Secondary LHON Mutations Research Articles

Genetic analysis in a cohort of patients with hereditary optic neuropathies in Southwest of China

We report the results of molecular screening in 121 patients with suspected hereditary optic neuropathies. The 34 primary and 9 secondary LHON mutations were screened in all the patients. In the familial cases, OPA1 was also tested when negative finding for the mtDNA mutations screening. Molecular defects were identified in 35 patients (28.9% of screened patients). Among these, 33 patients (94.3%) had an mtDNA mutation, including m.11778G > A (69.7%), m.14484 T > C, m.3460G > A, m.3635G > A, m.14502 T > C and three secondary mutations m.3316G > A, m.3394 T > C, m.3497C > T. Two novel OPA1 mutations, c.1301 T > G (p.Leu434Arg) and c.985-1G > A (IVS9-1G > A), were also detected in families with the evidence of father-to-son transmission. In conclusion, we reported the results of the molecular screening of 121 patients with hereditary optic neuropathies from southwest of China. Our results highlight the importance of investigating LHON-causing mtDNA mutations and OPA1 mutations in cases of suspected hereditary optic neuropathy.

Coexistence of mitochondrial 12S rRNA C1494T and CO1/tRNASer(UCN) G7444A mutations in two Han Chinese pedigrees with aminoglycoside-induced and non-syndromic hearing loss

Mutations in mitochondrial DNA are one of the important causes of hearing loss. We report here the clinical, genetic, and molecular characterization of two Han Chinese pedigrees with maternally transmitted aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the wide range of severity, age-at-onset, and audiometric configuration of hearing impairment in matrilineal relatives in these families. The penetrances of hearing loss in these pedigrees were 20% and 18%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees were 10% and 15%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA C1494T and CO1/tRNASer(UCN) G7444A mutations. Their distinct sets of mtDNA polymorphism belonged to Eastern Asian haplogroup C4a1, while other previously identified six Chinese mitochondrial genomes harboring the C1494T mutation belong to haplogroups D5a2, D, R, and F1, respectively. This suggested that the C1494T or G7444A mutation occurred sporadically and multiplied through evolution of the mitochondrial DNA (mtDNA). The absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in their mtDNA suggest that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the 12S rRNA C1494T and CO1/tRNASer(UCN) G7444A mutations in those Chinese families. However, aminoglycosides and other nuclear modifier genes play a modifying role in the phenotypic manifestation of the C1494T mutation in these Chinese families.

Maternally inherited aminoglycoside-induced and nonsyndromic hearing loss is associated with the 12S rRNA C1494T mutation in three Han Chinese pedigrees

We report here the clinical, genetic and molecular characterization of three Han Chinese pedigrees with maternally transmitted aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the wide range of severity, age-at-onset and audiometric configuration of hearing impairment in matrilineal relatives in these families. The penetrances of hearing loss in these pedigrees were 28%, 20%, and 15%, with an average of 21%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees were 21%, 13% and 8%, with an average of 14%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA C1494T mutation, in addition to distinct sets of mtDNA polymorphism belonging to Eastern Asian haplogroups F1a1, F1a1 and D5a2, respectively. This suggested that the C1494T mutation occurred sporadically and multiplied through evolution of the mtDNA. The absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in their mtDNA suggests that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the C1494T mutation in those Chinese families. In addition, the lack of significant mutation in the GJB2 gene ruled out the possible involvement of GJB2 in the phenotypic expression of the C1494T mutation in those affected subjects. However, aminoglycosides and other nuclear modifier genes play a modifying role in the phenotypic manifestation of the C1494T mutation in these Chinese families.

Very low penetrance of hearing loss in seven Han Chinese pedigrees carrying the deafness-associated 12S rRNA A1555G mutation

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here the clinical, genetic and molecular characterizations of seven Han Chinese pedigrees with aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the variable phenotype of hearing impairment including severity, age-at-onset and audiometric configuration in these subjects. The penetrance of hearing loss in these pedigrees ranged from 3% to 29%, with an average of 13.6%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees varied from 0% to 17%, with an average of 5.3%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA A1555G mutation, in addition to distinct sets of mtDNA polymorphism belonging to East Asian haplogroups B4, D4, D5 and F1, respectively. This suggested that the A1555G mutation occurred sporadically and multiplied through evolution of the mtDNA in China. Despite the presence of several evolutionary conservative variants in protein-encoding genes, there was the absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in these seven Chinese families. These suggest that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the A1555G mutation in those Chinese families with very low penetrance of hearing loss. However, aminoglycosides appear to be a major modifier factor for the phenotypic manifestation of the A1555G mutation in these Chinese families.

