autism and its co-morbidities

In the previous post I looked at the different levels of complexity involved in classifying things, including behaviour. I want to apply this idea to the behaviours involved in autism.

Classifying autistic behaviours

Autism is defined in terms of impairments in three types of behaviour; social interaction, communication and flexibility (people diagnosed with autism show ‘restricted, repetitive and stereotyped patterns of behaviour’). The definition is at a high level of complexity – each type of behaviour involved is the equivalent of a class in the Linnaean system. Many behaviours come under the heading ‘communication’, an even larger number under ‘social interaction’ and ‘restricted, repetitive and stereotyped patterns of behaviour’ could refer to almost anything. It’s true that the DSM narrows things down a bit by listing certain aspects of impairments in these behavioural classes, but there’s still a lot of scope for variation between individuals. Even the specific behaviours mentioned, such as impaired eye-to-eye gaze, delayed speech or persistent preoccupation with parts of objects could have different causes in different people. Jon Brock has calculated the number of possible combinations of the 12 types of behaviour listed in the DSM criteria here; the figure would be much higher if individual variations in these were taken into account.

I’ve illustrated the complexity of the behavioural classes by mapping out the relationship between a low-level behaviour that would qualify as an impairment in the class of behaviours that we call ‘communication’. I’ve chosen one of the behaviours noted by Kanner – ‘pronominal reversal’ (reversal of pronouns). Pronoun errors are common in young children. Very young children often don’t use them at all – ‘Harry do it’ – or sometimes use only one as a default – everyone is referred to as ‘he’. ‘Pronoun error’ is ambiguous because it could mean several different things, but it’s very clear what’s meant by pronoun reversal. Ironically, despite listing ‘pronomial reversal’ as one of the essential common characteristics of his syndrome, in five of the six cases where Kanner records pronoun errors, the children don’t consistently reverse pronouns. The reversals appear to be due to the use of echolalia e.g. ‘you want candy’ instead of ‘I want candy’ or ‘want me to draw a spider’ for ‘I want you to draw a spider’. Jon Brock expands on this point in his blog.)

classification of pronoun reversal

My classification of this behaviour is not exhaustive or authoritative. Nor does it show all the linkages between levels; it simply illustrates the levels of complexity between communication in general and pronoun reversal in particular. Note also that the diagram illustrates the way pronoun reversal could be classified – it doesn’t reflect the way children actually develop language. As I pointed out in the previous post, each level of complexity is equally valid; pronoun reversal could accurately be described as an impairment of pronoun use, or of pragmatics, syntax, language, verbal communication or communication in general. But even if a description at each level of complexity is equally valid, it doesn’t mean each level of complexity is equally useful for all purposes.

Here’s the same diagram again, but this time showing the impairments in communication a doctor diagnosing autism would be looking for. One feature would need to be observed.

diagnostic criteria for impairments in communication

Levels of complexity and autism

Although the diagnostic criteria listed in the DSM appear at first glance to be precise, when mapped onto a diagrammatic representation of the set of behaviours involved in communication, it’s clear that the criteria are at quite a high level of complexity, so the impairments might manifest themselves in different ways and there might be more than one possible cause for each impairment.

A key problem with the definition of autism, as I see it, is that it is framed at too high a level of complexity to be useful in determining what’s causing an individual’s developmental impairments. There is no doubt that a child diagnosed with autistic disorder has impairments in social interaction, communication and flexible behaviour, because that’s how autistic disorder is defined. But because those classes of behaviour encompass so many low-level behaviours, people with totally different impairments to each other can all end up with a diagnosis of autistic disorder. And the atypicalities of people with autism aren’t confined to behaviours; some somatic (bodily) symptoms frequently occur alongside autism. They are referred to as co-morbidities.

Autism and its co-morbidities

When diagnosing a somatic disorder, doctors tend to look at a patient’s low-level symptoms – the type of breathing difficulty, cough, pain or rash. Many diagnostic tests are at an even lower level – the shape of cells or presence of specific molecules. The reason for this is that many somatic disorders have very similar symptoms, so it’s important to identify exactly what symptoms each patient has. In the case of autism the diagnostic process is different. A doctor might first rule out any medical conditions known to cause autistic characteristics (e.g. Fragile X) and might note all the patient’s symptoms, but what’s seen as important is not all the patient’s symptoms, but whether or not the patient’s behaviour fits the criteria for autistic disorder.

