Improved diagnosis of Alzheimer’s disease
Measuring the ratio:
Amyloid-beta (1-42) / Amyloid-beta (1-40) in CSF
Introduction
Over the last 15 years measuring Amyloid-beta (1-42) peptide has gained acceptance as a tool to aid in the diagnosis of Alzheimer’s
disease. Yet, clinical sensitivity and specificity usually is less than 85%. This can be largely attributed to the Gaussian distribution of
amyloid-beta production in the population. It leads to false positives in the group of “low” Abeta producers and to false negatives in
the group of “high” Abeta producers. Normalizing the Amyloid-beta (1-42) values to the most abundant and stably produced Abeta
(1-40) isoform overcomes this limitation and significantly improves the diagnostic value to well above 90%. IBL International has set its
goal to develop high quality immunoassays for convenient and accurate measurement of Amyloid-beta (1-40) and Amyloid-beta (1-42)
in CSF for optimal ratio determination.
Results
Assay Performance
Anja Matzen and Michael Habig
R&D Team IBL International, Hamburg, Germany
Excellent inter- and intra-assay CVs and inter-lot CVs profiles due to internal quality control standards
Table 1:
Cross reactivity (determined as described in Deshpande, SS (1996))
Peptide
Amyloid-beta (1-42)
Amyloid-beta (1-40)
Amyloid-beta (1-38)
Amyloid-beta (2-40)
Table 2:
Figure 1:
Amyloid-beta (1-42)
ELISA
100%
0.003%
0.57%
0.02%
Intra-assay CV (n=20)
Sample No.
1
2
3
4
5
Amyloid-beta (1-40)
ELISA
0.84%
100%
0.01%
1.29%
Table 3: Inter-lot and -operator CV (n=10, 3 lots, 3-4 operators)
Amyloid-beta (1-40) ELISA
Amyloid-beta (1-42) ELISA
mean
[pg/mL]
4732
9937
3080
10497
13506
mean
[pg/mL]
548
1023
849
951
1034
CV
[%]
1.8
2.1
4.5
1.9
2.8
Method comparison for the detection of
Amyloid-beta (1-40) in 119 native CSF Samples
CV
[%]
3.4
3.0
3.0
3.1
3.1
Sample No.
1
2
3
4
5
Figure 2:
Amyloid-beta (1-40) ELISA
Amyloid-beta (1-42) ELISA
mean
[pg/mL]
2418
3830
19407
13164
9405
mean
[pg/mL]
193
476
661
728
873
CV
[%]
5.4
6.3
4.1
5.8
2.7
Method comparison for the detection of
Amyloid-beta (1-42) in 120 native CSF Samples
CV
[%]
4.5
7.6
6.9
4.7
7.4
Clinical Validation
Prof. Dr. med. P. Alexopoulos, Klinik und Poliklinik für Psychiatrie und Psychotherapie, Klinikum rechts der Isar der Technischen
Universität München, München, Germany
100%
Amyloid-beta (1-42)
90%
80%
Ratio:
Amyloid-beta (1-42) /
Amyloid-beta (1-40)
TPR (Sensitivity)
70%
60%
50%
Amyloid-beta (1-42)
Ratio:
Amyloid-beta (1-42) /
Amyloid-beta (1-40)
Sensitivity
85%
98%
Specificity
84%
91%
40%
30%
20%
10%
0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
FPR (1-specificty)
Diagnosis
AD
control
Ratio: Amyloid-beta (1-42) / Amyloid-beta (1-40)
AD
control
39
1
4
39
Similar results were obtained by Prof. Dr. med. Piotr Lewczuk, Lab for Clinical Neurochemistry and Neurochemical Dementia Diagnostics,
Universitätsklinikum Erlangen, Department of Psychiatry and Psychotherapy, Erlangen, Germany. These will be independently
published.
Conclusion
Extensive internal and external data show that we achieved our goal for convenient and accurate measurement of Amyloid-beta (1-40)
and Amyloid-beta (1-42) in CSF for optimal ratio determination:
• Assay procedures and sample dilution for both ELISAs the same
• Assay time 3.5 hours
• Can be performed at room temperature
• Both assays automatable
• Excellent Specificity
• Intra-assay CVs < 5%
• Inter-lot and -operator CVs < 8%
• Method comparison with commercially available Amyloid-beta (1-40) ELISA: R2=0.944
• Method comparison with commercially available Amyloid-beta (1-42) ELISA: R2=0.9492
• Clinical sensitivity and specificity well above 90%