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Leigh syndrome (LS)/Leigh-like syndrome (LLS) is one of the most common mitochondrial disease subtypes, caused by mutations in either the nuclear or mitochondrial genomes. Here, we identified a novel intronic mutation (c.82-2 A > G) and a novel exonic insertion mutation (c.290dupT) in TMEM126Bfrom a Chinese patient with clinical manifestations of LLS. In silico predictions, minigene splicing assays and patients’ RNA analyses determined that the c.82-2 A > G mutation resulted in complete exon 2 skipping, and the c.290dupT mutation provoked partial and complete exon 3 skipping, leading to translational frameshifts and premature termination. Functional analysis revealed the impaired mitochondrial function in patient-derived lymphocytes due to severe complex I content and assembly defect. Altogether, this is the first report of LLS in a patient carrying mutations in TMEM126B. Our data uncovers the functional effect and the molecular mechanism of the pathogenic variants c.82-2 A > G and c.290dupT, which expands the gene mutation spectrum of LLS and clinical spectrum caused by TMEM126Bmutations, and thus help to clinical diagnosis of TMEM126Bmutation‐related mitochondrial diseases.

TOM70 is a member of the TOM complex that transports cytosolic proteins into mitochondria. Here, we identified two compound heterozygous variants in TOMM70[c.794C>T (p.T265M) and c.1745C>T (p.A582V)] from a patient with severe anemia, lactic acidosis, and developmental delay. Patient-derived immortalized lymphocytes showed decreased TOM70 expression, oligomerized TOM70 complex, and TOM 20/22/40 complex compared with expression in control lymphocytes. Functional analysis revealed that patient-derived cells exhibited multi-oxidative phosphorylation system (OXPHOS) complex defects, with complex IV being primarily affected. As a result, patient-derived cells grew slower in galactose medium and generated less ATP and more extracellular lactic acid than did control cells. In vitro cell model compensatory experiments confirmed the pathogenicity of TOMM70variants since only wild-type TOM70, but not mutant TOM70, could restore the complex IV defect and TOM70 expression in TOM70 knockdown U2OS cells. Altogether, we report the first case of mitochondrial disease-causing mutations in TOMM70and demonstrate that TOM70 is essential for multi-OXPHOS assembly. Mutational screening of TOMM70should be employed to identify mitochondrial disease-causing gene mutations in the future.

Leigh syndrome is one of the most common subtypes of mitochondrial disease. Mutations in encoding genes of oxidative phosphorylation complexes have been frequently reported, of which, MTATP6was one of the most frequently reported genes for Leigh syndrome. In this study, by using next-generation sequencing targeted to MitoExome in a patient with clinical manifestations of Leigh syndrome, two missense mutations of NDUFS3(c.418 C > T/p.R140W and c.595 C > T/p.R199W) were identified, of which c.418 C > T was novel. Functionally, the patient derived lymphoblastoid cells showed decreased amount of NDUFS3 and complex I assembly when compared with two control cells. Although NDUFS3mutations have been related to late onset Leigh syndrome, we found that the patient carrying these two mutations developed an early onset Leigh syndrome. To our knowledge, this is the second study on patient carrying NDUFS3mutations. In conclusion, we identified a novel Leigh syndrome causing NDUFS3mutation and expanded the clinical spectrum caused by NDUFS3mutations in this study.

By using next-generation sequencing targeted to MitoExome including the entire mtDNA and exons of 1033 genes encoding the mitochondrial proteome, we described here a novel m.11240C>T mutation in the mitochondrial ND4 genefrom a patient with Leigh syndrome. High mutant loads of m.11240C>T were detected in blood, urinary epithelium, oral mucosal epithelium cells, and skin fibroblasts of the patient. Decreased mitochondrial complex I activity was found in transmitochondrial cybrids containing the m.11240C>T mutation with biochemical analysis. Furthermore, functional investigations confirmed that mitochondria with the m.11240C>T variant exhibited lower adenosine triphosphate-related mitochondrial respiration. However, complex I assembly in mutant cybrids was not affected. While this mutation was located in the fourth hydrophobic trans-membrane region of ND4 gene, we suggested that mutation of m.11240C>T might impair the proton pumping channel of complex I but had little effect on the complex I assembly. In conclusion, we identified m.11240C>T as a novel mitochondrial disease-related mtDNA mutation.

Mutations in the fukutin-related protein (FKRP) gene have been associated with dystroglycanopathies, which are common in Europe but rare in Asia. Our study aimed to retrospectively analyze and characterize the clinical, myopathological and genetic features of 12 Chinese patients with FKRPmutations. Three patients were diagnosed with congenital muscular dystrophy type 1C (MDC1C) and nine patients were diagnosed with limb girdle muscular dystrophy type 2I (LGMD2I). Three muscle biopsy specimens had dystrophic changes and reduced glycosylated a-dystroglycan staining, and two showed reduced expression of laminin a2. Two known and 13 novel mutations were identified in our single center cohort. Interestingly, the c.545A>G mutation was found in eight of the nine LGMD2I patients as a founder mutation and this founder mutation in Chinese patients differs from the one seen in European patients. Moreover, patients homozygous for the c.545A>G mutation were clinically asymptomatic, a less severe phenotype than in compound heterozygous patients with the c.545A>G mutation. The 13 novel mutations of FKRP significantly expanded the mutation spectrum of MDC1C and LGMD2I, and the different founder mutations indicate the ethnic difference in FKRPmutations.

The originally published version of this article contained an error in Figure 1. The correct figure of this article should have read as below. This has now been corrected in the PDF and HTML versions of the article. The authors apologize for any inconvenience caused.