Abstract: Objective To study the suspected autosomal STR loci mutation cases. Methods A total of 227 suspected autosomal STR loci mutation cases were selected from Center of Forensic Sciences, Beijing Genomics Institute. The allelic mutation cases were screened and the number of mutation of each STR loci was statistically analyzed. The CPI value was calculated in order to study the characteristics and rules of the mutations. Results In the 227 suspected mutation cases, 3 cases were excluded paternity, and 228 mutations were observed at 18 STR loci in the rest of the cases. The average number of STR mutation loci was 1-2. The maximum of mutation step was 4. After using 20A amplification kit, the CPI values in 3 non-parentage cases were all less than 10⁴. After using 20A and 10G amplification kits, the CPI values were all larger than 10⁴ in all standard parents-child triplet cases and in 99.45% of diad cases. Conclusion The allelic mutation of STR loci is relatively common in forensic cases. By increasing the number of the required STR loci and supplementing the samples of  the triplet, the identification errors could be decreased to a great extent when suspected autosomal STR loci mutation occurs.

Key words: forensic genetics, mutation, chromosome aberrations, short tandem repeat, paternity testing