Genetic causality in schizophrenia and bipolar disorder: out with the old and in with the new.

Schizophrenia (SZ) and bipolar disorder are highly heritable forms of major mental illness. Great hopes were held out for a major breakthrough with the advent of genome wide association studies, but to date there have been no obvious low hanging fruit. A richer harvest of strong candidates has however emerged from molecular cytogenetics and copy number variant mapping strategies promise to add more. Both strategies identify gene mutations, paving a direct path to biological studies and tests of causality. Risk genes and convergent biological pathways common to both disorders are being revealed, offering hope for a better understanding of aetiological factors and for the development of biomarkers to aid in diagnosis and prognosis.