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A considerable body of evidence supports a role for oxidative stress in breast carcinogenesis. Due to their role in producing energy via oxidative phosphorylation, the mitochondria are a major source of production of reactive oxygen species, which may damage DNA. The mitochondrial genome may be particularly susceptible to oxidative damage leading to mitochondrial dysfunction. Genetic variants in mtDNA and nuclear DNA may also contribute to mitochondrial dysfunction. In this review, we address the role of alterations in mtDNA in the etiology of breast cancer. Several studies have shown a relatively high frequency of mtDNA mutations in breast tumor tissue in comparison with mutations in normal breast tissue. To date, several studies have examined the association of genetic variants in mtDNA and breast cancer risk. The G10398A mtDNA polymorphism has received the most attention and has been shown to be associated with increased risk in some studies. Other variants have generally been examined in only one or two studies. Genome-wide association studiesmay help identify new mtDNA variants which modify breast cancer risk. In addition to assessing the main effects of specific variants, gene-gene and gene-environment interactions are likely to explain a greater proportion of the variability in breast cancer risk. [ABSTRACT FROM AUTHOR]

Although there has been considerable debate about whether paternal mitochondrial DNA (mtDNA) transmission may coexist with maternal transmission of mtDNA, it is generally believed that mitochondria and mtDNA are exclusively maternally inherited in humans. Here, we identified three unrelated multigeneration families with a high level of mtDNA heteroplasmy (ranging from 24 to 76%) in a total of 17 individuals. Heteroplasmy of mtDNA was independently examined by high-depth whole mtDNA sequencing analysis in our research laboratory and in two Clinical Laboratory Improvement Amendments and College of American Pathologists-accredited laboratories using multiple approaches. A comprehensive exploration of mtDNA segregation in these families shows biparental mtDNA transmission with an autosomal dominantlike inheritance mode. Our results suggest that, although the central dogma of maternal inheritance of mtDNA remains valid, there are some exceptional cases where paternal mtDNA could be passed to the offspring. Elucidating the molecular mechanism for this unusual mode of inheritance will provide new insights into how mtDNA is passed on from parent to offspring and may even lead to the development of new avenues for the therapeutic treatment for pathogenic mtDNA transmission. [ABSTRACT FROM AUTHOR]

Background: Congenital myasthenic syndrome caused by mutations in AGRN, a gene encoding a protein with a crucial function at the neuromuscular junction, is a rare disorder. There are few studies in this area. We here present two cases with novel mutations of AGRN of which we further investigated possible pathogenesis.Results: Patient 1 had general limb weakness with fluctuation and deterioration in the afternoon and in hot weather. Patient 2 had early-onset weakness of lower extremities with suspected fluctuation in the early stages, which then progressed to the upper limbs. Both distal and proximal muscles were involved. Repetitive stimulation on EMG in both patients showed decrement in proximal and distal limbs. Patient 2 showed a marked response to salbutamol while Patient 1 did not. By targeted exome sequencing, two novel homozygous missense variants, p.L1176P and p.R1698C, in the SEA and LG2 domain of agrin were identified respectively. Further functional analysis revealed instability of the protein and impaired clustering of the acetylcholine receptor (AChR) by both mutations.Conclusions: The mutations identified in AGRN in our study may cause congenital myasthenic syndrome by damaging protein stability and interfering with AChR clustering. These results broaden the understandings on the phenotype, genotype and pathogenesis of this rare disorder. [ABSTRACT FROM AUTHOR]

Background: Mitochondrial presequence proteases perform fundamental functions as they process about 70 % of all mitochondrial preproteins that are encoded in the nucleus and imported posttranslationally. The mitochondrial intermediate presequence protease MIP/Oct1, which carries out precursor processing, has not yet been established to have a role in human disease. Methods: Whole exome sequencing was performed on four unrelated probands with left ventricular non-compaction (LVNC), developmental delay (DD), seizures, and severe hypotonia. Proposed pathogenic variants were confirmed by Sanger sequencing or array comparative genomic hybridization. Functional analysis of the identified MIP variants was performed using the model organism Saccharomyces cerevisiae as the protein and its functions are highly conserved from yeast to human. Results: Biallelic single nucleotide variants (SNVs) or copy number variants (CNVs) in MIPEP, which encodes MIP, were present in all four probands, three of whom had infantile/childhood death. Two patients had compound heterozygous SNVs (p.L582R/p.L71Q and p.E602*/p.L306F) and one patient from a consanguineous family had a homozygous SNV (p. K343E). The fourth patient, identified through the GeneMatcher tool, a part of the Matchmaker Exchange Project, was found to have inherited a paternal SNV (p.H512D) and a maternal CNV (1.4-Mb deletion of 13q12.12) that includes MIPEP. All amino acids affected in the patients' missense variants are highly conserved from yeast to human and therefore S. cerevisiae was employed for functional analysis (for p.L71Q, p.L306F, and p.K343E). The mutations p. L339F (human p.L306F) and p.K376E (human p.K343E) resulted in a severe decrease of Oct1 protease activity and accumulation of non-processed Oct1 substrates and consequently impaired viability under respiratory growth conditions. The p.L83Q (human p.L71Q) failed to localize to the mitochondria. Conclusions: Our findings reveal for the first time the role of the mitochondrial intermediate peptidase in human disease. Loss of MIP function results in a syndrome which consists of LVNC, DD, seizures, hypotonia, and cataracts. Our approach highlights the power of data exchange and the importance of an interrelationship between clinical and research efforts for disease gene discovery. [ABSTRACT FROM AUTHOR]

Diagnosis of mitochondrial disease is often a challenge because of the extreme heterogeneity of the clinical phenotype and the variety of underlying gene defects. Insight into the range of clinical phenotypes associated with a particular mitochondrial DNA mutation will facilitate better recognition of patients at risk by focused gene testing. We present a family affected by the mitochondrial m.13513G>A (p.D393N, ND5) mutation, illustrating a previously unreported degree of clinical heterogeneity, varying from mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) in a 10-year-old female, to a fatal neonatal course with metabolic acidosis and hypotonia in a younger sister, to absence of medical problems in the mother. The mutation loads ranging from 66% in the deceased neonate to 30% in the female with MELAS and 7% in the asymptomatic mother, correlated with severity of the clinical phenotype. The importance of proactive collection and storage of appropriate samples during the diagnostic work-up of an acutely ill or deceased neonate, allowing subsequent mitochondrial investigations, is hereby illustrated. [ABSTRACT FROM AUTHOR]

Assesses the utility of quantitative and qualitative analysis of mitochondrial DNA (mtDNA) in longitudinal peripheral blood samples from HIV-infected patients treated with nucleoside reverse transcriptase inhibitor (NRTI) agents. Performance of a complete analysis of the entire mtDNA genome in addition to mtDNA depletion; Inability to detect depletion in blood mtDNA levels of subjects with clinical mitochondrial toxicities; Identification of NRTI use as the only factor associated with mtDNA depletion.