The mitochondrial DNA A3243G mutation in Werner's syndrome

Damaged mitochondria in Fanconi anemia - an isolated event or a general phenomenon?

Fanconi anemia (FA) is known as an inherited bone marrow failure syndrome associated with cancer predisposition and susceptibility to a number of DNA damaging stimuli, along with a number of clinical features such as upper limb malformations, increased diabetes incidence and typical anomalies in skin pigmentation. The proteins encoded by FA-defective genes (FANC proteins) display well-established roles in DNA damage and repair pathways. Moreover, some independent studies have revealed that mitochondrial dysfunction (MDF) is also involved in FA phenotype. Unconfined to FA, we have shown that other syndromes featuring DNA damage and repair (such as ataxia-telangiectasia, AT, and Werner syndrome, WS) display MDF-related phenotypes, along with oxidative stress (OS) that, altogether, may play major roles in these diseases. Experimental and clinical studies are warranted in the prospect of future therapies to be focused on compounds scavenging reactive oxygen species (ROS) as well as protecting mitochondrial functions.

Spontaneous event of mitochondrial DNA mutation, A3243G, found in a family of identical twins

A mutation in mitochondrial DNA (mtDNA) A3243G is an important cause of some serious mitochondrial diseases, and maternal inheritance of the mutation has been reported. In order to investigate the heredity of the mutation, we measured the ratio of the mutated mtDNA molecule among 32 families of identical twins. Both twins from one family showed 20.16% and 18.49% mutated molecules, and the level is significantly high in comparison with members of other families and control subjects (0.23-0.86%). Their parents, however, showed normal level of mutated molecules (0.70% and 0.66%). The high-level mutation of the twins may be due to a spontaneous event, which occurred during development of germ line of their mother, or oogenesis of their mother, or during early stage of their development.

Mitochondrial dysfunction in some oxidative stress-related genetic diseases: Ataxia-Telangiectasia, Down Syndrome, Fanconi Anaemia and Werner Syndrome

Oxidative stress is a phenotypic hallmark in several genetic disorders characterized by cancer predisposition and/or propensity to premature ageing. Here we review the published evidence for the involvement of oxidative stress in the phenotypes of Ataxia-Telangiectasia (A-T), Down Syndrome (DS), Fanconi Anaemia (FA), and Werner Syndrome (WS), from the viewpoint of mitochondrial dysfunction. Mitochondria are recognized as both the cell compartment where energetic metabolism occurs and as the first and most susceptible target of reactive oxygen species (ROS) formation. Thus, a critical evaluation of the basic mechanisms leading to an in vivo pro-oxidant state relies on elucidating the features of mitochondrial impairment in each disorder. The evidence for different mitochondrial dysfunctions reported in A-T, DS, and FA is reviewed. In the case of WS, clear-cut evidence linking human WS phenotype to mitochondrial abnormalities is lacking so far in the literature. Nevertheless, evidence relating mitochondrial dysfunctions to normal ageing suggests that WS, as a progeroid syndrome, is likely to feature mitochondrial abnormalities. Hence, ad hoc research focused on elucidating the nature of mitochondrial dysfunction in WS pathogenesis is required. Based on the recognized, or reasonably suspected, role of mitochondrial abnormalities in the pathogenesis of these disorders, studies of chemoprevention with mitochondria-targeted supplements are warranted.

Markedly different clinical features in 2 diabetes mellitus patients with extremely high tissue levels of the mitochondrial DNA A3243G mutation

BACKGROUND

Mitochondrial DNA (mtDNA) A3243G mutation is one of the major causative factors of mitochondrial diabetes mellitus. We found that tissues from 2 of 142 diabetes mellitus patients showed extremely high levels of the mutation.

OBJECTIVE

To investigate the level of the mutation in each tissue and to find the relationship between the mutation level and clinical features of the patients.

METHODS

Patient 1 was a 51-year-old woman, diagnosed as having diabetes mellitus at the age of 17, and was admitted to hospital because of cerebral infarction. Patient 2 was an 82-year-old woman who was admitted because of respiratory failure. mtDNA A3243G levels were measured in tissues collected at autopsy.

RESULTS

In patient 1, mtDNA A3243G levels were found to vary among the tissues. The patient's highest mtDNA A3243G value was 42% and the lowest value was 9%, whereas the level in most individuals is usually less than 1%. Although patient 2 did not exhibit serious clinical symptoms of diabetes mellitus, the mtDNA A3243G level was extremely high in all of the tissues surveyed (range 32-47%).

CONCLUSION

Although both patients showed high levels of the mtDNA A3243G mutation, their clinical conditions differed greatly. Thus, mitochondrial diabetes mellitus patients may show a wide variety of clinical features and large variations in life span.

Genetic contribution of the tumour necrosis factor (TNF) B + 252*2/2 genotype, but not the TNFa,b microsatellite alleles, to systemic lupus erythematosus in Japanese patients

The contribution of the tumour necrosis factor (TNF) B + 252 (TNFB) dimorphism and microsatellite polymorphisms of TNFa and TNFb to the pathogenesis of systemic lupus erythematosus (SLE) was studied in Japanese patients. The TNFB dimorphism was determined using the restriction fragment length polymorphism (RFLP) method with NcoI digestion followed by specific polymerase chain reaction (PCR) amplification. TNFa and TNFb microsatellite polymorphisms were determined using the DNA sequencer and GeneScan program (Applera Corporation, Foster City, CA) followed by specific PCR amplification. HLA-DRB1*15 typing was carried out by the PCR-sequence specific conformational polymorphism (SSCP) method. In SLE, the allele frequency of TNFB*2 significantly increased (68.9%, P < 0.05) and the genotype frequency of TNFB*2/2 also increased (52.8%, P < 0.05). TNFB*2 showed no significant linkage disequilibrium with HLA-DRB1*1501. The prevalence of TNFa13 and TNFb4 showed very slight increases, but these increases were not significant. An association analysis indicated that TNFB*2/2 conferred greater, or at least equal, susceptibility to SLE in Japanese patients in comparison with HLA-DRB1*1501. The TNFB*2/2 genotype may contribute additively with DRB1*1501 to SLE in Japanese patients. No association was observed between auto-antibodies and TNF. TNFB*2 is a genetic marker for SLE in Japanese patients, while TNFa and TNFb microsatellites are not associated with SLE.