Diagnostic Capability Of Cerebrospinal Fluid A/T/N Framework In Alzheimer’s Disease And Study On An APP Variant

Background:Alzheimer’s disease(AD)is the most common type of dementia in the world,most of which are sporadic.A minority of the patients with a positive AD family history are called familial AD(FAD).Two hallmarks of AD pathologies are recognized as toxic senile plaques formed by extracellular β-amyloid deposition and neurofibrillary tangles formed with intracellular accumulation of hyperphosphorylated tau in the brain Currently there is no specific treatment to cure the disease and present clinical drug trials only show limited effect in patients at early stage,hence an early diagnosis is critical.Studies found that alterations of some biological markers in AD patients appeared long before the clinical presentations,indicating AD-related pathological changes.The most well-known biomarkers are cerebrospinal fluid(CSF)biomarkers,including decreased CSF β amyloid protein with 42 amino acids(△β42),increased CSF total tau(t-tau)and phosphorylated tau(p-tau).Although these biomarkers have been promoted in clinical practice,efficient quantitative indicators on evaluation of their impact in clinical diagnosis of AD are limited and so far,no such investigations have been performed in the Chinese Han populationSection I:Diagnostic capability of cerebrospinal fluid A/T/N framework in Alzheimer’s diseaseAim:To explore the clinical capability of CSF biomarkers in the diagnosis of AD as well as differential diagnosis of other dementiasMethods:A total of 137 inpatients with an initial diagnosis of dementia received CSF tests of Aβ42,t-tau and p-tau.Their CSF biomarker results were then categorized and interpreted by A/T/(N)framework.Neurologists provided a pre-and a post-CSF biomarker diagnosis with a corresponding diagnostic confidence(DC).We summarized all revisions of diagnosis and made comparisons between the impact on diagnostic confidence(DC)due to different biomarker category changesResults:All initial diagnosis included 79 patients with AD and 58 patients with non-AD and the results of CSF biomarkers led to a diagnostic change of 28%in the cohort which had a diagnosis of 74 AD and 63 non-AD.Approximately 81.5%(n=53)of the diagnosis in 65 patients whose CSF biomarker showed an underlying AD pathology were finally revised as AD,with an increase of 17.5%in DC.Thirty-seven CSF biomarker results indicating non-AD pathologic changes contributed to an exclusion of AD in 56.8%(n=31)of the patients,whereas 35 patients with normal CSF biomarkers maintained an original diagnosis of non-AD in 68.6%(n=24)of the group.The average DC in the final non-AD group increased by 9.8%and 7.6%due to the latter two categories,respectivelyConclusion:This is the first study performed in the Chinese Han population that discussed the clinical capability of CSF biomarkers A/T/(N)framework on the diagnosis and differential diagnosis of AD by introducing the quantitative indicator of DC.We confirmed the contribution of CSF biomarkers in verifying the diagnosis of AD as well as the exclusionSection Ⅱ:Study on an APP variantAim:We described genetic variants found in a Chinese FAD pedigree and performed preliminary functional experiments on an APP variant by with unknown pathogenicityMethods:We performed whole-exome sequencing(WES)in the progenitor from a Chinese FAD pedigree and determined the pathogenicity of detected variants by ACMG guideline.Regarding an APP variant with unknown pathogenicity,we further performed in vitro cell experiments including cell transfection,western blot and enzyme-linked immunoassays(ELISA)of extracellular Aβ detection to identify its influence on APP protein function.Results:Three gene variants related to clinical phenotype were found in the proband(APP:p.R747C,APP:p.Q48R;NOTCH3:p.F324Y),the latter two of which were classified as non-pathogenic while APP:p.R747C was likely pathogenic.In vitro cell experiments determined that the R747C variant either affected the expression or localization of APP protein.The detection of extracellular Aβ and corresponding Aβ42/Aβ40 ratio showed no difference between the variant and the wild typeConclusion:Although evidence of clinical data,co-segregation and software prediction highly suggested the R747C variant be the pathologic mutation in the current FAD pedigree,the current in-vitro cell experiments indicated that the variant didn’t affect the APP protein function.We supposed there are other pathogenic mechanisms of the variant and further experimental investigations are required.