Genes underpin mood-incongruent psychosis in bipolar disorder
MedWire News: Specific genes are associated with the presence of mood-incongruent psychosis in patients with bipolar disorder, conclude European researchers who say the findings should be taken into account in future bipolar disorder studies.
It is traditionally assumed that schizophrenia and bipolar disorder are separate disease entities. However, clinical and genetic studies have challenged this assumption, with a recent investigation indicating that two specific genes are linked to mood-incongruent psychotic features that may represent a homogenous subset of the bipolar phenotype.
To investigate further, Nick Craddock, from Cardiff University in the UK, and colleagues studied families multiply affected by bipolar spectrum mood disorder from the UK, the Republic of Ireland, Germany, Italy, and Andalusia. In total, 383 affected relative pairs were genotyped for 1441 markers and covariate linkage analysis for chromosomal regions linked to bipolar disorder was perfomed.
Of the genotyped relative pairs, 152 had neither member of the pair affected by mood-incongruent psychosis, while 131 had one member affected, and 100 had both members affected.
The team reports in the journal Bipolar Disorders that there was significant familiality of incongruent psychosis, at an intra-class correlation coefficient of 0.309.
It was estimated that a logarithm of the odds (LOD) score of 4.96 would be required for genome-wide significance, and a score of 2.86 for suggestive linkage. While no chromosomal region met genome-wide significance, three regions at chromosomes 1q32.2, 7p13, and 20q13.31 had suggestive evidence for linkage.
Chromosome 1q32.3 had a covariate LOD score of 4.15, and would be expected to occur by chance 0.12 times per genome scan. In comparison, chromosome 7p12.3 had a covariate LOD score of 3.32 and would be expected to occur by chance 0.47 times per genome scan, while the equivalent values for chromosome 20q13.31 were 2.98 and 0.82 times per genome scan.
The team writes: “Our linkage findings, together with our demonstration of the familiality of the occurrence of mood-incongruent psychotic features, support the likely general utility of this phenotypic variable in genetic investigation of bipolar spectrum disorders.
“Moreover, our findings suggest specifically that further work aimed at identifying susceptibility or course modifying genes in these regions should take into account the level of mood-incongruent psychosis features within the clinical samples being used.”
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By Liam Davenport