Lehmann S, Schraen-Maschke S, Vidal JS, Delaby C, Buee L, Blanc F, Paquet C, Allinquant B, Bombois S, Gabelle A, Hanon O, BALTAZAR study group. Clinical value of plasma ALZpath pTau217 immunoassay for assessing mild cognitive impairment. J Neurol Neurosurg Psychiatry. 2024 Oct 16;95(11):1046-1053. PubMed.
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The blood biomarker p-tau217 is currently being studied for improving the mild cognitive impairment (MCI) differential AD diagnosis. This recent study offers new insights into its benefits and limitations. Below is a brief summary of the major findings from this multicenter, prospective study of the BALTAZAR cohort:
▶ Plasma p-tau217's Prediction of Amyloid Status in MCI Population:
The p-tau217 biomarker accurately predicts CSF amyloid status with 86.60 percent specificity and 86.21 percent sensitivity at a cutoff of 0.44 pg/mL. This underlines its effectiveness in identifying amyloid-positive patients. These results align with data previously described (Ashton et al., 2024).
▶ CSF Aβ42/Aβ40 Ratio’s Prediction of MCI to Alzheimer's Dementia Conversion:
CSF Aβ42/Aβ40 ratio predicts MCI patients who progressed to Alzheimer's dementia symptoms with 78.3 percent sensitivity and 56.9 percent specificity. The associated false positive rate was 58.0 percent in this study. These results are in line with previously described data, which concluded that the lack of specificity raised questions about clinical utility (Ritchie et al., 2014).
▶ Plasma pTau217's Prediction of MCI to Alzheimer's Dementia Conversion:
p-Tau217 predicts conversion to AD dementia symptoms within three years with 86.1 percent sensitivity and 60.1 percent specificity (these performances were calculated based on the data presented in the article). The associated false positive rate was 53.7 percent in this study. These results are very similar with CSF Aβ42/Aβ40 ratio and raise questions about clinical utility of p-tau217 to predict AD symptom conversion in the MCI population.
In conclusion, this article described that p-tau217 is a biomarker of choice as a screening blood test to identify MCI patients with abnormally high amyloid loads. Integrating it in the rollout of Leqembi could decrease the need for numerous amyloid PET scans and CSF assays. Nevertheless, while both plasma p-tau217 and the CSF Aβ42/Aβ40 biomarkers could be considered as risk factors for AD, their positivity doesn’t establish a diagnosis of AD or other cognitive disorder. (See the FDA’s evaluation of automatic class II designation for Lumipulse G 13-Amyloid Ratio (1-42/1-40), decision summary.) Therefore, it is essential to develop new biomarkers that can be used alongside p-tau217 to enhance diagnostic accuracy and patient management by predicting symptoms of AD dementia.
References:
Ashton NJ, Brum WS, Di Molfetta G, Benedet AL, Arslan B, Jonaitis E, Langhough RE, Cody K, Wilson R, Carlsson CM, Vanmechelen E, Montoliu-Gaya L, Lantero-Rodriguez J, Rahmouni N, Tissot C, Stevenson J, Servaes S, Therriault J, Pascoal T, Lleó A, Alcolea D, Fortea J, Rosa-Neto P, Johnson S, Jeromin A, Blennow K, Zetterberg H. Diagnostic Accuracy of a Plasma Phosphorylated Tau 217 Immunoassay for Alzheimer Disease Pathology. JAMA Neurol. 2024 Mar 1;81(3):255-263. PubMed.
Ritchie C, Smailagic N, Noel-Storr AH, Takwoingi Y, Flicker L, Mason SE, McShane R. Plasma and cerebrospinal fluid amyloid beta for the diagnosis of Alzheimer's disease dementia and other dementias in people with mild cognitive impairment (MCI). Cochrane Database Syst Rev. 2014 Jun 10;6:CD008782. PubMed.
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