Importance: Community functioning is a core component of the functional deficits in schizophrenia, yet little systematic research on the origins of these functional deficits has been performed.
Objectives: To examine 3 key domains of community functioning--social activity, independent behavior, and functioning in school or work--before first hospitalization for schizophrenia and to determine whether these domains are familial.
Design, setting, and participants: In this population-based, prospective study that included a sibling-control comparison, data from the Israeli National Draft Board Registry were linked with data from the Israeli Psychiatric Hospitalization Case Registry. The merged file included data for all male adolescents who visited the draft board and were followed up for as much as 25.4 years from draft board assessment (through the end of 2010). The 3 functional domains for cases, their unaffected siblings, and controls were compared by time between assessment and time to hospitalization. Analyses were conducted from March 13, 2014, to October 19, 2014.
Main outcomes and measures: The trajectories and familiality of 3 key components of community functioning--social activity, independent behavior, and functioning in school or work--in the years preceding hospitalization for schizophrenia.
Results: Participants included 723,316 Israeli male adolescents who underwent a mandatory behavioral assessment to determine eligibility for military service. Linkage identified 3929 individuals hospitalized for schizophrenia. Data for 338,550 sibling pairs, 1659 hospitalized with schizophrenia, were similarly ascertained. Among those with schizophrenia, impairments in social activity (effect size [d], 0.55) and functioning in school or work (d = 0.37) were recognizable up to 15 years before hospitalization. Independent behavior seemed preserved until the few years before first admission. For social activity, differences between cases and controls were progressively greater for patients admitted closer to time of testing (F = 115.33, P < .001). Unaffected siblings had small impairments compared with controls in social activity (F = 28.25, P < .001) and functioning in school or work scales (F = 14.77, P < .001). Group familial (sibling) correlations were relatively high for social activity (r = 0.40; 95% CI, 0.39-0.41) and functioning in school or work (r = 0.50; 95% CI, 0.49-0.51) but nil for independent behavior (r = 0; 95% CI, -0.01 to -0.01). Impairments in siblings had no progressive increase and were unrelated to their affected sibling's time of illness onset (time trend: social activity: F = 5.463, P = .02; independent behavior: F = 0.908, P = .34; and functioning in school or work: F = 1.386, P = .24).
Conclusions and relevance: Various components of impaired community functioning in schizophrenia followed different developmental trajectories. Our results indicate that impairments in social activity and functioning in school or work are familial.