RESUMO
Atypical situations arise during the constant resolution of paternity cases, which constitute challenges requiring additional genetic systems and non-standard methods. We report a paternity case presenting three alleged father (AF)-child incompatibilities for the markers TPOX, D2S441, and the indel locus B02 (11/11 vs 8/8; 14/14 vs 10/10; 2/2 vs1/1, respectively). Considering the presence of mutations/null alleles, the residual paternity indexes (PI) obtained with 23 autosomal short tandem repeats (STRs) and 38 indels suggest that the AF is the father (PI = 1.94e+011). Although the presence of few incompatibilities also could imply paternity of the AF brother, this hypothesis was less probable (PI = 3.20e+9) (W = 98.4 vs 1.6%, respectively). The inclusion of 23 Y-STR loci confirmed the paternity relationship in this case (global PI = 6.08e+15). However, the two multistep STRs and one indel incompatibilities allow discarding the mutation possibility. On the other hand, the confirmation of the homozygous STR genotypes with two different human identification kits and the low probability to find three null alleles (3.10e-8) allow rejecting the null allele presence hypothesis. Conversely, the child's homozygous genotype for maternal alleles in four markers located in the p and q arms of the chromosome 2 (TPOX, D2S441, D2S1338, and B02) suggests that maternal uniparental isodisomy better explains the relationship despite the presence of three paternal incompatibilities. In brief, when multiple incompatibilities are observed in paternity testing, the chromosomal location of the excluding loci and the use of additional genetic systems can be crucial to get confident kinship conclusions.