INSTABILITY IN THE ATCT VARIABLE NUMBER TANDEM REPEAT LOCUS VWEVNTR-IIN INTRON-40 OF THE VON-WILLEBRAND-FACTOR GENE

The von Willebrand factor gene intron 40 variable number tandem repeat VWEVNTR I exhibits 10 alleles making it highly polymorphic and useful for parentage and forensic testing. 45 unrelated families (210 meioti c events) were tested for VWEVNTR I alleles. One spontaneous mutation was observed in a family member. Haplotype analysis demonstrated that this mutation was due to a gain of one motif repeat by a paternal alle le. Sequence analysis confirmed the difference in the number of motif repeats between the proband and the alleles expressed by the parents. This instability emphasizes the importance of demonstrating exclusion in at least two separate loci in parentage testing.