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Self-injurious behaviour in Cornelia de Lange Syndrome


Introduction

Since Dr. William Nyhan’s early reports that selfinjurious behaviour might be associated with Cornelia de Lange Syndrome (Nyhan, 19721), the syndrome has generally been known as one in which self-injury frequently occurs and it has often been argued that the behaviour may have a biological cause. As a result of these assertions, two types of studies have attempted to see if an association does indeed exist between Cornelia de Lange Syndrome and self-injurious behaviour. First, there have been studies that have reported on relatively small numbers of people with Cornelia de Lange Syndrome. Many of these studies have looked at patients in clinical settings (see Box 4.1).

Also within this category of ‘small scale studies’, are the many single case reports that have been published in academic journals. These have simply described children and adults with Cornelia de Lange Syndrome and the selfinjurious behaviour that they display. There are two problems with this type of small scale research. As many of these studies include only individuals who were being seen in clinical settings, it is possible that they may have been seen or referred to the authors precisely because they showed self-injurious behaviour. This would have the effect of elevating the prevalence figures of self-injury.

Secondly, with regard to the individual case reports, because of both Nyhan’s early reports that Cornelia de Lange Syndrome and self-injury are associated, and the intriguing nature of selfinjury which has caused a great deal of academic interest, it is possible that a bias has emerged. Due to this, researchers may have been more likely to observe and describe individuals with Cornelia de Lange Syndrome who engage in selfinjury, publishing reports that in turn make the association look stronger. Consequently, the combination of Nyhan’s early reports associating Cornelia de Lange Syndrome and self-injurious behaviour, together with the studies in clinical settings, and the individual case studies, has tended to give the impression that self-injurious behaviour was shown by relatively high numbers of people with Cornelia de Lange Syndrome. Given the limitations of this research, it is important to also look at the results from the second type of study, large scale surveys.

Following on from the small-scale studies, several large surveys have been conducted, usually via the Cornelia de Lange Syndrome Foundation. Such studies are less likely to be biased, because they aim to recruit as many different people with Cornelia de Lange Syndrome as possible, regardless of the behaviours they display. As a result, this type of research is perhaps the best indicator of the true prevalence of self- injurious behaviour in Cornelia de Lange Syndrome. However, the prevalence of selfinjury in these large-scale surveys is, in fact, similar to that seen in the smaller studies, approximately 60%. This figure of 60% shows us very clearly that there is not a one-to-one relationship between the syndrome and self-injurious behaviour (see Box 4.2).


Comparing self-injury in Cornelia de Lange Syndrome with self-injury in intellectual disability

Even though the prevalence of self-injurious behaviour in Cornelia de Lange Syndrome is certainly higher than that in all people with intellectual disability (5-10%, see Chapter 3) this still does not necessarily mean that self-injurious behaviour is any more common in Cornelia de Lange Syndrome then we would expect by chance. The reason for this is that some of the risk markers for self-injurious behaviour that are seen in all people with intellectual disability (see Section 3.4) might also be evident or more common in those individuals with Cornelia de Lange Syndrome who show self-injurious behaviour. It may be these risk markers, rather than the syndrome itself, that leads to a high prevalence of self-injurious behaviour.

In order to determine whether self-injurious behaviour is more common in Cornelia de Lange Syndrome than we would expect by chance, we conducted a study in which we compared 54 people with Cornelia de Lange Syndrome with 46 people without the syndrome. We aimed to recruit as many people with Cornelia de Lange Syndrome into the study as possible and contacted families through a number of sources. Following this, we recruited individuals without Cornelia de Lange Syndrome and matched the groups in terms of age, gender, level of mobility and degree of intellectual disability. By doing this, we were trying to ensure that any risk markers for self-injury were the same for both groups.

We visited participants in their day-care settings, and obtained further information through both questionnaires and interviews with parents, carers and teachers. We asked whether self-injurious behaviour had occurred in the previous month. Self-injurious behaviour was defined as ‘non accidental behaviours producing temporary marks or reddening of the skin, or cause bruising, bleeding or other temporary or permanent tissue damage’. When we did this, we found that 55.6% of those with Cornelia de Lange Syndrome had showed self-injurious behaviour, whilst 41.3% of those in the comparison group had displayed the behaviour. This showed us that in people with Cornelia de Lange Syndrome, self-injurious behaviour was more likely to occur than for people of the same age, gender and degree of disability who did not have the syndrome. However, this still does not necessarily mean that the behaviour is associated with Cornelia de Lange Syndrome. It could be that this 14.3% difference is due to chance (see Box 4.3). 

Chance levels in statistics

In scientific research, statistical tests are carried out to determine whether chance can reasonably explain the differences found between two groups. In other words, a calculation determines the probability that the results observed could be obtained if there was no real difference between the groups. Groups are considered significantly different from one another if the probability of obtaining the difference by chance alone is no greater than 5% (0.05). However, when the probability is 5% or greater, chance cannot be ruled out as an explanation for the difference.

