A constant and similar assembly defect of mitochondrial respiratory chain complex I allows rapid identification of NDUFS4 mutations in patients with Leigh syndrome

AbstractIsolated complex I deficiency is a frequent cause of respiratory chain defects in childhood. In this study, we report our systematic approach with blue native PAGE (BN-PAGE) to study mitochondrial respiratory chain assembly in skin fibroblasts from patients with Leigh syndrome and CI deficiency. We describe five new NDUFS4 patients with a similar and constant abnormal BN-PAGE profile and present a meta-analysis of the literature. All NDUFS4 mutations that have been tested with BN-PAGE result in a constant and similar abnormal assembly profile with a complete loss of the fully assembled complex I usually due to a truncated protein and the loss of its canonical cAMP dependent protein kinase phosphorylation consensus site. We also report the association of abnormal brain MRI images with this characteristic BN-PAGE profile as the hallmarks of NDUFS4 mutations and the first founder NDUFS4 mutations in the North-African population

The human OPA1delTTAG mutation induces premature age-related systemic neurodegeneration in mouse

Dominant optic atrophy is a rare inherited optic nerve degeneration caused by mutations in the mitochondrial fusion gene OPA1. Recently, the clinical spectrum of dominant optic atrophy has been extended to frequent syndromic forms, exhibiting various degrees of neurological and muscle impairments frequently found in mitochondrial diseases. Although characterized by a specific loss of retinal ganglion cells, the pathophysiology of dominant optic atrophy is still poorly understood. We generated an Opa1 mouse model carrying the recurrent Opa1(delTTAG) mutation, which is found in 30% of all patients with dominant optic atrophy. We show that this mouse displays a multi-systemic poly-degenerative phenotype, with a presentation associating signs of visual failure, deafness, encephalomyopathy, peripheral neuropathy, ataxia and cardiomyopathy. Moreover, we found premature age-related axonal and myelin degenerations, increased autophagy and mitophagy and mitochondrial supercomplex instability preceding degeneration and cell death. Thus, these results support the concept that Opa1 protects against neuronal degeneration and opens new perspectives for the exploration and the treatment of mitochondrial diseases

Relative frequencies of inherited retinal dystrophies and optic neuropathies in Southern France: assessment of 21-year data management

PURPOSE: Inherited retinal dystrophies (IRDs) and inherited optic neuropathies (IONs) are rare diseases defined by specific clinical and molecular features. The relative prevalence of these conditions was determined in Southern France. METHODS: Patients recruited from a specialized outpatient clinic over a 21-year period underwent extensive clinical investigations and 107 genes were screened by polymerase chain reaction/sequencing. RESULTS: There were 1957 IRD cases (1481 families) distributed in 70% of pigmentary retinopathy cases (56% non-syndromic, 14% syndromic), 20% maculopathies and 7% stationary conditions. Patients with retinitis pigmentosa were the most frequent (47%) followed by Usher syndrome (10.8%). Among non-syndromic pigmentary retinopathy patients, 84% had rod-cone dystrophy, 8% cone-rod dystrophy and 5% Leber congenital amaurosis. Macular dystrophies were encountered in 398 cases (30% had Stargardt disease and 11% had Best disease). There were 184 ION cases (127 families) distributed in 51% with dominant optic neuropathies, 33% with recessive/sporadic forms and 16% with Leber hereditary optic neuropathy. Positive molecular results were obtained in 417/609 families with IRDs (68.5%) and in 27/58 with IONs (46.5%). The sequencing of 5 genes (ABCA4, USH2A, MYO7A, RPGR and PRPH2) provided a positive molecular result in 48% of 417 families with IRDs. Except for autosomal retinitis pigmentosa, in which less than half the families had positive molecular results, about 75% of families with other forms of retinal conditions had a positive molecular diagnosis. CONCLUSIONS: Although gene discovery considerably improved molecular diagnosis in many subgroups of IRDs and IONs, retinitis pigmentosa, accounting for almost half of IRDs, remains only partly molecularly defined

Assembly defects induce oxidative stress in inherited mitochondrial complex I deficiency

Complex I (CI) deficiency is the most common respiratory chain defect representing more than 30% of mitochondrial diseases. CI is an L-shaped multi-subunit complex with a peripheral arm protruding into the mitochondrial matrix and a membrane arm. CI sequentially assembled into main assembly intermediates: the P (pumping), Q (Quinone) and N (NADH dehydrogenase) modules. In this study, we analyzed 11 fibroblast cell lines derived from patients with inherited CI deficiency resulting from mutations in the nuclear or mitochondrial DNA and impacting these different modules. In patient cells carrying a mutation located in the matrix arm of CI, blue native-polyacrylamide gel electrophoresis (BN-PAGE) revealed a significant reduction of fully assembled CI enzyme and an accumulation of intermediates of the N module. In these cell lines with an assembly defect, NADH dehydrogenase activity was partly functional, even though CI was not fully assembled. We further demonstrated that this functional N module was responsible for ROS production through the reduced flavin mononucleotide. Due to the assembly defect, the FMN site was not re-oxidized leading to a significant oxidative stress in cell lines with an assembly defect. These findings not only highlight the relationship between CI assembly and oxidative stress, but also show the suitability of BN-PAGE analysis in evaluating the consequences of CI dysfunction. Moreover, these data suggest that the use of antioxidants may be particularly relevant for patients displaying a CI assembly defect

Labour management of a woman with carnitine palmitoyl transferase type 2 deficiency

Carnitine palmitoyl transferase (CPT) type 2 deficiency is a disorder of mitochondrial fatty acid oxidation. In situations where energy stores are inadequate, such as may occur during labour women with CPT type 2 deficiency are at risk of rhabdomyolysis. There is limited experience in the management of women with this condition in labour. We report a case of successful labour management of a woman with CPT type 2 deficiency, together with a brief review of the published case reports and a discussion of the issues surrounding anaesthetic management.E.M. Slater, R. Grivell and A.M. Cyn