Subtyping schizophrenia according to outcome or severity: a search for homogeneous subgroups

There is a growing consensus that current definitions of schizophrenia (SZ) include different disorders, or else different dimensions underlain by different pathophysiologies. This article reviews the evidence for the validity of three novel strategies to subtype SZ according to outcome or severity (deficit vs. nondeficit, Kraepelinian vs. non-Kraepelinian, congenital vs. adult-onset). Medline and bibliographies were used to locate articles. The methodology of the studies was reviewed, and their results were grouped according to seven validating criteria. Several differences were found between subtypes, particularly for the deficit/nondeficit subtypes. However, for most of these differences, replications have yet to be undertaken. Important indicators of etiology from the environmental risk factors and genetic domains have received very little attention. These three subtyping strategies represent promising attempts to address the etiologic heterogeneity of SZ. However, one cannot conclude whether these strategies identify etiologically distinct SZ subgroups. We propose ten methodological and conceptual recommendations for future studies aimed at the identification of valid SZ subtypes according to outcome or severity.