Background Next generation sequencing has become the core technology for gene discovery in rare inherited disorders. However, the interpretation of the numerous sequence variants identified remains challenging. We assessed the application of exome sequencing for diagnostics in complex I deficiency, a disease with vast genetic heterogeneity.
Methods Ten unrelated individuals with complex I deficiency were selected for exome sequencing and sequential bioinformatic filtering. Cellular rescue experiments were performed to verify pathogenicity of novel disease alleles.
Results The first filter criterion was ‘Presence of known pathogenic complex I deficiency variants’. This revealed homozygous mutations in NDUFS3 and ACAD9 in two individuals. A second criterion was ‘Presence of two novel potentially pathogenic variants in a structural gene of complex I’, which discovered rare variants in NDUFS8 in two unrelated individuals and in NDUFB3 in a third. Expression of wild-type cDNA in mutant cell lines rescued complex I activity and assembly, thus providing a functional validation of their pathogenicity. Using the third criterion ‘Presence of two potentially pathogenic variants in a gene encoding a mitochondrial protein’, loss-of-function mutations in MTFMT were discovered in two patients. In three patients the molecular genetic correlate remained unclear and follow-up analysis is ongoing.
Conclusion Appropriate in silico filtering of exome sequencing data, coupled with functional validation of new disease alleles, is effective in rapidly identifying disease-causative variants in known and new complex I associated disease genes.
- Exome sequencing
- mitochondrial complex I deficiency
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Funding This work was supported by the Impulse and Networking Fund of the Helmholtz Association in the framework of the Helmholtz Alliance for Mental Health in an Ageing Society (HA-215), the German Federal Ministry of Education and Research (BMBF) funded Systems Biology of Metabotypes grant (SysMBo #0315494A), and the German Network for Mitochondrial Disorders (mitoNET #01GM0867 and 01GM0862). TM is supported by the BMBF funded German Center for Heart Research. TM and TMS were supported by the European Commission 7th Framework Program, Project N. 261123, GEUVADIS and the German Ministry for Education and Research (01GR0804-4). JAM was supported by the Wissenschaftspreis 2008 of the Austrian Paediatric Society (ÖGKJ), WS was supported by the Jubiläumsfonds of Oesterreichische Nationalbank (#12568) and JAM, FZ and WS were supported by the Vereinigung zur pädiatrischen Forschung und Fortbildung Salzburg. MT, HH, and JZ were supported by research project PRVOUK of the Charles University in Prague - First Faculty of Medicine (program MOLMED. VS was supported by the Bundesministerium für Bildung und Forschung (BMBF 01GM0863; mitoNET) and IW by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 815, Project Z1 (Redox-Proteomics). MZ was supported by Telethon GPP 10005, Telethon GGP11011, Cariplo 2011-05-26.
Competing interests None.
Patient consent Obtained.
Ethics approval Ethics approval was provided by the ethics committee of the medical faculty of the Technical University of Munich. Written informed consent was obtained from all study participants or their guardians and the study was approved at the recruiting centre.
Provenance and peer review Not commissioned; externally peer reviewed.