Identification by mtDNA  of exchanged human body remains

Cruz, Carla; Ribeiro, Teresa; Vieira - Silva, Cláudia; Lucas, Isabel; Geada, Helena; Espinheira, Rosa

http://hdl.handle.net/10400.26/44053

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Authors

Cruz, Carla

Ribeiro, Teresa

Vieira - Silva, Cláudia

Lucas, Isabel

Geada, Helena

Espinheira, Rosa

Abstract(s)

MtDNA offers some advantages over genomic DNA markers for the identification of human remains. Its sequence is completely determined and the high copy number increases the chance to obtain mtDNA in cases of limited quantity or degraded autosomal DNA. The maternal mode of inheritance without recombination during the meiosis process allows maternal lineage identification by a simple direct comparison of the mtDNA sequence of mother and child or between brothers and sisters. CASE HISTORY: Five Portuguese citizens were killed in African. Three of them were identified and removed to Portugal, where they were buried. Two children were reported as missing. One year later, two skeletons were found in a grave 500 metres from the crime scene. Genetic typing of DNA extracted from skeletal remains was performed in order to establish their identities. One of the mothers of the two missing minors was excluded from the maternity of the skeletal remains. The hypothesis was raised of an identity exchange of the three corpses previously removed to Portugal. These were then exhumed and subjected to genetic analysis to achieve biological identification. Although teeth and bones are reliable sources of DNA, it was difficult to obtain results namely from those retrieved in Africa. As we expected, these required more modifications to standard protocol. The state of the bones samples from this continent was poor, probably due to the humidity, temperature and other African environmental conditions and soil characteristics that accelerate the degradation process. Low amounts, high fragmentation, and contamination of the DNA are the main problems associated with this kind of sample. In some cases, increasing the amount of DNA helped to overcome the first problem, but in some others lead to negative results, which can be explained by an increase of Taq polymerase inhibitors in the mix reaction. Regarding the degraded DNA, the application of different primers to the HVI and HVII regions allowed the amplification of two shorter overlapping fragments for each region and the reconstruction of HVI and HVII sequences. Several dilutions of DNA extract were tested to decrease the hypothetical contaminants that would act as Taq polymerase inhibitors. The coincidence of each of the five body sequences with one of the alleged mothers suggests a maternal relationship. A fraternal relationship was detected between bodies 2 and 5. These share the same mtDNA sequence with mother 3. The results supported the hypothesis of exchanged human body remains. Autosomal STR loci analysis was performed and confirmed the identity of the human remains. MtDNA analysis was a useful tool to solve this case. Although it cannot be used to definitely identify the corpses, it provided evidence of a maternal relationship and, consequently, the exchange of human body remains.