Background Mitochondrial complex I deficiency is the most common cause of mitochondrial disease in childhood. Identification of the molecular basis is difficult given the clinical and genetic heterogeneity. Most patients lack a molecular definition in routine diagnostics.
Methods A large-scale mutation screen of 75 candidate genes in 152 patients with complex I deficiency was performed by high-resolution melting curve analysis and Sanger sequencing. The causal role of a new disease allele was confirmed by functional complementation assays. The clinical phenotype of patients carrying mutations was documented using a standardised questionnaire.
Results Causative mutations were detected in 16 genes, 15 of which had previously been associated with complex I deficiency: three mitochondrial DNA genes encoding complex I subunits, two mitochondrial tRNA genes and nuclear DNA genes encoding six complex I subunits and four assembly factors. For the first time, a causal mutation is described in NDUFB9, coding for a complex I subunit, resulting in reduction in NDUFB9 protein and both amount and activity of complex I. These features were rescued by expression of wild-type NDUFB9 in patient-derived fibroblasts.
Conclusion Mutant NDUFB9 is a new cause of complex I deficiency. A molecular diagnosis related to complex I deficiency was established in 18% of patients. However, most patients are likely to carry mutations in genes so far not associated with complex I function. The authors conclude that the high degree of genetic heterogeneity in complex I disorders warrants the implementation of unbiased genome-wide strategies for the complete molecular dissection of mitochondrial complex I deficiency.
- Mitochondrial complex I deficiency
- high resolution melting curve analysis
- lentiviral complementation
- genetic screening/counselling
- molecular genetics
- metabolic disorders
- Complex I, neurology
- neuromuscular disease
- muscle disease
- clinical genetics
Statistics from Altmetric.com
TBH, FM, MH and EL contributed equally to this work.
Funding TM and HP were 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) and the German Federal Ministry of Education and Research (BMBF) funded German Center for Diabetes Research (DZD e.V.) and Systems Biology of Metabotypes grant (SysMBo #0315494A). EL, FI, TM, MZ and HP were supported by the grant RF-INN-2007-634163 from the Italian Ministry of Health. TM, PF and HP were supported by the BMBF funded German Network for Mitochondrial Disorders (mitoNET #01GM0867). EL, FI and MZ were supported by the Pierfranco and Luisa Mariani Foundation Italy, Fondazione Telethon Italy grants number GGP07019 and GGPP10005, Fondazione MitoCon-ONLUS, Fondazione Giuseppe Tomasello–ONLUS, and grant RF-INN-2007-634163. JAM and WS were supported by the Österreichische Nationalbank-Jubiläumsfonds grant number 12568 and the Vereinigung zur Pädiatrischen Forschung und Fortbildung Salzburg.
Competing interests None.
Patient consent Obtained.
Ethics approval Ethics committee, Faculty of Medicine, Technical University of Munich.
Provenance and peer review Not commissioned; externally peer reviewed.