Migration, heredity, and schizophrenia

Risk of schizophrenia, schizoaffective, and bipolar disorders by migrant status, region of origin, and age-at-migration: a national cohort study of 1.8 million people

BACKGROUND

We assessed whether the risk of various psychotic disorders and non-psychotic bipolar disorder (including mania) varied by migrant status, a region of origin, or age-at-migration, hypothesizing that risk would only be elevated for psychotic disorders.

METHODS

We established a prospective cohort of 1 796 257 Swedish residents born between 1982 and 1996, followed from their 15th birthday, or immigration to Sweden after age 15, until diagnosis, emigration, death, or end of 2011. Cox proportional hazards models were used to model hazard ratios by migration-related factors, adjusted for covariates.

RESULTS

All psychotic disorders were elevated among migrants and their children compared with Swedish-born individuals, including schizophrenia and schizoaffective disorder (adjusted hazard ratio [aHR]migrants: 2.20, 95% CI 1.96-2.47; aHRchildren : 2.00, 95% CI 1.79-2.25), affective psychotic disorders (aHRmigrant1.42, 95% CI 1.25-1.63; aHRchildren: 1.22 95% CI 1.07-1.40), and other non-affective psychotic disorders (aHRmigrant: 1.97, 95% CI 1.81-2.14; aHRchildren: 1.68, 95% CI 1.54-1.83). For all psychotic disorders, risks were generally highest in migrants from Africa (i.e. aHRschizophrenia: 5.24, 95% CI 4.26-6.45) and elevated at most ages-of-migration. By contrast, risk of non-psychotic bipolar disorders was lower for migrants (aHR: 0.58, 95% CI 0.52-0.64) overall, and across all ages-of-migration except infancy (aHR: 1.20; 95% CI 1.01-1.42), while risk for their children was similar to the Swedish-born population (aHR: 1.00, 95% CI 0.93-1.08).

CONCLUSIONS

Increased risk of psychiatric disorders associated with migration and minority status may be specific to psychotic disorders, with exact risk dependent on the region of origin.

A reassessment of the higher-order factor structure of the German Schizotypal Personality Questionnaire (SPQ-G) in German-speaking adults

The Schizotypal Personality Questionnaire (SPQ) is a widely-used self-report instrument for the assessment of schizotypal personality traits. However, the factor structure of scores on English and non-English translations of the SPQ has been a matter of debate. With little previous factorial evaluation of the German version of the SPQ (SPQ-G), we re-assessed the higher-order factor structure of the measure. A total of 2,428 German-speaking adults from Central Europe (CE) and the United Kingdom (UK) completed the SPQ-G. Confirmatory factor analysis - testing proposed 2-, 3-, and 4-factor models of SPQ-G scores - indicated that the 4-factor solution had best fit. Partial measurement invariance across cultural group (CE and UK) and sex was obtained for the 4-factor model. Further analyses showed CE participants had significantly higher scores than UK participants on one schizotypal facet. These results suggest that scores on the SPQ-G are best explained in terms of a higher-order, 4-factor solution in German migrant and non-migrant adults.

Testing Ødegaard's selective migration hypothesis: a longitudinal cohort study of risk factors for non-affective psychotic disorders among prospective emigrants

BACKGROUND

The selection hypothesis posits that the increased rates of psychosis observed among migrants are due to selective migration of people who are predisposed to develop the disorder. To test this hypothesis, we examined whether risk factors for psychosis are more prevalent among future emigrants.

METHOD

A cohort of 49,321 Swedish military conscripts was assessed at age 18 years on cannabis use, IQ, psychiatric diagnosis, social adjustment, history of trauma and urbanicity of place of upbringing. Through data linkage we examined whether these exposures predicted emigration out of Sweden. We also calculated the emigrants' hypothetical relative risk compared with non-emigrants for developing a non-affective psychotic disorder.

RESULTS

Low IQ [odds ratio (OR) 0.5, 95% confidence interval (95% CI) 0.3-0.9] and 'poor social adjustment' (OR 0.4, 95% CI 0.2-0.8) were significantly less prevalent among prospective emigrants, whereas a history of urban upbringing (OR 2.3, 95% CI 1.4-3.7) was significantly more common. Apart from a non-significant increase in cannabis use among emigrants (OR 1.6, 95% CI 0.8-3.1), there were no major group differences in any other risk factors. Compared to non-emigrants, hypothetical relative risks for developing non-affective psychotic disorder were 0.7 (95% CI 0.4-1.2) and 0.8 (95% CI 0.7-1.0), respectively, for emigrants narrowly and broadly defined.

CONCLUSIONS

This study adds to an increasing body of evidence opposing the selection hypothesis.

Do risk factors for schizophrenia predispose to emigration?

OBJECTIVE

Increased incidence rates of schizophrenia in immigrants still lack a satisfactory explanation. The aim of this study was to examine the hypothesis that risk factors for schizophrenia also increase the risk of emigration to a foreign country. If valid, Danes emigrating from Denmark carry a higher predisposition to develop schizophrenia compared to Danes living in Denmark.

