Objective: A common means of subtyping schizophrenia is to use family history. Familial schizophrenia is defined by a family history of psychotic disorders, and sporadic schizophrenia is defined by the absence of such a history. Some writers have proposed that familial cases are mostly genetic, while the causes of sporadic schizophrenia are primarily environmental. The object of this report is to consider the theoretical and empirical support for the validity of this classification.
Method: A review of studies examining the familial-sporadic distinction in schizophrenia was based on papers located through a MEDLINE search and published bibliographies. Because of the great variation in the methodological rigor of the studies, the authors rated them on a scale assessing 10 methodological features. Studies achieving at least 50% of the maximum possible score were selected for review.
Results: Only 29 of 69 studies located met the selection criteria, and even among the studies selected, important methodological shortcomings were noted. Despite an impressive number of comparisons between groups of subjects with familial and sporadic schizophrenia, few differences were found. In addition, few differences were replicated and supported by studies using designs other than the familial-sporadic distinction.
Conclusions: The scarcity of studies with adequate methodology precludes any definitive judgment about the validity of the familial-sporadic distinction in schizophrenia. The delineation of predominantly genetic and predominantly environmental subtypes of schizophrenia will likely require large sample sizes, valid methods for the diagnosis of relatives, and stringent definitions of familiarity and sporadicity. Moreover, research strategies other than the familial-sporadic distinction may be better suited to identify such subtypes.