Abstract
Bipolar disorder (BD) overlaps schizophrenia in its clinical presentation and genetic liability. Alternative approaches to patient stratification beyond current diagnostic categories are needed to understand the underlying disease processes and mechanisms. To investigate the association between common-variant liability for schizophrenia, indexed by polygenic risk scores (PRSs), and psychotic presentations of BD. This case-control study in the United Kingdom used multinomial logistic regression to estimate differential PRS associations across categories of cases and controls. Participants included in the final analyses were 4436 cases of BD from the Bipolar Disorder Research Network. These cases were compared with the genotypic data for 4976 cases of schizophrenia and 9012 controls from the Type 1 Diabetes Genetics Consortium study and the Generation Scotland study. Data were collected between January 1, 2000, and December 31, 2013. Data analysis was conducted from March 1, 2016, to February 28, 2017. Standardized PRSs, calculated using alleles with an association threshold of P < .05 in the second Psychiatric Genomics Consortium genome-wide association study of schizophrenia, were adjusted for the first 10 population principal components and genotyping platforms. Multinomial logit models estimated PRS associations with BD stratified by Research Diagnostic Criteria subtypes of BD, by lifetime occurrence of psychosis, and by lifetime mood-incongruent psychotic features. Ordinal logistic regression examined PRS associations across levels of mood incongruence. Ratings were derived from the Schedules for Clinical Assessment in Neuropsychiatry interview and the Bipolar Affective Disorder Dimension Scale. Of the 4436 cases of BD, 2966 (67%) were female patients, and the mean (SD) age at interview was 46 [12] years. Across clinical phenotypes, there was an exposure-response gradient, with the strongest PRS association for schizophrenia (risk ratio [RR] = 1.94; 95% CI, 1.86-2.01), followed by schizoaffective BD (RR = 1.37; 95% CI, 1.22-1.54), bipolar I disorder subtype (RR = 1.30; 95% CI, 1.24-1.36), and bipolar II disorder subtype (RR = 1.04; 95% CI, 0.97-1.11). Within BD cases, there was an effect gradient, indexed by the nature of psychosis. Prominent mood-incongruent psychotic features had the strongest association (RR = 1.46; 95% CI, 1.36-1.57), followed by mood-congruent psychosis (RR = 1.24; 95% CI, 1.17-1.33) and BD with no history of psychosis (RR = 1.09; 95% CI, 1.04-1.15). For the first time to date, a study shows a polygenic-risk gradient across schizophrenia and BD, indexed by the occurrence and level of mood-incongruent psychotic symptoms.
Highlights
MethodsSample Ascertainment Bipolar Disorder Sample In total, data from 4436 cases of Bipolar disorder (BD) with deep phenotypic information, European ancestry, and domicile in the United Kingdom were collected between January 1, 2000, and December 31, 2013, via the UK Bipolar Disorder Research Network using recruitment methods reported previously.[15,41,42] The sample contained 1399 cases not included in previous publications of the Bipolar Disorder Research Network.[15,40] All participants were assessed using a consistent protocol, which included the Schedules for Clinical Assessment in Neuropsychiatry (SCAN) interview[43] administered by trained research psychologists and psychiatrists, with very good to excellent interrater reliability for all domains of psychopathology.[44]
There was an exposure-response gradient, with the strongest polygenic risk scores (PRSs) association for schizophrenia, followed by schizoaffective Bipolar disorder (BD) (RR = 1.37; 95% CI, 1.22-1.54), bipolar I disorder subtype (RR = 1.30; 95% CI, 1.24-1.36), and bipolar II disorder subtype (RR = 1.04; 95% CI, 0.97-1.11)
Prominent mood-incongruent psychotic features had the strongest association (RR = 1.46; 95% CI, 1.36-1.57), followed by mood-congruent psychosis (RR = 1.24; 95% CI, 1.17-1.33) and BD with no history of psychosis (RR = 1.09; 95% CI, 1.04-1.15)
Summary
Sample Ascertainment Bipolar Disorder Sample In total, data from 4436 cases of BD with deep phenotypic information, European ancestry, and domicile in the United Kingdom were collected between January 1, 2000, and December 31, 2013, via the UK Bipolar Disorder Research Network using recruitment methods reported previously.[15,41,42] The sample contained 1399 cases not included in previous publications of the Bipolar Disorder Research Network.[15,40] All participants were assessed using a consistent protocol, which included the Schedules for Clinical Assessment in Neuropsychiatry (SCAN) interview[43] administered by trained research psychologists and psychiatrists, with very good to excellent interrater reliability for all domains of psychopathology.[44]. Local research and development approval was obtained in all participating National Health Service Trusts and Health Boards. Data analysis was conducted from March 1, 2016, to February 28, 2017
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