Many theories have been advanced for the causes of autism. Before looking at them in more detail, I want to examine a broader issue; the association between known medical disorders and autistic characteristics.
In their book The biology of the autistic syndromes, Christopher Gillberg and Mary Coleman devote an entire section (six chapters) to medical conditions associated with a formal diagnosis of autism. (My copy is of the 2nd edition published in 1992; the 1st edition came out in 1985, the 3rd in 2000 and the 4th, entitled The Autisms was published in 2012.) The authors don’t speculate on how the medical conditions they list might be related to autism, but it’s clear from this and later works that they are of the view that there are ‘autisms’, rather than a single disorder with different manifestations. From the preface of The Autisms;
“Although Kanner, who first accurately described autism in 1943, likely assumed it was a single disease entity…over time it became clear that this was not so, as multiple studies… were published. Instead autism was found to be a specific set of symptoms found in a conglomeration of different diseases some of which overlapped with the intellectual disability/mental retardation syndromes.” (p.xi)
I think Gillberg and Coleman are suggesting that autistic characteristics (which by definition form a syndrome) arise as a consequence of a range of medical conditions, implying that the causes for autistic characteristics are probably different in different patients – hence the authors referring to ‘autisms’ in the plural. In 1974 Coleman had studied a group of 78 autistic children. In an interview with Adam Feinstein for A History of Autism, she says;
“As a result of this  study, I came to realize that autism is like mental retardation – it’s a final common pathway in the brain affected by many different underlying causes, many different disease entities.” (p.147)
I’ve summarised below the ‘disease entities’ listed by Gillberg and Coleman as associated with autism. (The list is from the 1992 edition; later research has expanded on it.)
Gillberg and Coleman are by no means the only authors to identify an association between autistic characteristics and other medical disorders. Here are the ‘organic conditions’ reported by Wing and Gould (1979) in children who met Kanner’s criteria in their Camberwell study:
severe perinatal complications
multiple congenital abnormalities
unconfirmed viral illness under 1 year
gastroenteritis under 1 year
unconfirmed head injury under 1 year
operation for cleft palate under 1 year.
“The last issue concerns the question of etiological heterogeneity within the field of autism syndromes. We have already noted that there is undoubted heterogeneity. The very fact that the clinical picture of autism can arise from diseases as diverse as congenital rubella, tuberous sclerosis, encephalopathy, infantile spasms with hypsarrhythmia, cerebral lipoidosis and neurofibromatosis makes that clear.” [references omitted](p.28)
Patterns of association
Because autistic characteristics involve high-level processes, the relationships between autistic disorder and other medical disorders are likely to be complex and varied. However, the relationships between autistic characteristics, somatic symptoms and underlying causes will fall into one of four basic patterns, as shown below.
The section on other medical conditions in Gillberg and Coleman’s book was originally entitled “Disease entities that have a subgroup of patients with autistic symptoms” – in other words, not all children diagnosed with a particular disease entity were autistic, suggesting that for each disease entity:
the sub-group of children with autistic symptoms had a distinct second disorder (an autistic syndrome)
the sub-group of children with autistic symptoms had a predisposition to develop those symptoms and that they have been triggered by the disease entity.
Patterns of association and diagnosis
Depending on how strong the association is between autistic characteristics and a particular medical disorder, diagnosis is likely to proceed as follows;
A. If a medical disorder (e.g. disorder A) is frequently associated with autistic symptoms, it’s likely that the medical disorder will be assumed to account for the autistic symptoms and the child will get a single diagnosis of disorder A.
B. If a medical disorder (e.g. disorder B) is only occasionally associated with autistic symptoms, it’s likely that the medical disorder will be assumed not to account for the autistic symptoms and the child will get a dual diagnosis of disorder B and autistic disorder.
C. If the child has somatic symptoms that don’t fit the criteria for any known medical disorder, unless severe, those symptoms are likely to be overlooked and the child will get a diagnosis relating only to their behaviour – autistic disorder.
Each of these options is problematic if the cause of the child’s symptoms is to be identified, because in each group – A, B or C – the autistic characteristics might or might not be caused by whatever causes the somatic symptoms. The only ways to find out would be either to investigate all the symptoms shown by each individual, or to look at the differences between individuals who are autistic and those who aren’t, in respect of each of the other medical disorders.
What isn’t helpful is to assume that everybody’s autism has the same cause.
Coleman, M & Gillberg, C. (2012) The Autisms (4th edn). Oxford University Press.
Feinstein, A. (2010). A History of Autism. Wiley-Blackwell.
Gillberg, C. & Coleman, M. (1992) The Biology of the Autistic Syndromes (2nd edition). Mac Keith Press.
Rutter, M. & Schopler, E. (1988). Concepts and diagnostic issues in E. Schopler & G.B. Mesibov (eds.) Diagnosis and assessment in autism. Springer.
Wing, L. & Gould, J. (1979). Severe impairments of social interaction and associated abnormalities in children: Epidemiology and classification, Journal of Autism and Childhood Schizophrenia, 9, 11-29.