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 dif ferent pathophysiologies. This article reviews the evidence for the validit y 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 acc ording to seven validating criteria. Several differences were found between subtypes, particularly for the deficit/nondeficit subtypes. However, for m ost of these differences, replications have yet to be undertaken. Important indicators of etiology from the environmental risk factors and genetic dom ains 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 etiologicall y distinct SZ subgroups. We propose ten methodological and conceptual recom mendations for future studies aimed at the identification of valid SZ subty pes according to outcome or severity.