (Dykens et al., 1991, Konstantareas and Hewitt, 2001, Petty et al., 1984, Sheitman et al., 2004). Furthermore, behavioral differences between the two groups have been reported in face orientation and recognition (Bölte et al., 2002, Sasson et al., 2007). Individuals with autism performed poorer in face orientation and recognition tasks compared to individuals with schizophrenia. No studies were found in which other behavioral characteristics were compared between the two disorders. For this reason, the precise behavioral overlap and differences between the two disorders are still not clear.

Furthermore, the abovementioned studies regarding behavioral differences and overlap between autism and schizophrenia were predominantly executed in children or adolescents. To our knowledge, only three studies addressed adolescent or adult groups. In two of these studies, the average full scale IQ of the majority of the participants was below 80, which indicates mild intellectual impairment (Bölte et al., 2002, Konstantareas and Hewitt, 2001). One study examined adults with average intelligence (Sasson et al., 2007). However, this study encompassed small research groups, with 10 individuals each. Moreover, the aim of this particular study was limited to face orientation and recognition in the two groups. Therefore, there is only little knowledge about which behavioral features can validly differentiate between high functioning adults with autism and schizophrenia. It is important to be aware of the behavioral overlap and differences between the two disorders for different reasons. Firstly, it increases the fundamental knowledge about the two disorders and how they may be related. Secondly, an increase of knowledge in this area can help clinicians to distinguish between the two disorders in adults, which facilitates the diagnostic process in these chronical psychiatric disorders and which enables recommending appropriate treatment and guidance.

Therefore, the present study aims to examine behavioral differences and overlap in high functioning adults with autism and schizophrenia. Furthermore, the relationship between behavioral characteristics of autism and schizophrenia will be investigated.