Risk factors for the deficit syndrome of schizophrenia.

Previous studies have found two risk factors associated with the deficit syndrome of schizophrenia: an increase in summer births, compared to others with schizophrenia; and a higher risk of schizophrenia in relatives. In data from the Camberwell Register Psychosis Series, a population-based sample that approximated a treated-incidence sample, the deficit/nondeficit categorization was made using a previously validated proxy method. Associations were found between the deficit syndrome and both summer birth and a family history of schizophrenia. In contrast, nondeficit schizophrenia was associated with a family history of psychiatric problems other than schizophrenia. The deficit group also had poorer insight. An early age of onset was associated with disorganization, but not with the deficit or nondeficit group. The deficit/nondeficit differences could not be attributed to confounding by demographic features or the severity of hallucinations, delusions, or formal thought disorder.