DIFFERENTIAL VALIDITY OF INFORMANT-BASED DIAGNOSES OF DEMENTIA AND DEPRESSION IN INDEX SUBJECTS AND IN THEIR FIRST-DEGREE RELATIVES

There is no study indicating that informant-derived information on dem entia and depression (i.e. family history information) is equivalently valid for first-degree relatives and for index subjects (i.e. patient s and control subjects). However, this unproven assumption is the basi s for the frequent, possibly inappropriate. use of instruments validat ed for patients and control subjects in family studies which focus on frequencies of psychiatric disorders in first-degree relatives. Conseq uently, there is a need to compare the validity of family history info rmation for both disorders in index subjects and their first-degree re latives. Validity was assessed by comparison of family history informa tion for dementia and depression with interview-derived diagnoses in 7 5 index subjects and 195 age-matched first-degree relatives. The valid ity of informant-derived information varied for different disorders, i .e. dementia and depression, and different samples, i.e. index subject s and first-degree relatives. In agreement with the study hypothesis, the sensitivity of surrogate information on dementia was significantly reduced in first-degree relatives in comparison with index subjects. In contrast, the sensitivity to detect depression was equivalent in su bjects and in relatives. The results indicate the necessity to assess the validity of the psychiatric diagnoses of interest in the sample of interest, e.g. dementia or depression in first-degree relatives of pa tients and of control subjects. Observations in selected samples, i.e. subjects treated, hospitalised and/or autopsied, cannot be generalise d to first-degree relatives in family studies.