Extremely low penetrance of hearing loss in four Chinese families with the mitochondrial 12S rRNA A1555G mutation

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here the clinical, genetic, and molecular characterization of four Chinese pedigrees with aminoglycoside-induced and nonsyndromic hearing impairment. Clinical evaluation revealed the variable phenotype of hearing impairment including audiometric configuration in these subjects, although these subjects share some common features: bilateral and sensorineural hearing impairment. Strikingly, these Chinese pedigrees exhibited extremely low penetrance of hearing loss (5.2%, 4.8%, 4.2%, and 13.3%, respectively, and with an average 8% penetrance). In particular, four of all five affected matrilineal relatives of these pedigrees had aminoglycoside-induced hearing loss. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the distinct sets of mtDNA polymorphism, in addition to the identical homoplasmic A1555G mutation, associated with hearing impairment in many families from different genetic backgrounds. The fact that mtDNA of those pedigrees belonged to different haplogroups R9a, N9a, D4a, and D4 suggested that the A1555G mutation occurred sporadically and multiplied through evolution of the mtDNA in China. However, there was the absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in these Chinese families. These data imply that the nuclear background or/and mitochondrial haplotype may not play a significant role in the phenotypic expression of the A1555G mutation in these Chinese pedigrees. However, aminoglycoside appears to be a major modifier factor for the phenotypic manifestation of the A1555G mutation in these Chinese families.

Study of mitochondrial DNA mutations in patients with migraine with prolonged aura.

Ten patients with migraine with prolonged aura were studied for the presence of mitochondrial DNA point mutations utilizing DNA isolated from blood and hair samples. We analyzed for nine point mutations reported in patients with MELAS (A3243G, C3256T, T3271C, T3291C, A5814G, T8356C, T9957C, G13513A, and A13514G) and three secondary LHON mutations (T4216C, A4917G, and G13708A). None of the patients tested had any of these mutations in mitochondrial DNA. However, one patient was found to have a tRNA(Gln) A4336G mitochondrial DNA variant. From this study it appears that migraine with prolonged aura is not an oligosymptomatic form of MELAS and is not related to secondary LHON mutations. The significance of the tRNA A4336G variant is unknown.

Sequence Analysis of the Entire Mitochondrial Genome in Parkinson's Disease

The pathogenesis of Parkinson's disease (PD) is largely unknown. Indirect evidence suggests that mutations in mitochondrial DNA (mtDNA) might play a role, but previous studies have not consistently associated any specific mutations with PD. However, these studies have generally been confined to limited areas of the mitochondrial genome. We therefore sequenced the entire mitochondrial genome from substantia nigra of 8 PD and 9 control subjects. Several sequence variants were distributed differently between PD and control subjects, but all were previously reported polymorphisms. Several secondary LHON mutations were found, as well as a number of novel missense mutations, but all were rare and did not differ between PD and control subjects. Finally, PD and control subjects did not differ in the total number of all mutations, nor the total number of missense mutations. Thus, mtDNA involvement in PD, if any, is likely to be complex and should be reconsidered carefully.

Characterization of the mitochondrial genome in childhood multiple sclerosis. II. Multiple sclerosis without optic neuritis and LHON-associated genes.

The occurrence of mitochondrial mutations with primary pathogenic significance for Leber's hereditary optic neuropathy in patients with a multiple sclerosis-like phenotype and the preferential maternal transmission points to an involvement of the mitochondrial genome in conferring increased susceptibility to MS. To evaluate the link between MS and mtDNA variations we investigated a total of thirteen children with MS as well as twenty controls by sequencing eight mitochondrial encoded genes which are known to be the loci for LHON-associated mutations. Numerous synonymous nucleotide substitutions and common polymorphisms were excluded from comparative analyses. No primary LHON mutations were found. Secondary LHON mutations were identified more frequently in control subjects than in the children with MS. The remaining eight discrete missense mutations were chosen for further characterization. Only two of them were found in more than one patient. Our results suggest that nucleotide substitutions within the ND1, ND2, ND4, ND5, ND6, COI, COIII or cytochrome b genes of mtDNA do not contribute to the etiology of typical MS. However, the association of LHON mutations with visual impairment in MS as well as the relationship between phenotypic diversity in certain subgroups of patients with individual mtDNA genotypes merits further investigations.

