Real-time quantitative PCR analysis of factor XI mRNA variants in human platelets

Coagulation factor XI (FXI) plays an essential role in blood coagulation. A deficiency of FXI is an unusual hemorrhagic diathesis in that the bleeding tendency can be highly variable, ranging from severe deficiencies with no symptoms to mild and moderate deficiencies requiring multiple blood transfusions for hemorrhages. This variability in bleeding has been attributed to a number of factors including the presence of a novel form of FXI associated with platelets, which ameliorates the bleeding in some cases of FXI deficiency. However, the nature of this platelet FXI molecule is controversial. Hsu et al. (J Biol Chem 1998; 273: 13787-93) suggest that it is a product of normal FXI - but lacking exon V whilst Martincic et al. (Blood 1999; 94: 3397-404) were unable to detect this alternatively spliced variant using RT-PCR. In order to resolve this controversy, we have employed the highly sensitive technique of real-time quantitative RT-PCR using RNA isolated from FXI-deficient patients. Our results indicate that the platelets of both normal and FXI deficient individuals contain FXI mRNA that is identical to the mRNA found in liver. An exon V deleted splice variant was not detected. Thus the FXI message is not alternatively spliced in platelets and therefore would not be able to produce an unusual FXI protein.