Leber’s hereditary optic neuropathy is associated with the mitochondrial ND4 G11696A mutation in five Chinese families

Mitochondrial Diabetes Is Associated with the ND4 G11696A Mutation

Type 2 diabetes mellitus (T2DM) is a common endocrine disorder which remains a large challenge for clinicians. Previous studies have suggested that mitochondrial dysfunction plays an active role in T2DM progression, but a detailed mechanism is still elusive. In the current study, two Han Chinese families with maternally inherited T2DM were evaluated using clinical, genetic, molecular, and biochemical analyses. The mitochondrial genomes were PCR amplified and sequenced. Phylogenetic and bioinformatic analyses were used to assess the potential pathogenicity of mitochondrial DNA (mtDNA) mutations. Interestingly, the matrilineal relatives of these pedigrees exhibited variable severity of T2DM, in particular, the age at onset of T2DM varied from 26 to 65 years, with an average of 49 years. Sequence analysis revealed the presence of ND4 G11696A mutation, which resulted in the substitution of an isoleucine for valine at amino acid (AA) position 312. Indeed, this mutation was present in homoplasmy only in the maternal lineage, not in other members of these families, as well as 200 controls. Furthermore, the m.C5601T in the tRNA^Ala and novel m.T5813C in the tRNA^Cys, showing high evolutional conservation, may contribute to the phenotypic expression of ND4 G11696A mutation. In addition, biochemical analysis revealed that cells with ND4 G11696A mutation exhibited higher levels of reactive oxygen species (ROS) productions than the controls. In contrast, the levels of mitochondrial membrane potential (MMP), ATP, mtDNA copy number (mtDNA-CN), Complex I activity, and NAD⁺/NADH ratio significantly decreased in cell lines carrying the m.G11696A and tRNA mutations, suggesting that these mutations affected the respiratory chain function and led to mitochondrial dysfunction that was involved in T2DM. Thus, our study broadened the clinical phenotypes of m.G11696A mutation.

Major depressive disorder is correlated with the mitochondrial ND1 T3394C mutation in two Han Chinese families: Two case reports

BACKGROUND

Major depressive disorder (MDD) is the most frequent reason of disabled people in the world, as reported by the World Health Organization. However, the diagnosis of MDD is mainly based on clinical symptoms.

CASE SUMMARY

The clinical, genetic, and molecular characteristics of two Chinese families with MDD are described in this study. There were variable ages of onset and severity in depression among the families. Both Chinese families had a very low pre-valence of MDD. The mitochondrial genomes of these pedigrees were sequenced and indicated a homoplasmic T3394C (Y30H) mutation, with the polymorphism located at a highly conserved tyrosine at position 30 of ND1. The analysis also revealed unique sets of mitochondrial DNA (mtDNA) polymorphisms orig-inating from haplogroups M9a3 and M9a.

CONCLUSION

This finding of the T3394C mutation in two unrelated depressed patients provides strong evidence that this mutation may have a part in the etiology of MDD. However, In these two Chinese families having the T3394C mutation, no functional mtDNA mutation was observed. Therefore, T3394C mutations are related with MDD, and the phenotypic manifestation of these mutations may be affected by changes in nuclear genes or environmental factors.

Leber Mitochondrial Optic Neuropathy in Pediatric Females With Focus on Very Early Onset Cases

The aim of this study was to describe the phenotype of Leber hereditary optic neuropathy occurring in pediatric females. This disease generally affects young adult males, but it can occur also in females, and research data in this population is lacking. The very early onset can challenge the diagnosis and delay treatment. We searched PubMed through February 2021 and identified 226 pediatric females with genetically confirmed Leber hereditary optic neuropathy and added a new case of a 3-year-old female. The male-female ratio was 1.8:1; the mean onset age in females was 11 years with the onset at 3 years of age occurring in 3 females only. Acute onset with mild visual impairment was the most common presentation, associated with optic disc edema in 16%. Differential diagnoses are pseudotumor cerebri, optic nerve drusen and optic neuritis. The outcome is poor with partial recovery in 50%, despite some receiving Idebenone therapy.

Mitochondrial respiratory complexes: Significance in human mitochondrial disorders and cancers

Mitochondria are pivotal organelles that govern cellular energy production through the oxidative phosphorylation system utilizing five respiratory complexes. In addition, mitochondria also contribute to various critical signaling pathways including apoptosis, damage-associated molecular patterns, calcium homeostasis, lipid, and amino acid biosynthesis. Among these diverse functions, the energy generation program oversee by mitochondria represents an immaculate orchestration and functional coordination between the mitochondria and nuclear encoded molecules. Perturbation in this program through respiratory complexes' alteration results in the manifestation of various mitochondrial disorders and malignancy, which is alarmingly becoming evident in the recent literature. Considering the clinical relevance and importance of this emerging medical problem, this review sheds light on the timing and nature of molecular alterations in various respiratory complexes and their functional consequences observed in various mitochondrial disorders and human cancers. Finally, we discussed how this wealth of information could be exploited and tailored to develop respiratory complex targeted personalized therapeutics and biomarkers for better management of various incurable human mitochondrial disorders and cancers.

A novel m.11406 T > A mutation in mitochondrial ND4 gene causes MELAS syndrome

Pathogenic point mutations of mitochondrial DNA (mtDNA) are associated with a large number of heterogeneous diseases involving multiple systems with which patients may present with a wide range of clinical phenotypes. In this study, we describe a novel heteroplasmic missense mutation, m.11406 T > A, of the ND4 gene encoding the subunit 4 of mitochondrial complex I in a 32-year-old woman with recurrent epileptic seizure, headache and bilateral hearing loss. Skeletal muscle histochemistry demonstrated that approximately 20% of fibers were cytochrome C oxidase (COX) deficient with increased activity of succinate dehydrogenase (SDH). Further investigations in muscle specimens showed significantly reduced level of ND4 protein. It is interesting that the subunits of complex I (ND1 and NDFUB8) and complex IV(CO1) were also remarkably decreased. These findings indicate that ND1, NDFUB8 and CO1 are more susceptible than other subunits to mutations in the mitochondrial ND4 gene.

Genotypic and phenotypic characteristics of Korean children with childhood-onset Leber's hereditary optic neuropathy

PURPOSE

We sought to identify the phenotypic and genotypic characteristics of Korean children with genetically confirmed Leber's hereditary optic neuropathy (LHON).

