Forensic evaluation of mitochondrial DNA heteroplasmy in Gujarat population, India

Owing to its high copy number and its small size, mtDNA analysis is the most reliable choice when biological materials from crime scenes are degraded or have mixed STR profiles. To examine the occurrence of heteroplasmy along with its frequency and pattern in both HV1 and HV2 regions of the mtDNA among unrelated individuals from India. Mitochondrial DNA control region [hypervariable region one (HV1) and hypervariable region two (HV2)] were analysed in blood and buccal tissues of 104 unrelated individuals from the Indian state of Gujarat. A high frequency of point heteroplasmy (PH) and length heteroplasmy (LH) was revealed. PH was detected in 7.69% of the population, with a higher frequency observed in blood than in buccal samples. However, there were no statistically significant differences in PH between the two tissues (Chi-square = 0.552, <i>p</i> ≥ 0.05). A total of six PH positions were detected: three at HV1, and another three at HV2. The studied population showed 46.15% LH in the HV1 and HV2 regions of both tissues. The LH positions observed in the Gujarat population were the same as those previously reported at HV1 np16184–16193 and HV2 np303–315. Our findings suggest that differences in the pattern of heteroplasmy found in different tissues can complicate the forensic analysis, on the other hand, the probability of a match between the questioned and reference samples increases when the heteroplasmy is identical in both tissues. Variability of PH among persons and even within tissues recommends analysing multiple tissue samples before drawing a conclusion in forensic mtDNA analyses.

鉴于线粒体DNA（mtDNA）拷贝数高且片段短小，当现场生物检材发生降解或存在混合的短串联重复序列（STR）分型时，mtDNA分析是最为可靠的检测方案。本研究旨在探究印度无关个体mtDNA高变区1（HV1）与高变区2（HV2）中异质性（heteroplasmy）的发生情况、发生频率及分布模式。我们对来自印度古吉拉特邦的104名无关个体的血液与口腔黏膜组织样本的线粒体DNA控制区[即高变区1（HV1）与高变区2（HV2）]进行了分析。研究结果显示，点异质性（PH）与长度异质性（LH）的检出频率较高。该群体中PH的检出率为7.69%，血液样本中的检出频率高于口腔黏膜组织样本，但两种组织样本的PH检出率差异无统计学意义（卡方值（Chi-square）=0.552，p≥0.05）。本次研究共检出6个PH位点：其中3个位于HV1区，另外3个位于HV2区。本次研究的群体在两种组织的HV1与HV2区中，LH的检出率为46.15%。古吉拉特邦群体中检出的LH位点与此前报道的HV1区np16184–16193及HV2区np303–315位点一致。本研究结果表明，不同组织中异质性的分布模式差异可能会使法医鉴定工作复杂化；反之，当可疑检材与参照样本的异质性特征一致时，二者匹配的概率会有所提升。个体间甚至同一组织内部的PH存在变异，这提示在法医mtDNA分析中，得出最终结论前应对多份组织样本进行检测分析。