Differential diagnosis of neurodegenerative diseases using serum: A new paradigm

Diagnosis of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic lateral sclerosis (ALS) can be difficult, especially in early stages where there is often an insidious onset of symptoms overlapping with different disorders. This results in delayed diagnosis and treatment initiation. The objective of this study is to validate the use of serum protein biomarkers for accurate, quantifiable, minimally invasive tools for differential diagnosis of the neurodegenerative diseases to help provide more effective treatment. Patient retrospective serum samples: 115 AD; 29 PD; 136 ALS; 24 AD/PD-like, including non-AD stroke related, Frontotemporal, Lewy body, and other dementias; non-PD Stroke-related parkinsonism, Multiple system atrophy, and other movement disorders; 33 ALS-like patients, including non-ALS disorders of motor neurons, muscles, nerves, and spinal cord; and age-matched normal controls (75 for AD/PD; 57 for ALS), from 2 sources, and prospective serum samples, 30 AD, 82 PD, and 70 controls from 2 additional clinical sites were analyzed by 2D gel electrophoresis, fluorescent staining, quantitative digital image analysis, and individual and multivariate biostatistics (validated quantitation: %CV≤20%; LOD ≥0.5ng/spot, 300μg/ml of blood serum), proteins characterized using tryptic peptide LC MS/MS, molecular weights and isoelectric points. Fifty-nine protein biomarker spots exhibited significant abnormal, disease specific serum concentrations. Individual biomarkers had significant, abnormal concentrations that also discriminated between patients with: AD vs. PD vs. ALS; AD vs. AD-Like, PD vs. PD-Like, and ALS vs. ALS-Like disorders. Furthermore, on the basis of Apo E protein isoforms, sets of biomarkers also discriminated between age-matched normal controls, and “forms” of AD, and PD, and between familial and sporadic ALS. Multivariate discriminate analysis, in independent training and test sets with combinations of multiple sets of biomarkers showed sensitivity and specificity of 80-95%, when the protein molecular identities, isoform specificities, post synthetic modifications and processing variants were considered. Disease-specific profiles reflected different mechanisms measurable in blood. Prospective clinical validation trials showed similar sensitivities and specificities (80-95%). Correlations of the concentrations of certain protein biomarkers with disease severity confirmed earlier results with retrospective samples. Concentration differences of fully characterized blood protein biomarkers can provide useful tools for early differential diagnosis of neurodegenerative diseases.