LAUSR

Abstract Background There is replicated evidence of a shared genetic load between affective and non-affective psychosis, but much less is known of whether affective psychosis is affected by the same environmental risk factors as well. The aim of this review and meta-analysis is to study the association between specific environmental risk factors of interest previously associated with schizophrenia and later affective psychoses (bipolar disorder and psychotic depression). Methods A systematic search of prospective studies was conducted in MEDLINE, EMBASE and PsycINFO databases, supplemented by hand searching. Selected exposures included: paternal age, maternal infection, obstetric and perinatal factors, childhood trauma, childhood infection, urbanicity, migration, stressful life events, head injury and cannabis or substance use. Relevant studies were selected systematically among those fulfilling inclusion criteria, and effect sizes were extracted. Pooled information was presented for those factors with enough number studies to combine extracted effect sizes, while the rest were presented in a narrative way. Results Approximately 60 studies addressing the associations between environmental risk factors of interest and later affective psychoses were identified. The compiled studies showed that paternal age, early gestational age, lifetime cannabis use, parental death during childhood and ethnic minority in UK are associated with future development of affective psychosis. Discussion These results show that, as per genetics, there may be some overlap in the environmental load between schizophrenia and affective psychosis, suggesting general risks for psychosis rather than diagnostic specific risks. Nonetheless, publish studies for some factors in this subgroup of patients are still scarce. More longitudinal studies addressing specific association between environmental risk factors and affective psychosis are warranted.