Mutation in paternally transmitted alleles at FGA microsatelite locus: A case of allele mismatch in the child

We investigated a case of paternity dispute with 10 autosomal STR loci and found a mismatch in one of the alleles of the FGA locus in the child. The composition of alleles of this locus in the mother, child and alleged father were, 19/24, 23/24 and 22/24 respectively. The combined paternity index (CPI) and probability of paternity (W) after including the mutation in the calculation was 2,932 and 0.9998 respectively which favored the paternity of alleged father as the biological father of the child. Inclusion of more loci in the analysis provided even stronger evidence in favor of paternity (CPI = 24,013, W = 0.99997). Further analysis using 16 Y-chromosome STR loci, revealed matching of all Y-chromosome alleles of the child with that of the alleged father. Since there was a perfect match of all the paternal alleles inherited (autosomal and Y-chromosomal STRs) in the child with those of the alleged father except the allele at FGA, it might therefore be a case of mutation. The results suggest that, either there was expansion of a complete repeat of the paternal allele 22 or a loss of a complete repeat from paternal allele 24 which was transmitted as allele 23 in the child.