Search

Objective: To analyze the genetic characteristics in nonsyndromic hearing impairment (NSHL) patients in Zhejiang province. Method: Peripheral blood samples were obtained from 1822 NSHL patients and 467 normal hearing controls in Zhejiang province. We carried out a systematic mutational screening of GJB2 gene in these subjects by amplifying the coding region of GJB2 gene and sequencing directly. Result: Thirty kinds of mutation were identified, including eleven pathogenic mutations, one hypomorphic allele, sixteen polymorphic mutations and two novel mutations. The c.235delC mutation was the most prevalent pathogenic mutation in this cohort (18.50%), and the rate of allele mutation was 12.16%. The frequency of c.299_300delAT,c.176_191del16,c.512_513insAACG,c.35delG,c.283G>A,c.427C>T,c.35insG,c.439G>A,c.571T>C,c.139G>T mutations were decreased in turn. Conclusion: c.235delC mutation is the hot spot of GJB2 gene mutation in NSHL patients in Zhejiang province and the most common mutational pattern is frame-shift mutation. The discovery of novel mutations enriches the spectrum and frequency of variants in GJB2 gene., Competing Interests: The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose., (Copyright© by the Editorial Department of Journal of Clinical Otorhinolaryngology Head and Neck Surgery.)

Objective: To investigate the mutation characteristics of GJB6 (gap juction bata 6) gene in 318 Han Chinese pedigrees with non-syndromic hearing loss. Method: Polymerase chain reaction was used to detect the coding region of GJB6 gene in 318 Han Chinese pedigrees with non-syndromic hearing loss.Gene arrays and second generation sequencing were used to detect 118 genes which had reported to be accosiated with deafness in members of pedigree which possibly carried pathogenic GJB6 gene mutation. Result: Here,we have screened the mutations of GJB6 gene in 318 Han Chinese pedigrees with non-syndromic hearing loss and found one pedigree carrying both GJB6 and GJB2 gene deletion.Clinical and molecular genetic evaluation revealed the variable phenotype of hearing impairments including age-at-onset,audiometric configuration and severity in these subjects.Mutational analysis of the GJB2 and GJB6 gene coding region showed a heterozygous 235 del C of GJB2 gene and a novel 228 del G of GJB6 gene. Conclusion: GJB6 gene 228 del G absent varies among 94 unrelated Chinese controls.Our finding suggest that GJB6 gene 228 del G absent varies among 94 unrelated Chinese controls.Our finding suggest that GJB6 gene 228 del G maybe a novel pathogenic mutation associated with non-syndromic hearing loss., Competing Interests: The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose., (Copyright© by the Editorial Department of Journal of Clinical Otorhinolaryngology Head and Neck Surgery.)

Objective: To assess the possible genotype-phenotype correlation for GJB2., Methods: Retrospectively analyzed GJB2 gene mutations with non-syndromic hearing impairment (NSHI) patients and their families audiological data. Individuals were grouped, according to non-truncated mutant (non-truncating, NT) and truncating mutations (truncating, T), into T/T group, T/NT group and NT/NT group. And according to whether they carry 235delC, grouped into 235delC/235delC group, 235delC/Non-235del group and Non-235delC/Non-235delC group., Results: Grouped according to whether the truncation mutants:Fisher exact statistical analysis showed that the degree of hearing loss among the three groups did not meet the random distribution (P = 0.003) , T/T group was significantly higher than T/NT group (P = 0.000) and NT/NT group (P = 0.000) on the degree of hearing loss. Grouped according to whether they carry 235delC mutation: degrees of hearing loss among the three groups were statistically significant differences. Respectively pairwise comparisons (Fisher exact test) found 235delC/235delC group was significantly higher than 235delC/Non-235delC on the degree of hearing loss group (P = 0.001) and Non-235delC/Non-235delC group (P = 0.000), 235delC/Non-235delC group higher than Non-235delC/Non-235delC group (P = 0.033). In GJB2 mutations homozygous and compound heterozygous mutation genotype:G109A/G109A, 235delC/512insAACG, 299delAT/G109A and 235delC/G109A degree of hearing loss caused by genotype was significantly lower than 235delC/235delC group., Conclusions: 235delC homozygotes have significantly more hearing impairment, when compared with 235delC/non-235delC compound heterozygotes. People with two non-235delC mutations have even less hearing impairment. Patients with non-truncation mutants (G109A) suffer from lighter hearing loss than truncation mutations(235delC, 299delAT).

