First Degree Family History of Alzheimer’s Disease Influences Simple Visual Reaction Time Performance and is Modified by Health Factors
Alzheimer’s disease (AD), the leading cause of dementia, is a progressive neurodegenerative disease that first presents itself clinically as deficits in cognition, including learning and memory. Currently, more than 5 million Americans are afflicted, costing over 315 million dollars. To this day, despite numerous clinical trials, there are no disease-modifying treatments, leaving risk reduction as the only currently viable means to slow or stop AD from turning into a chronic public health emergency.
Developing novel risk reduction approaches requires finding and understanding the complex environmental and genetic interactions leading to AD. To that end, we developed MindCrowd (www.MindCrowd.org), a fun and easy-to-use web-based study. Consenting participants take one test of simple visual reaction time (svRT), one test of paired associates learning, and answer 23 demographic, health, and lifestyle questions. To date, over 70,989 individuals, spread across the globe, have participated, with ages ranging from 18-85.
After this data was filtered (e.g., removing outliers & participants with brain diseases), our final cohort consisted of 61,253 participants. Outliers were identified using a standard method widely used across disciplines. Specifically, trials or participants with svRT values 1.5 times the interquartile range greater or less than from the third or first quartile respectively were removed. Outlying trials were removed within each subject, and outlying participants were removed based on the median svRT values of participants of the same age. The median svRT (ms), recalculated after outlier removal, served as our “criterion” (dependent variable) in multiple regression analysis (general linear model). All of the 23 demographic, health, and lifestyle questions were entered into our multiple regression analysis. A subset of these questions served as our “predictors” (independent variables), and the rest were used as “control variables.”
We found that sex was associated with svRT. As previously reported, men had faster svRTs as compared to women. Further, there was an inverse association between Educational Attainment and svRT; such that, as participants’ Educational Attainment increased, their svRT became faster. Notably, an FH x Age interaction and a main effect of FH were found. These coefficients indicated that FH+ participants had slower svRT as they aged when compared to their FH- counterparts. Participants under the age of 37 drove these associations. Moreover, the effect of FH on svRT was modified by a history of diabetes. The slower svRTs associated with FH were exacerbated in participants who indicated having a history of diabetes. Lastly, a history of stroke was associated with slower svRTs. Participants over the age of 45 drove this association. Here we show that FH is associated with slower svRT beginning around the fourth decade of life. In addition, we found that diabetes modified the association of FH on svRT. Diabetes, in conjunction with FH, appears to have a synergistic effect, slowing svRT.
Our findings highlight the positive effects whereby properly treating disease states, such as diabetes, can have on FH-associated risk, opening the door to the development of more targeted risk reduction approaches to combat AD.