The clinical
connections between schizophrenia (SCZ) and autism spectrum disorder (ASD) have
long been recognized. More than a century ago, Bleuler ascribed 4 primary symptoms to the group of
disorders he termed “schizophrenia”:
1) autism (turning inward to oneself)
2) ambivalence
3) affective disturbance
4) and loosening of associations
In 1933, Potter described childhood SCZ as including:
1) loss of interest in the environment
2) dereistic thinking
3) thought disturbance
4) difficulties with emotional rapport
5) decreased or distorted affect
6) behavioral alterations, such as markedly increased
or decreased activity, perseveration, or
stereotypies.
A decade later, when Leo
Kanner published his seminal case series, “Autistic disturbances of affective
contact”, the 11 youth he described were thought by many to be suffering from
infantile psychosis. Presenting with social detachment, absence of
communicative language, behavioral rigidity, and an interest in objects over
people, these children shared many of the symptoms outlined by Potter—an
apparent lack of interest in the environment, difficulties with emotional
rapport, decreased affect and abnormal behaviors, including perseverations and
stereotypies. However, Kanner’s cohort differed in one notable way—all had
symptom onset within the first 2 years of life. This difference in illness
onset and course ultimately proved to be the key factor supporting the
differentiation of ASD from childhood SCZ, a conceptual shift that occurred
gradually over a period of several decades.
The demarcation was clarified
in the 1980 publication of the third edition of the Diagnostic and Statistical
Manual of Mental Disorders (DSM III), which noted that the lack of psychotic symptoms and
prominence of social deficits clearly distinguished ASD from SCZ.
Thus, ASD moved out from under the
umbrella of psychotic disorders and began to be considered as a separate
entity.
Although DSM-5 maintains nosologic separation of ASD and SCZ, comparison of
the diagnostic criteria for the 2 disorders shows that they have marked similarities in clinical presentation. ASD is defined
by 2 major criteria:
1) persistent deficits in social
communication, social interactions, social-emotional reciprocity, and
communicative behaviors
2) restricted, repetitive patterns of
behavior, interests or activities, which include stereotyped or repetitive
movements, behavioral rigidity, odd or intense interests, and abnormally high
or low reactivity to sensory stimuli.
The DSM-5
diagnostic criteria for SCZ require at least 2 of the
following symptoms be present: hallucinations,
delusions, disorganized speech, grossly disorganized or catatonic behavior,
and/or negative symptoms.
Although hallucinations,
delusions, and thought (speech) disorder are essential features of SCZ (and are
not present in ASD), the negative symptoms are often more impairing, pervasive,
and treatment resistant. These negative symptoms, which include asociality,
alogia, and low levels of emotional expression (also an indicator of impaired
nonverbal communication) can be construed more broadly as deficits in social
communication and motivation. Thus, the negative symptoms of SCZ share many features in
common with the social deficits of ASD. Similarly,
grossly disorganized or abnormal motor behavior as described in SCZ includes a
number of signs and symptoms consistent with those of ASD Criterion B, such as
repeated stereotyped movements, echolalia, unpredictable agitation, and
decreased interaction with or interest in one’s environment.
Given the shared clinical manifestations of SCZ and ASD, it is not
surprising that the
2 disorders co-occur frequently. Nearly
30% of youth diagnosed with childhood onset SCZ in a large NIH cohort had
co-morbid ASD, and both epidemiologic and retrospective clinical studies
suggest an association between ASD diagnosis or childhood autistic traits and
later psychotic experiences.
Similar patterns of cognitive
deficits have also been noted. For example, studies designed to assess systems for
social processes demonstrate that facial recognition and emotion processing are
impaired in SCZ as well as in ASD. Further, both groups have been shown to have
deficits in social cueing associated with eye gaze, as well as in performance
on theory of mind tasks. Meta-analyses of SCZ reports suggests that deficits are correlated with negative
symptoms and disorganization.
Autism and SCZ also appear to share
biological underpinnings that may begin very early in neural development.
Whole exome sequencing analyses implicate ASD and SCZ risk genes in the
development of deep layer cortical projection neurons in the prefrontal and
primary motor-somatosensory cortical (ASD) and dorsolateral and ventrolateral
prefrontal cortical (SCZ) regions, respectively.
A number of neurodevelopmental disorders with known genetic defects are
associated with high rates of both ASD and SCZ, including 22q11.2 Deletion
Syndrome, Shank3 mutations, and duplications at the Williams Syndrome locus
(7q11.23), among others. Epigenetic effects and alterations in copy number
variants have been reported to contribute to abnormalities of cerebral
cytoarchitecture that have been related to SCZ and ASD. In addition,
environmental factors, such as advanced paternal age and maternal
infection/immune activation during pregnancy, have been reported to increase
risk of both ASD and SCZ.
In 1955, Eisenberg and Kanner wrote that early infantile autism was a “total psychobiological disorder” and
suggested that it was “probably related
generically” to SCZ. After more than 5 decades of research and clinical
experience, we are beginning to appreciate the veracity of their prediction,
and to understand the nature of this relationship. Exploring commonalities
between SCZ and ASD, while appreciating salient differences between the 2
disorders, should provide new insights into their etiology, pathophysiology,
treatment, and prevention. To forward these efforts, the Schizophrenia Bulletin
will provide occasional special features giving emphasis to key similarities
and differences between SCZ and ASD and also welcomes high quality reports
addressing these issues.
Rebecca E. Hommer; Susan E. Swedo
Posted by Kids Are
Special in AUTISM
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