The mitochondrial DNA (mtDNA) m.3243A>G mutation is one of the most common pathogenic mtDNA variants. The phenotypes associated with this mutation range from asymptomatic induviduals to well-defined clinical syndromes, or non-syndromic mitochondrial disorders. Variable clinical features in pediatric cases may cause difficulty in diagnosis. Kidney involvement in this mutation is uncommon and reported on a case-by-case basis. Here, we report on a patient with m.3243A>G mutation, who presented with short stature and proteinuria, and his family, who share the same genotype but exhibit different heteroplasmy levels in different tissues and variable phenotypes. A 15-year-old male patient was admitted to the pediatric endocrinology department with short stature. His examinations revealed nephrotic range proteinuria, hearing loss, impaired glucose tolerance, and Wolf-Parkinson-White syndrome. From family history, it was learned that diabetes mellitus (DM) and progressive sensorineural hearing loss were common in this family. The patient's mother, who had chronic kidney disease, DM, and hearing loss, had died suddenly for an unknown reason. Considering the family history, a genetic analysis was performed for mitochondrial disease. Mitochondrial DNA analysis revealed a m.3243A>G mutation with 47% heteroplasmy in blood, 62% heteroplasmy in buccal cells, and 96% heteroplasmy in urothelial cells in our patient. Short stature without any other complaint and renal involvement are rare findings in m.3243A>G mutation. In patients presenting with proteinuria, in the presence of conditions affecting many systems such as endocrine system pathologies, hearing loss, and cardiac pathologies, and in the presence of individuals with a similar family history of multiple organ involvement, mitochondrial diseases should be considered, and examined from this perspective. Our case illustrates the value of a detailed medical and family history.

Mithocondropathies are inherited disorders that can result from abnormalities in the mitochondrial or nuclear DNA. Genetic abnormalities impacting the mitochondrial DNA (mtDNA) are consequently passed down through the maternal line. Renal manifestations of mtDNA disorders are often poorly recognized or misdiagnosed for the widely diverse phenotypic expression of this condition. Here we describe the case of a 34-year-old man with a history of chronic kidney disease, proteinuria, diabetes mellitus and sensorineural hearing loss, with worsening renal function and proteinuria with positive family history. Kidney biopsy showed focal segmental glomerulosclerosis (FSGS) and whole exome sequencing revealed a mtDNA point mutation (A→G) at position 3243 which code for a transfer RNA (tRNALeu(UUR)). Different point mutations in mitochondrial DNA have now been associated with focal segmental glomerulosclerosis but genetic screening for mtDNA mutations is often neglected and this condition overlooked. Consideration of an underlying mitochondrial disease should be made in patients presenting with deafness, diabetes, renal failure and a positive family history of kidney disease.

The syndrome of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is one of the most common inherited mitochondrial disorders. A 33- year-old male was admitted due to edema, urinary retention, and reduce urinary output. The medical history included a pigmentary retinopathy (PR) at age of 22 and uveitis at age of 30, which were both treated with prednisolone. At age of 32, unapparent bilateral sensorineural hearing loss (SNHL) and symmetric basal ganglia calcifications were observed in neurologic study, and received prednisolone for the diagnosis of migraine and undefined vasculitis. Also, he described a right transient ischemic stroke (TIA) in the past 4 months. His family history included a dead brother, who had nearly similar components. Physical exam on admission corresponded with parkinsonism. The status points to MELAS but the genetic test was not available. Additional tests were applied, excluding all other disorders. Lactate was normal in serum and CSF. Kidney tests revealed a nephrotic syndrome and glomerulopathy, and the biopsy showed a single hyalinized glomerulus, which most likely suggests focal segmental glomerulosclerosis (FSGS). Muscle biopsy showed ragged red fibers. Here, we report a challenging case of MELAS syndrome with rare manifestations including uveitis, PR, parkinsonism, and FSGS in the absence of lactic acidosis with unapparent muscle or hearing impairments. Since, clinicians might misdiagnose MELAS as vasculitis or other disorders due to its heterogeneous presentations, a proper investigations should guide the diagnosis of these conditions to reduce the delay of diagnosis and ineffective treatments.

Primary coenzyme Q10 (CoQ10) deficiency refers to a group of mitochondrial cytopathies caused by genetic defects in CoQ10 biosynthesis. Primary coenzyme Q10 deficiency-6 (COQ10D6) is an autosomal recessive disorder attributable to biallelic COQ6 variants; the cardinal phenotypes are steroid-resistant nephrotic syndrome (SRNS), which inevitably progresses to kidney failure, and sensorineural hearing loss (SNHL). Here, we describe the phenotypes and genotypes of 12 children with COQ10D6 from 11 unrelated Korean families and quantitatively explore the beneficial effects of CoQ10 replacement therapy on SNHL. A diagnosis of SRNS generally precedes SNHL documentation. COQ10D6 is associated with progressive SNHL. Four causative COQ6 variants were identified in either homozygotes or compound heterozygotes: c.189_191delGAA, c.484C>T, c.686A>C, and c.782C>T. The response rate (no further hearing loss or improvement) was 42.9%; CoQ10 replacement therapy may thus limit and even improve hearing loss. Notably, the audiological benefit appeared to be genotype-specific, suggesting a genotype-phenotype correlation. The results of cochlear implantation were generally favorable, and the effects were sustained over time. Our results thus propose the beneficial effects of CoQ10 replacement therapy on hearing loss. Our work with COQ10D6 patients is a good example of personalized, genetically tailored, audiological rehabilitation of patients with syndromic deafness.

Primary Coenzyme Q10 deficiency is a rare mitochondriopathy with a wide spectrum of organ involvement, including steroid-resistant nephrotic syndrome mainly associated with disease-causing variants in the genes COQ2, COQ6 or COQ8B. We performed a systematic literature review, PodoNet, mitoNET, and CCGKDD registries queries and an online survey, collecting comprehensive clinical and genetic data of 251 patients spanning 173 published (47 updated) and 78 new cases. Kidney disease was first diagnosed at median age 1.0, 1.2 and 9.8 years in individuals with disease-causing variants in COQ2, COQ6 and COQ8B, respectively. Isolated kidney involvement at diagnosis occurred in 34% of COQ2, 10.8% of COQ6 and 70.7% of COQ8B variant individuals. Classic infantile multiorgan involvement comprised 22% of the COQ2 variant cohort while 47% of them developed neurological symptoms at median age 2.7 years. The association of steroid-resistant nephrotic syndrome and sensorineural hearing loss was confirmed as the distinctive phenotype of COQ6 variants, with hearing impairment manifesting at average age three years. None of the patients with COQ8B variants, but 50% of patients with COQ2 and COQ6 variants progressed to kidney failure by age five. At adult age, kidney survival was equally poor (20-25%) across all disorders. A number of sequence variants, including putative local founder mutations, had divergent clinical presentations, in terms of onset age, kidney and non-kidney manifestations and kidney survival. Milder kidney phenotype was present in those with biallelic truncating variants within the COQ8B variant cohort. Thus, significant intra- and inter-familial phenotype variability was observed, suggesting both genetic and non-genetic modifiers of disease severity.