Mitochondrial genome A3243G mutation in the tRNALeu(UUR)  encodinggene (MTTL)is the main cause of mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS). This mutation exists in heteroplasmic form and severity of the disease is affected by many factors including heteroplasmy level. In this study, a pediatric proband (female, 8 years old) was found to carry A3243G mutation at 77.6% of heteroplasmy by using PCR-RFLP in combination with real-time PCR. The results of  the A3243G mutation analysis of the proband’s family showed that her mother without any symptoms of encephalopathyalso carried the mutation at 7.9% of heteroplasmy whereas the mutation was not found in the proband’s healthy father and healthy sister, indicating that the proband received the A3243G mutation from her mother and the expression of MELAS syndromes depended on the level of heteroplasmy.

Tóm tắt: ột biến G11778A n m tr n gen ND4 ủ h gen ty thể người hiếm 50-70% trường hợp ủ hội hứng LHON. Trong nghi n ứu n y húng t i đã thiết l p phương pháp phát hi n v định lượng đột biến G11778A b ng re l-time PCR sử dụng mẫu dò huỳnh qu ng T qm n ó nul otide d ng ầu khó (LNA). Phương pháp ho thấy s tương qu n tỷ l nghị h giữ bản opy ủ gen đ h v giá trị hu kỳ ngưỡng o với h s hồi quy R 2 = 0 999. Phương pháp ho phép phát hi n đột biến ở tỷ l 0 1% trở l n. B ng vi sử dụng kết hợp k thu t PCR-RFLP v k thu t re l-time PCR húng t i đã phát hi n một b nh nhân nhi gái 7 5 tháng tu i m ng đột biến G11778A. ột biến tồn t i ở d ng kh ng đồng nhất v ó tỷ l đột biến l 2 710.12%. Trong khi b v m b nh nhân đ u kh ng m ng đột biến. ây l b nh nhân m ng đột biến G11778A đầu ti n đượ phát hi n t i Vi t N m.

A procedure for production of a real-time PCR kit for detection and quantitation of 6 common mitochondrial genome mutations including A3243G, G3380A, A8344G, T8993G, T8993C, G11778A using fluorescent locked nucleic acid (LNA) Taqman probes was reported. The procedure consists of designing of specific primers and LNA probes, selection of master mixture components and real-time PCR thermal conditions. The produced kit had specificity of 100% and sensitivity ≥ 1% and remained fully active after 7 days of storage at 25 oC or 20 days at 4 oC or 6 months at -20 oC. The kit was used to analyze A3243G, G3380A, A8344G, T8993G, T8993C, G11778A mutations from 69 patients tentatively diagnosed with mitochondrial diseases and 3 cases of A3243G carriers (4.34%) was found. In these cases, the A3243G mutation was heteroplasmic, maternally inherited, and the heteroplasmy level was shown to be related to the symptome expression.tome expression.