Insertion-/deletion polymorphisms close to the repeat region of STR loci can cause discordant genotypes with different STR kits

It is well known that mutations in the primer binding site of STR loci can cause "null alleles". If a sample is typed with different sets of PCR primers (for example if different kits or kits of different manufacturers are used) discordant results might be observed, thus making the use of different STR kits for deviant genotypes necessary. Here we present another reason for using different kits: Insertion-/deletion polymorphism between the repeat region of the STR locus and the primer binding site can also cause genotypes that vary between different kits/primer sets.