Frequency of null alleles in paternity cases from Mexico for the locus Penta E

Abstract

We report three peculiar motherless paternity cases received in our lab at consecutive months, which involved four father-child mismatches for Penta E, the autosomal STR loci included in the Powerplex Fusion system. In all these cases, based on the residual Paternity Index (PI), the kinship was confirmed between the father and three children (PI > 1.6 × 10+6). In the first case, the homozygous father 16/16 did not match with two homozygous children 5/5 for the Penta E locus. Unexpectedly, the next week we detected another unique mismatch for Penta E between one homozygous father 9/9 and the homozygous child 17/17. Finally, four months later, in another motherless case, the father was 14/14 and the child was 16/16 for Penta E. Consequently, these four paternity test mismatches were faced as null alleles, which are described as variants in the primer-binding region that can lead to allele dropout resulting as false homozygous. Interestingly, allele nulls for Penta E are not described in the STRBase (https://strbase.nist.gov/NullAlleles.htm). According with these findings and our previous lab’s records (García-Aceves et al. 2018), we estimated a preliminary null allele frequency for Penta E in Mexico (7/3300; 0.21%). Because this estimate comes from motherless paternity cases and only one Mexican paternity testing laboratory, eventually this frequency needs to be confirmed. In brief, this report provides helpful information for reliable interpretation of paternity cases with unique mismatches for Penta E in Mexico, promoting research or simple modification of the corresponding primers by the supplier.