Thinking within the spectrum: schizophrenic thought disorder in six Danish pedigrees Mette S. Væver a, * , Deborah M. Licht b , Lise Møller c , Dorthe Perlt c ,A ˚ ge Jørgensen d , Peter Handest d , Josef Parnas b,d a Department of Psychology, University of Copenhagen, Njalsgade 88, Copenhagen 2300, Denmark b The Danish National Research Foundation, Center for Subjectivity Research, Copenhagen, Denmark c Institute for Preventive Medicine, Copenhagen, Denmark d Department of Psychiatry, University of Copenhagen, Hvidovre Hospital, Hvidovre, Denmark Received 3 February 2004; received in revised form 31 March 2004; accepted 1 April 2004 Available online 7 June 2004 Abstract Formal thought disorder (FTD), a major symptom of schizophrenia, is known to aggregate in families. Our aim was to examine the specificity of FTD in the schizophrenia spectrum disorders and the hypothesized linear aggregation of FTD within pedigrees. Six individuals with a diagnosis of schizophrenia were identified in the Copenhagen High-Risk study and each pedigree was centered on one of the six original schizophrenic probands’ nuclear families. The 329 pedigree members in the study were considered at risk for schizophrenia spectrum disorders because most were genetically related to the originating schizophrenic probands. The participants were administered the Copenhagen Interview of Functional Illness to determine diagnoses and the Thought Disorder Index (TDI) was used to assess FTD. Individuals with a schizophrenia diagnosis had higher global levels of FTD, exhibited more severe types of FTD, and had a qualitatively different type of FTD than did participants with other diagnoses or no mental illness. Individuals with Cluster A diagnoses exhibited more FTD and FTD similar in quality to participants with schizophrenia. These results support the construct of a spectrum of schizophrenia conditions. There was a generally high level of FTD in the pedigrees, in part due to assortative mating in this sample. However, there was no apparent pattern of linear aggregation of FTD within the families. D 2004 Elsevier B.V. All rights reserved. Keywords: Formal thought disorder; TDI; Schizophrenia spectrum; Pedigree 1. Introduction Both Kraepelin (1971) and Bleuler (1950) argued that disturbances in thinking are primary features of the syndrome we now know as schizophrenia. Al- though their views generated much research, almost a century later we are still trying to define, measure, and probe the mechanism of formal thought disorder (FTD), which refers to disturbances in the way or mode of thinking, as distinguished from its content. Bleuler (1950) suggested the existence of a spec- trum that includes latent schizophrenia,a term 0920-9964/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.schres.2004.04.001 * Corresponding author. Tel.: +45-3532-8696; fax: +45-3532- 8745. E-mail address: Mette.Vaever@psy.ku.dk (M.S. Væver). www.elsevier.com/locate/schres Schizophrenia Research 72 (2005) 137 – 149