METHODS

The medical records of 64 genetically confirmed LHON patients were reviewed. Seventeen patients aged 13 years or younger with optic atrophy with positive mitochondrial DNA (mtDNA) mutations were considered to demonstrate childhood-onset LHON. The non-childhood-onset group included 47 patients with genetically confirmed LHON who experienced disease onset later than 13 years of age. The type of mtDNA mutation, visual acuity (VA), color vision, fundus photography, retinal nerve fiber layer (RNFL) thickness, and visual field were investigated.

RESULTS

Sequence analysis of the mitochondrial genome revealed five different kinds of LHON-associated mtDNA mutations among our childhood-onset patients, including m.11778G>A (58.8%), m.3496G>T (11.8%), m.3497C>T (5.9%), m.11696G>A (5.9%), and m.14502T>C (5.9%). The mean final best-corrected VA in the childhood-onset group was better than that in the non-childhood-onset group with the value of logMAR 0.29 (0.09-0.75) vs. 0.55 (0.27-1.29) (expressed as median (interquartile range); p = 0.05). Spontaneous visual recovery was observed in 35.3% of the childhood-onset group but in only 12.8% of the non-childhood-onset group (p = 0.04). Eight patients (47.1%) showed interocular asymmetry of the disease, with two presenting true unilateral involvement of the optic nerve and the other six patients demonstrating unilateral subclinical manifestations with bilateral optic atrophy.

CONCLUSION

Involvement of secondary mitochondrial mutations was confirmed in patients with childhood-onset LHON. Characteristic clinical features of childhood-onset LHON included a higher proportion of subacute or insidious onset of symptoms, better VA, higher spontaneous recovery, and asymmetrical ocular involvement.

Contribution of mitochondrial ND1 3394T>C mutation to the phenotypic manifestation of Leber's hereditary optic neuropathy

Mitochondrial DNA (mtDNA) mutations have been associated with Leber's hereditary optic neuropathy (LHON) and their pathophysiology remains poorly understood. In this study, we investigated the pathophysiology of a LHON susceptibility allele (m.3394T>C, p.30Y>H) in the Mitochondrial (MT)-ND1 gene. The incidence of m.3394T>C mutation was 2.7% in the cohort of 1741 probands with LHON. Extremely low penetrances of LHON were observed in 26 pedigrees carrying only m.3394T>C mutation, while 21 families bearing m.3394T>C, together with m.11778G>A or m.14484T>C mutation, exhibited higher penetrance of LHON than those in families carrying single mtDNA mutation(s). The m.3394T>C mutation disrupted the specific electrostatic interactions between Y30 of p.MT-ND1 with the sidechain of E4 and backbone carbonyl group of M1 of NDUFA1 (NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 1) of complex I, thereby altering the structure and function of complex I. We demonstrated that these cybrids bearing only m.3394T>C mutation caused mild mitochondrial dysfunctions and those harboring both m.3394T>C and m.11778G>A mutations exhibited greater mitochondrial dysfunctions than cybrids carrying only m.11778G>A mutation. In particular, the m.3394T>C mutation altered the stability of p.MT-ND1 and complex I assembly. Furthermore, the m.3394T>C mutation decreased the activities of mitochondrial complexes I, diminished mitochondrial ATP levels and membrane potential and increased the production of reactive oxygen species in the cybrids. These m.3394T>C mutation-induced alterations aggravated mitochondrial dysfunctions associated with the m.11778G>A mutation. These resultant biochemical defects contributed to higher penetrance of LHON in these families carrying both mtDNA mutations. Our findings provide new insights into the pathophysiology of LHON arising from the synergy between mitochondrial ND1 and ND4 mutations.

Analysis of Genetic Mutations in a Cohort of Hereditary Optic Neuropathy in Shanghai, China

Purpose

To evaluate the clinical classification and characteristics of hereditary optic neuropathy patients in a single center in China.

Method

Retrospective case study. Patients diagnosed with hereditary optic neuropathy between January 2014 and December 2015 in the neuro-ophthalmology division in Shanghai Eye and ENT Hospital of Fudan University were recruited. Clinical features as well as visual field, brain/orbital MRI, and spectrum domain optical coherence tomography (SD-OCT) were analyzed.

Results

Eighty-two patients diagnosed by gene test were evaluated, including 66 males and 16 females. The mean age of the patients was 19.4 years (range, 5–46 years). A total of 158 eyes were analyzed, including 6 unilateral, 61 bilateral, and 15 sequential. The median duration of the disease was 0.5 year (range, 0.1–20 years). Genetic test identified 68 patients with Leber hereditary optic neuropathy, 9 with dominant optic neuropathy, and 2 with a Wolfram gene mutation. There was also one case of hereditary spastic paraplegia, spinocerebellar ataxia, and polymicrogyria with optic nerve atrophy, respectively.

Conclusion

Leber hereditary optic neuropathy is the most common detected type of hereditary optic neuropathy in Shanghai, China. The detection of other autosomal mutations in hereditary optic neuropathy is limited by the currently available technique.

Leber's hereditary optic neuropathy is potentially associated with a novel m.5587T>C mutation in two pedigrees

Mitochondrial (mt)DNA mutations have been revealed to be associated with Leber's hereditary optic neuropathy (LHON). The present study conducted clinical, genetic and molecular evaluations of two Han Chinese families. A total of 4 (3 men and 1 female) out of 14 matrilineal relatives in the families exhibited visual impairment with variable severity and age of onset. The average age of onset of visual loss was 20.5 years old. Molecular analysis of the complete mitochondrial genome in these pedigrees demonstrated that the three primary mutations associated with LHON were not detected; however, the homoplasmic m.5587T>C mutation was identified, which was localized at the end of the mitochondrially encoded transfer (t)RNA alanine gene and may alter the tertiary structure of this tRNA. Subsequently, this structural alteration may result in tRNA metabolism failure. In addition, distinct sets of mtDNA polymorphisms belonging to haplogroup F1 were detected in both families tested. The findings of the present study suggested that the m.5587T>C mutation may be involved in the pathogenesis of visual impairment. In addition, the mtDNA variant m.15024G>A(p.C93H) in the mitochondrially encoded cytochrome B gene was detected in both families, which exhibited evolutionary conservation, indicating it may serve a potential modifying role in the development of visual impairment associated with m.5587T>C mutation in these families. Furthermore, other modifying factors, including nuclear modifier genes, and environmental and personal factors may also contribute to the development of LHON in subjects carrying this mutation.

