Amyloid-Independent Elevation of Plasma phosphorylated tau-217 Tracks Neurodegenerative Risk in Tuberous Sclerosis Complex: Implications for mTOR-Targeted Intervention
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Background
Tuberous sclerosis complex (TSC) is a rare autosomal dominant neurodevelopmental disorder caused by loss-of-function mutations in TSC1 or TSC2 , resulting in chronic hyperactivation of the mechanistic target of rapamycin (mTOR) pathway. TSC patients experience a wide spectrum of cognitive, behavioral, and psychiatric features collectively termed Tuberous Sclerosis Complex Associated Neuropsychiatric Disorders (TAND). Moreover, these patients develop a clinical trajectory in adulthood with clinical and neuropathological features overlapping those of Alzheimer’s disease (AD). Prior neuropathological studies have shown accumulation of AD-type mixed 3R/4R tau isoforms in adults with TSC that is amyloid-independent.
Methods
To further explore the biological convergence of TSC and AD, this study compared plasma levels of phosphorylated tau-217 (ptau-217), a sensitive and specific marker of early AD pathology, in 63 TSC, 25 AD, and 116 cognitively unimpaired (CU) patients.
Results
Findings revealed elevated levels of plasma ptau-217 in individuals with TSC at younger ages with a parallel age-related trajectory between TSC, AD, and CU cohorts. Multivariable linear regression showed that the log 2 ptau-217 concentrations were significantly lower in the CU cohort relative to TSC (β = −0.21, SE = 0.05, p < 0.0001) but were not significantly different between the TSC and AD cohorts (β = 0.17, SE = 0.09, p < 0.071). The comparison of slopes analysis (ANCOVA) supported that the slopes for the regression of log 2 ptau-217 versus age are not significantly different for the TSC and CU cohorts (TSC slope = 0.030, SE = 0.008; CU slope = 0.019, SE = 0.006; p = 0.26), nor for the TSC and AD cohorts (TSC slope = 0.030, SE = 0.01; AD slope = 0.06, SE = 0.03; p = 0.099).
Conclusions
These results suggest a novel link between TSC and AD that substantiates shared downstream neurodegenerative pathways. Furthermore, these results support the potential utility of ptau-217 as a minimally invasive biomarker for TAND severity, neurodegenerative risk, and AD-like prognosis in TSC and as a tool to guide new mTOR-targeted therapeutic strategies.
