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The clinical and cognitive phenotype of schizotypal personality disorder in childhood
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posted on 16.02.2017by Jones, Harvey
An increasing focus on the neurodevelopmental trajectories of schizophrenia spectrum disorders has spurred interest in childhood schizotypal personality disorder (SPD). Subsequent research has shown that between 6 and 25 percent of children with SPD go on to develop psychosis. Given that this represents an intermediate level of risk compared to adults with SPD and the general population, examining these children across development may provide insight into clinical and neurocognitive risk and protective markers. However, the clinical and cognitive phenotype of children with SPD remains under researched. Further, due to a lack of operationalised diagnostic criteria for SPD in childhood and limited childhood assessments for SPD, identifying these children is challenging. Thus, the current thesis aimed to (a) develop and examine a semi-structured assessment for children with SPD (the Melbourne Assessment of Schizotypy in Kids (MASK)), (b) use this measure to better understand the clinical phenotype of this disorder and (c) explore cognitive dysfunction in this cohort. While exploring these aims, it was also important to consider other neurodevelopmental disorders that present with similar symptoms such as autism spectrum disorder (ASD). A total of 68 children (21 SPD, 15 high functioning ASD, and 32 typically developing (TD) controls) between 5 and 12 years of age participated in the first two studies that examined different aspects of the MASK. The MASK is composed of semi-structured interviews for children and their parents, and a 57 item checklist of schizotypal symptoms that is completed by the examiner. In the first study, children and their parents were administered the MASK in conjunction with intellectual assessments (e.g. WPPSI-III or WISC-IV) and behaviour rating scales. The second study re-analysed the MASK scores to determine a cut-off score for children with SPD that maximised both sensitivity and specificity. Sixty-five of the children that participated in the first two studies (18 SPD, 15 ASD and 32 TD) were also administered a battery of neuropsychological tests. The first study showed that the MASK had high internal consistency and there was 90% agreement between two raters in a subsample of 15 participants. An analysis of group differences on the MASK showed that children with SPD recorded the highest MASK scores, while children with ASD scored higher than controls. Principal components analysis of the MASK revealed two factors: social/pragmatic symptoms; and positive schizotypal symptoms. Both factors were associated with a diagnosis of SPD or ASD, however, positive schizotypal symptoms were higher in the SPD group. The second study extended the validation of the MASK by showing that a score of 125 or above on the MASK had excellent sensitivity (95.24%) and specificity (91.49%) for identifying children with SPD. In the final study, we found that children with SPD had deficits in visuo-spatial skills, processing speed, short-term memory for complex information (verbal prose), intra-dimensional set-shifting, extra-dimensional set-shifting, mental arithmetic, learning spatial locations and delayed memory of verbal prose compared to the TD group. Children with ASD had similar impairments, but also had more widespread working memory deficits compared to controls. Despite these differing profiles, we were unable to show any significant differences between children with SPD and children with ASD. In conclusion, we found preliminary evidence to suggest that the MASK is a reliable, consistent and valid assessment of children with SPD between 5 and 12 years of age. Likewise, the use of this measure showed that childhood SPD is characterised by complex symptoms and focusing on the more positive symptoms may assist in distinguishing childhood SPD from the autism spectrum. Additionally, children with SPD and ASD appear to have a number of cognitive deficits that are indicative of frontal-striatal and medial temporal lobe impairments. Together, these findings set the foundations for further longitudinal investigations into the neurodevelopmental trajectory of childhood SPD.