Spectrum of pathogenic mtDNA mutations in Leber’s hereditary optic neuropathy families from Siberia

The results of clinical, genealogical and molecular investigation of eighteen families with Leber’s hereditary optic neuropathy (LHON), identified on the territory of Siberia during the period from 1997 to 2005, are presented. Comprehensive analysis of mitochondrial genome variations in probands and their matrilineal relatives revealed the presence of relatively frequent (G11778A, G3460A, and T14484C), as well as rare and new mutations with the established or presumptive pathological effect (T10663C, G3535A, C4640A, and A14619G). The G11778A mutation was detected in nine pedigrees (50%), mostly in the families of ethnic Russians. In eight of these families G11778A was found in preferred association with the coding-region substitutions, typical of western Eurasian mtDNA lineage (haplogroup) TJ. On the contrary, the G3460A mutation was detected in the three families belonging to the indigenous Siberian populations (Tuvinians, Altaians, and Buryats). It was associated with clearly different haplotypes of eastern Eurasian haplogroups, C3, D5, and D8. Unexpectedly, the G3460A de novo mutation was found in a large Tuvinian pedigree. At the same time, in eleven out of fourteen families of Caucasoid origin pathogenic mutations in the ND genes were associated with the T4216C and C15445A coding-region mutations, marking the root motif of haplogoup TJ. It is suggested that phylogenetically ancient mutations could have provided their carriers with the adaptive advantages upon the development of Central and Northern Europe at the end of the last glaciation (10 000 to 9000 years ago), thereby, contributing to the preservation of weekly pathogenic LHON mutations, appearing at specific genetic background.     

Genotype–phenotype correlation in long QT syndrome families

Heterogeneity in clinical manifestations is a well-known feature in Long QT Syndrome (LQTS). The extent of this phenomenon became evident in families wherein both symptomatic and asymptomatic family members are reported. The study hence warrants genetic testing and/or screening of family members of LQTS probands for risk stratification and prediction.Of the 46 families screened, 18 probands revealed novel variations/compound heterozygosity in the gene/s screened. Families 1–4 revealed probands carrying novel variations in KCNQ1 gene along with compound heterozygosity of risk genotypes of the SCN5A, KCNE1 and NPPA gene/s polymorphisms screened. It was also observed that families- 5, 6 and 7 were typical cases of “anticipation” in which both mother and child were diagnosed with congenital LQTS (cLQTS). Families- 16 and 17 represented aLQTS probands with variations in IKs and INa encoding genes. First degree relatives (FDRs) carrying the same haplotype as the proband were also identified which may help in predictive testing and management of LQTS. Most of the probands exhibiting a family history were found to be genetic compounds which clearly points to the role of cardiac genes and their modifiers in a recessive fashion in LQTS manifestation.     

Subclinical Leber’s hereditary optic neuropathy with pediatric acute spinal cord onset: more than meets the eye

Background

Leber’s hereditary optic neuropathy (LHON) is a mitochondrial disease characterized by visual loss consequent to optic nerve atrophy. In some cases, LHON is associated with heterogeneous neurological extraocular manifestations and is referred to as “Leber plus disease”; rarely it is associated with a multiple sclerosis (MS)-like syndrome known as Harding disease, but no pediatric extraocular acute spinal onset is reported.

Case presentation

We describe the case of a 5-year-old girl carrying the G3460A mtDNA mutation who was referred to clinical examination for bilateral upper and lower limb weakness with no sign of optic neuropathy. Spinal cord MRI showed hyperintense signal alterations in T2-weighted and restricted diffusion in DWI sequences in the anterior portion of the cervical and dorsal spinal cord resembling a spinal cord vascular injury. No association between this mutation and pediatric spinal cord lesions has previously been reported. Alternative diagnostic hypotheses, including infective, ischemic and inflammatory disorders, were not substantiated by clinical and instrumental investigations.

Conclusions

Our case reports a novel pediatric clinical manifestation associated with the m.3460G?>?A mtDNA mutation, broadening the clinical spectrum of this disease. Early identification of new cases and monitoring of carriers beginning in childhood is important to prevent neurological deterioration and preserve long-term function.