Because autistic disorder is defined in terms of behaviour, and because autistic behaviours are often the most obvious of a child’s symptoms, autistic disorder frequently becomes the primary diagnosis and any minor somatic symptoms associated with autism are relegated to the category of ‘co-morbidities’. (Also see Paul Whiteley’s blog on this topic). So sensory atypicalities, epilepsy, sleep disorders, hypermobile joints, growth abnormalities, dietary intolerances, digestive problems and allergies, unless serious, are seen as features that might or might not be caused by whatever causes the autistic characteristics. But because these somatic features aren’t typical of everyone diagnosed with autism, they don’t qualify as part of the autistic syndrome.

That’s fair enough if what you want to do is refine the definition of autism. But if you want to find out what might be causing an individual child’s developmental abnormalities, you need to look at all the child’s symptoms, autism being only one of them.

Harry and Sam

To illustrate this point, I want to look at the symptoms shown by Harry and Sam. Harry’s intelligent and has an excellent grasp of language and abstract ideas. He loves maths and science and has a photographic memory. But he can’t discriminate between some speech sounds or between some letters. He can’t keep track of what people are saying in noisy environments or unless they speak slowly and clearly, and his own speech is hesitant and mumbled. High-pitched sounds, such as children screaming, hurt his ears. He loses track of things that move quickly, like balls or other children, and his motor co-ordination is poor. If he puts his head back he feels sick and dizzy and sometimes blacks out. He finds light touch unbearably tickly but has a high pain threshold. He has a persistent dry cough, can fold his legs behind his head and often gets pain in his legs and chest when walking. He’s a fussy eater, is extremely skinny and his chest is sunken. Certain foods give him diarrhoea, and a casein-free diet has improved his energy levels considerably. Not surprisingly, Harry struggles with conversation, avoids social interaction if he can, and, because he finds almost everything he tries to do difficult, sticks to things he can do best and with least discomfort, like reading, lego, computer games or watching tv. But Harry’s diagnosis is ‘autistic disorder’; his specific problems with receptive and expressive speech, visual discrimination and tracking, auditory hyperacusis, motor and vestibular function, pain, joint mobility, growth and dietary issues just don’t come into the picture. There’s a group of children like Harry with almost identical symptoms at the ‘high-functioning’ end of the autistic spectrum. Their symptoms aren’t just behavioural, but involve sensory processing, motor function, skeletal development and digestion as well. Because the children have symptoms that are so similar (unlike the wide variation seen in ‘autistic disorder’) it’s quite possible that this group of children all have the same cause for their symptoms.

There are other groups with distinctive symptoms on the autistic spectrum too, such as ‘low-functioning’ children like Sam. Sam has little speech, intellectual impairment and poor motor control. He’s big for his age, has epilepsy, pica, is doubly incontinent and smears faeces. He often has tantrums, is aggressive to others, beats his head and throws himself against the walls and furniture. Sam also has a diagnosis of autistic disorder. Do Harry and Sam have the same medical condition? Unlikely, I’d say.

Note that I’m not saying the autistic spectrum can be divided into two sub-groups – ‘high-functioning’ and ‘low-functioning’. There are children across the autistic spectrum who have different symptoms to both Harry and Sam. I’ve just described patterns of symptoms that I’m most familiar with. I also want to emphasise that neither group, Harry’s or Sam’s, would form a sub-group of ‘autism’ because autism is only one of their symptoms. They have symptoms other than behavioural ones, but these are currently classified as ‘co-morbidities’ of autism, rather than being seen as symptoms in their own right.

Biological markers for genetic variations

There’s been a great deal of interest in recent years in the genetics of autism. The Autism Genome Project identified a number of genetic ‘rare variants’ associated with autistic disorders. What geneticists are keen to identify are biological markers that indicate the endophenotype that results from a specific genetic variation. A major problem with this approach is that because the diagnostic criteria for autistic disorder lump together everyone who has autism as one of their symptoms, scientists often aren’t looking for the biological markers for genetic variations in a specific individual, but for the biological markers for genetic variations in everybody diagnosed with autism. And only for the markers associated with autism, not with the other symptoms that individuals might have. It’s quite possible that these much sought-after biological markers are actually in plain sight in the form of co-morbidities, but are being ignored because autistic disorder is seen as the primary diagnosis and is framed only in terms of behaviours.

Next, I want to look at some of the possible causes of autism and its co-morbidities.