Applicability of Nanotrap Sg as a semen detection kit before male-specific DNA profiling in sexual assaults
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A commercially available semen detection kit, Nanotrap Sg, which employs a one-step detection test based on immunochromatographic assay for the semenogelin protein, was evaluated for profiling male-specific DNA in sexual assault casework samples. While semen diluted with phosphate-buffered saline held and kept at 4°C for 1 week showed a relatively strong signal intensity with Nanotrap Sg, the signal intensity was decreased by dilution after storage at 4°C or freezing and thawing repeated more than three times. The reproducibility of Nanotrap Sg was tested on a total of 174 sexual assault casework samples from three forensic laboratories using intra- and interassay and no variation was observed in the semenogelin (Sg) signal. The positive signal ratio was 12.6% higher for prostate-specific antigen immunochromatographic membrane tests than Nanotrap Sg. Although spermatozoa were not confirmed in 61 (35%) out of 174 samples, Sg-positive signals could be detected from 41 (67%) of the 61 samples. Female genetic profiles could be observed in 95% of the samples, which tested negative for Sg on the Nanotrap Sg test, but no male genetic profiles could be observed. These results suggest that Nanotrap Sg can positively identify samples containing male DNA even in the absence of detectable intact spermatozoa. Further, Sg-positive signals identified samples for which male-specific DNA profiling could be performed, even if no sperm could be detected from the sample. The potential of Nanotrap Sg for identifying forensic samples with male-specific DNA was clearly demonstrated.
KeywordsForensic sciences Semen Semenogelin Immunochromatography Sexual assault
The authors wish to thank Mr. Koichiro Kojima, R&D division, Rohto Pharmaceutical, Osaka, Japan, for providing excellent technical support in this study. Also we wish to express special thanks to Mr. Antony de Simone, Italian Embassy, Tokyo, Japan and Miss Atsuko Yoshikawa, Msc. Department of Microbiology and Immunology, The Institute of Medical Science, Tokyo University, Tokyo, Japan for their encouragement and helpful advice during the corroborative study and the preparation of this manuscript. This research was partially supported by Ministry of Education, Culture and Sports, Science and Technology of Japan, Grant-in-Aid for Encouragement of Young Scientists (17791096).
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