Jean Ikanga ^1,2* Kharine Jean ³ Priscilla Medina ⁴ Saranya S. Patel ^3* Megan Schwinne ⁵ Emmanuel Epenge ⁶ Guy Gikelekele ² Nathan Tshengele ² Immaculee Kavugho ⁷ Samuel Mampunza ² Lelo Mananga ⁶ Charlotte E. Teunissen ⁸ Anthony Stringer ¹ Julio C. Rojas ⁹ Brandon Chan ⁹ Argentina Lario Lago ⁹ Joel Kramer ⁹ Adam L. Boxer ⁹ Andreas Jeromin ¹⁰ Alden L. Gross ¹¹ Alvaro Alonso ¹²

• ¹ Department of Rehabilitation Medicine, Emory University, Atlanta, United States
• ² University of Kinshasa and Catholic University of Congo, School of Medicine, Kinshasa, Democratic Republic of Congo
• ³ Emory University, Atlanta, United States
• ⁴ Department of Psychology, Mercer University, Atlanta, Georgia, United States
• ⁵ Department of Biomedical Informatics, Emory University, Atlanta, Georgia, United States
• ⁶ Department of Neurology, University of Kinshasa, Kinshasa, Kinshasa, Democratic Republic of Congo
• ⁷ Memory Clinic of Kinshasa, Kinshasa, Democratic Republic of Congo
• ⁸ Department of Clinical Chemistry, Amsterdam Neuroscience, Amsterdam University Medical Center, Amsterdam, Netherlands
• ⁹ Memory and Aging Center, Medical Center, University of California, San Francisco, San Francisco, California, United States
• ¹⁰ ALZpath, Inc, San Francisco, United States
• ¹¹ Bloomberg School of Public Health, Department of Epidemiology, Johns Hopkins Medicine, Johns Hopkins University, Baltimore, Maryland, United States
• ¹² Rollins School of Public Health, Department of Epidemiology, Emory University, Atlanta, United States

Background: Western countries have provided reference values (RV) for Alzheimer's disease (AD) plasma biomarkers, but there are not available in Sub-Saharan African populations.Objective: We provide preliminary RV for AD and other plasma biomarkers including amyloid-β (Aβ42/40), phosphorylated tau-181 and 217 (p-tau181, p-tau217), neurofilament light (Nfl), glial fibrillary acidic protein (GFAP), interleukin 1b and 10 (IL-1b and IL-10) and tumor necrosis factor α (TNFα) in Congolese adults with and without dementia.Methods: 85 adults (40 healthy and 45 dementia) over 50 years old were included. Blood samples were provided for plasma AD biomarkers Aβ42/40 and p-tau181, p-tau217; Nfl and GFAP; IL-1b and IL-10 and TNFα analyzed using SIMOA. Linear and logistic regressions were conducted to evaluate differences in biomarkers by age and gender and neurological status, and for the prediction of dementia status by each individual biomarker. RV were those that optimized sensitivity and specificity based on Youden's index.In this sample of 85 adults, 45 (53%) had dementia, 38 (45%) were male, overall mean age was 73.2 (SD 7.6) years with 8.3 (5.4) years of education. There were no significant differences in age, gender, and education based on neurological status. Biomarker concentrations did not significantly differ by age except for p-tau181 and GFAP and did not differ by sex. Preliminary normal value cutoffs of various plasma in pg/ml were 0.061 for Aβ42/40, 4.50 for p-tau 181, 0.008 for p-tau 217, 36.5 for Nfl, 176 for GFAP, 1.16 for TNFa, 0.011 for IL-1b, and 0.38 for IL-10. All AUCs ranged between 0.64-0.74. P-tau 217 [0.72 (95% CI: 0.59, 0.84)] followed by GFAP [0.72 (95% CI: 0.61, 0.83)], and Nfl [0.73 (95% CI: 0.62, 0.84)] had the highest AUC compared to other plasma biomarkers.This study provides RV which could be of preliminary utility to facilitate the screening, clinical diagnostic adjudication, and classification, and prognosis of dementia in Congolese adults.