Objective: We reported here the clinical and genetic evaluations as well as mutational analysis of mitochondrial DNA(mtDNA) in a Chinese family with maternally transmitted non-syndromic hearing loss and investigated the influence of the mitochondrial tRNA(Asp) A7551G mutation to the phenotypic manifestation of the deafness., Methods: One Chinese Han pedigrees of maternally transmitted nonsyndromic hearing loss were collected. The proband and family members underwent clinical, genetic, and molecular evaluations, such as audiological examinations, mutational analysis of mitochondrial genome and mutational analysis of GJB2 gene., Results: Six people of this pedigree suffered from hearing loss, including four matrilineal members, and others did not have significant clinical abnormalities. Sequence analysis of the complete mitochondrial genome in the proband showed that there were 28 mtDNA polymorphisms belonging to East -Asian haplogroup A4.In addition to the A7551G homogeneity mutation, there were no other functionally significant variants found in this family. The A7551G mutation located immediately at the three prime end to the anticodon, corresponding with the conventional position 37 of tRNA(Asp), and its' CI value was 100% compared with other 15 primate species. The A7551G mutation was absent in other Chinese controls. The mutations on GJB2 were detected by direct sequence analysis,GJB2 235delC and 299delAT which was associated with hearing loss were found in the genomic DNA of the proband and some matrilineal members. Clinical evaluation showed a variable phenotype of severity, age-at-onset and audiometric configuration of hearing loss in the matrilineal relatives in these families., Conclusions: The A7551G mutation may modify the secondary structure of the tRNA, and affect the stabilization of tRNA(Asp), produce non-normal functional tRNA(Asp) ultimately. And it may cause the phenotypic manifestation of the deafness that associated with A7551G mutation. Therefore, the mitochondrial tRNA(Asp) A7551G mutation may be a new mitochondrial mutation for hearing loss.

Dyslipidemia is defined as high levels of serum cholesterol and/or triglycerides. Dyslipidemia often leads to severe cardiovascular diseases including coronary heart disease and stroke as the first clinical manifestation, thus threatening the health of human beings. Dyslipidemia diseases can be caused by the genetic factors, including the Mandelian or polygenic inheritance. Traditional methods of identifying genes associated with dyslipidemia are mainly DNA sequencing and linkage analysis, suitable for Mendelian genetic dyslipidemia disease. The rise of next-generation sequencing technology applies to not only Mandelian inheritance, but also complex forms of dyslipidemia diseases. Since 2006, genome-wide association studies (GWAS) screened out many causative genes associated with dyslipidemia, and most of these genes were the previously identified ones by the pedigree-based classic approaches. Furthermore, GWAS revealed that there were the different frequencies of gene variations related to complex forms of dyslipidemia diseases. Most of the identified single nucleotide polymorphisms (SNPs) associated with dyslipidemia are located in non-coding regions and thus people gradually focus on the gene variations of these loci. The identification of the causative genes will provide new insights into the pathophysiology of dyslipidemia diseases and a step toward therapeutic intervention. This review summarized recent pro-gress in heritable dyslipidemia.

