Familial predisposition for psychiatric disorder: comparison of subjects treated for cannabis-induced psychosis and schizophrenia.
BACKGROUND
Cannabis-induced psychosis is considered a distinct clinical entity in the existing psychiatric diagnostic systems. However, the validity of the diagnosis is uncertain.


OBJECTIVE
To establish rate ratios of developing cannabis-induced psychosis associated with predisposition to psychosis and other psychiatric disorders in a first-degree relative and to compare them with the corresponding rate ratios for developing schizophrenia spectrum disorders.


METHODS
A population-based cohort was retrieved from the Danish Psychiatric Central Register and linked with the Danish Civil Registration System. History of treatment of psychiatric disorder in family members was used as an indicator of predisposition to psychiatric disorder. Rate ratios of cannabis-induced psychosis and schizophrenia associated with predisposition to psychiatric disorders were compared using competing risk analyses.


METHODS
Nationwide population-based sample of all individuals born in Denmark between January 1,1955, and July 1, 1990 (N = 2,276,309). Patients During the 21.9 million person-years of follow-up between 1994 and 2005, 609 individuals received treatment of a cannabis-induced psychosis and 6476 received treatment of a schizophrenia spectrum disorder.


RESULTS
In general, the rate ratios of developing cannabis-induced psychosis and schizophrenia spectrum disorder associated with predisposition to schizophrenia spectrum disorder, other psychoses, and other psychiatric disorders in first-degree relatives were of similar magnitude. However, children with a mother with schizophrenia were at a 5-fold increased risk of developing schizophrenia and a 2.5-fold increased risk of developing cannabis-induced psychosis. The risk of a schizophrenia spectrum disorder following a cannabis-induced psychosis and the timing of onset were unrelated to familial predisposition.


CONCLUSIONS
Predisposition to both psychiatric disorders in general and psychotic disorders specifically contributes equally to the risk of later treatment because of schizophrenia and cannabis-induced psychoses. Cannabis-induced psychosis could be an early sign of schizophrenia rather than a distinct clinical entity.
Arendt
Mikkel
M
Centre for Psychiatric Research, Aarhus University Hospital, Skovagervej 2, Risskov, 8240 Risskov, Denmark. mca@psykiatri.aaa.dk
Mortensen
Preben B
PB
Rosenberg
Raben
R
Pedersen
Carsten B
CB
Waltoft
Berit L
BL
D000293:Adolescent; D000328:Adult; D002186:Cannabinoids / Q000633:toxicity*; D015331:Cohort Studies; D015897:Comorbidity; D003718:Denmark; D003937:Diagnosis, Differential; D005260:Female; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006306:Health Surveys; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000534:rehabilitation*; D008875:Middle Aged; D016017:Odds Ratio; D011605:Psychoses, Substance-Induced / Q000175:diagnosis / Q000235:genetics* / Q000534:rehabilitation; D011618:Psychotic Disorders / Q000175:diagnosis / Q000235:genetics* / Q000534:rehabilitation; D012559:Schizophrenia / Q000139:chemically induced* / Q000175:diagnosis / Q000235:genetics* / Q000534:rehabilitation
D002186:Cannabinoids