The aetiology of schizophrenia: what have the Swedish Medical Registers taught us?

To review the last thirty years of studies that, using Swedish population registers, have added to our understanding of the aetiology of schizophrenia A literature search was performed to systematically review all studies that using Swedish Population based registers have investigated the aetiology of schizophrenia. Key authors in the field, predominately from Swedish institutions, were additionally contacted and key journals hand searched, for missing references. A quality assessment methodological review was then conducted on each study. Data was extracted and tabulated on identified aetiological themes 61 articles were included corresponding to 10 identified aetiological themes. Although the majority of included studies were retrospective cohort studies, case control studies were also included where they used population based registers. Confirming previous research, schizophrenia was found to have a multi-factorial aetiological basis with pregnancy and birth factors, parental age, social adversity, genetics, substance misuse, migration and ethnicity, personality, non-psychiatric co-morbidity, psychiatric history and poor cognitive performance all found to be significantly associated with an increased risk of later schizophrenia. Although some difficulties exist in analysing the interplay between each of these factors, the Swedish population registers have added considerably to our understanding of each of the presented individual aetiological themes. The ability to study the whole population over several decades has been particularly useful in determining the timing of exposures.