Concordance rates for cognitive impairment among older African American twins

Background: There is significant attention to the growing elderly African American population and estimating who and how many within this population will be affected by cognitive impairment. Objective: The etiology of cognitive impairment has not been well studied in African Americans and the contribution of genetic and environmental influences to cognitive impairment is not clear. Methods: We calculated concordance rates and heritability for cognitive impairment in 95 same-sexed pairs of African American twins from the Carolina African American Twin Study on Aging (CAATSA). The sample had an average age of 59.6 years (SD = 8.6 years, range 50-88 years) and 60% were female. The Telephone Interview for Cognitive Status (TICS) was used to assess cognitive impairment with a lower cutoff based on our previous research with African Americans. Results: Thirteen of the monozygotic (MZ) twins (30.2%) and 9 of the dizygotic (DZ) twins (17.3%) were cognitively impaired. The concordance rate was 72% for MZ and 45% for DZ. We found the heritability for cognitive impairment to be 54%. Conclusions: The study findings indicate that cognitive impairment is highly heritable, suggesting that genetics may play a relatively large role in the development of cognitive impairment in African American twins.