Tau protein is a scaffold protein in the microtubule associated protein family. Tau proteins are mainly enriched, in normal neurons, around neuronal axons, regulating, maintaining microtubule stability, and assisting in neuronal axon transport. It supports the neuronal cytoskeleton and microtubule stability by promoting tubular polymerization. It is encoded by the microtubule associated protein tau (MAPT) gene, an unfolded protein that undergoes PTM, which alters the structure and affects their function, interaction, and aggregation. PTMs such as phosphorylation, methylation and acetylation regulate the normal function of Tau. Post-translational modifications (PTMs) of Tau proteins have been found to be an important way to regulate their protein structure and function.

Aβ 40 is a protein fragment consisting of 40 amino acid residues. It is the product of enzymatic cleavage of amyloid precursor protein (APP) between valine 711 and isoleucine 712 by protein hydrolase. It contains the most abundant amyloid peptide in cerebrospinal fluid (CSF) and plasma (10- to 20-fold higher than that in Aβ42).

Aβ 42 can activate microglia and complement, release cytokines, free radicals, NO and toxins during agglutination, induce inflammation, affect microtubule stability, contribute to the abnormal phosphorylation of microtubule-associated protein Tau, and activate apoptotic signalling pathway, resulting in neuronal apoptosis and necrosis. It is the main form of neuronal loss in AD patients.

P-tau 181, the phosphorylation of Tau protein at threonine 181, is a highly specific pathological marker for AD, since it is normal in patients with other dementias (i.e., dementias other than AD). So P-tau181 can be used as a highly specific biomarker for AD. As an important blood biomarker for AD, P-tau181 is less invasive and more readily available than markers based on CSF, where it is expected to be used for early and accurate detection of AD in a large population.

P-tau 217 is the phosphorylation of Tau protein at threonine 217. Multiple studies have demonstrated that the burden of nerve tangles at the 217 site is highly correlated with disease severity compared to P-tau181. P-tau217 in blood samples can effectively differentiate AD from other neurodegenerative disorders, thus P-tau217 can be used as a highly specific biomarker for AD.

P-tau 231, the phosphorylation of Tau protein at threonine 231, is a promising new biomarker for AD pathology.

NF-L (neurofilament-light), as a component of nerve fibre skeleton protein, is one of the components of neurofilaments (NFs), and plays an important role in maintaining axonal morphology and nerve transmission. After nerve axonal injury, the assembly and transportation of NFs cannot be completed normally, resulting in axonal lesions, mainly manifested as reduced neuronal axon diameter and impaired nerve conduction. NFs are elevated in the cerebrospinal fluid of many neurological diseases, such as multiple sclerosis, amyotrophic lateral sclerosis, vascular dementia, traumatic brain injury, and Alzheimer's disease. So, NFs are the biomarkers of neural axonal injury. The detection of neurofilament protein light chain can be used to determine neurodegenerative behaviours in AD.

GFAP is the English abbreviation for glial fibrillary acidic protein and it is a marker of astrocyte activation. Glial fibrillary acidic protein. GFAP is an intermediate filament III protein that exists in monomeric form. Astrocyte proliferation is often accompanied by increased expression of GFAP. Therefore, GFAP can serve as a biomarker for astrocyte proliferation following central nervous system injury.

α- Synuclein is the most critical protein in the pathogenesis of Parkinson's disease and a major structural component of Lewy bodies. Aggregation of a-Synuclein is closely associated with the formation of the Lewy body and the death of dopaminergic neurons

S-100β protein is a calcium-binding protein secreted by glial cells. Approximately 96% of S-100β protein is expressed in astrocytes in the brain, which can nourish the nerves, and also influence the growth, proliferation and differentiation of glial cells, maintain calcium homeostasis in the brain, promote brain development, improving learning and memory.

BDNF is the most important neurotrophic factor in the brain. It is a generic term for protein molecules maintaining the survival of neurons, encouraging differentiation (synaptic elongation and expression of neurotransmitter synthase, etc.), promoting maturation, and regulating function. BDNF is secreted mainly by astrocytes and is one of the most widely distributed and studied neurotrophic factors in mammals. Its prominent function is to regulate neuronal development and synapse formation.

Human APOE gene consists of three alleles based on two SNP loci (rs429358 and rs7412): ε2, ε3 and ε4. 6 genotypes of APOE gene: ε2/ε2, ε2/ε3, ε2/ε4, ε3/ε3, ε3/ε4, ε4/ε4. The Epsilon 3 allele is the wild type, playing an important role in the normal physiological function of the body; The variant E4 has been implicated in a high prevalence of Alzheimer's disease, depression, and cardio-tubular diseases; Variant E2 is a protective factor against Alzheimer's disease, stroke, cerebral infarction, and coronary heart disease.