抄録
When DNA analysis is applied to hairs left at a crime scene, their surface could be contaminated with various materials. In this study, we examined washing methods to remove the contaminations from hairs. Hair shafts cut into approximately 1 cm were dipped in blood, saliva or semen, and left at room temperature for one night to dry the contaminated body fluids. The hairs were then washed by vortexing in water or washed with three detergent methods: agitating at 56℃ in 5% Terg-A-Zyme, agitating at 56℃ in DNA Away, or ultrasonicating in DNA Away. The washed hair samples were examined with ABO blood test, short tandem repeat (STR) analysis and mitochondrial DNA analysis. In ABO blood test, we examined one scalp hair and one pubic hair from one individual. In STR test and mitochondrial DNA test, we examined three scalp hairs and three pubic hairs from three individuals.
In ABO blood test using the immunohistochemical staining, only the ultrasonication in DNA Away was examined. This washing method effectively removed the contaminant, and showed only the blood type derived from the hair. In STR analysis using the Identifiler plus kit, when 150 RFU was used as a threshold value, the contaminant peaks were observed in 37/54 samples (68.5%) by the water wash, but in 2/162 samples (1.23%) in total by the three detergent methods. When 30 RFU was used as a threshold value, the contaminant peaks were observed in 46/54 samples (85.2%) by the water wash, but in 66/162 samples (40.7%) in total by the three detergent methods. This result indicated that the three detergent methods all could decrease the peaks contaminated from the blood, the saliva and the semen better than the water wash. In the mitochondrial DNA analysis, the water-washed samples provided the mixed sequences of the hair and the contaminants, while the detergent-washed samples provided only the peaks of the hair.
The three detergent-washing methods examined in this study were all effective to remove the contamination. However, they could affect hair root and make the STR analysis difficult. Therefore, caution should be considered when applying the detergent-washing methods to hair root of plucked hair.
