Environmental Factors in Schizophrenia: The Role of Migrant Studies

Abstract

There is now compelling evidence that migrant groups in several countries have an elevated risk of developing schizophrenia and other psychotic disorders. Though the findings of earlier studies were greeted with skepticism, and ascribed by some to have methodological shortcomings and diagnostic biases, the more rigorous recent studies, from a variety of countries, have still found markedly increased incidence rates. While this phenomenon is an important health issue in its own right, understanding the reasons for the increased rates may provide valuable insights into the causes of schizophrenia and other psychotic disorders in general. The challenge for the next phase of studies is to identify the relevant risk factors and how they might interact to increase the risk of psychosis, both in migrant groups and in the general population.

Schizophrenia in black Caribbeans living in the UK: an exploration of underlying causes of the high incidence rate

“…Increased awareness of these factors in the black Caribbean community may contribute to early diagnosis and rapid access to appropriate treatment, which in turn are likely to translate into improved long-term outcomes of the patient, and monitored for inter-rater and intercentre reliability. 6 There are two explanations for misdiagnosis of schizophrenia -'clinician bias', where psychiatrists misinterpret symptoms and overdiagnose schizophrenia, and 'cultural relativity', which describes the different ways in which schizophrenia is exhibited in different ethnic and cultural groups. 21 The former argues that diagnostic bias by clinicians has inflated the true incidence in some ethnic groups.…”

“…6 The UK-based Aetiology and Ethnicity in Schizophrenia and Other Psychoses (AESOP) multisite (Bristol, south-east London, and Nottingham) study is one of the largest studies to examine ethnic variations in schizophrenia incidence. 7 In 2006, AESOP reported a ninefold increase in the risk of developing schizophrenia in black Caribbeans when compared with the white British population: the increased risk was 5.8 in black Africans and 1.4 in South Asians.…”

Impact of trauma on attenuated psychotic symptoms

“…First, there is a current research interest in the impact of past experiences. The presence of certain psychosocial risk factors at certain points in the lifespan such as urban upbringing (Krabbendam & van Os, 2005), adverse childhood development and trauma (Janssen et al, 2004) and migration (Fearon & Morgan, 2006) have been linked to the later development of psychosis. Several lines of evidence suggest a possible association between trauma in childhood and the presence of psychotic symptoms as well as sub-threshold psychotic symptoms (Shevlin, Dorahy, & Adamson, 2006;Kelleher et al, 2008;Read, van Os, Morison, & Ross, 2005;Spauwen, Krabbendam, Lieb, Wittchen, & van Os, 2006).…”

The Prevention of Schizophrenia--What Can We Learn From Eco-Epidemiology?

“…Thus far, we know that urban birth and living, 7 being a migrant or their offspring, 8 being a member of a minority group 9 or exposure to a range of negative events across the life course, are associated with higher rates of disorder. 10 The effect sizes (rate ratios) for these ''risk factors'' are of an order of magnitude higher than nearly all corresponding genetic effects (Few exceptions exist, but a deletion on chromosome 22, which results in velocardiofacial [VCS] syndrome [or 22q11 deletion syndrome], has been established with a large increased risk of schizophrenia. An estimated 30% of people with VCS go onto experience psychosis.…”