Boo Johansson1, Birgitta Andersson1, David Karlsson1,2, & Gerald E. McClearn3
In a population-based study, like OCTO Twin, we face the entire range of memory and cognitive functioning among the oldest old; from those with preserved abilities to individuals with severe dementia. In addition, the longitudinal design identifies new cases with dementia. This presents problems for standardized psychometric methods in scoring performances (such as zero-scorers') that require considerations in data analysis. So far, we have employed a conservative approach in which OCTO twins suspected of dementia have been excluded in the analyses (e.g., McClearn et.al., 1997). Dementia also present problems for interpretations of heritabilities within the cognitive domain in late life. In OCTO Twin a diagnostic workup was conducted in those suspected for dementia. This routine includes a neuropsychological workup, a review of medical records, and a diagnosis conference. Diagnoses are determined using current standards and cases are followed to autopsy. The outcomes from the diagnostic work-up in the first two waves of the five measurement occasion OCTO Twin study are presented in the current study. In the first wave, including only complete pairs, 89 twins were identified as suspects of dementia. The criteria for a dementia diagnosis (DSM-III-R) were met for eighty-one. For main type of dementia, 53% met criteria for Alzheimer's (DAT) and 30% for dementia of vascular type (VaD). The percentages for incident cases at the 2-year follow-up were nearly identical. At both occasions, concordant pairs were typically found among MZ twins with a DAT diagnosis. The concordance rate for MZ twins with DAT however increased to the follow-up, while it remained in the DZ twins. These preliminary findings demonstrate the need for a longitudinal design in studying genetic influences on dementia in late life.
Address: Box 1038, SE-551 55 Jonkoping, Sweden, Phone: + 46 - 36 -32 49 00, Fax: +46 - 36 -32 49 16, Boo.Johansson@hhj.hj.se, ACKNOWLEDGEMENT:, The OCTO Twin Study is supported by NIA (AG 08861).
1Institute of gerontology, University College of Health Sciences, Jonkoping, Sweden 2Department of Geriatric Medicine, Värnamo hospital, County of Jönköping, Sweden 3Center for Developmental and Health Genetics, Pennsylvania State University, USA