INTRODUCTION
Hemophilia A (HA) is a recessive hemorrhagic disease linked to the X
chromosome, characterized by reduced levels of clotting factor VIII
(FVIII). According to factor VIII levels, HA is classified as severe
(less than 1%), moderate (1-5%) or mild (6-30%). In severe and
moderate forms, the disease is characterized by hemorrhagic episodes on
the joints (i.e., hemarthrosis), soft tissues and muscles after minor
trauma or even spontaneously (1). Although the lack of FVIII is the main
factor predisposing to the disease, the differences in bleeding
phenotype could be related to several factors that may influence
clinical presentation and response to treatment in patients with HA (2).
Among these factors, the role of platelets and their associated
microvesicles expressing tissue factor on their membrane has been
considered to be important (3). Moreover, several studies have also
reported alterations in platelet function that challenged the classical
view maintaining that platelet function is normal in hemophilic patients
(4-5). However, the association between platelet function and HA is far
from clear and a recent review has discussed the possible existence of a
publication bias to favor only publication of studies with positive
results (6).
The present work is directed to the investigation of some modulating
factors of the hemorrhagic phenotype in patients with severe HA treated
under the regimen of prophylaxis. Among the modulating factors that we
are going to study are the platelets and microvesicles. The main
objective of the study is to analyze if the administration of FVIII
modifies this hemorrhagic phenotype, comparing a baseline sample
(washing period / 72h without factor VIII) with respect to a sample 15
minutes after administration of FVIII.