von Willebrand disease family studies: comparison of three methods of analysis of the von Willebrand factor gene polymorphism related to a variable number tandem repeat sequence in intron 40.

A region with a variable number of tandem ATCT repeats (VNTR) has previously been localized within intron 40 of the von Willebrand factor (vWF) gene. In the present report we describe the use of this polymorphism as a genetic marker to study the inheritance pattern in five families affected with various types of von Willebrand disease (vWD): types I, IIA, IIB, IIC and the newly characterized variant with totally defective FVIII binding. Three means of investigation previously reported, all using polymerase chain reaction (PCR) amplification of this vWF gene region, were compared in terms of informativeness. The two direct single-step procedures analysing only partial sequences of the VNTR region turned out to be less informative (three studies informative out of five) than the third method characterizing the variability of the whole VNTR sequence. This latter approach, based on the analysis of the Alu I restriction pattern of the VNTR region, was informative in all the families investigated, therefore avoiding the need to combine it with other genetic marker studies for efficient gene tracking. In conclusion, this two-step (PCR and digestion) method is the most informative for the characterization of the inheritance of the different subtypes of vWD and for the prenatal diagnosis of its severe forms.