Letters Bipolar disorder

The genetics of bipolar disorder

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f530 (Published 07 February 2013) Cite this as: BMJ 2013;346:f530
  1. Frances S Price, medical student1,
  2. James A Morris, consultant pathologist and associate director of undergraduate medical education2
  1. 1Faculty of Health and Medicine, Lancaster University, Lancaster, UK
  2. 2University Hospitals of Morecambe Bay NHS Foundation Trust, Royal Lancaster Infirmary, Lancaster LA1 4RP, UK
  1. Jim.A.Morris{at}mbht.nhs.uk

Anderson and colleagues state that “Bipolar I disorder has a heritability of 0.75 explained largely by common variant alleles, which partly overlap with those for schizophrenia.”1 In fact, very little of the heritability of bipolar disorder is explained by common polymorphisms. The largest genome-wide association study of bipolar disorder,2 with 4387 cases and 6209 controls, found an odds ratio of 1.45 for ANK3 (a gene involved in the function of voltage gated sodium channels) and 1.18 for CACNA1C (a gene encoding a protein that is part of a voltage dependent calcium channel). Only ANK3 achieved the study’s threshold significance of less than 5×10−8.

The genetic basis of both bipolar disorder and schizophrenia is likely to be explained by the synergistic interaction of a small number of rare heterozygous deleterious mutations, rather than the interaction of common variant alleles.3 4 This will be revealed in the next generation of genetic studies using whole exome or whole genome screening.


Cite this as: BMJ 2013;346:f530


  • Competing interests: None declared.