Monday November 26 2007
Participants suffered from "excessive washing"
People with obsessive-compulsive disorder (OCD) have less grey matter in the region of the brain “that is important in suppressing responses and habits”, reported BBC News. “Brain scans might be able to reveal which people are at genetic risk of developing obsessive compulsive disorder,” the BBC added.
The Sun also reports on the study, but focuses on the finding that immediate family members of people with OCD, who themselves do not have the disorder, perform worse on ability tests and have similar deficits in grey matter. This is “the first time a genetic link has been found”, and people with OCD “may inherit the condition from their families”, the newspaper said.
The study is well-conducted, but whether OCD could be diagnosed using a brain scan remains to be seen. Currently, the condition is diagnosed using a clinical history of the person having certain distressing "obsessions" and "compulsions" that are significant enough to interfere with normal function for a certain period of time every day (usually greater than one hour). The number of people included in this study was small and only people with particular OCD symptoms were included. This limits whether the results can be applied to all OCD sufferers and their families.
Where did the story come from?
Dr Lara Menzies and colleagues from the Brain Mapping Unit at the University of Cambridge and other medical institutes in Cambridge carried out this research. The study was funded by the National Alliance for Research on Schizophrenia and Depression, the Wellcome Trust, the Hartnett Fund, the Medical Research Council and the National Institutes of Mental Health and Biomedical Imaging and Bioengineering. It was published in the peer-reviewed medical journal: Brain.
What kind of scientific study was this?
This was a cross-sectional study where the researchers were investigating possible “endophenotypes” of OCD. OCD is known to be an inheritable disease, but because of the difficulty of identifying genes that may cause it, another approach is to look for “endophenotypes” – measurable physical characteristics (such as differences in brain structure in this case) which suggest how the disease might be inherited.
In this study, the researchers enrolled 31 people with a diagnosis of OCD, 31 of their first-degree relatives who were unaffected, and 31 healthy controls (unrelated to the previous groups). In order to have a group with similar types of OCD, they included people who had symptoms of excessive washing or checking, but not those with hoarding behaviour or tics. The researchers acquired structural MRI pictures of all of the participants’ brains and also investigated their ”stop signal reaction time” (SSRT). SSRT is a well-known method of testing how people control repetitive behaviour. Finally, the researchers compared the results of the MRIs and the SSRT tests between the three different groups to see whether there was any significant differences.
The researchers used complex mathematical analysis to see how the scores on the SSRT were related to brain abnormalities across the entire brain system.
What were the results of the study?
The researchers found a significant difference between the groups on mean SSRT score. Sufferers of OCD and their first-degree relatives took longer to be stop their repetitive behaviour than those in the control group. There was no difference between the OCD sufferers and their relatives’ scores.
The study also found a link between the density of grey matter in the brain and the scores on the SSRT. Reduced density of grey matter in a region of the brain thought to be involved with control of tasks and inhibiting response was associated taking longer to control repetitive behaviour. They also found that sufferers of OCD and their relatives had structural abnormalities in these regions compared with healthy volunteers.
What interpretations did the researchers draw from these results?
The researchers say that they have shown that people with OCD and their first-degree relatives have impaired ability to control repetitive behaviour, and that certain brain systems are associated with this impairment. They report that people with OCD and their relatives have structural abnormalities in their brains that can be inherited). These findings, they say, show that cognitive testing (such as the SSRT) and brain imaging (using MRI) can be used to identify an “endophenotype” of OCD.
What does the NHS Knowledge Service make of this study?
This is a complex piece of research. Its limitations arise from the size and nature of the sample that was included:
- Only 31 people were included in each group. This is a small sample size for a study of this design.
- Only people displaying excessive washing or checking were included to represent OCD sufferers. There are a multitude of different obsessions and compulsions found in OCD, and this population may not be representative of all sufferers. The researchers say that people with different symptom profiles may have different underlying brain abnormalities, so more research is needed to understand the applicability of these findings to these groups.
- The study was a cross-sectional study describing the characteristics of three different groups of people. Fropm this study, it is not possible to say that the brain abnormalities “caused” OCD. The neurological, psychological, or possible genetic causes of OCD remain uncertain.
- This study is most relevant for scientifists researching neuropsychiatric disorders. The work will be important for encouraging further research aimed at unravelling the causes of neuropsychiatric disorders.
- However, it is a long way from identifying the genes responsible for the structural differences in the brain and therefore a long way from using this discovery to help with the treatment of OCD.
- This work may lead to new avenues of diagnosis of OCD. However, as the condition is currently recognised and treated on the basis of patient history, without any need for further investigation, if and how the findings from these MRI studies will be used by doctors in their clinical work with patients, remains to be seen.
Sir Muir Gray adds...
MRI scans are so powerful that they often reveal phenomena whose meaning is uncertain; what is certain is that people may become very anxious if they have a test that gives an unclear result. This needs to remain a research tool until it is demonstrated that it does more good than harm.