Cannabis and other variables affecting age at onset in a schizophrenia founder population

  • JL Roos Department of Psychiatry, University of Pretoria, Pretoria, South Africa
  • HW Pretorius Human Neurogenetics Laboratory, Rockefeller University, New York, USA
  • M Karayiorgou Department of Statistics, University of Pretoria, Pretoria, South Africa
  • H Boraine Department of Statistics, University of Pretoria, Pretoria, South Africa


Objective: An ongoing collaborative study between the Human Neurogenetic Laboratory of Rockefeller University, New York and the Department of Psychiatry at the University of Pretoria, has been taking place since 1997, to map genes for schizophrenia. Aspects of cannabis use/abuse will be reported.

Method: The Diagnostic Interview for Genetic Studies [DIGS] is used for all diagnosis. A narrative report is completed. From this database we determined: gender, diagnostic subtype, age of illness onset, early insults, early deviant behaviour, cannabis use/abuse and family history of schizophrenia.

Results: From 341 subjects we found: 61% [n=209] males and 39% [n=132] females. In males, 75% [n=156] had schizophrenia and 25% [n=53] schizoaffective disorder[SADJ]. In females 74% [n=97] had schizophrenia and 26% [n=35] SAD. 35% of subjects, [n=118], 44% [n=91] males and 20% [n=27] female's used/abused cannabis. The mean age at onset of illness for the males was 20.5 years. This is significantly earlier than that of males with no cannabis use/abuse group as well as for both these groups in females. The long-term course of illness was similar in both cannabis use/abuse and non-use/abuse groups. An analysis of variance was used to determine the contribution of different factors in determining the age of criteria onset. According to the results obtained, early deviant behaviour was the most important determining age of criteria onset. The group with the lowest mean age of criteria were male users of cannabis with severe early deviant behaviour [18,4 years].

Conclusion: Cannabis use/abuse is common amongst male schizophrenia subjects, and affects age at onset of illness. Early deviant behaviour in the first ten years of life in these subjects is more important in this regard, and may be seen as a possible endophenotypical marker.

Keywords: cannabis, psychosis, schizophrenia, founder population

South African Psychiatry Review Vol. 9(2) 2006: 99-103

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eISSN: 1994-8220