     

Previously unclassified mutation of mtDNA m.3472T>C: Evidence of pathogenicity in Leber’s hereditary optic neuropathy

Leber’s hereditary optic neuropathy (LHON) refers to a group of mitochondrial diseases and is characterized by defects of the mitochondrial electron transport chain and decreased level of oxidative phosphorylation. The list of LHON primary mtDNA mutations is regularly updated. In this study, we describe the homoplasmic nucleotide substitution m.3472T>C in the MT-ND1 (NADH-ubiquinone oxidoreductase chain 1) gene and specific changes in cell metabolism in a patient with LHON and his asymptomatic sister. To confirm the presence of mutation-related mitochondrial dysfunction, respiration of skin fibroblasts and platelets from the patient and his sister was studied, as well as the mitochondrial potential and production of reactive oxygen species in the skin fibroblasts. In addition, based on characteristics of the toxic effect of paraquat, a new approach was developed for detecting the functional activity of complex I of the mitochondrial respiratory chain.     

Phenylalanine hydroxylase deficiency in the Slovak population: Genotype–phenotype correlations and genotype-based predictions of BH4-responsiveness

We investigated the mutation spectrum of the phenylalanine hydroxylase gene (PAH) in a cohort of patients from 135 Slovak PKU families. Mutational screening of the known coding region, including conventional intron splice sites, was performed using high-resolution melting analysis, with subsequent sequencing analysis of the samples showing deviated melting profiles compared to control samples. The PAH gene was also screened for deletions and duplications using MLPA analysis. Forty-eight different disease causing mutations were identified in our patient group, including 30 missense, 8 splicing, 7 nonsense, 2 large deletions and 1 small deletion with frameshift; giving a detection rate of 97.6%. The most prevalent mutation was the p.R408W, occurring in 47% of all alleles, which concurs with results from neighboring and other Slavic countries. Other frequent mutations were: p.R158Q (5.3%), IVS12 + 1G>A (5.3%), p.R252W (5.1%), p.R261Q (3.9%) and p.A403V (3.6%). We also identified three novel missense mutations: p.F233I, p.R270I, p.F331S and one novel variant: c.− 30A>T in the proximal part of the PAH gene promoter. A spectrum of 84 different genotypes was observed and a genotype based predictions of BH4-responsiveness were assessed. Among all genotypes, 36 were predicted to be BH4-responsive represented by 51 PKU families. In addition, genotype–phenotype correlations were performed.     

Caspase-independent death of Leber’s hereditary optic neuropathy cybrids is driven by energetic failure and mediated by AIF and Endonuclease G

Leber’s hereditary optic neuropathy (LHON) is associated with mitochondrial DNA point mutations affecting different subunits of complex I. By replacing glucose with galactose in the medium, cybrids harboring each of the three LHON pathogenic mutations (11778/ND4, 3460/ND1, 14484/ND6) suffered a profound ATP depletion over a few hours and underwent apoptotic cell death, which was caspase-independent. Control cybrids were unaffected. In addition to cytochrome c, apoptosis inducing factor (AIF) and endonuclease G (EndoG) were also released from the mitochondria into the cytosol in LHON cybrids, but not in control cells. Exposure of isolated nuclei to cytosolic fractions from LHON cybrids maintained in galactose medium caused nuclear fragmentation, which was strongly reduced by immuno-depletion with anti-AIF and anti-EndoG antibodies. In conclusion, the caspase-independent death of LHON cybrids incubated in galactose medium is triggered by rapid ATP depletion and mediated by AIF and EndoG.     

