Mitochondrial DNA involvement in frontotemporal lobar degeneration : analysis of sequence variants in MTND genes

Abstract

Mitochondria dysfunction and oxidative damage have been suggested to have an important role in ageing-related neurodegenerative diseases. One of the possible mechanisms is related to mitochondrial DNA (mtDNA) alterations that may impair mitochondrial respiratory chain function. Contrary to other neurological disorders, frontotemporal lobar degeneration (FTLD) pathophysiology is still poorly understood, and the etiology of most cases remains unknown. Recently, two mtDNA alterations were reported in a patient with FTLD and another study proposed an association between FTLD and a specific mtDNA haplogroup. To determine if mtDNA is involved in FTLD, we sequenced 4 mtDNA genes encoding subunits of NADH dehydrogenase from 17 patients. The alterations detected were submitted to in silico analysis for evaluating possible pathogenicity. In 82% patients we found 29 different alterations, including polymorphisms (62.1%), mutations already associated to other diseases (27.1%) and unpublished variants (13.8%). Many of the alterations detected (69%) were not associated to a change in the amino acid translated and so are not expected to cause mitochondrial dysfunction. The non-synonymous variants are predicted to be benign, according to the in silico analysis. However, even if these alterations are not primarily pathogenic, an interaction with other mutations may occur, leading to the disease, worsening its expression or influencing age of onset. Our study is still preliminary, but the high number of mtDNA alterations identified suggests a possible role of this genome in FTLD. However, it is not yet possible to determine whether these variants are part of the etiology or an epiphenomenon