Mitochondrial 12S rRNA A1555G mutation has been associated with both aminoglycoside-induced and nonsyndromic hearing loss. In this report, we performed a clinical and genetic evaluation, and mitochondrial genome analysis of one hearing-impaired Chinese family carrying the A1555G mutation. Strikingly, the penetrances of hearing loss in this family, which were 81% and 66.7%, respectively, when aminoglycoside-induced hearing loss was included or excluded. The penetrances of hearing loss in this family were significantly higher than those in other Chinese families carrying the A1555G mutation. Sequence analysis of their mitochondrial genomes revealed the presence of homoplasmic tRNAIle A4317G mutations and 38 mtDNA polymorphisms belonging to East-Asian haplogroup B4c1b2. Further analysis revealed that other mitochondrial DNA variants were not functional significantly, while the A4317G mutation is localized to a highly conserved nucleotide (conventional site 59) at tRNAIle TΨC loop of tRNAIle. The mutation may alter secondary structure and function of this tRNA, thereby leading to mitochondrial dysfunction. Allelic analysis showed that this mutation was absent in 961 hearing normal Chinese controls. Thus, the altered tRNAIle metabolism by the A4317G mutation may aggravate mitochondrial dysfunction associated with the A1555G mutation, and contribute to the higher penetrance of hearing loss. Therefore, the tRNAIle A4317G mutation may act as a mitochondrial modifier to influence the phenotypic manifestation of the A1555G mutation.

To evaluate the correlation between genetic mutations and the age in nonsyndromic hearing impairment (NSHI) and the clinical characteristics of NSHI, 215 patients with NSHI were enrolled between April 2006 and April 2012. All patients were divided into four groups according to ages of hearing loss onset and clinic presentation (0-3, 3-6, 6-18 and 18+ years). The mutations of GJB2 and mitochondria DNA (mtDNA) 1555G/C1494T were screened from peripheral blood samples in each age group. The prevalence of mutations and the age ratio were obtained. The study showed that 18.14% of all patients were found to have GJB2 mutations and 11.16% were found to have mtDNA A1555G/C1494T mutations. The prevalence of GJB2 mutation in adult group (5.26%) was lower than juvenile group who sought medical attention at 0-18 years of age (22.36%), while the prevalence of mtDNA A1555G/C1494T in adult group (31.48%) was higher than juvenile group (4.97%). Significant differences in the prevalence of GJB2 (χ2=7.108, P=0.008) and mtDNA A1555G/C1494T (χ2=20.852, P=0.000) were observed in both of two groups. The prevalence of GJB2 mutations between adult and juvenile groups according to ages of hearing loss onset was statistically significant different (0%, 20.10%, respectively, and P=0.023), while the prevalence of mtDNA A1555G/C1494T mutations was not different (14.29%, 11.34%, respectively, and P=0.698). The onset age of 66.67% of patients with GJB2 mutations was less than 1 year old, while the onset of patients with mtDNA A1555G/C1494T mutations could be found at any age group. Different standardizations of hearing loss could also show different results. These data strongly suggest that most of GJB2 mutations are found in congenital deafness and mtDNA A1555G/C1494T mutations mainly represent acquired deafness, which can be induced or aggravated by aminoglycoside antibiotics in all age groups and should be tested mainly ranging from 4 kHz to 8 kHz. Both newborn hearing screening and genetic testing are important to find early deafness.

Mitochondrial 12S rRNA A1555AG mutation is one of the important causes of aminoglycoside-induced and nonsyndromic deafness. We report here the clinical, genetic and molecular characterization of 25 Chinese families carrying the A1555G mutation.Clinical and genetic characterizations of these Chinese families exhibited a wide range of penetrance, severity and age-at-onset of hearing impairment. The average penetrances of deafness were 28.1% and 21.5%, respectively, when aminoglycoside-induced hearing loss was included or excluded. Furthermore, the average age-of-onset for deafness without aminoglycoside exposure ranged from 1 and 15 years old. Their mitochondrial genomes exhibited distinct sets of polymorphisms including 16 novel variants, belonging to ten Eastern Asian haplogroups A, B, D, F, G, M, N and R, respectively. Strikingly, these Chinese families carrying mitochondrial haplogroup B exhibited higher penetrance and expressivity of hearing loss. In addition, 7 known secondary mutations and 21 variants resided at the highly conservative residues may enhance the penetrace of hearing loss in these Chinese families. Moreover, the absence of mutation in GJB2 gene suggested that GJB2 may not be a modifier for the phenotypic expression of the A1555G mutation in these Chinese families. These observations suggested that mitochondrial haplotypes and other modifiers may modulate the variable penetrance and expressivity of deafness among these Chinese families.

