Validity of the ICD-9 schizophrenia classification. A blind family history study.

Within the framework of the multifactorial-polygenic model of inheritance, multiple threshold strategy was applied to a large set of pedigree data to examine the clinico-genetical position of some subtypes within the ICD-9 classification of schizophrenic psychoses. It appeared highly probable that the ICD-9 subtypes examined, based mainly on the classical Kraepelin-Bleulerian classification (simplex, hebephrenic, catatonic, paranoid, schizo-affective) are not homogeneous from the clinico-genetical point of view and genetical factors cannot be held primarily responsible for the clinical differences between the subtypes.