And if variations in gene number contribute to schizophrenia, but not to bipolar disorder, can one assume that gene-number variations play a greater role in schizophrenia susceptibility than gene mutations do? No, Kirov replied, and here's why: "So far the only firm findings [in schizophrenia] support the role of variations in gene number. However, the ones that we know are pathogenic are very rare, probably found combined in just around 3 percent of patients. I don't think that number will increase tremendously.... This leaves a larger role for mutations in genes. Sequencing studies are only now coming up, so in the next two to three years, I expect a lot of mutations to be found. I personally expect that point mutations will explain a larger part of the genetics of schizophrenia than copy-number variations will."