Although the basic principles for the function of peripheral auditory system have been known for many years, the molecular mechanisms which affect deafness are not clear. In recent years, the study of hereditary deafness associated mouse models has revealed the molecular basis which is related with the formation and function of the hair bundle and the mechanosensory organelle of hair cell. This review focused on the role of protein network, which is formed by the proteins encoded by the Usher syndrome type 1 genes, in hair-bundle development and mechanotransducer channel gating. And the review also showed how the stereocilia rootlets contribute to the hair bundle's mechanical properties and how the hair bundle produces suppressive masking. Finally, the review revealed multiple roles of the tectorial membrane and extracellular matrix in the hair bundles stimulating in the cochlea.

We reported here the clinical, genetic, and molecular characterization of Leber's hereditary optic neuropathy (LHON) with C5601T mutation in seven Chinese families. The ophthalmologic examinations of seven Chinese families who were clinically diagnosed LHON were conducted. Strikingly, these families exhibited very low penetrance of visual impairment, and the penetrance was 9.5%, 14.3%, 4.5%, 8.3%, 10.0%, 22.2% and 25.0%. Meanwhile, entire mitochondrial genome of seven probands was amplified by PCR using 24 pairs of oligonucleotide primers with overlapping fragments. Molecular analysis of mitochondrial DNA (mtDNA) in these pedigrees revealed the absence of three common LHON associated G11778A, G3460A and T14484C mutations but the presence of homoplastic LHON associated tRNAAla C5601T mutation in probands and other matrilineal relatives. These mtDNA polymorphism sites belongs to the Asian haplogroups G2, G2a1, G2a1, G2, G2b, G2a1 and G2. By analyzing mitochondrial genome, seven LHON families all carry the C5601T mutation. The C5601T mutation occurs at the highly conserved nucleotide (conventional position 59) of tRNAAla, thereby contributing to the structural formation and stabilization of functional tRNAs and leading to mitochondrial dysfunction involved in visual impairment. The incomplete penetrance of visual loss in these seven Chinese pedigrees strongly indicates that the tRNAAla C5601T mutation was itself insufficient to produce a clinical phenotype. The lack of functional mtDNA variants in these pedigrees ruled out the role of mitochondrial background in the phenotypic expression of visual loss. Therefore, nuclear backgrounds and environmental factors seem to be modifying factors for the phenotypic manifestation of the tRNAAla C5601T mutation in the seven Chinese families.

Objective: To evaluate the effect of mitochondrial DNA(mtDNA) secondary mutations, haplotypes, GJB2 gene mutations on phenotype of 1494C>T mutation, and to study the molecular pathogenic mechanism of maternally transmitted aminoglycoside-induced and nonsyndromic hearing loss., Methods: Two Chinese Han pedigrees of maternally transmitted aminoglycoside induced and nonsyndromic hearing loss were collected. The two probands and their family members underwent clinical, genetic and molecular evaluations including audiological examinations and mutational analysis of mitochondrial genome and GJB2 gene., Results: Clinical evaluation revealed wide range of severity, age-at-onset and audiometric configuration of hearing impairment in matrilineal relatives in both families, for which the penetrance of hearing loss was respectively 42.9% and 28.6% when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss were 14.3% and 14.3%. Sequence analysis of mitochondrial genomes identified a known 12S rRNA 1494C>T mutation, in addition with distinct sets of mtDNA polymorphisms belonging to Eastern Asian haplogroups C4a1a and B4b1c, respectively., Conclusion: Mitochondrial 12S rRNA 1494C>T mutation probably underlie the deafness in both families. Lack of significant mutation in the GJB2 gene ruled out involvement of GJB2 in the phenotypic expression. However, aminoglycosides and other nuclear modifier genes may still modify the phenotype of the 1494C>T mutation in these families. The B4b1c is a newly identified haplogroup in aminoglycoside-induced and nonsyndromic hearing loss family carrying the 1494C>T mutation. The 1494C>T mutation seems to have occurred sporadically through evolution.

