Four-state MVR-PCR: increased discrimination of digital DNA typing by simultaneous analysis of two polymorphic sites within minisatellite variant repeats at D1S8.

Minisatellite variant repeat mapping by PCR (MVR-PCR) provides a digital approach to DNA typing that can reveal huge levels of variation at minisatellite loci. MVR-PCR has so far been applied to three human minisatellites, including the hypervariable locus D1S8. Previous analysis at D1S8 was based on the discrimination of repeat unit types that differ by a single base substitution. We now show that a second polymorphic site within D1S8 repeats may be assayed simultaneously with the first to define four classes of repeat units ('four-state MVR-PCR'). This approach can also be applied to the other end of D1S8 alleles in 'reverse four-state MVR-PCR'. Both of these procedures substantially increase the informativeness of MVR analysis at D1S8 and should prove useful in studies of minisatellite biology and potentially in forensic DNA typing.