Psychiatric Co-morbidities in ASD: A Focus on Schizophrenia

I recently read a great article on spectrum news about psychiatric co-morbidities in adults with autism (ASD) and attention deficit hyperactivity disorder (ADHD). The news article was summarizing a recent paper by Norwegian researchers published in Biological Psychiatry. 

Researchers studied records of 1.7 million Norwegian adults–some with a diagnosis of ASD, some with ADHD, some with both ASD and ADHD, and others with neither ASD nor ADHD. The goal was to better understand patterns of psychiatric co-morbidities (co-occurring diagnoses) in adults with ASD, ADHD, or both. In particular, researchers focused on the following co-morbid diagnoses: anxiety disorders, major depressive disorder, bipolar disorder, personality disorders, schizophrenia, and substance use disorders.

Overall, co-morbid psychiatric disorders were between 2-14 times more common in adults with ADHD and/or ASD compared to adults with neither diagnosis. The pattern of which co-morbid disorders were the most common differed between groups. Bipolar disorders, major depressive disorder, personality disorders, and substance use disorders were more common in adults with ADHD than in adults with ASD. However, adults with ASD were significantly more likely to have schizophrenia than adults with ADHD. In fact, adults with ASD were about 14 times more likely to have schizophrenia than adults in the general population (adults with ADHD were about 4 times more likely to have schizophrenia than adults in the general population). 

I am particularly interested in the findings related to schizophrenia and ASD given the history of the two conditions and our current understanding of how they may overlap. Historically, ASD and schizophrenia were considered a single condition, and the term "autism" was used interchangeably with schizophrenia until the 1970s. Hindsight is always 20/20, so it is easy to dismiss our previous thoughts about this overlap as no longer relevant. However, studies like the above highlight an important point about ASD and schizophrenia that has been increasingly recognized over the past 10 years: these two conditions seem to share some common features.

These commonalities have been observed behaviorally, and with genetic and neuroscience research. 

Behaviorally, both conditions share difficulties with social interactions and reciprocity. Individuals with ASD who have difficulty engaging in reciprocal conversations with others are often thought of as having "flat affect", which is a commonly reported feature of schizophrenia.

In terms of genetics, there is evidence for heritability between the disorders. Research has found evidence that children are at higher risk of ASD if they have a parent with schizophrenia. That is, a diagnosis of schizophrenia in a parent increases the risk of ASD in children. 

Neuroscience research has demonstrated that both groups show hypoactivation of the prefrontal cortex when viewing faces and when engaging in theory of mind tasks. This highlights similarities between the two conditions in how the brain reacts to social stimuli. This is particularly interesting in light of behavioral observations that social interactions are difficult for both of these groups. 

Clinically, it is quite difficult to diagnose schizophrenia in ASD, or ASD in schizophrenia. A clinician must do an interview and try to tease apart so-called negative symptoms of schizophrenia (withdrawal, flat affect, reduced speech) from social symptoms associated with ASD. 

This type of diagnosis is particularly important in young adults with ASD who might be experiencing psychosis for the first time, and who urgently need treatment. Unfortunately, symptoms that are indicative of a first psychotic episode are sometimes ignored in young adults with ASD if clinicians and caregivers assume that the symptoms are part of ASD. We have seen a few cases like this in the clinic, and delayed treatment for young adults who are experiencing the first signs of psychosis has a negative impact on long-term outcomes. 

Overall, it is clear that the similarities and overlap between these two conditions cannot be ignored, and should not be dismissed as an out of date idea. There is a particular need for better and more accurate interviews in order to diagnose schizophrenia in ASD, or ASD in those with schizophrenia, as this will help improve outcomes for individuals living with these conditions.