It has been shown that mitochondria not only control their own Ca(2+) concentration ([Ca(2+)]), but also exert an influence over Ca(2+) signaling of the entire cell, including the endoplasmic reticulum or the sarcoplasmic reticulum, the plasma membrane, and the nucleus. That is to say, mitochondria couple cellular metabolic state with Ca(2+) transport processes. This review focuses on the ways in which the mitochondrial Ca(2+) handling system provides integrity and modulation for the cell to cope with the complex actions throughout its life cycle, enumerates some indeterminate aspects about it, and finally, prospects directions of future research.

Mitochondrial DNA (mtDNA) mutations are one of the important causes of deafness. In particular, the 12S rRNA gene is the hot spots for mutations associated with both aminoglycoside ototoxicity and nonsyndromic deafness. In this report, a total of 318 Chinese pediatric hearing-impaired subjects were recruited from otology clinics in the Zhejiang Province, China. These subjects underwent clinical, genetic evaluation and molecular analysis of 12S rRNA gene. Mutational analysis identified 34 variants in the 12S rRNA gene in this cohort. The incidences of the known deafness-associated 1555A>G, 1494C>T and 1095T>C mutations were 9.1%, 0.6% and 1.25% in this cohort, respectively. Other mtDNA variants were evaluated by structural and phylogenetic analysis. Of these, the 839A>G and 1452T>C variants could confer increased sensitivity to aminoglycosides or nonsyndromic deafness as they were not present in 449 Chinese controls and localized at highly conserved nucleotides of the 12S rRNA. However, other variants appeared to be polymorphisms. These data further support the idea that mitochondrial 12S rRNA is one of major targets for aminoglycoside ototoxicity. These data have been providing valuable information to predict which individuals are at risk for ototoxicity, to improve the safety of aminoglycoside antibiotic therapy, and eventually to decrease the incidence of deafness.

Mitochondrial DNA (mtDNA) exhibits matrilineal inherence. Familial mitochondrial diseases caused by mtDNA mutations are generally involved in organs featuring high energy consumption, which include heart, brain and skeletal muscle. Recently, it has been found that some essential hypertension patients featured classical maternal inheritance, which has confirmed and enriched mtDNA mutations as one of the molecular mechanisms underlying maternally inherited hypertension. Nevertheless, more general as well as radical questions are still to be answered. This article reviews recent advance in mitochondrial genome evolution, mtDNA genetics and the role of mtDNA mutations in maternally inherited hypertension.

Objective: To explore clinical, genetic and molecular features of two Chinese Han families with Leber's hereditary optic neuropathy (LHON)., Methods: Ophthalmologic examinations revealed variable severity and age-at-onset of visual loss among probands and other matrilineal relatives of both families. The families exhibited extremely low penetrance of visual impairment. The entire mitochondrial genome of two probands was amplified by PCR in 24 overlapping fragments using sets of oligonucleotide primers., Results: Sequence analysis of complete mitochondrial genome in the pedigrees excluded three common LHON associated mutations G11778A, G3460A and T14484C, but revealed the presence of a known homoplasmic tRNA(Thr) A15951G mutation. It also showed distinct sets of mtDNA polymorphisms belonging to Eastern Asian haplogroup D4b1. The A15951G mutation is located at the extremely conserved nucleotide (conventional position 71) of tRNA(Thr). Thus, this mutation may alter the structure and stability of mitochondrial tRNA(Thr), thereby leading to a failure in the tRNA metabolism and mitochondrial dysfunction, causing visual impairment., Conclusion: The results suggested that the A15951G mutation might be involved in the pathogenesis of Leber's hereditary optic neuropathy in the two families.