Mitochondrial DNA sequencing and large-scale genotyping identifies MT-ND4 gene mutation m.11696G>A associated with idiopathic oligoasthenospermia

Genetic variants of mitochondrial DNA (mtDNA) were implicated to be associated with male infertility. Our previous whole mitochondrial genome sequencing and association study has identified two susceptibility mtDNA variants for oligoasthenospermia in Han Chinese men. In this study, we tested promising associations in an extended validation using 670 idiopathic oligoasthenospermia cases and 793 healthy controls to identify additional risk variants. We found that the genetic variant of m.11696G>A showed significantly higher frequency in the case group than that in the control group (odds ratio (OR) 2.21, 95% CI 1.21-4.04) (P=7.90×10⁻³). To elucidate the exact role of the genetic variants in spermatogenesis, two main sperm parameters (sperm count and motility) were taken into account. We found that m.11696G>A was associated with low sperm motility, with the OR of 2.38 (95 % CI 1.27-4.46) (P =5.22×10⁻³). These results advance our understanding of the genetic susceptibility to oligoasthenospermia and more functional studies are needed to provide insights into its pathogenic mechanism.

Whole mitochondrial genome analysis in South Indian patients with Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a mitochondrial DNA (mtDNA) associated neurodegenerative disorder of retinal ganglion cells. In this study, whole mitochondrial genome sequencing of 75 LHON patients and 40 controls was performed to identify the mutation frequency and haplogroup background of South Indian population. Analysis of mtDNA revealed 559 different variants in LHON patients, including 7 pathogenic mutations, 30 private, and 22 other disease associated variants. A significantly higher (p=0.0008) overall variation load per individual was noted among LHON patients versus controls. We reported for the first time, the association of M haplogroup (p=0.028) with LHON in this cohort.

Mitochondrial haplogroup D4j specific variant m.11696G > a(MT-ND4) may increase the penetrance and expressivity of the LHON-associated m.11778G > a mutation in Chinese pedigrees

Leber's hereditary optic neuropathy (LHON) is one of the most common mitochondrial disorders. We report here the clinical, genetic and molecular analysis of mitochondrial DNA (mtDNA) in eight Han Chinese families carrying the known mitochondrial 11778G > A(MT-ND4) mutation. Thirty-seven (26 males/11 females) of 77 matrilineal relatives in these families exhibited the variable severity and age-at-onset of optic neuropathy. The penetrances were from 25% to 75%, with the average of 42%, and the age-at-onset for visual impairment varied from 10 to 25 years, with the average of 17 in these Chinese pedigrees. Molecular analysis of their mtDNA identified distinct sets of variants belonging to the Eastern Asian haplogroupD4j. Except the known m.11778G > A mutation, the m.11696G > A(MT-ND4) mutation caused the substitution of an isoleucine for valineat amino acid position 313, located in a predicted transmembrane region of ND4. And, it is reported that the m.11696G > A mutation was associated with LHON, and appeared to contribute to higher penetrance in these nine Chinese families than other Chinese families carrying only the m.11778G > A mutation. Therefore, the mitochondrial haplogroup D4j specific m.11696G > A mutation may act in synergy with the primary LHON-associated m.11778G > A mutation, thereby increasing the penetrance and expressivity of visual loss in these Chinese families.

Mitochondrial tRNA(Thr) A15951G mutation may not be associated with Leber's Hereditary Optic Neuropathy

Mutation in mitochondrial DNA (mtDNA) has been found to play an important role in the pathogenesis of Leber's Hereditary Optic Neuropathy (LHON). Three primary mutations, the ND4 G11778A, ND6 T14484C, and ND1 G3460A, have been found to account more than 90% of LHON patients in many families worldwide. In addition to the mutations in genes encoding the respiratory chain complex I, reports concerning the mt-tRNA gene mutations associated with LHON have increased, some pathogenic mutations caused the failure in mt-tRNA metabolism, thereby worsened the mitochondrial dysfunction that is responsible for LHON. Recently, the A15951G mutation in mt-tRNA(Thr) gene has been reported to be a "modified" factor in increasing the penetrance and expressivity of LHON-associated ND4 G11778A mutation in three Chinese families. However, evolutionary conservation analysis of this mutation suggested a poor conservation index and the pathogenicity scoring system showed that this mutation was a neutral polymorphism.

Mitochondrial tRNAThr 15891C>G mutation was not associated with Leber's hereditary optic neuropathy in Han Chinese patients

Mutations in mitochondrial DNA (mtDNA) were the most important causes of Leber's hereditary optic neuropathy (LHON). To date, approximately 25 LHON-associated mtDNA mutations have been identified in various ethnic populations. Three primary mutations, the 3460G > A, 11778G > A and 14484T > C, in genes encoding the subunits of respiratory chain complex I, were the most common LHON-associated mtDNA mutations. Moreover, secondary mutations in mt-tRNA genes have been reported increasingly to be associated with LHON, simply due to the high mutation rates of mt-tRNAs. There is a lack of functional analysis and a poor genetic evaluation of a certain mt-tRNA mutation, which failed to meet the classic pathogenicity scoring system. As a result, how to classify a pathogenic mutation in mt-tRNA gene became important for both geneticist and clinician to diagnosis the LHON or the suspicious of LHON. In this study, we reassessed the role of a point mutation in mt-tRNA(Thr) gene which had been reported to be a mutation associated with LHON, the pathogenicity of this mutation has been discussed in this context.

Leber's hereditary optic neuropathy is associated with the T3866C mutation in mitochondrial ND1 gene in three Han Chinese Families

PURPOSE

To investigate the pathophysiology of Leber's hereditary optic neuropathy (LHON).

METHODS

Seventy-one subjects from three Chinese families with LHON underwent clinical, genetic, molecular, and biochemical evaluations. Biochemical characterizations included the measurements of the rates of endogenous, substrate-dependent respirations, the adenosine triphosphate (ATP) production and generation of reactive oxygen species using lymphoblastoid cell lines derived from five affected matrilineal relatives of these families and three control subjects.

RESULTS

Ten of 41 matrilineal relatives exhibited variable severity and age at onset of optic neuropathy. The average age at onset of optic neuropathy in matrilineal relatives of the three families was 5, 11, and 24 years, respectively. Molecular analysis identified the ND1 T3866C (I187T) mutation and distinct sets of polymorphisms belonging to the Eastern Asian haplogroups D4a, M10a, and R, respectively. The I187T mutation is localized at the highly conserved isoleucine at a transmembrane domain of the ND1 polypeptide. The marked reductions in the rate of endogenous, malate/glutamate-promoted and succinate/glycerol-3-phosphate-promoted respiration were observed in mutant cell lines carrying the T3866C mutation. The deficient respiration is responsible for the reduced ATP synthesis and increased generation of reactive oxygen species.

CONCLUSIONS

Our data convincingly show that the ND1 T3866C mutation leads to LHON. This mutation may be insufficient to produce a clinical phenotype. Other modifier factors may contribute to the phenotypic manifestation of the T3866C mutation. The T3866C mutation should be added to the list of inherited factors for molecular diagnosis of LHON. Thus, our findings may provide new insights into the understanding of pathophysiology and valuable information on the management of LHON.

Leber's hereditary optic neuropathy with the 3434, 9011 mitochondrial DNA point mutation

BACKGROUND

Leber's hereditary optic neuropathy (LHON) contains several well-known mitochondrial DNA (mtDNA) point mutations. We report a case with characteristic clinical manifestations of LHON involving a possible new LHON point mutation.

CASE

A 34-year-old man was diagnosed with LHON. The patient exhibited (1) sudden onset of bilateral visual loss, (2) normal light reflex, and (3) swelling of the peripapillary nerve fiber layer. After subsequent development of bilateral optic disc pallor, we concluded that the patient had LHON. mtDNA analysis was conducted using non-radioisotopic single-strand conformational polymorphism followed by direct sequencing. There was no change in the patient's visual acuity during the 26-month follow-up period.

OBSERVATIONS

The mtDNA point mutations were found at T3434C, G3483A, and V9011A. The confirmed mtDNA substitutions included (1) A-G at nucleotide position 3434, (2) G-A at nucleotide position 3483, and (3) C-T at nucleotide position 9011. The amino acid code at the nucleotide positions 3434 and 9011 was phylogenetically highly conserved.

CONCLUSION

The 3434 and 9011 mtDNA point mutations are candidates for a new LHON mutation.

[The mitochondrial ND5 T12338C mutation may be associated with Leber's hereditary optic neuropathy in two Chinese families]

Leber's hereditary optic neuropathy (LHON) associated with mitochondrial DNA mutation is a maternally inherited eye disease. We reported here the clinical, genetic and molecular characterization of two Han Chinese families with Leber's hereditary optic neuropathy. Ophthalmologic examinations revealed that the variable severity and age-of-onset in visual impairment among probands and other matrilineal relatives of these families. Strikingly, there were extremely low penetrances of visual impairment in these families. Sequence analysis of complete mitochondrial genomes in these pedigrees identified the homoplasmic ND4 G11696A and ND5 T12338C mutation and distinct sets of polymorphism belonging to haplogroups F2. It is well known that mitochondrial DNA ND4 G11696A is associated with LHON. The ND5 T12338C mutation resulted in replacement of the first amino acid, translation-initiating methionine with a threonine, and shortening two amino acids of ND5. This mutation also locates in two nucleotides adjacent to the 3' end of the tRNALeu(Cun). Thus, this mutation may alter structural formation and stabilization of functional tRNA, thereby leading to a failure in protein synthesis and mitochondrial dysfunction involved in visual impairment. Therefore, the ND4 G11696A and ND5 T12338C mutation is likely associated with LHON in these two Chinese families. But these families exhibited extremely low penetrances of visual impairment. It suggests that other factors, such as nuclear modifier gene(s) or environmental factor(s), may play a role in the phenotypic expression of the LHON-associated ND4 G11696A and ND5 T12338C mutation.

Leber's hereditary optic neuropathy is associated with the T12338C mutation in mitochondrial ND5 gene in six Han Chinese families

PURPOSE

To investigate the molecular pathogenesis of Leber's hereditary optic neuropathy (LHON) in Chinese families.

DESIGN

Six Han Chinese families who seem to have maternally transmitted LHON were studied by clinical, genetic, and molecular evaluations.

PARTICIPANTS

One hundred twenty-seven subjects from 6 Chinese families with a wide range of age-at-onset and severity of visual impairment.

METHODS

All subjects underwent clinical examination, genetic evaluation, and molecular analysis of mitochondrial DNA (mtDNA).

MAIN OUTCOME MEASURES

The ophthalmologic examinations included visual acuity, visual field examination, visual evoked potentials, and fundus photography. The mtDNA analysis included the polymerase chain reaction (PCR) amplification of entire mtDNA and subsequent sequence determination.

RESULTS

Six families exhibited low penetrance of visual impairment, with an average of 10.8%. In particular, 9 (6 males/3 females) of 86 matrilineal relatives in these families exhibited variable severity and age at onset in visual dysfunction. The average age at onset of visual loss was 20 years. Molecular analysis of mtDNA in these families identified the homoplasmic ND5T12338C mutation and distinct set of variants belonging to the Asian haplogroup F2. The T12338C mutation is only present in the maternal lineage of those pedigrees and not in 178 Chinese controls. This mutation resulted in the replacement of the first amino acid, a translation-initiating methionine with a threonine, shortening 2 amino acids of ND5 polypeptide. The T12338C mutation is also located in 2 nucleotides adjacent to the 3' end of the tRNA(Leu(CUN)). Thus, this mutation may alter ND5 mRNA metabolism and the processing of RNA precursors. As a result, this mutation impairs respiratory function, leading to visual impairment.

CONCLUSIONS

Several lines of evidence suggest that the mitochondrial ND5T12338C mutation is associated with LHON. The tissue specificity of this mutation is likely due to the involvement of nuclear modifier genes. The identification of nuclear modifiers is important for the elucidation of the pathogenic mechanism of LHON and an open avenue for therapeutic interventions. The T12338C mutation should be added to the list of inherited risk factors for future molecular diagnosis. Our findings are helpful for counseling families with LHON.

Mitochondrial ND6 T14502C variant may modulate the phenotypic expression of LHON-associated G11778A mutation in four Chinese families

We report here the clinical, genetic, and molecular evaluations of four Han Chinese families with Leber's hereditary optic neuropathy. Thirty-one (20 males/11 females) of 83 matrilineal relatives in these families exhibited the variable severity and age-at-onset in visual impairment. The average age-of-onset of vision loss was 22years old. Strikingly, these penetrances of visual impairment in these Chinese families were higher than those in other 11 Chinese pedigrees carrying the only ND4 G11778A mutation. Molecular analysis identified the known G11778A mutation and distinct sets of variants belonging to the Asian haplogroups M10a and M7c2. Of these, the T14502C mutation caused the substitution of a highly conserved isoleucine for valine at position 58 in ND6. This mutation has been associated with LHON in other Chinese families with very low penetrance of LHON. Thus, the deficient activities of complex I, caused by G11778A mutation, would be worsened by the T14502C mutation in these four Chinese families. As a result, mitochondrial dysfunctions would lead to the high penetrance and expressivity of visual loss in these Chinese families carrying both G11778A and T14502C mutations than other 11 Chinese families carrying only G11778A mutation. These data suggested that the T14502C variant may modulate the phenotypic manifestation of the G11778A mutation in these Chinese pedigrees.

[Leber's hereditary optic neuropathy may be associated with the mitochondrial tRNAGlu A14693G mutation in three Chinese families]

We reported here the clinical, genetic and molecular characterization of three Han Chinese families with Leber's hereditary optic neuropathy. Ophthalmologic examinations revealed the variable severity and age-at-onset of visual loss among probands and other matrilineal relatives of these families. Strikingly, these families exhibited extremely low penetrances of visual impairment. Sequence analysis of complete mitochondrial genomes in these pedigrees identified the known homoplasmic tRNAGlu A14693G mutation and distinct sets of polymorphism belonging to haplogroups Y1b, Y1 and Y1, respectively. The A14693G mutation occurs at the extremely conserved nucleotide (conventional position 54) of tRNAGlu. Thus, this mutation may alter structural formation and stabilization of functional tRNAs, thereby leading to a failure in tRNA metabolism and mitochondrial dysfunction involved in visual impairment. However, none of other variants showed the evolutionary conservation and functional significance. These observations suggested that the tRNAGlu A14693G mutation may be involved in the pathogenesis of optic neuropathy in these families.

Very low penetrance of Leber's hereditary optic neuropathy in five Han Chinese families carrying the ND1 G3460A mutation

We report here the clinical, genetic, and molecular characterization of five Han Chinese families with Leber's hereditary optic neuropathy (LHON). Strikingly, there were very low penetrances of visual impairment in these Chinese families, ranging from 4.2% to 22.2%, with an average of 10.2%. In particular, only 7 (4 males/3 females) of 106 matrilineal relatives in these families exhibited the variable severity and age-at-onset in visual dysfunction. The age-at-onset for visual impairment in matrilineal relatives in these families, varied from 20 to 25 years, with an average of 21.8 years old. Molecular analysis of mitochondrial genomes identified the homoplasmic ND1 G3460A mutation and distinct sets of variants, belonging to the Asian haplogroups B5b, C4a1, D5, F1, and R9, respectively. This suggests that the G3640A mutation occurred sporadically and multiplied through evolution of the mtDNA in China. However, there was the absence of known secondary LHON-associated mtDNA mutations in these Chinese families. Very low penetrance of visual loss in these five Chinese pedigrees strongly indicated that the G3640A mutation was itself insufficient to develop the optic neuropathy. The absence of secondary LHON mtDNA mutations suggest that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the G3640A mutation in those Chinese families with low penetrance of vision loss. However, nuclear modifier genes, epigenetic and environmental factors appear to be modifier factors for the phenotypic manifestation of the G3640A mutation in these Chinese families.

[Leber's hereditary optic neuropathy and limbs abnormity claudication may be associated with the mitochondrial ND1 T3866C mutation]

Mutations in mitochondrial DNA have been associated with a wide spectrum of clinical abnormalities. We reported here the clinical, genetic and molecular characterization of a five-generation Han Chinese pedigree with Leber's Hereditary Optic Neuropathy (LHON) and limbs abnormity claudication. Of 27 matrilineal relatives, four exhibited only LHON, one suffered from only limbs abnormity claudication, and four had both LHON and limbs abnormity claudication. Sequence analysis of mitochondrial genome in this family identified the known T3866C mutation in ND1 gene and other 43 variants belonging to the Asian haplogroup D4a3. The T3866C (I187T) mutation resulted in the replacement of isoleucine at position 187 with theronine. The isoleucine at position 187 located at one of transmembrane domain in ND1 polypeptide. The isoleucine at position 187 was extremely conserved among 29 organisms, while other variants showed no evolutionarily conservation. Furthermore, the T3866C was absence in 135 Chinese control subjects. The T3866C mutation likely alters the complex I activity, which causes mitochondrial dysfunction associated with LHON and limbs abnormity claudication. Therefore, the T3866C mutation is likely associated with LHON and limbs abnormity claudication.

Mitochondrial haplotypes may modulate the phenotypic manifestation of the deafness-associated 12S rRNA 1555A>G mutation

Mitochondrial 12S rRNA 1555A>G mutation is one of the important causes of aminoglycoside-induced and nonsyndromic deafness. Our previous investigations showed that the A1555G mutation was a primary factor underlying the development of deafness but was insufficient to produce deafness phenotype. However, it has been proposed that mitochondrial haplotypes modulate the phenotypic manifestation of the 1555A>G mutation. Here, we performed systematic and extended mutational screening of 12S rRNA gene in a cohort of 1742 hearing-impaired Han Chinese pediatric subjects from Zhejiang Province, China. Among these, 69 subjects with aminoglycoside-induced and nonsyndromic deafness harbored the homoplasmic 1555A>G mutation. These translated to a frequency of approximately 3.96% for the 1555A>G mutation in this hearing-impaired population. Clinical and genetic characterizations of 69 Chinese families carrying the 1555A>G mutation exhibited a wide range of penetrance and expressivity of hearing impairment. The average penetrances of deafness were 29.5% and 17.6%, respectively, when aminoglycoside-induced hearing loss was included or excluded. Furthermore, the average age-of-onset for deafness without aminoglycoside exposure ranged from 5 and 30years old, with the average of 14.5years. Their mitochondrial genomes exhibited distinct sets of polymorphisms belonging to ten Eastern Asian haplogroups A, B, C, D, F, G, M, N, R and Y, respectively. These indicated that the 1555A>G mutation occurred through recurrent origins and founder events. The haplogroup D accounted for 40.6% of the patient's mtDNA samples but only 25.8% of the Chinese control mtDNA samples. Strikingly, these Chinese families carrying mitochondrial haplogroup B exhibited higher penetrance and expressivity of hearing loss. In addition, the mitochondrial haplogroup specific variants: 15927G>A of haplogroup B5b, 12338T>C of haplogroup F2, 7444G>A of haplogroup B4, 5802T>C, 10454T>C, 12224C>T and 11696G>A of D4 haplogroup, 5821G>A of haplogroup C, 14693A>G of haplogroups Y2 and F, and 15908T>C of Y2 may enhance the penetrace of hearing loss in these Chinese families. Moreover, the absence of mutation in nuclear modifier gene TRMU suggested that TRMU may not be a modifier for the phenotypic expression of the 1555A>G mutation in these Chinese families. These observations suggested that mitochondrial haplotypes modulate the variable penetrance and expressivity of deafness among these Chinese families.

Leber's hereditary optic neuropathy is associated with mitochondrial ND6 T14502C mutation

We report here the clinical, genetic, and molecular characterization of three Chinese families with Leber's hereditary optic neuropathy (LHON). There were variable severity and age of onset in visual impairment among these families. Strikingly, there were extremely low penetrances of visual impairment in these Chinese families. Sequence analysis of complete mitochondrial genomes in these pedigrees showed the homoplasmic T14502C (I58V) mutation, which localized at a highly conserved isoleucine at position 58 of ND6, and distinct sets of mtDNA polymorphisms belonging to haplogroups M10a, F1a1, and H2. The occurrence of T14502C mutation in these several genetically unrelated subjects affected by visual impairment strongly indicates that this mutation is involved in the pathogenesis of visual impairment. Here, mtDNA variants I187T in the ND1, A122V in CO1, S99A in the A6, and V254I in CO3 exhibited an evolutionary conservation, indicating a potential modifying role in the development of visual impairment associated with T14502C mutation in those families. Furthermore, nuclear modifier gene(s) or environmental factor(s) may play a role in the phenotypic manifestation of the LHON-associated T14502C mutation in these Chinese families.

Leber's hereditary optic neuropathy is associated with mitochondrial ND1 T3394C mutation

We report here the clinical, genetic and molecular characterization of four Chinese families with Leber's hereditary optic neuropathy (LHON). There were variable severity and age-of-onset in visual impairment among these families. Strikingly, there were extremely low penetrances of visual impairment in these Chinese families. Sequence analysis of complete mitochondrial genomes in these pedigrees showed the homoplasmic T3394C (Y30H) mutation, which localized at a highly conserved tyrosine at position 30 of ND1, and distinct sets of mtDNA polymorphisms belonging to haplogroups D4b and M9a. The occurrence of T3394C mutation in these several genetically unrelated subjects affected by visual impairment strongly indicates that this mutation is involved in the pathogenesis of visual impairment. However, there was the absence of functionally significant mtDNA mutations in these four Chinese pedigrees carrying the T3394C mutation. Therefore, nuclear modifier gene(s) or environmental factor(s) may play a role in the phenotypic expression of the LHON-associated T3394C mutation.

Etiological profile of presumptive optic neuritis in China

To determine the diagnoses in a population of patients with presumed optic neuritis (ON) in China and compare the spectrum of etiologies with those in western countries, we studied a group of 204 patients referred to a teaching hospital with a presumptive diagnosis of ON. We conducted detailed medical and family history, thorough ophthalmologic and neurological examinations, and laboratory tests including neuroimaging. Patients were diagnosed using international diagnostic criteria. One hundred and thirteen patients (55.4%) met ON criteria, among whom 83 patients (73.5%) were diagnosed with idiopathic demyelinating optic neuritis (IDON). Brain MRI white matter lesions were found in 11 of 78 (14.1%) clinically "isolated" IDON patients. Tuberculosis meningitis was found in 2 patients and syphilis in 1 patient. The cause of ON in 26 patients (23.0%) remained uncertain, but it was still likely to be IDON accompanied by secondary axonal degeneration. Leber's hereditary optic neuropathy (LHON) was found in 38 patients (18.6%), confirmed by mitochondrial DNA point mutation screening. Seventeen patients (8.3%) had ischemic optic neuropathy. A spectrum of other entities mimicked ON. Therefore, idiopathic demyelinating ON was the most common type of optic neuropathy in our group. Despite minor differences regarding the causes and prognosis, the etiology of ON in our population is similar to that reported in Western countries.

Maternally inherited hypertension is associated with the mitochondrial tRNA(Ile) A4295G mutation in a Chinese family

Mutations in mitochondrial DNA have been associated with cardiovascular disease. We report here the clinical, genetic, and molecular characterization of one three-generation Han Chinese family with maternally transmitted hypertension. All matrilineal relatives in this family exhibited the variable degree of hypertension at the age at onset of 36 to 56 years old. Sequence analysis of the complete mitochondrial DNA in this pedigree revealed the presence of the known hypertension-associated tRNA(Ile) A4295G mutation and 33 other variants, belonging to the Asian haplogroup D4j. The A4295G mutation, which is extraordinarily conserved from bacteria to human mitochondria, is located at immediately 3' end to the anticodon, corresponding to conventional position 37 of tRNA(Ile). The occurrence of the A4295G mutation in several genetically unrelated pedigrees affected by cardiovascular disease but the absence of 242 Chinese controls strongly indicates that this mutation is involved in the pathogenesis of cardiovascular disease. Of other variants, the tRNA(Glu) A14693G and ND1 G11696A mutations were implicated to be associated with other mitochondrial disorders. The A14693G mutation, which is a highly conserved nucleoside at the TpsiC-loop of tRNA(Glu), has been implicated to be important for tRNA structure and function. Furthermore, the ND4 G11696A mutation was associated with Leber's hereditary optic neuropathy. Therefore, the combination of the A4295G mutation in the tRNA(Ile) gene with the ND4 G11696A mutation and tRNA(Glu) A14693G mutation may contribute to the high penetrance of hypertension in this Chinese family.

The ND4 G11696A mutation may influence the phenotypic manifestation of the deafness-associated 12S rRNA A1555G mutation in a four-generation Chinese family

We report here the clinical, genetic and molecular characterization of a large Han Chinese family with aminoglycoside-induced and nonsyndromic hearing loss. The penetrance of hearing loss (affected matrilineal relatives/total matrilineal relatives) in this pedigree was 53%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrance of hearing loss in this pedigree was 42%. These matrilineal relatives exhibited a wide range of severity of hearing loss, varying from profound to normal hearing. Furthermore, these affected matrilineal relatives shared some common features: bilateral hearing loss of high frequencies and symmetries. Sequence analysis of mitochondrial DNA (mtDNA) in the pedigree identified the homoplasmic 12S rRNA A1555G mutation and other 35 variants belonging to Eastern Asian haplogroup D4. Of these, the V313I (G11696A) mutation in ND4 was associated with vision loss. However, the extremely low penetrance of visual loss, and the mild biochemical defect and the presence of one/167 Chinese controls indicted that the G11696A mutation is itself not sufficient to produce a clinical phenotype. Thus, the G11696A mutation may act in synergy with the primary deafness-associated 12S rRNA A1555G mutation in this Chinese family, thereby increasing the penetrance and expressivity of hearing loss in this Chinese pedigree.

Pathogenic mitochondrial DNA mutations in protein-coding genes

More than 200 disease-related mitochondrial DNA (mtDNA) point mutations have been reported in the Mitomap (http://www.mitomap.org) database. These mutations can be divided into two groups: mutations affecting mitochondrial protein synthesis, including mutations in tRNA and rRNA genes; and mutations in protein-encoding genes (mRNAs). This review focuses on mutations in mitochondrial genes that encode proteins. These mutations are involved in a broad spectrum of human diseases, including a variety of multisystem disorders as well as more tissue-specific diseases such as isolated myopathy and Leber hereditary optic neuropathy (LHON). Because the mitochondrial genome contains a large number of apparently neutral polymorphisms that have little pathogenic significance, along with secondary homoplasmic mutations that do not have primary disease-causing effect, the pathogenic role of all newly discovered mutations must be rigorously established. A scoring system has been applied to evaluate the pathogenicity of the mutations in mtDNA protein-encoding genes and to review the predominant clinical features and the molecular characteristics of mutations in each mtDNA-encoded respiratory chain complex.

The coexistence of mitochondrial ND6 T14484C and 12S rRNA A1555G mutations in a Chinese family with Leber’s hereditary optic neuropathy and hearing loss

We report here the clinical, genetic and molecular characterization of one three-generation Han Chinese family with Leber's hereditary optic neuropathy (LHON) and hearing loss. Four of 14 matrilineal relatives exhibited the moderate central vision loss at the average age of 12.5 years. Of these, one subject exhibited both LHON and mild hearing impairment. Sequence analysis of the complete mitochondrial genomes in the pedigree showed the presence of homoplasmic LHON-associated ND6 T14484C mutation, deafness-associated 12S rRNA A1555 mutation and 47 other variants belonging to Eastern Asian haplogroup H2. None of other mitochondrial variants was evolutionarily conserved and functional significance. Therefore, the coexistence of the A1555G mutation and T14484C mutations in this Chinese family indicate that the A1555G mutation may play a synergistic role in the phenotypic manifestation of LHON associated ND6 T14484C mutation. However, the incomplete penetrance of vision and hearing loss suggests the involvement of nuclear modifier genes and environmental factors in the phenotypic expression of these mtDNA mutations.

The mitochondrial tRNAGlu A14693G mutation may influence the phenotypic manifestation of ND1 G3460A mutation in a Chinese family with Leber’s hereditary optic neuropathy

We report here the clinical, genetic, and molecular characterization of one Han Chinese family with maternally transmitted Leber's hereditary optic neuropathy (LHON). Three of seven matrilineal relatives in this family exhibited the variable degree of central vision loss at the age of 12, 14, and 16 years old, respectively. Sequence analysis of the complete mitochondrial DNA in this pedigree revealed the presence of the ND1 G3460A mutation and 47 other variants, belonging to the Asian haplogroup M7b2. The G3460A mutation is present at homoplasmy in matrilineal relatives of this Chinese family. Of other variants, the homoplasmic A14693G mutation is of special interest as it was implicated to be associated with other mitochondrial disorders. This mutation is located at the TpsiC-loop, at conventional position 54 of tRNA(Glu). The uridine at this position (U54), which is highly conserved from bacteria to human mitochondria, has been implicated to be important for tRNA structure and function. Thus, the A14693G mutation may alter the tertiary structure of this tRNA, cause a failure in this tRNA metabolism, thereby worsening the mitochondrial dysfunction associated with the primary G3460A mutation. Therefore, the tRNA(Glu) A14693G mutation may have a potential modifier role in the phenotypic manifestation of the primary LHON-associated G3460A mutation in this Chinese family.

Mitochondrial DNA and its mutations: novel fields in a new era

Az utóbbi két évtizedet tartják a klinikai mitokondriális DNS-kutatás aranykorának. Folyamatosan bővül a patológiás variánsok száma, amelyek betegséggel társulnak, illetve bővül az ismeretanyag azokról az entitásokról, melyek hátterében a mitokondriális DNS kóros elváltozásai állnak. A cirkuláris mitokondriális DNS öröklődése eltér a Mendel-féle szabályoktól, anyai öröklésmenetet mutat; számos vonatkozásban eltérő sajátosságokkal rendelkezik a nukleáris DNS-hez viszonyítva. A molekuláris biológiai módszerek terjedésével egyre több kórkép ismerhető fel, noha a diagnosztika manapság is komoly kihívást jelent. Napjainkban a mitokondriális medicina számos orvosi szubspecialitáshoz kapcsolódóan jelentős előrelépéseket mutatott; így körvonalazódott a mitokondriális gasztroenterológia, endokrinológia, otológia, oftalmológia, nefrológia, hematológia, onkológia, reproduktív medicina és pszichiátria, mintegy az adott szubspecialitás mitokondriális DNS-sel kapcsolatos, többé-kevésbé részleges önállósodással megjelenő territóriuma. A jelen összefoglaló közlemény a mitokondriális medicina rövid, általános összefoglalása mellett e fejezetekre próbál rátekintést nyújtani.

Analysis of disease-associated ND4 mutations: How do we know which mutation is pathogenic?

It is not uncommon to identify more than one mtDNA replacement mutations in the specimens from patients. However, we usually do not know if the identified mtDNA mutation is pathogenic or not. Even functional assays are available to use, we would not know which mutation(s) is to be tested. To provide a rapid method for initial evaluation for the pathogenicity of the replacement mutation, we compared three evolutional analyses: primate conservation index (PCI), mammalian conservation index (MCI), and conservation index across a wide spectrum of species (CI). After analyzing 35 so-called diseases-associated replacement mutations of ND4, we found 8 pathogenic mutations, 15 nonpathogenic mutations, and 12 mutations of undetermined significance. The MCI classification appears to be the best one among the three systems. This study demonstrates that evolutional analysis can serve as a rapid evaluation for the pathogenicity of mtDNA replacement mutations.

