Serum transthyretin level and its relationship with cognitive function in community-dwelling older people: Cross sectional and longitudinal study

Background: Serum transthyretin (TTR) level has suggested association with mild cognitive impairment (MCI) and dementia. To clarify its usefulness as a biomarker of change in cognitive function in older individuals with normal cognitive function (NC) as a phenotype, we investigated the relationship between cognitive scores and TTR levels. We also investigated the involvement of TTR in the transition from NC to MCI.Methods: Cognitive function was evaluated using Addenbrooke's Cognitive Examination-Revised (ACE-R). A cross-sectional study was conducted in community-dwelling older people (n = 211) with NC, MCI, or dementia according to ACE-R scores. A 32-month longitudinal study was then conducted (n = 29).Results: Mean TTR levels did not differ between the NC, MCI and dementia groups. Linear regression analysis showed a significant relationship in people with NC between TTR and ACE-R (beta = -0.192; p < 0.001). Multiple regression analysis adjusted for stepwise procedure-selected covariates showed that TTR was significantly associated with ACE-R in people with NC (beta = -0.130; p = 0.014). Furthermore, multiple regression analysis showed significant association between TTR level and memory (beta = -0.584; p = 0.002) and with language (beta = -0.743; p = 0.031) in people with NC. In the longitudinal study, mean TTR level at baseline in women with MCI was significantly higher than that in women with NC (p = 0.044).Conclusions: Serum TTR level is suggested to be associated with cognitive scores in people with NC and to be an indicator of progression from NC to MCI.