14 However, children of schizophrenic mothers who were adopted away and then reared in adverse circumstances have a higher risk than those brought, up in loving homes by stable adoptive parents.148 Furthermore, Mirsky et al149 noted that children with known genetic risk for schizophrenia were more likely to develop the disorder if they lived

on a kibbutz, rather than in a family home. Overall, kibbutz children did not have a higher risk, suggesting that high-risk children carry a genetic vulnerability to the social environment. The effect of being born or brought up in a city Several Inhibitors,research,lifescience,medical studies in the 1990s indicated that being born or brought up in a city increases the risk for schizophrenia.150 In one of the most impressive, Mortensen et al151 examined a Danish national sample and showed that the relative risk for schizophrenia, associated with urban birth was 2.4

and that, there was a dose-response relationship (the larger the town of birth, Inhibitors,research,lifescience,medical the greater the risk) suggesting a causal effect. Mortensen and colleagues pointed out that because so many people are born and live in cities, a relatively small increase in risk would cause a large increase in the numbers of people with Inhibitors,research,lifescience,medical the disease. Indeed, they calculated that the population-attributable risk (PAF) for urban birth was 34.6 %, compared with 9 % or 7 % for having a mother or father with schizophrenia, respectively. The estimate of PAF appears robust, as a similar PAF has previously been reported in data from another country,152

Inhibitors,research,lifescience,medical where, in addition, it was shown that the effect of urban birth/upbringing is not confounded by urban residence in adult life.153 Finally, in a further analysis of the above Danish study, Pederscn and Mortensen154 have shown that Inhibitors,research,lifescience,medical the association between urbanization and schizophrenia is based on continuous or repeated exposures during upbringing (not just, urban birth), and that there is indeed a dose-response relationship between urban upbringing and risk for schizophrenia. The risk associated with isolation The Swedish conscript study discussed above also looked at the interaction of premorbid personality and social isolation. Young men who felt, they were more sensitive than their peers, had fewer than two close friends, and did not have a girlfriend had an increased from risk of later developing the disorder.155 Once again this raises the question of whether these characteristics are an expression of a schizoid or schizotypal personality or whether they are in themselves find more independent risk factors. Until proven otherwise, it is wise to consider that both may be true, ie, individuals with a schizoid or schizotypal personality may be less able to make social relationships, and then the social isolation itself may cause them to become increasingly deviant.