Genetic research to evaluate tri-allelic peaks on D21S11 locus

Abstract

　Tri-allelic peaks are rarely detected from single-source DNA in the case of testing with commercial STR kits, while homozygous or heterozygous peaks are frequently observed at each locus. Tri-allelic patterns can possibly occur in healthy people, and the peak balance of various tri-alleles from different origins can cause some problems that discern from artifact peaks affecting the result of STR typing, or difficulties in the evaluation of kinship.

　In this study, different samples from a volunteer with D21S11 tri-alleles (alleles 26, 29, and 30) were tested using routine STR analysis methods. The peak balances of the tri-allele varied significantly between samples, therefore a type 1 tri-allelic pattern caused by somatic mutation in the early stages of differentiation was possible because the sum of the lower two peak heights was roughly equal to the highest peak height in every case. Direct sequence analysis of the individual's family members revealed that the tri-allelic pattern was not inherited from the mother, nor was it passed down to the daughter. In addition, a mutated form of one of the tri-alleles and its mutated repeat unit and numbers were identified.

　When tri-allelic peaks are suspected, it is essential to analyze not only intra-locus peak balance but also the whole electropherogram profile. This means that STR typing is necessary considering the fact that pull-up peaks or stutter peaks could resemble tri-allelic peaks.