Characterization of the mitochondrial genome in childhood multiple sclerosis. I. Optic neuritis and LHON mutations.

The occurrence of optic neuropathy in patients with MS-like disorders who carry one of the pathogenetically significant LHON mutations as well as the higher incidence of maternal transmission in familial cases of MS support the hypothesis that mitochondrial genes may be implicated in susceptibility to MS. We sequenced the entire mtDNA of six children with MS who developed optic neuritis as early and prominent visual involvement. The analysis revealed a high degree of nucleotide variations relative to the standard mtDNA sequence. After excluding various synonymous nucleotide changes and common neutral polymorphisms, eight discrete novel missense mutations within the protein coding, tRNA or rRNA genes were detected. None of the eight polymorphic sites were found in common between the patients with MS. Of particular interest was the observation that five of six children carried a total of nine secondary LHON mutations at nucleotide positions 4216, 4917 or 13708. We conclude that variation in mtDNA is unlikely to contribute to genetic predisposition for MS. However, secondary LHON mutations may be regarded as additional risk factor for developing prominent optic nerve involvement. The association of individual sets of mtDNA variations with phenotypic presentation in certain subgroups of MS patients remains to be clarified.

Novel mutations of mitochondrial complex I in pathologically proven Parkinson disease.

Complete sequence analysis of all mitochondrial complex I genes was performed in 22 cases of neuropathologically confirmed idiopathic Parkinson disease (PD). DNA from the substantia nigra was used as a template for polymerase chain reaction-based genomic sequencing. Seven novel mutations causing the exchange of amino acids were detected in subunit genes ND1 (3992 C/ T, 4024 A/G), ND4 (11253 T/C, 12084 C/T), ND5 (13711 G/A, 13768 T/C), and ND6 (14582 T/C). In addition, five known missense mutations affecting the ND1 (3335 T/C, 3338 T/C), ND2 (5460 G/A), ND3 (10398 A/G), and ND5 (13966 A/G) genes as well as three secondary LHON mutations (4216 T/C, 4917 A/ G, 13708 G/A) were found in the PD group. Among the novel mutations, the 11253 T/C transition which changes a conserved isoleucine residue into threonine is most likely to be of functional relevance. Furthermore, 43 synonymous polymorphisms were detected in PD brains, including 20 novel sequence variants. Haplogroup analysis revealed that most unique missense mutations were found in PD cases belonging to the D(c) haplogroup. Our data are in line with the view that PD is not a single disease entity but comprises a genetically heterogeneous group of disorders. The results of our study further suggest that 90% or more of all idiopathic PD cases are not due to sequence variation of mitochondrial complex I, but that mitochondrial mutations may play a pathogenic role in a subset of PD patients.

Mitochondrial DNA mutations in multiple sclerosis patients with severe optic involvement.

Preferential maternal transmission in familial cases and the occasional association of multiple sclerosis (MS) and LHON suggests an involvement of mtDNA mutations in the aetiology of MS. DNA obtained from 100 MS patients with pathological alterations in visually evoked potentials and 100 controls, was used for PCR amplification of mtDNA segments. Mutations were identified by restriction enzyme analysis and DNA sequencing. Whereas primary LHON mutations are not detected, MS patients show a higher percentage of secondary LHON mutations, usually in a combinatorial manner, than controls. Two neighbouring base pair substitutions that are alleles in a HpaII-polymorphism in the mt tRNA(Thr) gene are significantly more frequent in MS patients than in controls (p = 0.00018). Primary LHON mutations are not characteristic for MS with optic involvement, but secondary LHON mutations and two substitutions abolishing a HpaII site in the mt tRNA(Thr) gene may contribute to the aetiology of MS with optic involvement.