Genome copy number variant burden not increased in bipolar disorder
MedWire News: Bipolar disorder patients, unlike those with schizophrenia, do not have an increased burden of copy number variants (CNVs) in their DNA, study results indicate.
There is extensive copy number variation in the human genome, and such variations may play an important role in disease susceptibility, including neuropsychiatric disorders such as schizophrenia and autism, explain Nick Craddock, from Cardiff University in the UK, and colleagues.
To determine associations between CNVs and bipolar disorder, the team conducted a genome-wide survey of large (>100,000 base pairs) and rare (in <1% of the population) CNVs in 1697 bipolar disorder patients and 2806 nonpsychiatric individuals, as well as in 440 schizophrenia patients.
There were no significant differences in the global CNV burden between bipolar disorder cases and controls, although there was a nominally significant decrease in the number of deletions in patients versus controls.
Furthermore, there were no significant differences in the burden of singleton CNVs between bipolar disorder patients and controls, nor in the burden of CNVs >1 Mb, whereas significant differences were observed between schizophrenia patients and controls.
The researchers report in the Archives of General Psychiatry that there were also no significant differences in the burden of CNVs that disrupt genes between bipolar disorder patients and controls, and individual CNVs previously linked to schizophrenia were not altered in bipolar disorder patients.
“We found that CNV load was not elevated in bipolar disorder compared with controls and that deletions larger than 1 Mb were less common in probands with bipolar disorder than in those with schizophrenia,” they explain.
“Our findings suggest that schizophrenia and bipolar disorder differ with respect to CNV burden in general and association with specific schizophrenia-associated CNVs in particular.”
The team concludes: “Our data are consistent with the possibility that possession of large, rare deletions may modify the phenotype in those at risk of psychosis: those possessing such events are more likely to be diagnosed as having schizophrenia, and those without them are more likely to be diagnosed as having bipolar disorder.”
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By Liam Davenport