RNASEH1 Mutations Impair mtDNA Replication and Cause Adult-Onset Mitochondrial Encephalomyopathy.

TitleRNASEH1 Mutations Impair mtDNA Replication and Cause Adult-Onset Mitochondrial Encephalomyopathy.
Publication TypeJournal Article
Year of Publication2015
AuthorsReyes, A, Melchionda, L, Nasca, A, Carrara, F, Lamantea, E, Zanolini, A, Lamperti, C, Fang, M, Zhang, J, Ronchi, D, Bonato, S, Fagiolari, G, Moggio, M, Ghezzi, D, Zeviani, M
JournalAm J Hum Genet
Date Published2015 Jul 02
KeywordsAdult, Amino Acid Sequence, Base Sequence, Blotting, Southern, Blotting, Western, DNA Replication, DNA, Mitochondrial, Female, High-Throughput Nucleotide Sequencing, Humans, Male, Middle Aged, Mitochondrial Encephalomyopathies, Molecular Sequence Data, Mutation, Ophthalmoplegia, Chronic Progressive External, Pedigree, Ribonuclease H, RNA

Chronic progressive external ophthalmoplegia (CPEO) is common in mitochondrial disorders and is frequently associated with multiple mtDNA deletions. The onset is typically in adulthood, and affected subjects can also present with general muscle weakness. The underlying genetic defects comprise autosomal-dominant or recessive mutations in several nuclear genes, most of which play a role in mtDNA replication. Next-generation sequencing led to the identification of compound-heterozygous RNASEH1 mutations in two singleton subjects and a homozygous mutation in four siblings. RNASEH1, encoding ribonuclease H1 (RNase H1), is an endonuclease that is present in both the nucleus and mitochondria and digests the RNA component of RNA-DNA hybrids. Unlike mitochondria, the nucleus harbors a second ribonuclease (RNase H2). All affected individuals first presented with CPEO and exercise intolerance in their twenties, and these were followed by muscle weakness, dysphagia, and spino-cerebellar signs with impaired gait coordination, dysmetria, and dysarthria. Ragged-red and cytochrome c oxidase (COX)-negative fibers, together with impaired activity of various mitochondrial respiratory chain complexes, were observed in muscle biopsies of affected subjects. Western blot analysis showed the virtual absence of RNase H1 in total lysate from mutant fibroblasts. By an in vitro assay, we demonstrated that altered RNase H1 has a reduced capability to remove the RNA from RNA-DNA hybrids, confirming their pathogenic role. Given that an increasing amount of evidence indicates the presence of RNA primers during mtDNA replication, this result might also explain the accumulation of mtDNA deletions and underscores the importance of RNase H1 for mtDNA maintenance.

Alternate JournalAm. J. Hum. Genet.
Citation Key10.1016/j.ajhg.2015.05.013
PubMed ID26094573
PubMed Central IDPMC4572567
Grant List322424 / / European Research Council / International
GGP11011 / / Telethon / Italy
GTB12001 / / Telethon / Italy
MC_UP_1002/1 / / Medical Research Council / United Kingdom