Geographical variation in rate of schizophrenia in rural Ireland by place at birth vs place at onset

This study examined geographical variation in rate of occurrence of schizop hrenia by place at birth vs place at onset, among a rural Irish catchment a rea population of unusual stability and socioeconomic homogeneity. Within a catchment area of 21 520 persons, all cases of schizophrenia were sought u sing current inpatient and outpatient records and key informants active in the community. Suspected cases were interviewed personally and diagnosed us ing DSM-III-R criteria. Place at birth and place at onset of psychosis were specified among the 32 District Electoral Divisions constituting the study region. For the 72 cases ascertained, an unremarkable overall prevalence r ate/morbid risk obscured substantial and significant geographical variation s therein between District Electoral Divisions. Particularly after controll ing for high-density families, men demonstrated prominent geographical vari ation both by place at birth and by place at onset, with most men remaining unmarried and becoming ill at their place of birth; conversely, women demo nstrated prominent variation by place at birth but more limited variation b y place at onset, despite more frequent transitions from the parental home to the marital home before onset. Even when cases changed their location be fore the onset of psychosis, geographical variation in rate of occurrence o f schizophrenia remained associated more strongly with factors related to t he place of their birth. (C) 1999 Elsevier Science B.V. All rights reserved .