Use of the polymerase chain reaction (PCR) to amplify variable numbers of tandem repeat (VNTR) loci has become widely used in genetic typing. Unfortunately, preferential amplification of small allelic products relative to large allelic products may result in incorrect or ambiguous typing in a heterozygous sample. The mechanism for preferential amplification has not been elucidated. Recently, PNA oligomers (peptide nucleic acids) have been used to detect single base mutations through PCR clamping. PNA is a DNA mimic that exhibits several unique hybridization characteristics. In this report we present a new application of PNA which exploits its unique properties to provide enhanced amplification. Rather than clamping the PCR, PNA is used to block the template making it unavailable for interstrand and intrastrand interactions while allowing polymerase to displace the PNA molecules and extend the primer to completion. Preferential amplification is reduced and overall efficiency is enhanced.

A paternity case involving a putative father who had died a few years earlier in an automobile accident was referred to the laboratory for testing. The child and his mother, the deceased's parents, and nine of the deceased's siblings were available for analysis. As previously reported, paternity testing using red blood cell groups, human leukocyte antigens (HLA), red blood cell enzymes, serum proteins, and immunoglobulin allotypes gave a cumulative paternity index of 43 300 and a combined probability of paternity equal to 99.998%. RFLP analysis using Hinf 1 and Sau 3A single digests and the minisatellite deoxyribonucleic acid (DNA) probes 15.1.11.4 and 6.3 showed no exclusion of paternity and gave nearly conclusive evidence that the putative father was the biological father of the child.

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