A Polygenic Basis for Major Disorders?

Recent studies have shown associations between large copy number variations and several major psychiatric disorders, including schizophrenia and autism (JW Psychiatry Sep 8 2008, Jun 23 2008, and Mar 17 2008). Three study consortia, reporting in a series of letters in Nature, used another approach: They examined very large samples for common polymorphisms that individually exert a small effect, but which, as a group, might have a substantial genetic role.

Purcell and colleagues performed a genomewide association study, genotyping the International Schizophrenia Consortium population (3332 patients with schizophrenia and 3587 controls, all of European ancestry) for approximately 1 million single nucleotide polymorphisms (SNPs). This method wa…