We had previously found a Vietnamese Leigh syndrome patient harboring m.8993T>C mutation with heteroplasmy. The main purpose of this study was to further evaluate the mutation’s inheritance and its characteristics in the extended family members of the patient. The extended family has nine members, belonging to three nuclear families and three generations

1. CHARACTERIZATION OF MITOCHONDRIAL MUTATION
m.8993T>C INHERITANCE OF LEIGH SYNDROME IN A
VIETNAMESE FAMILY
Student: Weerasinghe Arachchige Lahiru Chamara Student ID: 13002361
Faculty: Biology Course: QH.2013.T.CQ
Supervisors: Prof. Dr. Phan Tuan Nghia, Dr. Vu Thi Thu
Abstract:
Leigh syndrome is a progressive neurodegenerative disorder that affects 1 in 40,000
live births and usually results in death. To date, mutations in over 60 genes, both nuclear and
mitochondrial DNA encoded, have shown to cause this syndrome. About 10-20% of Leigh
syndrome patients have a mutation in MT-ATP6 gene, especially at the mtDNA position 8993.
The transition mutation, m.8993T>C, converts the conserved leucine residue to a proline
residue of the Atp6 subunit protein. This change reduces the ATP synthase activity and
increases the ROS/RNS production of the cell, triggering cell necrosis in neurons and muscles.
We had previously found a Vietnamese Leigh syndrome patient harboring m.8993T>C
mutation with heteroplasmy. The main purpose of this study was to further evaluate the
mutation’s inheritance and its characteristics in the extended family members of the patient.
The extended family has nine members, belonging to three nuclear families and three
generations
To screen the m.8993T>C mutation, extracted DNA templates from those members
were subjected to PCR-RFLP and real-time PCR. The results showed that percentages of
heteroplasmy in samples taken from the proband, his mother, his first cousin, his second cousin,
his aunt and his grandmother were 94.5%, 72.0%, 87.0%, 91.0%, 67.0% and 16.5%,
respectively. In contrast, the mutation was not found in his father, his uncle and his grandfather.
Both quantitative and qualitative analyses have concluded that the m.8993T>C mutation
follows the maternal inheritance pattern in the family, and therefore, the proband has putatively
received the mutation from his mother. Furthermore, the results also concluded that the
mutation was vertically accumulated through generations.
Keywords: Leigh syndrome, m.8993T>C, mtDNA, real-time PCR, vertical mutation
accumulation, mtDNA bottleneck effect, mtDNA genetic drift.