Schizotypal dimensions: continuity between schizophrenia and bipolar disorders.
BACKGROUND
Family studies have suggested that schizophrenia and bipolar disorders share some susceptibility factors. Schizotypal personality disorder (SPD) may be an intermediate phenotype common both to schizophrenia and bipolar disorders. We explored the familiality of schizotypal dimensions by comparing the magnitude of schizotypal dimensions between schizophrenic and bipolar relatives. We also looked for intra-familial resemblance for these dimensions, and for an increased familial risk of schizophrenia and/or bipolar disorders associated with a particular schizotypal dimension.


METHODS
We used the Schizotypal Personality Questionnaire (SPQ) to study the three schizotypal dimensions (disorganization, negative and positive) in a sample of unaffected first-degree relatives of schizophrenic (N=85), psychotic bipolar (N=63) and bipolar (N=32) probands. Differences between groups were tested using a two-tailed t-test or ANOVA for continuous variables and a chi-squared test for discrete variables. We used the intraclass correlation method to study the intra-familial correlation. Linear mixed models were used to measure the familial risk.


RESULTS
The disorganization dimension appears to be common to relatives of both schizophrenia and psychotic bipolar disorders, but not in the relatives of non-psychotic bipolar probands. This dimension also increases the familial risk of these two disorders. The negative dimension shows intra-familial resemblance (R=0.29), we failed to observe the expected familiality for the disorganized dimension.


CONCLUSIONS
The shared nature of the disorganization dimension shown by a similar familial risk for schizophrenia and psychotic bipolar disorders suggests that same genetic background may underlie psychotic disorders. Although, negative dimension is familial, it is not associated for an increased familial risk for both disorders.
Schürhoff
Franck
F
Département hospitalo-universitaire de Psychiatrie, Hôpital Albert Chenevier et Henri Mondor (AP-HP), 40 rue Mesly, 94000 Créteil, France. schurhof@ext.jussieu.fr
Laguerre
Audrey
A
Szöke
Andreï
A
Méary
Alexandre
A
Leboyer
Marion
M
D001714:Bipolar Disorder / Q000175:diagnosis* / Q000523:psychology* / Q000534:rehabilitation; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005190:Family / Q000523:psychology; D005260:Female; D006760:Hospitalization; D006778:Hospitals, Psychiatric; D006801:Humans; D008297:Male; D008875:Middle Aged; D012559:Schizophrenia / Q000175:diagnosis* / Q000534:rehabilitation; D012565:Schizophrenic Psychology; D012569:Schizotypal Personality Disorder / Q000175:diagnosis* / Q000523:psychology* / Q000534:rehabilitation; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires