Recurrent De Novo Dominant Mutations in SLC25A4 Cause Severe Early-Onset Mitochondrial Disease and Loss of Mitochondrial DNA Copy Number

Abstract

Mutations in SLC25A4 encoding the mitochondrial ADP/ATP carrier AAC1 are well-recognized causes of mitochondrial disease. Several heterozygous SLC25A4 mutations cause adult-onset autosomal-dominant progressive external ophthalmoplegia associated with multiple mitochondrial DNA deletions, whereas recessive SLC25A4 mutations cause childhood-onset mitochondrial myopathy and cardiomyopathy. Here, we describe the identification by whole-exome sequencing of seven probands harboring dominant, de novo SLC25A4 mutations. All affected individuals presented at birth, were ventilator dependent and, where tested, revealed severe combined mitochondrial respiratory chain deficiencies associated with a marked loss of mitochondrial DNA copy number in skeletal muscle. Strikingly, an identical c.239G>A (p.Arg80His) mutation was present in four of the seven subjects, and the other three case subjects harbored the same c.703C>G (p.Arg235Gly) mutation. Analysis of skeletal muscle revealed a marked decrease of AAC1 protein levels and loss of respiratory chain complexes containing mitochondrial DNA-encoded subunits. We show that both recombinant AAC1 mutant proteins are severely impaired in ADP/ATP transport, affecting most likely the substrate binding and mechanics of the carrier, respectively. This highly reduced capacity for transport probably affects mitochondrial DNA maintenance and in turn respiration, causing a severe energy crisis. The confirmation of the pathogenicity of these de novo SLC25A4 mutations highlights a third distinct clinical phenotype associated with mutation of this gene and demonstrates that early-onset mitochondrial disease can be caused by recurrent de novo mutations, which has significant implications for the application and analysis of whole-exome sequencing data in mitochondrial disease.

Biallelic mutations in mitochondrial tryptophanyl‐tRNA synthetase cause Levodopa‐responsive infantile‐onset Parkinsonism

“…Control fibroblasts were purchased from Coriell Institute for Medical Research. For quantification of WARS2 and oxidative phosphorylation in dermal fibroblasts, human fibroblasts were trypsinized, pelleted, and resuspended in cell lysis buffer as previously described, using the following antibodies: COXI (Abcam cat# ab14705), SDHA (Abcam cat# ab14715), UQCRC2 (Abcam cat# ab14745), NDUFB8 (Abcam cat# ab110242), MT‐ATP6 (ProteinTech cat# 55313‐1‐AP), WARS2 (kind gift from Prof. Roger D. Cox, and from SAB1406979, Sigma Aldrich) and α‐tubulin (Abcam cat# ab7291), and HRP‐conjugated secondary antibodies (Dako Cytomation).…”

“…18 Control fibroblasts were purchased from Coriell Institute for Medical Research. For quantification of WARS2 and oxidative phosphorylation in dermal fibroblasts, human fibroblasts were trypsinized, pelleted, and resuspended in cell lysis buffer as previously described, 19 3 | RESULTS…”

OXA 1L mutations cause mitochondrial encephalopathy and a combined oxidative phosphorylation defect

“…Protein extraction from human skeletal muscle and fibroblast samples for SDS–PAGE and subsequent Western blotting was carried out as described previously (Thompson et al , ). Blue Native PAGE was conducted on mitochondria isolated from skeletal muscle and fibroblasts samples as described previously (Oláhová et al , ) using antibodies against COXI (Abcam ab14705), SDHA (Abcam ab14715), Porin/VDAC1 (Abcam ab14734), UQCRC2 (Abcam ab14745), NDUFB8 (Abcam ab110242), ATP5A (Abcam ab14748), ATP5B (Abcam ab14730) and OXA1L (Proteintech 21055‐1‐AP).…”

The inner mitochondrial membrane protein ANT1 modulates IL‐6 expression via the JNK pathway in macrophages

“…In the present study, we focused on the function of ANT1 in immune cells. ANT1 is a critical protein for mitochondrial function and its gene is responsible for mitochondrial diseases . ANT1 functions have been primarily examined in the heart and brain, where ANT1 is strongly expressed , but they have not been clarified in immune cells.…”