Mutations in mitochondrial DNA (mtDNA) are one of the molecular bases of hypertension. Among these, the tRNAMet A4435G, tRNAMet/tRNAGln A4401G, tRNAIle A4263G, T4291C and A4295G mutations have been reported to be associated with essential hypertension. These mutations alter the structure of the corresponding mitochondrial tRNAs and cause failures in tRNA metabolism. These shortages of these tRNAs lead to an impairment of mitochondrial protein synthesis and a failure in the oxidative phosphorylation function. These result in a deficit in ATP synthesis and an increase of generation of reactive oxygen species. As a result, these mitochondrial dysfunctions may contribute to the development of hypertension. Furthermore, the tissue specificity of these pathogenic mtDNA mutations might be associated with tRNA metabolism and nuclear modifier genes. These mtDNA mutations should be considered as inherited risk factors for future molecular diagnosis. Thus, these findings provide new insights into the molecular mechanism, management and treatment of maternally inherited hypertension. This review summarized the association between mtDNA mutations and hypertension.

Objective: To study the effect of the mitochondrial 12S rRNA mutations on aminoglycoside-induced and nonsyndromic hearing loss, to carry out the clinical and molecular characterization of five Han Chinese pedigrees with maternally transmitted aminoglycoside-induced and nonsyndromic hearing loss., Methods: Five pedigrees of maternally transmitted aminoglycoside-induced and nonsyndromic hearing loss were collected, genomic DNA was extracted, and complete mitochondrial genomes and the gap junction protein beta 2 (GJB2) gene were amplified and sequenced., Results: Clinical evaluation revealed a wide range of severity, age-at-onset and audiometric configuration of hearing impairment in the matrilineal relatives in these families. The penetrance rates of hearing loss in these pedigrees were 17.6%, 50.0%, 66.7%, 31.3% and 23.1%, with an average of 37.7%, when aminoglycoside-induced deafness was included. Sequence analysis of the complete mitochondrial genomes in these pedigrees identified the known 1555A>G mutation and distinct sets of mitochondrial DNA(mtDNA) polymorphisms belonging to Eastern Asian haplogroups D4b2b, B4c1b1, F3, C1 and D5a, respectively. Of these variants, ND1 L89T and CO3 A200T mutations resided at the highly conservative regions. However, there were no functionally significant mutations in tRNAs and rRNAs or secondary known mutations. No hearing loss related GJB2 gene mutation was observed., Conclusion: The lack of significant mutation in the ruled out the possible involvement of GJB2 in the phenotypic expression of the 1555A>G mutation in those affected subjects. However, aminoglycosides, mtDNA variations and other nuclear modifier genes may play an important role in the phenotypic manifestation of the 1555A>G mutation in these Chinese families.

Mutations in the mitochondrial DNA have been found to be one of the most important causes of sensorineural hearing loss. In particular, these mutations often occur in the mitochondrial 12S rRNA and tRNA genes. Of these, the homoplasmic A1555G and C1494T mutations in the 12S rRNA have been associated with both aminoglycoside induced and nonsyndromic hearing impairment in many families worldwide. Children carrying the A1555G or C1494T mutation are susceptible to the exposure of ototoxic drugs, thereby inducing or worsening hearing loss. Individuals harboring A1555G or C1494T mutation can also develop hearing loss even in the absence of aminoglycoside exposure. However, matrilineal relatives of intra-families or inter-families carrying the A1555G or C1494T mutation exhibit a wide range of severity, age-at-onset, and audiometric configuration of hearing impairment. These indicate that the A1555G or C1494T mutation is a primary factor underlying the development of deafness but insufficient to produce the clinical phenotype.Thus, other modifier factors, such as aminoglycoside(s), mitochondria l DNA haplotype(s) or nuclear modifier gene(s), play a role in the phenotypic expression of the deafness-associated mitochondrial 12S rRNA A1555G or C1494T mutation. In this review, we summarize the modifier factors for the phenotypic expression of deafness-associated 12S rRNA A1555G and C1494T mutations and propose the molecular pathogenetic mechanism of maternally inherited deafness.

