While >300 disease-causing variants have been identified in the mitochondrial DNA (mtDNA) polymerase γ, no mitochondrial phenotypes have been associated with POLRMT, the RNA polymerase responsible for transcription of the mitochondrial genome. Here, we characterise the clinical and molecular nature of POLRMT variants in eight individuals from seven unrelated families. Patients present with global developmental delay, hypotonia, short stature, and speech/intellectual disability in childhood; one subject displayed an indolent progressive external ophthalmoplegia phenotype. Massive parallel sequencing of all subjects identifies recessive and dominant variants in the POLRMT gene. Patient fibroblasts have a defect in mitochondrial mRNA synthesis, but no mtDNA deletions or copy number abnormalities. The in vitro characterisation of the recombinant POLRMT mutants reveals variable, but deleterious effects on mitochondrial transcription. Together, our in vivo and in vitro functional studies of POLRMT variants establish defective mitochondrial transcription as an important disease mechanism.
- MeSH
- dítě MeSH
- DNA řízené RNA-polymerasy chemie genetika MeSH
- dospělí MeSH
- fibroblasty metabolismus patologie MeSH
- genetická transkripce * MeSH
- kojenec MeSH
- lidé MeSH
- messenger RNA genetika metabolismus MeSH
- mitochondriální DNA genetika MeSH
- mitochondrie genetika MeSH
- mladiství MeSH
- mladý dospělý MeSH
- mutace genetika MeSH
- nemoci nervového systému genetika patologie MeSH
- oxidativní fosforylace MeSH
- podjednotky proteinů metabolismus MeSH
- proteinové domény MeSH
- rodokmen MeSH
- Check Tag
- dítě MeSH
- dospělí MeSH
- kojenec MeSH
- lidé MeSH
- mladiství MeSH
- mladý dospělý MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
Isolated complex I deficiency is a common biochemical phenotype observed in pediatric mitochondrial disease and often arises as a consequence of pathogenic variants affecting one of the ∼65 genes encoding the complex I structural subunits or assembly factors. Such genetic heterogeneity means that application of next-generation sequencing technologies to undiagnosed cohorts has been a catalyst for genetic diagnosis and gene-disease associations. We describe the clinical and molecular genetic investigations of four unrelated children who presented with neuroradiological findings and/or elevated lactate levels, highly suggestive of an underlying mitochondrial diagnosis. Next-generation sequencing identified bi-allelic variants in NDUFA6, encoding a 15 kDa LYR-motif-containing complex I subunit that forms part of the Q-module. Functional investigations using subjects' fibroblast cell lines demonstrated complex I assembly defects, which were characterized in detail by mass-spectrometry-based complexome profiling. This confirmed a marked reduction in incorporated NDUFA6 and a concomitant reduction in other Q-module subunits, including NDUFAB1, NDUFA7, and NDUFA12. Lentiviral transduction of subjects' fibroblasts showed normalization of complex I. These data also support supercomplex formation, whereby the ∼830 kDa complex I intermediate (consisting of the P- and Q-modules) is in complex with assembled complex III and IV holoenzymes despite lacking the N-module. Interestingly, RNA-sequencing data provided evidence that the consensus RefSeq accession number does not correspond to the predominant transcript in clinically relevant tissues, prompting revision of the NDUFA6 RefSeq transcript and highlighting not only the importance of thorough variant interpretation but also the assessment of appropriate transcripts for analysis.
- MeSH
- alely MeSH
- fenotyp MeSH
- fibroblasty patologie MeSH
- genetická heterogenita MeSH
- kojenec MeSH
- lidé MeSH
- mitochondriální nemoci genetika MeSH
- mitochondriální proteiny genetika MeSH
- mitochondrie genetika MeSH
- mutace genetika MeSH
- respirační komplex I nedostatek genetika MeSH
- sekvence aminokyselin MeSH
- sekvenční seřazení MeSH
- Check Tag
- kojenec MeSH
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Background: Mutations in the RMND1 (Required for Meiotic Nuclear Division protein 1) gene have recently been linked to infantile onset mitochondrial disease characterised by multiple mitochondrial respiratory chain defects. Methods: We summarised the clinical, biochemical and molecular genetic investigation of an international cohort of affected individuals with RMND1 mutations. In addition, we reviewed all the previously published cases to determine the genotype-phenotype correlates and performed survival analysis to identify prognostic factors. Results: We identified 14 new cases from 11 pedigrees that harbour recessive RMND1 mutations, including 6 novel variants: c.533C>A, p.(Thr178Lys); c.565C>T, p.(Gln189*); c.631G>A, p.(Val211Met); c.1303C>T, p.(Leu435Phe); c.830+1G>A and c.1317+1G>T. Together with all previously published cases (n=32), we show that congenital sensorineural deafness, hypotonia, developmental delay and lactic acidaemia are common clinical manifestations with disease onset under 2 years. Renal involvement is more prevalent than seizures (66% vs 44%). In addition, median survival time was longer in patients with renal involvement compared with those without renal disease (6 years vs 8 months, p=0.009). The neurological phenotype also appears milder in patients with renal involvement. Conclusions: The clinical phenotypes and prognosis associated with RMND1 mutations are more heterogeneous than that were initially described. Regular monitoring of kidney function is imperative in the clinical practice in light of nephropathy being present in over 60% of cases. Furthermore, renal replacement therapy should be considered particularly in those patients with mild neurological manifestation as shown in our study that four recipients of kidney transplant demonstrate good clinical outcome to date.
We report a sporadic case of congenital muscular dystrophy (CMD) in a 13-year-old girl with early manifestation of muscle weakness and hypotonia, severe contractures, bulbar syndrome, progressive external ophtalmoplegia, and white matter changes on magnetic resonance imaging (MRI) of the brain, but no mental defect. Serum creatine kinase (CK) level was normal. Muscle biopsy revealed a dystrophic picture with a prominent inflammatory infiltrate mimicking inflammatory myopathy-typical histological findings in CMD. Immunostaining showed normal expression of merosin, alpha and beta-dystroglycans. Mutation analyses of calpain3, dysferlin, and SEPN1 genes were negative. An electron microscopy revealed the accumulation of abnormally enlarged mitochondria located under the sarcolemma. Measurement of respiratory chain enzyme activities did not reveal any biochemical defect and mitochondrial genetic studies, including sequencing of the entire mitochondrial genome, were unremarkable. Phenotypic presentation of our patient is very unusual and differs considerably from other CMD variants.
- MeSH
- financování organizované MeSH
- kreatinkinasa krev MeSH
- lidé MeSH
- magnetická rezonanční tomografie metody MeSH
- mladiství MeSH
- mozek patofyziologie MeSH
- myotonická dystrofie komplikace krev patologie MeSH
- neuroglie patologie MeSH
- oftalmoplegie etiologie MeSH
- Check Tag
- lidé MeSH
- mladiství MeSH
- ženské pohlaví MeSH
- Publikační typ
- kazuistiky MeSH
2nd ed. 12, 940 s. : il.
- MeSH
- péče o pacienty v kritickém stavu MeSH
- Publikační typ
- příručky MeSH
- Konspekt
- Patologie. Klinická medicína
- NLK Obory
- anesteziologie a intenzivní lékařství
- ošetřovatelství
3rd ed. XLVIII, 2363 s. : obr., tab., grafy ; 28 cm
2nd ed. xlvi, 1998 s.
- Konspekt
- Patologie. Klinická medicína
- NLK Obory
- anesteziologie a intenzivní lékařství
- NLK Publikační typ
- kolektivní monografie
