Microvariant alleles are defined as alleles that differ from common allele variants of tested DNA markers by one or more base pairs. They are result of mutations and are most frequently found in more polymorphic loci such as D18S51, D21S11 and FGA.

In one of our routine paternity testing casework, using AmpFISTR Identifiler PCR amplification kit (Applied Biosystems), in mother and her three children from Albanian population in Republic of Macedonia, a microvariant allele was identified at the heterozygote FGA locus. The allele appeared as an off-ladder allele falling just between alleles 22 and 23 of the FGA allelic ladder, suggesting the allele size to be between 235-238 bp. Samples were analyzed using Genotyper 3.2 software. Comparing the fragment size to GeneScan 500 LIZ size standard and by using specific formula for calculation of the size of the allele, microvariant allele was found to be 22.2.

The possibility of presence of microvariant alleles can’t be excluded and if some of them are frequently found in a particular population, than it gives an importance for its inclusion in a statistical calculation.