In fact, when we conducted statistical tests to examine the significance of this finding we found that there was no significant difference between the two groups. This means that when we control for the risk markers, self-injurious behaviour to the point of tissue damage, is no more likely to occur in Cornelia de Lange Syndrome than in other people who have the same degree of intellectual disability, age and gender. Further analyses also showed that having a diagnosis of Cornelia de Lange Syndrome does not predict the presence of self-injury above the risk markers and characteristics that are associated with self-injury. In other words, if two individuals are of similar age, gender, level of mobility and degree of learning disability and have other similar characteristics otherwise associated with selfinjury, but one has Cornelia de Lange Syndrome and one does not, there would be no reason to predict that the person with Cornelia de Lange Syndrome would be more likely to engage in self-injurious behaviour.


Forms and site of self-injury in Cornelia de Lange Syndrome

In order to further understand the self-injurious behaviour that we see in Cornelia de Lange Syndrome, we visited and observed individuals with and without the syndrome over the course of a day in their usual day-care environment. Following this, we were able to examine the severity of self-injurious behaviour in the two groups and look at the types of self-injurious behaviour they displayed, together with the part of the body to which the behaviour was directed.

The comparisons conducted on the severity of self-injury and the frequency of self-injury showed no differences between the two groups. We also found no difference between the types of self-injurious behaviour shown by people with and without Cornelia de Lange Syndrome, except for the biting which was significantly higher in people with Cornelia de Lange Syndrome (see Box 4.4). Additionally, there were no differences between the two groups in terms of the part of the body to which self-injurious behaviour was directed, except that people with Cornelia the Lange Syndrome were more likely to injure their hands than the comparison group (see Box 4.5).

So, whilst the prevalence of self-injury is not significantly higher in Cornelia de Lange Syndrome than a comparison group, it is clear that children and adults who have Cornelia de Lange Syndrome are more likely to self-injure by biting and the site of injury is more likely to be on their hands. The significance of this is unclear but this may be related to peripheral sensory neuropathy (see Section 2.3) and this is further discussed in Chapter 5.

Types of self-injurious behaviour in Cornelia de Lange syndrome

The graph below indicates the frequency of different types of self-injury that were observed in individuals with Cornelia de Lange syndrome and individuals with intellectual disability without the syndrome. The only significant difference between these two groups with regard to the type of self-injury displayed was that individuals with Cornelia de Lange syndrome were more likely to engage in biting than the comparison group.
Types


Site of self-injurious behaviour in Cornelia de Lange Syndrome

The graph below indicates the parts of the body that were the most frequent sites of selfinjurious behaviour in individuals with Cornelia de Lange Syndrome compared to individuals with intellectual disability without the syndrome. The only significant difference between these two groups with regard to site of injury was that individuals with Cornelia de Lange Syndrome were more likely to injure their hands than the comparison group.
Site


Self-injury, compulsive behaviours and self-restraint in Cornelia de Lange Syndrome

In a further analysis of studies we have conducted we have been able to show that in Cornelia de Lange Syndrome there is an association between self-injurious behaviour, the presence of compulsive behaviours and selfrestraint (see Box 4.6). This finding is of interest because it may indicate that for some people with Cornelia de Lange Syndrome, the selfinjurious behaviour has a compulsive quality (see Chapter 2) and thus the behaviour is to some extent out of the individual’s control. Under these circumstances the person may show self-restraint or develop a preference for protective devices in order to assist with the control of their behaviour. In a second study that we conducted we did find that some behaviours were associated with self-injurious behaviour in both Cornelia de Lange Syndrome and our comparison group. These behaviours were: stereotyped behaviour, compulsive behaviour and hyperactivity. The presence of these three types of behaviours predicted the presence of self-injurious behaviour. This is of interest because it may indicate that there is a motor disorder or a problem with behavioural inhibition that underpins all of these behaviours in Cornelia de Lange Syndrome. Recently it has been speculated that the area of the brain that might be responsible for this association and these motor disorders is the Basal Ganglion (see Section 3.4 and Box 3.6).


Summary

Self-injurious behaviour is shown by approximately 60% of individuals who have Cornelia de Lange Syndrome. Interestingly, although this is a high figure, people with Cornelia de Lange Syndrome are not necessarily more likely to show self-injurious behaviour than people with the same degree of intellectual disability and other risk marker characteristics. However, the self-injury does differ in three potentially important ways. First self-injury is more likely to be directed towards the hands. Second, self-injurious behaviour is more likely to take the form of biting and third there is some tangential evidence that for some people with Cornelia de Lange Syndrome the behaviour appears to need active control by self-restraint.


References

Chris Oliver

by Chris Oliver Jo Moss Jane Petty Kate Arron Jenny Sloneem Scott Hall

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Ultima modifica di Gerritjan Koekkoek il 2021/05/23 15:47
Creato da Gerritjan Koekkoek il 2021/05/23 15:44

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                


  

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