Background:
Two distinct schizophrenia subtypes have recently been identified by the Western Australian Family Study of Schizophrenia by grade of membership (GoM) analysis of the phenotype (Hallmayer et al. 2005; Jablensky 2006): one characterized by pervasive cognitive deficit (CD) and low scores on personality trait measures and one featuring significant personality deviations but with relatively intact cognitive performance [cognitively spared (CS)]. Whole-genome scan of 93 families discovered significant linkage to 6p25-22 for the CD subtype, while the linkage for CS subtype was definitively excluded for that region. The aim of this study was to investigate by another method whether differences between these subtypes are qualitative or quantitative.
Methods:
Several taxometric procedures, originally proposed by P. Meehl (1994, 1996, 1998), were used to analyze taxonicity of schizophrenia subtypes: mean-above-mean-below-a-cut, maximum-eigenvalue and latent mode analyses in a sample of 138 individuals with schizophrenia and schizophrenia spectrum disorders.
Results:
Three independent taxometric procedures showed consistently a latent taxonomic structure in our sample of patients with schizophrenia. Estimated mean base rates for CD taxon ranged from 0.37 to 0.43, suggesting that about 40% of patients with schizophrenia belong to this taxon.
Conclusions:
CD schizophrenia subtype is discrete, that is, taxonic. Taxometric analyses have further corroborated the existence of an etiologically discrete schizophrenia subtype.
