Mutations in NDUFAF3 (C3ORF60), encoding an NDUFAF4 (C6ORF66)-interacting complex I assembly protein, cause fatal neonatal mitochondrial disease.

Mitochondrial complex I deficiency is the most prevalent and least understood disorder of the oxidative phosphorylation system. The genetic cause of many cases of isolated complex I deficiency is unknown because of insufficient understanding of the complex I assembly process and the factors involved. We performed homozygosity mapping and gene sequencing to identify the genetic defect in five complex I-deficient patients from three different families. All patients harbored mutations in the NDUFAF3 (C3ORF60) gene, of which the pathogenic nature was assessed by NDUFAF3-GFP baculovirus complementation in fibroblasts. We found that NDUFAF3 is a genuine mitochondrial complex I assembly protein that interacts with complex I subunits. Furthermore, we show that NDUFAF3 tightly interacts with NDUFAF4 (C6ORF66), a protein previously implicated in complex I deficiency. Additional gene conservation analysis links NDUFAF3 to bacterial-membrane-insertion gene cluster SecF/SecD/YajC and to C8ORF38, also implicated in complex I deficiency. These data not only show that NDUFAF3 mutations cause complex I deficiency but also relate different complex I disease genes by the close cooperation of their encoded proteins during the assembly process.

TMEM70 mutations are a common cause of nuclear encoded ATP synthase assembly defect: further delineation of a new syndrome.

BACKGROUND: The TMEM70 gene defect was recently identified as a novel cause of autosomal recessive ATP synthase deficiency. Most of the 28 patients with TMEM70 disorder reported to date display a distinctive phenotype characterised by neonatal onset of severe muscular hypotonia hypertrophic cardiomyopathy, facial dysmorphism, profound lactic acidosis, and 3-methylglutaconic aciduria. Almost all share a common Roma descent and are homozygous for a single founder splice site mutation. METHODS: Six new patients from four separate families, with clinical and biochemical diagnosis of ATP synthase deficiency, were studied. TMEM70 sequence analysis of the three exons and their flanking splice junction consensus sequences was performed in all patients. In addition their clinical phenotype and disease course was strictly studied. RESULTS: Four novel deleterious homozygous TMEM70 mutations were identified. The previously described clinical spectrum was expanded to include infantile onset cataract, early onset gastrointestinal dysfunction and congenital hypertonia with multiple contractures resembling arthrogryposis. The first characterisation of fetal presentation of the syndrome is also provided, featuring significant intrauterine growth retardation, severe oligohydramnios, fetal hypotonia, and myocardial wall thickening. CONCLUSIONS: The current report corroborates the previously described unique phenotype of TMEM70 deficiency. The study identifies TMEM70 gene defect as a pan-ethnic disorder and further redefines it as the most common cause of nuclear-origin ATP synthase deficiency.

The unique neuroradiology of complex I deficiency due to NDUFA12L defect.

In two patients who presented at late infancy with hypotonia, nystagmus and ataxia, interspersed with acute episodes of encephalopathy, we identified a mutation in a complex I assembly factor, NDUFA12L, which resulted in a marked reduction of the NDUFA12L protein and of complex I activity. The involvement of the mamillothalamic tracts, substantia nigra/medial lemniscus, medial longitudinal fasciculus, the corpus medullare and the cerebellum, with relative sparing of the cortex and subcortical white matter was distinctive and resembled the findings in the first and only known patient with mutation in the NDUFA12L gene.