Mutation spectrum of phenylketonuria in Syrian population: Genotype–phenotype correlation

Characterization of the molecular basis of phenylketonuria (PKU) in Syria has been accomplished through the analysis of 78 unrelated chromosomes from 39 Syrian patients with PKU. Phenylalanine hydroxylase (PAH) gene mutations have been analyzed by using molecular detection methods based on the restriction fragment length polymorphism (RFLP), artificial constructed restriction sites (ACRS) PCR and direct DNA sequencing. 56.4% of the patients had cPKU. A mutation detection rate of 79.49% was achieved and sixteen different mutations were found: missense 56.25%, splice site 37.5%, and frameshift 6.25%. The predominant mutation in this population sample was p.R261Q G>A, p.F55>Lfs and p.R243Q G>A. No mutation in six PKU patients was observed. In 57.9% of patient genotypes, the metabolic phenotype could be predicted. The identification of the mutations in the PAH gene and the genotype–phenotype correlation should facilitate the evaluation of metabolic phenotypes, diagnosis, implementation of optimal dietary therapy, and determination of prognosis in the patients and genetic counseling for the patient's relatives.     

Variations in genotype–phenotype correlations in phenylalanine hydroxylase deficiency in Chinese Han population

Background

The value of genotyping to predict variant phenotypes in patients with phenylalanine hydroxylase (Pah) deficiency is a matter of debate. However, there exists no comprehensive population relationship study focused on the Han Chinese.

Methods

We analyzed genotype–phenotype correlation for 186 different genotypes in 338 unrelated Chinese patients harboring 109 different Pah mutations. Two systems were used in this process. The first was a phenotype prediction system based on arbitrary values (AV) attributed to each mutation. The second was a pair-wise correlation analysis. The observed phenotype for AV analysis was the corresponding metabolic phenotype stratified according to the pretreatment phenylalanine (Phe) value.

Results

We found that the observed phenotype matched the predicted phenotype in 54.41% of 272 patients for whom AV information was available; the highest degree of concordance (61.83%) was found in patients with null/null genotypes, whereas the lowest “concordance rate” (32.69%) was observed for patients with expected mild-PKU phenotype. There are repeated inconsistencies for such mutations as R241C, R243Q, R261Q, V388M, V399V, R408Q, A434D and EX6-96A>G which are associated with variable phenotypes in patients with identical genotype. Significant correlations were disclosed between pretreatment Phe values and predicted residual activity (r = − 0.45643, P < 0.0001) or AV sum (r = − 0.59523, P < 0.0001).

Conclusion

Our study supports the notion that the Pah mutation genotype is the main determinant of metabolic phenotype in most patients in a particular population, and provided novel insights into the values that underpin the subsequent treatment and the prognosis of PKU in Chinese.     

No evidence for ‘skewed’ inactivation of the X-chromosome as cause of Leber's hereditary optic neuropathy in female carriers

Leber’s hereditary optic neuropathy (LHON) is a maternally inherited disorder of the optic nerves. It has been proposed that the specific mutations in the mitochondrial DNA (mtDNA) that are associated with LHON require and X-chromosomally encoded permissive factor in order to become expressed. This would explain both the preponderance of male patients and the fact that most carriers of specific mtDNA mutations remain unaffected. Although linkage studies have been negative so far, the existence of such a factor has not been ruled out. We investigated the genealogical data of 24 large LHON pedigrees and concluded that the presumed X-linked factor would be recessively inherited and that at least 57% of the affected females would be heterozygous. Therefore, these females must be the victim of nonrandom X-chromosomal inactivation (skewed lyonization). However, analysis of X-chromosomal methylation patterns in 16 LHON-affected females revealed substantial skewing in only 15%–20% of cases, which is not significantly different from the patterns in 49 controls. Moreover, we found the frequency of LHON in daughters of affected heterozygous females to be twice to three times as high as in daughters of unaffected heterozygous females, which cannot be explained by an X-chromosomally inherited factor. We conclude that the results of our investigations do not support the hypothesis that LHON is a digenic disease with an X-linked factor being the main cause of loss of vision in the presence of relevant mtDNA mutations. Received: 1 June 1995 / Revised: 20 September 1995     

Structure–function correlations in tyrosinases

Tyrosinases are metalloenzymes belonging to the type-3 copper protein family which contain two copper ions in the active site. They are found in various prokaryotes as well as in plants, fungi, arthropods, and mammals and are responsible for pigmentation, wound healing, radiation protection, and primary immune response. Tyrosinases perform two sequential enzymatic reactions: hydroxylation of monophenols and oxidation of diphenols to form quinones which polymerize spontaneously to melanin. Two other members of this family are catechol oxidases, which are prevalent mainly in plants and perform only the second oxidation step, and hemocyanins, which lack enzymatic activity and are oxygen carriers. In the last decade, several structures of plant and bacterial tyrosinases were determined, some with substrates or inhibitors, highlighting features and residues which are important for copper uptake and catalysis. This review summarizes the updated information on structure–function correlations in tyrosinases along with comparison to other type-3 copper proteins.     