METHODS

Utilizing data from the Danish Civil Registration System, we established a population-based cohort of 1.10 million native Danes. We assessed relative risks of emigration to a foreign country in relation to sex, age, urban birth, parental age, and a history of mental illness.

RESULTS

Urban birth in Denmark was a significant predictor of emigration to a foreign country. A maternal history of psychiatric contact during childhood and a parental history of bipolar affective disorder increased the risks of emigration. A personal history of mental illness decreased the risk of emigration, mostly for people diagnosed with schizophrenia.

CONCLUSIONS

Our study provided evidence that Danish emigrants residing in a foreign country have both a higher predisposition of schizophrenia due to differential exposure to birth in urban areas and a lower predisposition of schizophrenia due to differential exposure to a history of mental illness. Although competing selection mechanisms operate, the combined effect of these different selection mechanisms was limited, thus suggesting a potential role for yet to be identified adverse environmental effects operating either before or after emigration.

The social causes of psychosis in North American psychiatry: a review of a disappearing literature

OBJECTIVE

To review the North American literature with respect to the role of social factors in the etiology of psychosis, including schizophrenia.

METHOD

Relevant publications were identified through a search of MEDLINE from 1966 to 2006. Identified studies and articles had to originate in Canada or the United States to be included in the review. Articles written prior to 1966 were identified by cross-referencing bibliographies and reference lists. Articles were considered relevant if they discussed ethnoracial or other social factors as being causal or contributing to the development of psychosis or schizophrenia.

RESULTS

The relation between the etiology of psychosis and such social factors as poverty, migration, and racial discrimination has been neglected in the North American psychiatric literature for the last 40 years. In Canada and the United States, there is a dearth of research on these issues: the study of social causes of psychosis has been replaced by a focus on the clinical encounter, in which clinician bias is presumed to be responsible for widespread misdiagnosis of psychosis in minority (mainly African-American) populations. The reasons for neglecting social causes of psychosis in the North American psychiatric literature are obscure but may have to do with the rise of genetic-biological paradigms in recent decades.

CONCLUSIONS

The neglect of social causes of psychosis in the North American psychiatric literature has been coincident with an increase in scholarly concern among European clinicians and researchers. Careful reading of the European literature may reveal helpful avenues for future investigation in the North American context. In addition, drawing on social science literature and methods may help to clarify mechanisms underlying poverty, migration, and racial discrimination that contribute to psychosis in vulnerable individuals and groups.

A review of the evidence from family, twin and adoption studies for a genetic contribution to adult psychiatric disorders

Family, twin and adoption studies have provided major evidence for the role of genetics in numerous psychiatric disorders including obsessive-compulsive disorder, panic disorder, major depressive disorder, bipolar disorder, schizophrenia and Alzheimer's disease. As the search for patterns of inheritance and candidate genes of these complex disorders continues, we review relevant findings from quantitative genetic studies and outline the main challenges for the field of psychiatric genetics to focus on in order to more definitively establish the underpinnings of genetic and environmental influences of adult psychopathology.

Mobility of schizophrenic patients, non-psychotic patients and the general population in a case register area

This preliminary study attempts to evaluate the effect of a community psychiatric service on residential mobility by comparing a cohort of schizophrenic patients over a 5-year period with that of non-psychotic and general population control groups in South Verona, a case register area in Northern Italy. No significant differences were found between the groups for different types of movement (within South Verona/outside catchment area of South Verona/outside City of Verona), except for movements within South Verona between the schizophrenic group and neurotic group. The former tended to move less than the latter. The sociodemographic factors associated with movements of the general population in Verona were being male and single, whereas place of birth was less important. The results showed that in the two patient groups as well as in the general population in South Verona, the percentages of those who moved outside the case-register area ranged between 1.5%-4.4% over a one-year period, and between 7.3%-13.8% over a five-year period, indicating a relatively consistent denominator for the Case Register.

Genetic methods and preventive psychiatry

1. The meaning of the consistently high estimates of heritability of psychiatric disorders such as affective disorders and schizophrenia is that a small proportion of families accounts for a very large proportion of the population diagnostic variance. 2. This implies that the classic community mental health services model of a randomly distributed risk in a geographically defined catchment area population is inappropriate, and that efficient case finding and follow-up would result from tracing illness within pedigrees of known cases. 3. Application to clinical practice of family study methods developed in genetic research enables efficient identification of unrecognized and untreated cases, and early provision of care (secondary prevention). The use of family study methods will also uncover milder and variant ("spectrum") forms of illness in relatives of known patients, which then become accessible to treatment. 4. A family study of affective illness at the United States National Institute of Mental Health, demonstrated how additional ill persons including previously untreated cases could be identified. Starting with 86 Bipolar probands, we interviewed all available first degree relatives, and saw second degree relatives if there was indicated psychopathology by history. 5. Of the 405 living first degree relatives of 86 Bipolar I patients, the study found 1.2% had lifetime diagnosis of untreated Bipolar illness, 2.7% had untreated Unipolar illness, 4% had less severe personality disorders and 2% suffered from behavioral disorders such as drug abuse or alcoholism.