The association between early autistic traits and psychotic experiences in adolescence

Abstract

Background

There has been growing interest in the clinical and biological links between autistic spectrum disorder and psychotic disorders, and between symptoms of these disorders that exist below diagnostic thresholds. Whilst autism and schizophrenia are regarded as distinct disorders, recent studies support an overlap in the genetic architecture across these conditions. Although early neurodevelopmental impairment is associated with psychotic disorders in later life, evidence from longitudinal studies of the relationship between autistic traits and psychotic experiences is limited.

Aims

The aim of the study is to explore whether children with early autistic traits (social interaction and communication problems, and restricted, repetitive interests and behaviours) are more likely to present with psychotic experiences in early adolescence.

Method

Longitudinal study using the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort. The mothers of 8232 children were asked about autistic traits in their children as part of the Development and Well-Being Assessment (DAWBA) at the age of 7. Of those, 6439 children completed a semi-structured clinical assessment for psychotic experiences at the age of 12.

Results

Children whose mothers had concerns about autistic traits in early life, in particular with regard to speech development or ‘rituals’/‘habits’, were more likely to develop psychotic experiences in early adolescence. The greater the number of early autistic traits a child had, the greater their risk of developing psychotic experiences. These associations were not confounded by IQ, family history of depression or schizophrenia, gender or socio-demographic characteristics.

Conclusions

Childhood autistic traits, and particularly speech problems and odd rituals or unusual habits, are associated with psychotic experiences in adolescence. This may be a result of a shared aetiology or because autistic traits may also be an early precursor of psychotic experiences.

Introduction

There has been increasing interest in the links between symptoms of autistic spectrum disorder (ASD) and psychotic disorders such as schizophrenia. The existence of a possible association between these disorders is not a new concept, and schizophrenia itself is widely regarded as a neurodevelopmental disorder (Murray and Lewis, 1987, Weinberger, 1987, Rapoport et al., 2009, Owen et al., 2011).

From a clinical perspective, two large studies showed that childhood-onset schizophrenia is preceded by and comorbid with pervasive developmental disorder in 30% to 50% of cases (Rapoport et al., 2009), whilst it is recognised that individuals on the autistic spectrum, such as those with Asperger's syndrome, often present with psychotic experiences in early adult life (WHO, 1992). Symptoms of autism are also seen in adults with schizophrenia (Stahlberg et al., 2004, Morgan et al., 2008).

Epidemiological and large longitudinal cohort studies have shown that subtle neurodevelopmental impairments are increased in those who develop schizophrenia, in particular motor development delay and impairment in receptive language and cognitive function (Jones et al., 1994, Isohanni et al., 2000, Cannon et al., 2002, Rapoport et al., 2009). Schizophrenia has also been associated with earlier difficulties including relationship difficulties with peers and social adjustment (Done et al., 1994, Cannon et al., 2001, Rutter et al., 2006), a core feature of autism. Schizophrenia, autism and other neurodevelopmental syndromes are all associated with cognitive impairment, are more common in males, and are often associated with neurological soft signs (Owen et al., 2011).

Neuroimaging studies into psychotic disorders and autism also support a neurodevelopmental overlap between these two disorders (Toal et al., 2009), and there is evidence of accelerated trajectories of anatomic brain development around the peak age of onset for both disorders (Rapoport et al., 2009).

Findings from candidate gene and linkage studies as well as from expression studies also show overlap across these disorders (Rapoport et al., 2009), whilst, rare chromosomal micro-deletions or duplications (copy number variants) which are significantly associated with schizophrenia are also associated with autism and other neurodevelopmental disorders (Sebat et al., 2009, Basset et al., 2010, Williams et al., 2010).

However, there are few longitudinal studies which have followed up individuals diagnosed with ASD in early childhood into adolescence and adulthood, particularly looking at symptoms of disorders which tend to have a more typical adult onset, such as psychotic disorders. A recent follow-up study of individuals with ASD, which was distinctive in its low attrition rate and use of systematic interviews, revealed no cases of schizophrenia (Hutton et al., 2008). However, as with a previous study (Volkmar and Cohen, 1991), this may not have been large enough to examine such a rare outcome. The studies also included subjects with low IQ and minimal language skills, and the assessment of psychotic experiences in such individuals is not reliable. There have been calls for large longitudinal and other studies, to examine the links further between neurodevelopmental syndromes (Rapoport et al., 2009, Owen et al., 2011).

Recent research interest has extended to the association between autistic traits and psychotic experiences below the diagnostic threshold. Non-clinical psychotic experiences have been found to be substantially more common than clinical psychotic disorders in the general population (Van Os and Kapur, 2009), are associated with a wide range of established risk factors for schizophrenia (Myin-Germeys et al., 2003, Van Os and Kapur, 2009), and, in a minority of individuals, show persistence over time (Dominguez et al., 2011, Mackie et al., 2011) and progression to impaired function and clinical disorder (Poulton et al., 2000, Hanssen et al., 2005, Rossler et al., 2007, Welham et al., 2009). However, links between sub-threshold symptoms of autism and schizophrenia have yet to be investigated.

The aim of the present study was to test the hypothesis that sub-threshold traits of autistic spectrum disorder would be associated with subsequent onset of psychotic experiences during early adolescence in a large population-based birth cohort.