Neurodevelopmental Disorders and Spectrum Bias

Pettersson E, Anckarsäter H, Gillberg C, & Lichtenstein P (2013). Different neurodevelopmental symptoms have a common genetic etiology. Journal of child psychology and psychiatry, and allied disciplines, 54 (12), 1356-65 PMID: 24127638


Christopher Gillberg: "When children display problems in one area, it might be more important to, as early as possible, set up a strategy for helping with all related symptoms rather than trying to help only with a specific diagnosis (which often will change over time)." Dorothy Bishop: “We may feel comfortable with our domain-specific labels for neurodevelopmental disorders, but they do not capture the clinical reality.”

Did we end up going down this path because of spectrum bias? Most children that are seen in clinics are seen by a single focus practitioner. Even when they are seen by a team for diagnostic purposes, they are still treated individually by practitioners such as OT, PT and educational psychologists. In addition only those with the highest level of behavioural problems get past the GPs who act as gatekeepers. This has been thought to be the reason why more boys than girls are diagnosed with neurodevelopmental disorders; the boys display more extreme behaviours thereby getting more attention.

As much research goes on in secondary centres, that is within the hospital or with the community consultant, rather than in primary care, those that haven't made it past the GP gatekeepers will not end up being part of the research cohort. This means that the wider population of those with neurodevelopmental disorders will not have been studied, leading to a spectrum bias when formulating the diagnostic criteria and tests.

Additionally, because of spectrum bias, children will have been filtered into specific subgroups resulting in confirmation of domain-specific labels. One of the 'gold standards' for research in autism has been not the diagnosis of autism but whether or not the researchers have administered DISCO, ADOS or similar diagnostic criteria. This immediately excludes any children who do not present with the main core characteristics of autism as observed by the specific diagnostic test. Additionally it has been shown that children who receive a positive diagnosis under one of these tests at a young age, can often fail to meet the threshold at an older age, then again with the passing of time, perhaps to adolescence or young adulthood, with a different diagnosed test, will regain the specific diagnoses. This will result in not just very specific subgroups, but will concentrate the focus of any intervention or further observation into one small black and white clearly defined area.

The experience of families is very different. They 'study' a single subject, N=1. They see the whole child, rather than the subset of clinical features seen by each of the child's practitioners. They come to support groups confused by the long list of individual diagnoses the child has collected over the years, asking just what it is about their child that is making it difficult for them to access education or social situations. Often referral to practitioners is done serially, that is one after the other, not at the same time. There can be practical reasons for this, such as the increased anxiety caused by multiple appointments, as well as logistic concerns, especially if the different practitioners are spread over a wide geographical area. However, it also means that only one aspect of the child is dealt with at once, whereas in reality all aspects of a child's development will be interacting together. For instance speech and language therapy will be affected by visual disturbances, physiotherapy will be affected by receptive speech problems, social skills training will be affected by nociceptive hypersensitivity.

All of these situations will be well known by parents and carers, but because of the way that researchers and practitioners have been approaching neurodevelopmental disorders, the wider picture has not always been appreciated in the clinical setting.

Christopher Gillberg's paper is a welcome change to the way we look at neurodevelopmental disorders, but will that change filter down into the clinical settings that so may parents find counterproductive? Only time will tell.

The paper (behind the pay wall) can be found here
Dorothy Bishop's review can be found here