Amyloid precursor protein in platelets: a peripheral marker for the diagnosis of sporadic AD.
BACKGROUND
An altered pattern of amyloid precursor protein (APP) forms consisting in a reduced ratio between the upper (130 kDa) and the lower (106 to 110 kDa) immunoreactivity bands has been described in platelets of patients with AD.


OBJECTIVE
To evaluate the sensitivity and the specificity of platelet APP forms' ratio (APPr) as a marker for AD.


METHODS
Eighty-five patients with probable AD and 95 control subjects (CON), including healthy individuals and neurologic patients, entered the study. Platelet APPr was evaluated by means of Western Blot analysis and immunostaining in the whole platelet homogenate, and calculated by the ratio between the optical density (OD) of the upper (130 kDa) and the lower (106 to 110 kDa) APP immunoreactive bands.


RESULTS
Mean APPr levels were decreased in AD patients (mean OD +/- SD = 0.35 +/- 0.18) compared with the CON group (mean OD +/- SD = 0.92 +/- 0.38) (DF 1, 178, p < 0.0001). Accuracy levels measured by Receiver Operating Curve analysis showed that a cut-off level of 0.57 resulted in a sensitivity of 88.2% and a specificity of 89.4%, with an area under the curve of 0.945. APPr levels were significantly associated with disease severity (mild AD versus moderate AD: p < 0.0001; moderate AD versus severe AD: p < 0.05).


CONCLUSIONS
Platelet APPr allowed to differentiate AD from normal aging and other dementing disorders with high sensitivity and specificity. These findings suggest that platelet APPr may be of help as an adjunctive diagnostic tool in clinical practice.
Padovani
A
A
Dipt. Scienze Mediche e Chirurgiche, Unità di Neurologia, Università degli Studi di Brescia, Italy. padovani@bshosp.osp.unibs.it
Pastorino
L
L
Borroni
B
B
Colciaghi
F
F
Rozzini
L
L
Monastero
R
R
Perez
J
J
Pettenati
C
C
Mussi
M
M
Parrinello
G
G
Cottini
E
E
Lenzi
G L
GL
Trabucchi
M
M
Cattabeni
F
F
Di Luca
M
M
D000368:Aged; D000544:Alzheimer Disease / Q000097:blood* / Q000523:psychology; D016564:Amyloid beta-Protein Precursor / Q000097:blood*; D015415:Biomarkers / Q000097:blood*; D001792:Blood Platelets / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales
D016564:Amyloid beta-Protein Precursor; D015415:Biomarkers