Concordance for cognitive impairment: a study of 50 community-dwelling elderly female-female twin pairs.
The present study sought to determine concordance of cognitive impairment among elderly female twins. Cognitive testing was performed by telephone interview in a sample of 100 female-female twins older than 65 years. The participants were 32 monozygotic (MZ) and 18 dizygotic (DZ) female twin pairs, all between the ages of 65 and 86 years; their mean age was 70.2 +/- 4.6 years. All were recruited from the Institute of Psychiatry Volunteer Twin Register (IPVTR). We used the Telephone Interview for Cognitive Status (TICS) and analyzed the modified total score. Correlation's of age and zygosity were computed in relation to score on cognitive interview, and differences between MZ twin pairs (n = 32) and DZ pairs (n = 18) were analyzed using the general linear model procedure. Five subjects of the 64 MZ females (7.8%) and one DZ female (2.4%) were found to be cognitively impaired. In no case was the second twin affected. No differences in cognitive score were found between MZ and DZ twin pairs. In both groups a highly significant correlation was found between age and lower score: R(2) = -0.32, P =.009. We conclude that aging-related impairment in cognitive testing did not differ between MZ and DZ elderly female twins. Although the overall sample size was relatively small and error variance may have been introduced by imprecise measures of zygosity, the present findings are suggestive of gender differences in cognitive performance that need further evaluation.