A high mutation load of m.14597A>G in MT-ND6 causes Leigh syndrome

Yoshihito Kishita,Masaru Shimura,Kazuto Nakada,Akira Ohtake,Masakazu Kohda,Takuya Fushimi,Jun-Ichi Hayashi,Yasushi Okazaki,Kei Murayama,Kaori Ishikawa

doi:10.1038/s41598-021-90196-5

Abstract

Leigh syndrome (LS) is an early-onset progressive neurodegenerative disorder associated with mitochondrial deficiency. m.14597A>G (p.Ile26Thr) in the MT-ND6 gene was reported to cause Leberʼs hereditary optic neuropathy (LHON) or dementia/dysarthria. In previous reports, less than 90% heteroplasmy was shown to result in adult-onset disease. Here, by whole mitochondrial sequencing, we identified m.14597A>G mutation of a patient with LS. PCR–RFLP analysis on fibroblasts from the patient revealed a high mutation load (> 90% heteroplasmy). We performed functional assays using cybrid cell models generated by fusing mtDNA-less rho0 HeLa cells with enucleated cells from patient fibroblasts carrying the m.14597A>G variant. Cybrid cell lines bearing the m.14597A>G variant exhibited severe effects on mitochondrial complex I activity. Additionally, impairment of cell proliferation, decreased ATP production and reduced oxygen consumption rate were observed in the cybrid cell lines bearing the m.14597A>G variant when the cells were metabolically stressed in medium containing galactose, indicating mitochondrial respiratory chain defects. These results suggest that a high mutation load of m.14597A>G leads to LS via a mitochondrial complex I defect, rather than LHON or dementia/dysarthria.

Highlights

Leigh syndrome (LS, MIM 256,000) is a severe neurodegenerative disorder that is characterized by bilateral symmetric signs and symptoms of brainstem and/or basal ganglia disease[1,2]
Five MT-ND6 mutations associated with LS have previously been reported as described above
This study identified the m.14597A>G variant in MT-ND6 associated with LS

Summary

Introduction

Leigh syndrome (LS, MIM 256,000) is a severe neurodegenerative disorder that is characterized by bilateral symmetric signs and symptoms of brainstem and/or basal ganglia disease[1,2]. More than 85 disease-associated genes of LS encoded in the mitochondrial and nuclear genome have been r eported[2,3]. Thirteen of the 37 mtDNA-encoded genes (MT-ND1, 2, 3, 4, 5, 6, MT-COIII, MT-ATP6, MT-TL1, MT-TK, MT-TV, MT-TW and MT-TI) have been found to be associated with LS. Our previous study of 104 Japanese LS patients described the clinical features, mitochondrial biochemical properties and genetic backgrounds in Japanese p atients[4]. Most MT-ND6 mutations cause Leber hereditary optic neuropathy (LHON), but some mutations have been reported to lead to LS. M.14597A>G has been shown to cause L HON11 and dementia/dysarthria based on information in ClinVar. m.14597A>G was associated with pathologies other than LHON or dementia/dysarthria, but it was unclear whether it was related to other disease types. We here report that a high mutation load of m.14597A>G causes LS with complex I deficiency

Methods

Results

Conclusion