Expanded mutational spectrum of the GLI3 gene substantiates genotype–phenotype correlations

Greig cephalopolysyndactyly syndrome (GCPS) and isolated preaxial polydactyly type IV (PPD-IV) are rare autosomal dominant disorders, both caused by mutations in the GLI3 gene. GCPS is mainly characterised by craniofacial abnormalities (macrocephaly/prominent forehead, hypertelorism) and limb malformations, such as PPD-IV, syndactyly and postaxial polydactyly type A or B (PAPA/B). Mutations in the GLI3 gene can also lead to Pallister?CHall syndrome (PHS) and isolated PAPA/B. In this study, we investigated 16 unrelated probands with the clinical diagnosis of GCPS/PPD-IV and found GLI3 mutations in 12 (75?%) of them (nine familial and three sporadic cases). We also performed a detailed clinical evaluation of all 12 GLI3-positive families, with a total of 27 patients. The hallmark triad of GCPS (preaxial polydactyly, macrocephaly/prominent forehead, hypertelorism) was present in 14 cases (52?%), whereas at least one typical dysmorphic feature was manifested in 17 patients (63?%). Upon sequencing of the GLI3 gene, we demonstrated eight novel and two previously reported heterozygous point mutations. We also performed multiplex ligation-dependent probe amplification (MLPA) to screen for intragenic copy number changes and identified heterozygous deletions in the two remaining cases (16.7?%). Our findings fully support previous genotype?Cphenotype correlations, showing that exonic deletions, missense mutations, as well as truncating variants localised out of the middle third of the GLI3 gene result in GCPS/PPD-IV and not PHS. Additionally, our study shows that intragenic GLI3 deletions may account for a significant proportion of GCPS/PPD-IV causative mutations. Therefore, we propose that MLPA or quantitative polymerase chain reaction (qPCR) should be implemented into routine molecular diagnostic of the GLI3 gene.     

Genotype–phenotype correlations for <Emphasis Type="Italic">SLC26A4-</Emphasis>related deafness

Pendred syndrome (PS) and non-syndromic enlarged vestibular aqueduct (EVA) are two recessive disorders characterized by the association of sensorineural hearing loss (SNHL) with inner ear malformations that range from isolated EVA to Mondini Dysplasia, a complex malformation that includes a cochlear dysplasia and EVA. Mutations in the SLC26A4 gene, coding for the protein pendrin, have been implicated in the pathophysiology of both disorders. In order to determine whether SLC26A4 genotypes can be correlated to the complexity and severity of the phenotypes, we ascertained 1,506 deaf patients. Inner ear abnormalities were present in 474 patients (32%). Mutation screening of SLC26A4 detected two mutations in 16% of patients, one mutation in 19% of patients and zero mutation in 65% of patients. When the distribution of SLC26A4 genotypes was compared across phenotypes, a statistically significant difference was found between PS patients and non-syndromic EVA–Mondini patients (P = 0.005), as well as between EVA patients and Mondini patients (P = 0.0003). There was a correlation between phenotypic complexity of inner ear malformations and genetic heterogeneity—PS patients have the most severe phenotype and the most homogeneous etiology while EVA patients have the least severe phenotype and the most heterogeneous etiology. For all patients, variability in the degree of hearing loss is seen across genotypes implicating other genetic and/or environmental factors in the pathogenesis of the PS–Mondini–EVA disease spectrum.     

The molecular basis and genotype–phenotype correlations of congenital adrenal hyperplasia (CAH) in Anatolian population

Molecular Biology Reports - Congenital adrenal hyperplasia (CAH) is an autosomal recessive genetic disorder due to presence of mutations in the genes involved in the metabolism of steroid hormones...