Using biological indices to classify schizophrenia and other psychotic patients

Although classification of mental disorders using more than clinical descri ption would be desirable, there is scant evidence that available laboratory tests (i.e, biological indices) would provide more valid classifications t han current diagnostic systems (e,g. DSM-IV). We used cluster analysis of f our biological variables to classify 163 psychotic patients and 83 nonpsych iatric comparison subjects, Analyses revealed a three-cluster solution with the first cluster reflecting electrodermal deviance, the second cluster re presenting nondeviant biological function, and the third cluster reflecting increased nailfold plexus visibility and ocular motor dysfunction. To asse ss the construct validity of proband clusters we examined ocular motor perf ormance in 156 first-degree relatives as a function of proband cluster memb ership. First-degree relatives of third cluster probands exhibited worse oc ular motor performance than relatives of other cluster probands. Additional ly, better classification sensitivity and specificity were obtained for the relatives when they were grouped by proband cluster than by proband DSM-IV diagnosis. When a single proband characteristic (i.e. eyetracking performa nce) was used to group relatives, classification sensitivity and specificit y failed to significantly increase over grouping by proband DSM-TV diagnosi s. Multivariate biologically defined clusters may offer an advantage over D SM-TV classification when examining nosology and etiology of psychotic diso rders. (C) 2001 Elsevier Science B,V, All rights reserved.