Cosegregation of the ND4 G11696A mutation with the LHON-associated ND4 G11778A mutation in a four generation Chinese family

We report here the characterization of a four-generation Han Chinese family with Leber's hereditary optic neuropathy (LHON). This Chinese family exhibited a variable severity and age-at-onset of visual loss. Notably, the average age-at-onset of vision impairment changed from 26 years (generation III) to 14 years (generation IV), with the average of 18 years in this family. In addition, 30% and 50% of matrilineal relatives in generation III and IV of this family developed visual loss with a variability of severity, ranging from blindness to normal vision. Sequence analysis of the complete mitochondrial DNA in this pedigree revealed the presence of the homoplasmic ND4 G11778A mutation and 33 other variants, belonging to the Asian haplogroup D4. Of other variants, the homoplasmic G11696A mutation in the ND4 gene is of special interest as it was implicated to be associated with LHON in a large Dutch family and five Chinese pedigrees with extremely penetrance of visual loss. In fact, the G11696A mutation caused the substitution of an isoleucine for valine at amino acid position 313, located in a predicted transmembrane region of ND4. These imply that the G11696A mutation may act in synergy with the primary LHON-associated G11778A mutation in this Chinese pedigree.

High penetrance of sequencing errors and interpretative shortcomings in mtDNA sequence analysis of LHON patients

For identifying mutation(s) that are potentially pathogenic it is essential to determine the entire mitochondrial DNA (mtDNA) sequences from patients suffering from a particular mitochondrial disease, such as Leber hereditary optic neuropathy (LHON). However, such sequencing efforts can, in the worst case, be riddled with errors by imposing phantom mutations or misreporting variant nucleotides, and moreover, by inadvertently regarding some mutations as novel and pathogenic, which are actually known to define minor haplogroups. Under such circumstances it remains unclear whether the disease-associated mutations would have been determined adequately. Here, we re-analyse four problematic LHON studies and propose guidelines by which some of the pitfalls could be avoided.

Leber’s hereditary optic neuropathy is associated with the mitochondrial ND6 T14484C mutation in three Chinese families

We report here the clinical, genetic, and molecular characterization of three Chinese families with maternally transmitted Leber's hereditary optic neuropathy (LHON). Clinical and genetic evaluations revealed the variable severity and age-of-onset in visual impairment in these families. In the affected matrilineal relatives, the loss of central vision is bilateral, the fellow eye becoming affected either simultaneously (45%) or sequentially (55%). The penetrances of vision loss in these pedigrees were 27%, 50%, and 60%, respectively. The age-at-onset of vision loss in these families was 14, 19, and 24 years, respectively. Furthermore, the ratios between affected male and female matrilineal relatives were 1:1, 1:1.2, and 1:2, respectively. Mutational analysis of mitochondrial DNA revealed the presence of homoplasmic ND6 T14484C mutation, which has been associated with LHON. The incomplete penetrance and phenotypic variability implicate the involvement of nuclear modifier gene(s), environmental factor(s) or mitochondrial haplotype(s) in the phenotypic expression of the LHON-associated T14484C mutation in these Chinese pedigrees.

The mitochondrial tRNAThr A15951G mutation may influence the phenotypic expression of the LHON-associated ND4 G11778A mutation in a Chinese family

We report here the characterization of a three-generation Han Chinese family with Leber's hereditary optic neuropathy (LHON). This Chinese family exhibited high penetrance and expressivity of visual impairment. The average age-of-onset was 19 years in this family. All male and 33% female matrilineal relatives in this Chinese family developed visual loss with a wide range of severity, ranging from blindness to normal vision. Sequence analysis of the complete mitochondrial DNA in this pedigree revealed the presence of the ND4 G11778A mutation and 40 other variants, belonging to the Asian haplogroup D4. The G11778A mutation is present at homoplasmy in matrilineal relatives of this Chinese family. Of other variants, the homoplasmic A15951G mutation is of special interest as it is located adjacent to 3' end, at conventional position 71 of tRNA(Thr). The adenine (A71) at this position of tRNA(Thr), highly conserved from bacteria to human mitochondria, has been implicated to be important for tRNA identity and pre-tRNA processing. In fact, the significant reduction of the steady-state levels in tRNA(Thr) was observed in cells carrying both the A15951G and G11778A mutations but not cells carrying only G11778A mutation. Thus, the A15951G mutation most probably leads to a failure in mitochondrial tRNA metabolism, worsening the mitochondrial dysfunction associated with the primary G11778A mutation. These imply that the tRNA(Thr) A15951G mutation may have a potential modifier role in increasing the penetrance and expressivity of the primary LHON-associated G11778A mutation in this Chinese family.

Updating the East Asian mtDNA phylogeny: a prerequisite for the identification of pathogenic mutations

Knowledge about the world phylogeny of human mitochondrial DNA (mtDNA) is essential not only for evaluating the pathogenic role of specific mtDNA mutations but also for performing reliable association studies between mtDNA haplogroups and complex disorders. In the past few years, the main features of the East Asian portion of the mtDNA phylogeny have been determined on the basis of complete sequencing efforts, but representatives of several basal lineages were still lacking. Moreover, some recently published complete mtDNA sequences did apparently not fit into the known phylogenetic tree and conflicted with the established nomenclature. To refine the East Asian mtDNA tree and resolve data conflicts, we first completely sequenced 20 carefully selected mtDNAs--likely representatives of novel sub-haplogroups--and then, in order to distinguish diagnostic mutations of novel haplogroups from private variants, we applied a 'motif-search' procedure to a large sample collection. The novel information was incorporated into an updated East Asian mtDNA tree encompassing more than 1000 (near-) complete mtDNA sequences. A reassessment of the mtDNA data from a series of disease studies testified to the usefulness of such a refined mtDNA tree in evaluating the pathogenicity of mtDNA mutations. In particular, the claimed pathogenic role of mutations G3316A, T3394C, A4833G and G15497A appears to be most questionable as those initial claims were derived from anecdotal findings rather than e.g. appropriate association studies. Following a guideline based on the phylogenetic knowledge as proposed here could help avoiding similar problems in the future.