Montreal platelet syndrome: a defect in calcium-activated neutral
proteinase (calpain)
JR Okita, MM Frojmovic, S Kristopeit, T Wong and TJ Kunicki
Blood Center of Southeastern Wisconsin, Milwaukee 53233.
Platelets from patients with Montreal platelet syndrome (MPS) consistently
display a defect in the mechanisms that regulate platelet size during shape
change and undergo spontaneous aggregation and stir- induced microaggregate
formation. We now provide data that the surface glycoprotein composition of
MPS platelets is indistinguishable from that of normal platelets. However,
a defect in calcium-activated neutral proteinase (calpain) was detected in
MPS platelets. The specific activity of calpain in the cytosolic fraction
of platelets from four MPS patients was found to be only 30% of that in
platelets from normal control donors (n = 18, P less than .001).
Additionally, platelets from MPS patients (n = 3) contained only 50% (P
less than .001) of the calpain I catalytic subunit antigen found in
platelets from normal control donors (n = 9). Platelets from the
asymptomatic father/grandfather of the MPS patients had normal amounts of
both total calpain proteolytic activity and calpain I catalytic subunit
antigen. This represents the first report of a defect in calpain in human
cells. The abnormally low calpain activity in MPS platelets may account for
the platelet defects characteristic of this disorder.
Volume 74,
Issue 2,
pp. 715-721,
08/01/1989
Copyright © 1989 by The American Society of Hematology
