Recently, a large-scale study indicates that there are significant genetic correlations found been patients with schizophrenia and a wide range of mental disorders including autism, obsessive-compulsive disorder, major depressive disorder and bipolar disorders. These findings suggest schizophrenia may share common aetiological factors and genetic causes with other mental disorders. However, at the phenotype level, it is still not clear how schizophrenia spectrum disorders are connected with and interact with other mental disorders.

On the other hand, it is commonly acknowledged that mental disorders can be conceptualized as a continuum from healthy individuals to mentally at-risk cases and clinically diagnosed patients. The shared genetic and phenotypic correlations found in clinically diagnosed samples may also extend to subclinical samples with an attenuated format.

Schizotypy has been conceptualized as a personality organization underlying schizophrenia and other related mental disorders and may serve as an important construct for us to address the above unclear issues. Investigating the correlation between individuals with schizotypy (or schizotypal traits) and other subclinical features may allow us to understand the relationship between schizophrenia spectrum disorders and other mental disorders, without the confounding effect of medication exposure and illness chronicity.

In order to address such a knowledge gap, Dr. Raymond Chan's team from the Neuropsychology and Applied Cognitive Neuroscience (NACN) Laboratory, Institute of Psychology of the Chinese Academy of Sciences has conducted two independent studies to examine the network structure between individuals with schizotypal traits and other subclinical features.

The first study used network analysis to examine connection between schizotypal traits and its commonly co-occurring traits by constructing a network consisting of schizotypal traits, autistic traits, obsessive-compulsive traits, anxiety and depressive symptoms. A total of 2204 college students were recruited and all of the participants completed a set of questionnaires capturing the mentioned traits.

They found that interpersonal features were the bridge node connecting schizotypal traits and autistic traits, while cognitive-perceptual and disorganization features were the schizotypal traits associated with obsessive-compulsive traits. Moreover, interpersonal features, disorganization and cognitive-perceptual features were also the overlap between depressive symptoms and schizotypal traits. However, there were few connections between anxiety symptoms and schizotypal traits. Subsequent follow-up of a sub-sample after a three-month interval also showed high predictability of the network.

In the second study, Dr. Chan's team has specifically examined the relationship between schizotypal and autistic traits. They first conducted a meta-analysis to quantify the correlation between autistic traits and the positive, negative and disorganization dimensions of schizotypal traits. Their findings showed that the strongest correlation was found between negative schizotypal traits and autistic traits, followed by the disorganization and positive dimensions.

They then conducted a network analysis on a sample of 2649 college students who completed a set of questionnaires capturing both autistic and schizotypal traits. Their findings reconfirmed the results from the meta-analysis showing that autistic traits, particularly the social and communication deficits, were significantly correlated with negative schizotypal traits. However, positive dimension of schizotypal traits were inversely correlated with autistic traits.

Taken together, these findings suggest that the substantial phenotypic overlaps are not limited to patients with various clinically diagnosed mental disorders but also extend to their corresponding subclinical counterparts. The observed relationships were very stable across time points as revealed by the follow-up network analysis at a 3-month interval.

These findings challenge the validity of the diagnostic boundaries presumed in the current mental disorders classification system. Moreover, the observed clinical manifestations can also be exhibited by individuals with corresponding subclinical features but at minor extent of manifestation.

These two studies were supported by grants from the National Key Research and Developmental Programme, the National Science Fund China, the Beijing Municipal Science & Technology Commission Grant, the Beijing Training Project for the Leading Talents in Science and Technology, the CAS key Laboratory of Mental Health, and the China Postdoctoral Science Foundation.

These two papers are now available online in Asian Journal of Psychiatry and Schizophrenia Research.