Evaluation and Usefulness of HUMFIBRA in Forensic Casework
N. Dimo-Simonin, F. Grange, C.
Brandt-Casadevall, and P. Mangin
Institut Universitaire de Medecine Legale, Bugnon 21, 1005 Lausanne, Switzerland
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The typisation of STR loci by PCR is the method of choice for the forensic identification of human DNA. Actually, the substitution of the first STR generation by new STR systems with higher polymorphism is necessary to increase the discrimination power for the DNA identification.
HUMFIBRA is a complex tetranucleotide (TCTT)n STR locus located in the third intron of the human alpha fibrinogen gene on chromosome 4. This highly polymorphic system includes 22 alleles differing generally by 4 or 2 bp in the range of 168 to 294 bp.
PCR products were detected by vertical polyacrylamide gel electrophoresis in a Tris/glycine discontinuous buffer.
A population sample of 188 individuals from South-West Switzerland was analyzed and the genotype frequencies were similar with those reported by others. Fifteen alleles and 45 genotypes were found. The observed heterozygosity and the discrimination power were 0.82 and 0.962 respectively. No mutations were found in 38 paternity cases confirmed by RFLP-VNTR.
A hundred samples from 20 forensic cases were extracted and typed: 70 evidence samples and 30 reference blood samples. Conclusive results were obtained were obtained for 96% of the evidence samples. The HUMFIBRA results confirmed patterns found with the other PCR systems: HLADQA1, HUMTH01, HUMVWFA31 and PolyMarker.
Seventy four samples from ten years old forensic cases (51) were extracted and typed: 86% of the samples gave an amplification product after chelex extraction. After increasing the albumin concentration in the amplification mix, the success rate was 94%. Three of the four remaining negative samples gave a positive result after further purification of the DNA using the Centricon method. Accordingly, conclusive results were obtained for 98.5% of the evidence samples.
The high polymorphism of the HUMFIBRA makes the identification of a mixture easier because the possibilities for the two fractions of being identical or for the minor fraction to coincide with the stutter band of the major fraction are decreased.
This validation study proves the great usefulness of the HUMFIBRA locus in the forensic laboratory increasing the individual discrimination of DNA evidence.
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