A comparison of selected risk factors for unipolar depressive disorder, bipolar affective disorder, schizoaffective disorder, and schizophrenia from a Danish population-based cohort

National Centre for Register-Based Research, University of Aarhus, Denmark.
The Journal of Clinical Psychiatry (Impact Factor: 5.14). 12/2007; 68(11):1673-81. DOI: 10.4088/JCP.v68n1106
Source: PubMed

ABSTRACT Growing evidence of an etiologic overlap between schizophrenia and bipolar disorder has become increasingly difficult to disregard. In this study, we examined paternal age, urbanicity of place of birth, being born "small for gestational age," and parental loss as risk factors for primarily schizophrenia and bipolar disorder, but also unipolar depressive disorder and schizo-affective disorder. Furthermore, we examined the incidence of the disorders in a population-based cohort and evaluated our results in the context of the Kraepelinian dichotomization.
We established a register-based cohort study of more than 2 million persons born in Denmark between January 1, 1955, and July 1, 1987. Overall follow-up began on January 1, 1973 and ended on June 30, 2005. Relative risks for schizophrenia, bipolar disorder, unipolar depressive disorder, and schizoaffective disorder (ICD-8 or ICD-10) were estimated by survival analysis, using Poisson regression.
Differences were found in age-specific incidences. Loss of a parent (especially by suicide) was a risk factor for all 4 disorders. High paternal age and urbanization at birth were risk factors for schizophrenia. Children born pre-term had an excess risk of all disorders except schizophrenia if they were born "small for gestational age."
An overlap in the risk factors examined in this study was found, and the differences between the phenotypes were quantitative rather than qualitative, which suggests a genetic and environmental overlap between the disorders. However, large gender differences and differences in the age-specific incidences in the 4 disorders were present, favoring the Kraepelinian dichotomization.

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    • "While many studies have identified alleles associated with depression, to our knowledge no study has shown an association between increased mutation rate and MDD. In one sample, for instance, paternal age was shown to be a risk factor for schizophrenia, but not unipolar depressive disorder (Laursen et al., 2007). This suggests that MDD is less likely than other psychiatric disorders to be caused by de novo genetic mutations that lead to biological malfunction. "
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    • "However, to our knowledge, no previous study has offered a lifecourse perspective examining whether the possible effects of late preterm birth on mental disorders extend across adult ages from young to old adulthood. Some studies suggest that the increased risk for mental disorders associated with preterm birth may characterize especially those preterm individuals who were born small for gestational age [SGA; defined as birth size at 42 standard deviations (S.D.s) or below the 5th or 10th percentile of that predicted by their gestational age; Laursen et al. 2007; Räikkönen et al. 2008; Strang-Karlsson et al. 2008; Monfils Gustafsson et al. 2009]. In fact, previous studies have shown that at least until young adulthood, individuals born SGA are at increased risk of severe mental disorders independently of their gestational age (Abel et al. 2010; Niederkrotenthaler et al. 2012; Nosarti et al. 2012). "
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    • "Risk factors for these sets of disorders are shared [migration and ethnicity (Cantor-Graae & Selten, 2005; Fearon et al. 2006) and childhood traumas (Laursen et al. 2007)] and unique [e.g. urban birth and upbringing (Mortensen et al. 1999), paternal age (Laursen et al. 2007), developmental delays ( Jones et al. 1994) and impaired pre-morbid cognition in schizophrenia (Reichenberg et al. 2002)], suggesting that there may be both overlapping and distinct aetiological pathways to psychotic disorder. "
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