Phosphorylated tau 217 in young adults with Down syndrome and Down syndrome regression disorder

Abstract Background Down syndrome regression disorder (DSRD) causes a rapid loss of cognitive, behavioral, and daily living skills, usually in adolescents and young adults with Down syndrome. Because people with Down syndrome have a high lifetime risk of Alzheimer’s disease, we examined whether DSRD is associated with an Alzheimer-related pattern of tau pathology. Methods In this prospective, single-center study, we measured plasma phosphorylated tau-217 (p-tau217), a blood marker of Alzheimer pathology, in 132 participants: 48 with DSRD, 39 with Down syndrome without regression (DSwR), and 45 neurodevelopmental controls. We compared p-tau217 concentrations across groups and examined relationships with demographic factors, medical conditions, treatment status, and diagnostic test abnormalities. Results Median p-tau217 concentrations were similar in the DSRD (0.082 pg/mL), DSwR (0.084 pg/mL), and neurodevelopmental control (0.080 pg/mL) groups (overall comparison, p = 0.57). Pairwise comparisons and models accounting for demographic and clinical factors also showed no statistically significant group differences. Among participants with DSRD, p-tau217 was not associated with treatment status or abnormalities on brain-wave testing, neuroimaging, or cerebrospinal fluid analysis. No clinical or demographic factor remained associated with p-tau217 after accounting for the number of analyses performed. Conclusions These findings provide no evidence of a group-level Alzheimer-related p-tau217 elevation in young people with DSRD and support DSRD as a condition distinct from Alzheimer’s disease. However, a single blood measurement cannot exclude Alzheimer pathology in an individual. Longitudinal studies using several complementary biomarkers are needed.