FLAIR MRI biomarkers of the Normal‐Appearing Brain Matter (NABM) are related to APOE‐4 status and CSF markers Aβ42 and Tau

Abstract

AbstractBackgroundReduced amyloid‐beta‐42 (Aβ42) and elevated total tau (t‐tau) protein concentrations in the CSF are characteristic of Alzheimer’s disease (AD) pathology [1]. Aβ42 contributes to extracellular plaque formation between neurons [2]. The total level of tau, a microtubule‐stabilizer in neuron axons [3], is associated with neuronal death [1]. Additionally, presence of ApoE4 (ε4) alleles is an established identifier for increased risk of AD [4]. Non‐invasive imaging‐based correlates of the CSF markers are lacking. This study examines correlations of novel FLAIR texture, intensity, and volume biomarkers, along with white matter lesion (WML) burden, with Aβ42, t‐tau, and ε4 status.MethodFLAIR volumes (n = 4044) from the ADNI database were used for analysis with CSF biomarkers. A subset (n = 921) was used for ε4 analysis based on available data. Normal‐appearing brain matter (NABM) was obtained by removing CSF and WML. Macrostructural damage (MAD), microstructural damage (MID), and integrity (MII) texture biomarkers [5] were extracted from each NABM volume (Fig. 1), along with median intensity, NABM/ICV ratio, and normalized WML volume [5]. Relationships between FLAIR biomarkers and AD markers were described using parametric statistical analyses. Statistical significance was set at p<0.05.ResultAll FLAIR biomarkers were statistically significantly correlated with CSF Aβ42 levels. All features except MID and WML burden were significantly correlated with CSF t‐tau levels (Table 1). MAD, MID, and WML burden showed negative correlations with Aβ42, while MAD showed a positive correlation with t‐tau. Opposite trends were seen with MII, intensity, and NABM/ICV (Fig. 2). Significant differences between groups without and with one ε4 allele were found in all FLAIR biomarkers except WML burden. Significant differences in MAD, MII and NABM/ICV were found between groups with one and two ε4 alleles (Table 2).ConclusionFLAIR biomarkers were inversely associated with CSF Aβ42 concentrations, suggesting they may be surrogate markers of Aβ plaque formation. They were associated with CSF t‐tau concentrations, suggesting they could also be indicators of GM degeneration and neuronal death. They could also be indicators for patients at increased risk of AD, as they demonstrated significant differences with the presence of ε4. Further longitudinal studies are required to establish the exact mechanism of neurodegeneration.