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.

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.

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.

Mutations in mitochondrial DNA have been associated with a wide spectrum of clinical abnormalities. We reported here the clinical and genetic evaluations as well as mutational analysis of mitochondrial DNA(mtDNA) in a three-generation Chinese Han family with maternally transmitted hearing loss and epilepsy. Of 14 matrilineal relatives, three suffered from hearing loss, three had epilepsy, and other did not have significant clinical abnormalities. Sequence analysis of mitochondrial genome in this family identified the novel 7472delC in tRNASer(UCN) and 33 variants belonging to Asian haplogroup B4b1a2. The 7472delC locates at the highly conserved residue of T-arm of this tRNA. In fact, the 7472insC at the same position of this tRNA has been associated with hearing loss and epilepsy in several genetically unrelated families. The 7472insC has been shown to lead to a failure in tRNA metabolism and mitochondrial dysfunction. Thus, 7472delC mutation, similar to 7472insC mutation, may result in the mitochondrial dysfunctions responsible for the hearing loss and epilepsy. Furthermore, none of mutation in deafness-associated GJB2 gene was detected in this Chinese family. Therefore, the 7472delC is likely a new mitochondrial mutation with hearing loss and epilepsy.

GJB2, SLC26A4 (PDS) and mitochondrial DNA (mtDNA) have been associated with sensorineural hearing loss. In the present study, the clinical, genetic and molecular analysis of 14 cochlear implant recipients and their parents was studied from April 2006 to September 2007. Of the 14 subjects, 35.7% had gene mutations; 28.6% had homozygous GJB2 235delC mutation, whose parents carried heterozygous GJB2 235delC mutation; and 7.1% had mtDNA A1555G mutation, whose mother carried mtDNA A1555G mutation too. There was no SLC26A4 (PDS) mutation. These results strongly suggested that the mutation in GJB2 gene was a major cause of deafness in cochlear implant recipients and the mutation of mtDNA A1555G was another important cause. Genetic test of hot-spots and analysis of family constellation can offer an accurate genetic counseling to deaf family and reduce the incidence of hearing loss.

We report here the clinical and genetic evaluations as well as mutational analysis of mitochondrial DNA (mtDNA) in a four-generation Chinese Han family with aminoglycoside-induced and nonsyndromic hearing loss. Strikingly, this family exhibited a high penetrance and expressivity of hearing loss. The penetrances of hearing loss in this family were 75% and 41.7% respectively, when aminoglycoside-induced deafness was included or was excluded. The severity of hearing loss in matrilineal relatives varied from profound hearing loss to normal hearing. Mutational analysis of mtDNA identified the homoplasmic A1555G mutation and a distinct set of mtDNA variants belonging to the Asian haplogroup B5b. Of these, the G15927A mutation absent in 156 Chinese controls is localized at the anticodon-stem of tRNAThr at conventional position 42. The guanine at this position (G42) of tRNAThr is highly conserved from bacteria to human mitochondria. Thus, it is antici-pated that the G15927A disrupted the highly conserved C-G base-pairing at the anticodon-stem of tRNAThr. The alteration of structure of this tRNA likely leads to a failure in tRNA metabolism, thereby worsens the mitochondrial dysfunction asso-ciated with the A1555G mutation. Thus, the G15927A mutation has a potential modifying role in increasing the penetrance and expressivity of hearing loss associated with the deafness-associated 12S rRNA A1555G mutation in this Chinese pedigree.

