Autism should be distinguished from sensory deficits and mental retardation or schizophrenia.
The question of whether there is a phenotype overlap or comorbidity between autism and schizophrenia dates back to 1943, when Dr. Kanner first used the term ‘autism’ to describe self-centeredness. The distinction between these disorders has remained unclear for nearly 30 years. In 1971, Dr. Colvin conducted an original study that made the distinction between autism and schizophrenia, and prompted the decision to classify these disorders into two different categories.
Patient age at symptom onset and clinical presentation distinguish autism from early schizophrenia. In addition, these disorders are treated in different ways. It is believed that schizophrenia may sometimes develop in individuals with autism. However, it should be noted that children with childhood schizophrenia have a rather high level of premorbid early developmental conditions.
Onset of psychosis before age 13 is considered a rare and severe form of schizophrenia. According to research, this severe form may be precluded or accompanied by symptoms that are similar to autism.
The first to describe the severity and frequency of comorbid developmental disorders in childhood schizophrenia was Dr. Colvin, who noted deficiencies in communication, motor development, and social attachment. Similar deficits were found in 28–55% of children with ASD, across several studies.
Retrospective studies of children with schizophrenia have identified delays in language acquisition and hand-eye coordination in early childhood prior to the onset of psychotic symptoms. The researchers looked at the premorbid history of children with schizophrenia and noted language delays as well as transient motor stereotypes (repetitive movements, postures, and patterned utterances). Their results suggest early developmental anomalies in the temporal and frontal lobes, as evidenced by prepsychotic language difficulties, and early transient motor stereotypes indicate abnormalities in the development of the basal ganglia.
General clinical features
Although the disorders are different, they share common clinical symptoms. Social withdrawal, impaired communication, and poor eye contact seen in ASD are similar to symptoms seen in young people with schizophrenia. When highly functional people with autism are stressed, they become very anxious and can sometimes appear erratic and paranoid, especially when asked to change the subject or stop an activity in which they are participating, and start a new activity.
Researchers use a variety of terms to describe this complex combination of mental comorbidity and developmental psychopathology. At the Yale Children’s Education Center, a subgroup of children with ASD was designated as a multidevelopmental disorder. Researchers in the Netherlands used the term Multiple Complex Developmental Disorders (MCDD) to describe children who met the criteria for ASD, as well as manifestations of dysregulation and thought disorders. Subsequent studies are of considerable interest, showing that 64% of children with MCDD have developed psychosis in adulthood.
The researchers concluded that children with MCDD are at high risk for psychosis later in life.
Although epidemiological studies of the genetic relationships between autism and schizophrenia are scarce, there is evidence for common genetic factors. As with most mental disorders and other common conditions, genetic complexity is compounded by phenotype complexity. Studies of copy number variants and rare alleles have found a link between autism and stippled and structural mutations in neurologins, neurexins, and related genes.
There is also information about the involvement of the neurexin family in schizophrenia. Neurologins are a family of postsynaptic proteins that bind transsynaptically to neurexins, presynaptic proteins that are likely required for both accelerated and delayed synaptogenesis and synapse maturation. This is consistent with neuropsychic stroke and imbalances in the transmission hypothesis for both autism and schizophrenia.