05 08 2016
Does incidence schizophrenia vary between countries? Faris and Dunham (1939) showed that disorganised neighbourhoods in Chicago had higher rates of schizophrenia sparking all sorts of explanations for this. WHO study in 1980’s found that incidence of narrowly defined schizophrenia did not differ across countries, but broadly defined illness did differ significantly across countries. In 2004, MCgrath et al summarised all relevant data from 161 studies and showed that there is a five fold difference across countries. It is also thought that there are possible significant regional differences with in countries as well.
What would explain such geographical differences? It is possible that factors like social deprivation, population density, urbanicity, social capital and social fragmentation may have some roles to play. There are theoretical meanings and explanatory models attached to these factors.
Is social deprivation associated with higher incidence of psychosis ? Brian O’Donoghue, Eric Roche and Abbie Lane looked at association between the level of social deprivation at the neighbourhood level and the incidence of psychotic disorders in this systematic review.They included 28 studies in the analysis.
Three types of places ( place of birth , place when high risk status was positive , place when schizophrenia emerged) and their association with illness status was explored in these studies.Most studied ( 21 studies) deprivation of the place where illness emerged.
Most studies (17/23) show that there is an association between incidence of illness and the level of social deprivation at the time of presentation.
Social deprivation at place of birth is less studied keeping the ‘drift theory’ alive. The largest study on this question ( place of birth ) did not support an association. However, a well designed Israel study ( Werner , 2007) showed that individuals who later on develop schizophrenia were more likely to be born in deprived areas.
Social causation can occur ( if at all it is happening), through multiple, direct/ indirect channels ( weaker social cohesion, poorer support systems). Established risk factors ( family history ,cannabis use, traumatic experiences ) can be more prevalent in such areas. They may also have more residential mobility in childhood which is now shown to be another possible risk factor.We do not know how much gene- environment interaction may be explaining these observed associations. The EU-GEI study ( European Genetic Interaction Study), which is now established, is likely to offer some insights .
How would we know more about environmental effects ? This review suggest that more studies on UHR/ psychotic symptoms in general population are needed to identify vulnerability periods and associated environmental risk factors.
Understanding these relationships have some practical , immediate relevance when we allocate resources , for example for early intervention services . Psychiatric Mapping Translated into Innovation for Care (PsyMaptic) is an example of a resource that predict the incidence in a geographical area to inform resource allocation. However, in countries where basic mental health data is lacking, these are distant dreams.
Summary of the article.
O’Donoghue B, Roche E, Lane A.
Soc Psychiatry Psychiatr Epidemiol. 2016 Jul;51(7):941-50. doi: 10.1007/s00127-016-1233-4. Epub 2016 May 13. Review.