We reported here the molecular analysis of mitochondrial genomes in sweetfish (Plecoglossus altivelis). Thirty-one specimens were recruited from Ruian, Zhejiang Province, Ningde, Fujian Province, and Dongzhang reservoir, Fujian Province. DNA segments spanning cytochrome b gene and D-loop region derived from these specimens were PCR-amplified and subsequently characterized by direct DNA sequence analysis. The resultant sequence data were compared with the consensus sequence and further analyzed for proportion of each nucleotide. The average A, T, C, and G con-tents in Cyt b gene were 19.72%, 29.71%, 32.25%, and 18.32%, respectively, while the contents of A+T and G+C were 49.43% and 50.57%. In the D-loop region, the average A, T, C and G contents were 29.99%, 29.29%, 23.80%, and 16.92% and the contents of A+T and G+C were 59.28% and 40.72%, respectively. There was only one variant in the Cyt b gene belong to two haplotypes and the nucleotide diversity (pi) was merely 0.00028. In the D-loop region, there were only 5 polymorphic sites belonging to 5 haplotypes and its nucleotide diversity (pi) was only 0.00199. These results showed that the genetic diversity of P. altivelis from these regions was very low.

Leber's hereditary optic neuropathy (LHON) is a maternally inherited disorder leading to rapid, painless, bilateral and usually permanent central vision loss in young adults, males are preferentially affected. The maternal transmission of this visual dysfunction in LHON families suggested that mutations in the mitochondrial DNA (mtDNA) are the molecular bases of the disorder. The ND1 G3460A, ND4 G11778A and ND6 T14484C mutations in the genes encoding the subunits of respiratory chain complex I, account for more than 50% of LHON families worldwide. These three mutations are designated to be primary mutations because they impart a high risk for LHON expression. However, matrilineal relatives within and among families, despite carrying the same LHON-associated mtDNA mutation(s), exhibit a wide range of onset, severity, and the progression of visual impairment. These findings strongly indicated that the LHON-associated primary mutation(s) are the primary factors underlying the development of vision loss, but they themselves are insufficient to produce a clinic phenotype. The prone to male, incomplete penetrance, and phenotypic variability of vision loss suggest that other modifier factors including personal factors, environmental factors, nuclear modifier genes and mitochondrial haplotypes contribute to the phenotypic expression of these mtDNA mutations. In particular, the mitochondrial haplotypes may play a synergic role in the development of vision loss in the families carrying the LHON-associated primary mtDNA mutation(s).

Objective: To report the clinical, genetic, and molecular characterization of two Chinese families with Leber's hereditary optic neuropathy (LHON)., Methods: Ophthalmological examinations showed that only probands in two families exhibited visual loss at the age of 10 and 17 years respectively. The entire mitochondrial genome of two probands was PCR amplified in 24 overlapping fragments using sets of oligonucleotide primers., Results: Mutational analysis of mitochondrial DNA (mtDNA) in these pedigrees revealed the absence of three common LHON associated G11778A, G3460A and T144484 mutations but the presence of homoplastic LHON associated ND4 G11696A mutation, which was present in one out of 167 Chinese healthy controls., Conclusion: Sequence analysis of the complete mitochondrial genomes in two pedigrees showed the distinct sets of mtDNA polymorphisms, belonging to Eastern Asian haplogroup D4. The incomplete penetrance of visual loss and the presence of one in 167 controls suggested that this mutation itself is insufficient to produce a clinical phenotype and other modifier factors play a role in the phenotypic manifestation. The lack of functional mtDNA variants in these pedigrees ruled out the role of mitochondrial background in the phenotypic expression of visual loss. Therefore, nuclear modifier gene(s) or environmental factor(s) may play a role in the phenotypic expression of the LHON-associated G11696A mutation in two Chinese pedigrees.