We found that paternal age at conception is a robust risk factor for schizophrenia, explaining perhaps a quarter of all cases.

Novartis Found Symp. 2008;289:196-203; discussion 203-7, 238-40.Links
Growth and schizophrenia: aetiology, epidemiology and epigenetics.Malaspina D, Perrin M, Kleinhaus KR, Opler M, Harlap S.
Department of Psychiatry, New York University School ofMedicine, New York, NY 10016, USA.

There is a strong genetic component for schizophrenia risk, but it is unclear how the illness is maintained in the population given the significantly reduced fertility of those with the disorder. One possibility is that new mutations occur in schizophrenia vulnerability genes. If so, then those with schizophrenia may have older fathers, since advancing paternal age is the major source of new mutations in humans. We found that paternal age at conception is a robust risk factor for schizophrenia, explaining perhaps a quarter of all cases. The predisposing genetic events appear to occur stochastically in proportion to advancing paternal age, and the possible mechanisms include de novo point mutations or defective epigenetic regulation of paternal genes. The risk might also be related to paternal toxic exposures, nutritional deficiencies, suboptimal DNA repair enzymes or other factors that influence the fidelity of genetic information in the constantly replicating male germ line. We propose that de novo genetic alterations in the paternal germline cause an independent and common variant of schizophrenia and that abnormal methylation of paternally imprinted genes could be the mechanism. These findings suggest exciting new directions for research into the aetiology of schizophrenia.