DNA analysis of hairs in a suspected case of child abuse

Hairs are often used for DNA analysis in criminal investigations. DNA analysis of hairs with root sheaths is easy in many cases, but analyses using only the shaft or tip of the hair are often difficult. Here we describe a suspected case of child abuse in which we were commissioned to perform DNA analysis. Among 100 hairs, PCR amplification was succeeded in 99 samples, and as a result of direct sequencing, mitochondrial DNA (mtDNA) of the 99 hairs were classified into 6 types. The most common type was the 8-base substitution type of 16,168T-16,172C-16,183C-16,189C-16,217C-16,249C-16,325C-16,390A, which was observed in 86 hairs. This corresponded to the type of the victim. Total 736 STRs (75.5%) in 975 loci of 65 hairs could be typed, and only an amelogenin locus was typed in another hair. All 15 loci were typed in 10 hairs. STR types of 65 (98.5%) in 66 hairs were consistent with that of the victim. From 10 naturally-shed hair of a person, only 37 STRs (30.8%) in 120 loci of 8 hairs were typed, and all 15 loci could not be typed in these hairs. This difference in success rates of STR analysis suggested strongly that the hairs in this case were not shed naturally but forcibly, and the relevance to child abuse was suspected.