Denial

In our experience many immigrants, both professional and lay, react by questioning the validity of the findings. This may be due to feelings of shame concerning the rates of psychosis and to the belief that the victims of the epidemic must be saved from the stigmatizing diagnosis of schizophrenia (Selten & Hoek, Reference Selten and Hoek2008). We are not aware of any Dutch, Danish or Swedish organization of immigrants that made an appeal to the government for an examination of the high rates of psychotic disorders. The situation in other European countries is unlikely to be much different. According to the immigrants there is no epidemic.

Psychiatrists remember the dogma from their textbooks that the rates of schizophrenia do not vary between sites, sexes, ethnic or cultural groups and that the heritability of the disorder is about 80–85%. Consequently, so they believe, there is hardly any room for an environmental effect, let alone for an epidemic. This becomes manifest at major international conferences, where psychiatrists talk about a haplotype of the gene for neuregulin, with a mean weighted relative risk of 1.22 (Li et al. Reference Li, Collier and He2006), not about the epidemic. However, risks for schizophrenia vary as much as they do for other complex disorders (McGrath, Reference McGrath2005) and the so-called ‘heritability’ of a complex disorder is misleading and represents a strong overestimation of the genetic effect (Schwartz & Susser, Reference Schwartz, Susser, MacCabe, O'Daly, Murray, McGuffin and Wright2006). In heritability analyses gene–environment interactions and gene–environment correlations are attributed entirely to the genetic effect. According to the psychiatrists there cannot be an epidemic.

It must be difficult for politicians to choose whom to believe: the white epidemiologist, who does not work in the prestigious areas of research like pharmacology, genetics or neuro-imaging, or the angry professional from an ethnic minority group, who claims that white psychiatrists and epidemiologists do not understand immigrants from non-western countries. A Dutch governmental report about the increasing demand for psychiatric help did not even mention the high psychosis rates among immigrants (Landelijke Commissie Geestelijke Volksgezondheid, 2002). For politicians it is safe (and cheap) to believe that there is no epidemic.

This situation has led to inadequate funding for research and care. There is hardly any information concerning the mental health of migrants in France, Italy, Spain or Germany. In the UK, the Netherlands and Scandinavia, there is little information on the range of the epidemic: does it extend to (psychotic or non-psychotic) mood disorders and to drug dependence? The question is relevant, for the high rates of mania among African-Caribbeans in the UK, for example, show that the epidemiological findings do not adhere to discrete DSM-IV diagnostic categories. To our knowledge, the mechanism underlying the ethnic density effect has not been examined in any other country apart from the UK (Kirkbride et al. Reference Kirkbride, Morgan, Fearon, Dazzan, Murray and Jones2008).

Aetiology

We agree with Morgan & Hutchinson (Reference Morgan and Hutchinson2009) that social adversity is the main cause of the high psychosis rates and that sensitization of the mesolimbic dopamine system probably plays a key role in pathogenesis. However, we feel that the concept of social adversity is too broad. If poverty, which is also a form of social adversity, were a risk factor for psychotic disorders, one would expect to find very high rates in developing countries. In the Netherlands one would expect higher rates for immigrants from Turkey than for immigrants from Surinam. Consequently, we feel that the concept of social defeat, defined as the chronic experience of an inferior position or social exclusion, may fit the data better (Selten & Cantor-Graae, Reference Selten and Cantor-Graae2005, Reference Selten and Cantor-Graae2007). The concept of social defeat is compatible with the evidence that those ethnic groups with the lowest status and the highest exposure to discrimination (African-Caribbeans in the UK, Moroccan males in the Netherlands, the Inuit in Denmark) are at highest risk (Selten et al. Reference Selten, Veen, Feller, Blom, Schols, Camoenië, Oolders, van der Velden, Hoek, Vladár Rivero, van der Graaf and Kahn2001; Fearon et al. Reference Fearon, Kirkbride, Morgan, Dazzan, Morgan, Lloyd, Hutchinson, Tarrant, Fung, Holloway, Mallet, Harrison, Leff, Jones and Murray2006; Cantor-Graae & Pedersen, Reference Selten and Cantor-Graae2007; Veling et al. Reference Veling, Selten, Susser, Laan, Mackenbach and Hoek2007). The following example may help to differentiate between the concepts of social adversity and social defeat. Life in Mogadishu is extremely stressful due to the shortage of food and the threats of war. However, if a Somali moves from Mogadishu to Western Europe he has to cope with a different type of stress: how to secure a place within the white European hierarchy. According to the social defeat hypothesis it is this second type of stress which predisposes to schizophrenia. With reference to the presumed sensitization of the mesolimbic dopamine system, it is important to note that the evidence for social defeat as a cause of this sensitization derives from some animal studies (e.g. Covington & Miczek, Reference Covington and Miczek2001), and that there have not been any studies in humans.

Second, Morgan & Hutchinson (Reference Morgan and Hutchinson2009) consider ‘biological’ factors as unimportant, but we believe that illicit drug use may contribute to the development of the epidemic. Animal studies have shown that episodes of social defeat lead to more intense cocaine self-administration (Covington & Miczek, Reference Covington and Miczek2001; Morgan et al. Reference Morgan, Grant and Gage2002). There have not been similar studies in humans, but the frequent onset of drug use (cannabis, amphetamines, cocaine) after negative life events is an established phenomenon. Furthermore, a well-designed study in humans has shown that the use of amphetamines leads to sensitization of the mesolimbic dopamine system (Boileau et al. Reference Boileau, Dagher, Leyton, Gunn, Baker, Diksic and Benkelfat2006). Consequently, in some subjects the experience of social defeat may lead to drug use, and drug use, in turn, may lead to changes in the dopamine system. In other patients, the experience of social defeat may cause sensitization of the mesolimbic dopamine system without a role of drug use. Thus, there could be an interaction (synergism or parallelism?) between the experience of social defeat and the use of illicit drugs in producing a sensitization of the mesolimbic dopamine system (Darroch, Reference Darroch1997).

Prevention

Since the causes of the epidemic are mainly of a social nature, prevention is primarily a job for politicians, not for psychiatrists. Psychiatrists could develop useful prevention strategies for those immigrants who are at an extremely high risk, for example, siblings of second-generation African-Caribbean patients in the UK or brothers of Moroccan patients in the Netherlands (Hutchinson et al. Reference Hutchinson, Takei, Fahy, Bhugra, Gilvarry, Moran, Mallett, Sham, Leff and Murray1996; Selten et al. Reference Selten, Blom, van der Tweel, Veling, Leliefeld and Hoek2008). However, as pointed out by Rose (Reference Rose1994), ‘a large number of people at a small risk may give rise to more cases than the small number who are at a high risk’. Consequently, prevention can best be achieved by improving the social status of immigrants.

It is worth considering the difference between Europe and the USA in the receipt of immigrants. Many immigrants to Europe are unemployed, receive income support and are forced to spend their day before the television set. They do not learn the language, do not meet with Europeans, and lose self-esteem. Immigrants to the USA, in contrast, who are forced to take two jobs to survive, participate in social life, learn the language and become proud of their achievements. The American system (opportunities and no income support) may work better than the reverse (income support and no opportunities). However, whether the psychosis risk for immigrants from developing countries to the USA is lower than that in Europe remains unknown and it is probably impossible to examine this, because the USA has no civil registration system. The important task for mental health professionals is to draw attention to the problems instead of obscuring them. Indeed, we see the denial of the epidemic and the negation of the need for appropriate measures as a form of discrimination in itself.