BACKGROUND: Schizophrenia is thought to be a genetically mediated illness affecting neural development from early childhood, with symptoms usually appearing during adolescence. However, in the last twenty years evidence has emerged supporting that social and environmental factors play a strong aetiological role in the development of schizophrenia. Robust findings include an association between migration and psychosis, which is not explained by a higher genetic risk among migrants (Morgan et al., 2010; Cantor-Graee et al., 2003); and between urban upbringing and psychosis (Pedersen et al., 2001; Pedersen et al, 2006). Other social risk factors include: childhood exposure to socioeconomic adversity (Wicks et al., 2005); family breakdown (Fearon et al., 2006); and bullying (Schreier et al., 2009). Selten & Cantor-Grae (2005) have proposed that "social defeat," representing repeated experiences of exclusion, discrimination and marginalisation, is the common underlying factor explaining the role of different social adversities in the development of psychosis.

In a Danish study of urban upbringing and increased risk of psychosis, Pedersen et al. (2001) found that it was a change of municipality rather than a change of address within the same municipality, that increased the risk of psychosis. In Denmark, a change of municipality always leads to a change of school. The authors speculated that the stress of changing school, making new friends, and perhaps worsening anxiety in those already prone to schizophrenia, might explain the increased risk of subsequent schizophrenia, i.e., the urban risk is partly mediated by a frequent change of schools. In a subsequent analysis, the authors found that the increased risk attributed to urban upbringing could not be entirely explained by familial factors (likely to be genetic risk); some of the risk was rooted in the individual (Pedersen & Mortensen, 2006). However, there are no studies which have further explored the hypothesis that repeated changes in school during childhood increase the risk of psychosis symptoms in adolescence.

AIMS: To explore whether repeated changes of school in childhood independently increase the risk of psychosis symptoms in early (and late) adolescence.

HYPOTHESES: 1) Children exposed to repeated changes of school will be at increased risk of PLIKS during adolescence. 2) There will be an independent association between changes in school and PLIKS when degree of urbanicity is controlled for 3) The predictive association between changes in school and increased risk of PLIKS will remain after controlling for other known confounders.

EXPOSURE VARIABLES: Number of school changes during childhood.

OUTCOME VARIABLES: Psychosis symptoms (PLIKS) at 12 years (and 17-18 years when available).

CONFOUNDING VARIABLES: Confounding variables have been selected for their previously reported associations with the likelihood of school change or psychosis symptoms. These include: socioeconomic adversity (as indexed by the Family Adversity Index); exposure to bullying during childhood; family breakdown (as indexed by exposure to domestic violence, harsh parenting and parental hostility); IQ of child; family history of schizophrenia; and urban/rural index at birth.

REFERENCES:

Cantor-Graae, E., et al., (2003). Migration as a risk factor for schizophrenia: a Danish population-based cohort study. Br J Psychiatry, 182, 177-22.

Fearon, P, et al. (2006). Incidence of schizophrenia and other psychoses in ethnic minority groups: results from the MRC AESOP Study. Psychol Med, 36, 1541-50.

Morgan, C., et al., (2010). Migration, ethnicity, and psychosis: toward a sociodevelopmental model. Schizophr Bull, 36, 655-64.

Pedersen, C.B., & Mortensen, P.B. (2001). Evidence of a dose-response relationship between urbanicity during upbrining and schizophrenia risk. Arch Gen Psychiatry, 58, 1039-46

Pedersen, C.B., & Mortensen, P.B. (2006). Are the cause(s) responsible for urban-rural differences in schizophrenia risk rooted in families or individuals? Am J Epidemiol, 163, 971-8.

Schreier, A., et al., (2009). Prospective study of peer victimisation in childhood and psychotic symptoms in a non-clinical population at 12 years. Arch Gen Psychiatry, 66, 527-36.

Selton, J.P., & Cantor-Graae, E. (2005). Social defeat: risk factor for schizophrenia? Br J Psychiatry, 187, 101-2.

Wicks, S., et al., (2005). Social adversity in childhood and the risk of developing psychosis: a national cohort study. Am J Psychiatry, 162, 1652-7.