The heterogeneity of m.13513G>A variant - related phenotypes depending on heteroplasmy level
2Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Russia
3The “Russian Clinical Research Center for Gerontology” of the Ministry of Healthcare of the Russian Federation, Pirogov Russian National Research Medical University, Russia
4State Autonomous Healthcare Institution of the Sverdlovsk Region «Clinical and Diagnostic Center "Maternal and Child Health Protection", Russia
5Saint-Petersburg State Medical Diagnostic Center (Genetic medical center), Russia
6Bashkir State Medical University, Russia
7State Budgetary Healthcare Institution of Nizhny Novgorod Region «Nizhny Novgorod Regional Children’s Clinical Hospital», Russia
8Research Institute of Eye Diseases, Russia
Background
The m.13513G>A substitution in the MT-ND5 gene is one of the common pathogenic variants causing primary mitochondrial disorders. In particular, it is a frequent cause of Leigh and MELAS syndromes. However, in several cases of Leber’s hereditary optic neuropathy (LHON) the disease causing variant m.13513G>A was revealed at low heteroplasmy level. Here we present a group of 17 unrelated patients with variable heteroplasmy levels of m.13513G>A influencing their clinical, biochemical and bioenergetic phenotype.
Methods
We describe a clinical data of 17 patients with Leigh syndrome (10/17, 8 females, 2 m MELAS (N=1, female) and LHON (6/17, males) having the m.13513G>A variant in DNA extracted from blood (N=17) and/or urine sediment (N=9) and cultured fibroblasts (N=8) from skin biopsy. The molecular analysis was provided by NGS of whole mtDNA, MLPA and Sanger’s sequencing. To evaluate a bioenergetic effect of heteroplasmy, we conducted the high-resolution respirometry (Oroboros corp., Austria) and assessed the membrane potential of the mitochondria with the fluorescent probe TMRM (Sigma, USA) in fibroblasts cultures (compared to N=10 and N=3 healthy controls respectively).
Results
The level of heteroplasmy in patients’ blood samples ranged from 24 % to 86% in Leigh syndrome patients with correlation of the phenotype severity and the level of urine organic acids; from 24% to 60% in LHON patients. We detected the high values of the respiratory rates and low level of mitochondrial membrane potential with the heteroplasmy of m.13513G>A above 50% in fibroblasts cell lines.
Discussion/Conclusion
Our results expand the clinical, biochemical and bioenergetic findings of patients with m.13513G>A variant-related phenotypes with varying heteroplasmy level. We also conclude that the m.13513G>A variant is an unusual but possible cause of LHON and we recommend screening for this variant in LHON patients.
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