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[A case of Kearns-Sayre syndrome whose asymptomatic mother had abnormal mitochondria in skeletal muscle].

The mode of inheritance of Kearns-Sayre syndrome (KSS) and chronic progressive external ophthalmoplegia (CPEO) have not yet been established, since most cases are sporadic. We studied skeletal muscle pathology and mitochondrial DNA (mtDNA) in a sporadic KSS patient (proband) and examined mitochondrial function of the muscle in his asymptomatic family members. The proband was a 56-year-old male with bilateral ptosis, external ophthalmoplegia, retinal degeneration and cardiac conduction disturbance. Biopsied deltoid muscle showed 9.7% of ragged red fibers without cytochrome oxidase (COX) activity and abnormal mitochondria on electron microscopy. Analysis of muscle mtDNA revealed a 4,977 bp deletion between nt. 8,483 and 13,459. None of the family members had symptoms similar to those of the proband. However, an aerobic exercise test of 15W for 15 minutes with an ergometer induced a marked increase in serum lactate levels in the proband's mother. Histology of her biopsied deltoid muscle showed 0.3% of ragged red fibers without COX activity and morphologically abnormal mitochondria. These findings indicate that the abnormal mitochondria of the proband were transmitted from his asymptomatic mother. This also suggests that some of the sporadic KSS/CPEO cases are inherited one.

Aged↗

[A case of chronic progressive external ophthalmoplegia with severe scoliosis].

The Authors reports a case of myopathy with severe scoliosis which can be classified within the context of chronic progressive external ophthalmoplegia (CPEO) and discusses the complex etiopathogenetic, histological and clinical aspects of this mitochondrial myopathy. In particular, they underlines the severity of the scoliosis and muscular, bone and respiratory symptoms in this case and the important role played by histological, histochemical and biochemical aspects in the diagnosis.

Adolescent↗

[Mitochondrial encephalomyopathies: 3243 mutation as a central matter].

Molecular diagnosis for mitochondrial diseases offers a powerful means to clarify that mitochondrial DNA (mtDNA) defects have different characteristics from those of nuclear DNA. Regarding the relationship between genotype and phenotype, there is a dual heterogeneity. It means that one mutation, for example, a 3243 mutation, has several clinical phenotypes, including MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes), myopathy only, diabetes and/or deafness and even CPEO (chronic progressive external ophthalmoplegia). Conversely, one phenotype, for instance, MELAS has several genetypes; 3243, 3271, and 3291 mutations. The second unique event in mitochondrial DNA mutation is heterogenous distribution of mutant mtDNA in a mitochondrion or a cell that is called heteroplasmy. The extend of heteroplasmy seems different from tissue to tissue providing clues to explain the variability of tissue impairment and heterogenous clinical symptoms. The above evidence suggests that we should take care in selecting tissues to be tested. The third problem remained is on maternal inheritance. It makes the genetic counselling on mitochondrial diseases at clinics difficult and laborious. In conclusion, mtDNA analysis must be used as a last resort to get final diagnosis.

Animals↗

Twelve Japanese patients with POLG-related disorders: Population-specific genetic differences of POLG variants in Japan and Europe.

BACKGROUND: POLG encodes mitochondrial DNA (mtDNA) polymerase γ. Pathogenic POLG variants cause mitochondrial diseases, including progressive external ophthalmoplegia. POLG-related disorders are relatively common in Europe, possibly because of the high prevalence of carriers in the general population, but remain rare in Japan for unclear reasons. METHODS: We performed long-range PCR on mtDNA from skeletal muscle and/or peripheral blood from 3146 patients with suspected mitochondrial disease between 1993 and 2021. We selected 167 individuals with clinical features suggestive of POLG-related disorders for POLG gene analysis; all lacked pathogenic mtDNA point mutations, and most had multiple mtDNA deletions and/or a family history of mitochondrial disease. RESULTS: Among the 167 patients (median age: 52 years, range: 0-83 years, 11% pediatric cases), we identified 12 Japanese patients with POLG-related disorders and six POLG variants, including one novel variant. The six variants were p.Y955C, p.R943H, p.T599I, p.M299L, p.Y1210* (c.3626_3629dupGATA), and the novel variant p.F377S (c.1130T>C). Neither these six variants nor the 10 previously reported cases from Japan included the POLG variants that are more frequent in Europe. We also analyzed three population databases: two whole-genome sequencing databases covering 61,000 and 9850 Japanese individuals, respectively, and one global population database (gnomAD) covering 730,000 individuals worldwide. POLG variants that are more frequent in Europe were not detected in the Japanese databases or among East Asian individuals in gnomAD. CONCLUSIONS: Our findings suggest population-specific genetic differences in POLG between Japanese and European populations, explaining the lower frequency of POLG-related disorders in Japan.

CPEO↗