Multimodal Biomarkers for Diagnosis and Prognosis in CAA

Overview

By combination of plasma (Aβ40, Aβ42, total tau, and phosphorylated tau, etc.), genetic (ApoE ε2 or ε4 allele), MRI (cerebral perfusion, microbleeds, cortical superficial siderosis, enlarged perivascular space, etc.) and PET imaging (amyloid and tau) biomarkers, the study aims to 1. Enhance the diagnostic potentials of the radiological biomarkers by combining MRI and amyloid PET in CAA patients. 2. Investigate the biological pathogenesis in CAA patients using the less invasive plasma biomarkers and to correlate with structural and function imaging, including MRI, amyloid and tau imaging. 3. Study the characteristics of long-term progression of amyloid deposition in CAA patients using the radiological, biochemical and genetic biomarkers. 4. Study the prognosis predicting markers.

Intracranial hemorrhage (ICH) consists of about a quarter of stroke subtype. For elderly, cerebral amyloid angiopathy (CAA) is a common etiology of ICH. In National Taiwan University Hospital, we have established a CAA team including neurologists, radiologists and nuclear medicine physicians since 2014. We hope to go deep into the diagnosis and pathophysiology of CAA. To the best of our knowledge, there is no other CAA team in Taiwan. In patients with CAA, abnormal beta amyloid protein diffusely deposits at cerebral vasculatures, which disrupts the normal vessel structure and increases the risk of bleeding. The standard diagnosis for CAA requires pathological evidences of amyloid deposition at cerebral arteries. Clinically, a diagnosis of CAA-related ICH is usually only made in an elderly developing cortical or subcortical lobar ICH without undergoing biopsy. Brain images using the SWI sequence of MRI study may show lobar microbleeds in patients with CAA. However, there is still no direct and precise non-invasive diagnostic tool for CAA until now. Amyloid PET, using 11C-PiB to image amyloid burden, has been used for detecting the cerebral amyloid protein deposition in patients with Alzheimer's dementia (AD) for years. Recently, amyloid PET has also been applied in the diagnosis of CAA. CAA patients showed diffusely increased global PiB retention as compared to control subjects and the distribution of PiB retention is also different from that seen in patients with AD in general. Nevertheless, the applications of amyloid PET in CAA diagnosis are still not well established and many important issues still need to be extensively addressed. Furthermore, tau PET has emerged as a potential molecular imaging marker for SVD. Tau PET provides a noninvasive method for measuring brain tau load. The correlation of tau PET findings in patients with CAA has not been investigated before. In addition, ApoE gene has been reported to be risk factor for sporadic CAA as well as AD. Biochemical biomarkers, such as the levels of Aβ40 and Aβ42, also help us understand the pathophysiology of CAA. Recently, immunomagnetic reduction (IMR) assay, using bio-functionalized magnetic nanoparticles, has been proved to be a sensitive and accurate tool for the detection of these biological molecules. By combination of plasma (Aβ40, Aβ42, total tau, and phosphorylated tau, etc.), genetic (ApoE ε2 or ε4 allele), MRI (cerebral perfusion, microbleeds, cortical superficial siderosis, enlarged perivascular space, etc.) and PET imaging (amyloid and tau) biomarkers, the study aims to 1. Enhance the diagnostic potentials of the radiological biomarkers by combining MRI and amyloid PET in CAA patients. 2. Investigate the biological pathogenesis in CAA patients using the less invasive plasma biomarkers and to correlate with structural and function imaging, including MRI, amyloid and tau imaging. 3. Study the characteristics of long-term progression of amyloid deposition in CAA patients using the radiological, biochemical and genetic biomarkers. 4. Study the prognosis predicting markers.