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Mitochondrial EFTs defects in juvenile-onset Leigh disease, ataxia, neuropathy, and optic atrophy.

ABSTRACT: OBJECTIVE: We report novel defects of mitochondrial translation elongation factor Ts (EFTs), with high carrier frequency in Finland and expand the manifestations of this disease group from infantile cardiomyopathy to juvenile neuropathy/encephalopathy disorders. METHODS: DNA analysis, whole-exome analysis, protein biochemistry, and protein modeling. RESULTS: We used whole-exome sequencing to find the genetic cause of infantile-onset mitochondrial cardiomyopathy, progressing to juvenile-onset Leigh syndrome, neuropathy, and optic atrophy in 2 siblings. We found novel compound heterozygous mutations, c.944G>A [p.C315Y] and c.856C>T [p.Q286X], in the TSFM gene encoding mitochondrial EFTs. The same p.Q286X variant was found as compound heterozygous with a splice site change in a patient from a second family, with juvenile-onset optic atrophy, peripheral neuropathy, and ataxia. Our molecular modeling predicted the coding-region mutations to cause protein instability, which was experimentally confirmed in cultured patient cells, with mitochondrial translation defect and lacking EFTs. Only a single TSFM mutation has been previously described in different populations, leading to an infantile fatal multisystem disorder with cardiomyopathy. Sequence data from 35,000 Finnish population controls indicated that the heterozygous carrier frequency of p.Q286X change was exceptionally high in Finland, 1:80, but no homozygotes were found in the population, in our mitochondrial disease patient collection, or in an intrauterine fetal death material, suggesting early developmental lethality of the homozygotes. CONCLUSIONS: We show that in addition to early-onset cardiomyopathy, TSFM mutations should be considered in childhood and juvenile encephalopathies with optic and/or peripheral neuropathy, ataxia, or Leigh disease.

SUBMITTER: Ahola S

PROVIDER: S-EPMC4150129 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Mitochondrial EFTs defects in juvenile-onset Leigh disease, ataxia, neuropathy, and optic atrophy.

Ahola Sofia S Isohanni Pirjo P Euro Liliya L Brilhante Virginia V Palotie Aarno A Pihko Helena H Lönnqvist Tuula T Lehtonen Tanita T Laine Jukka J Tyynismaa Henna H Suomalainen Anu A

Neurology 20140718 8

<h4>Objective</h4>We report novel defects of mitochondrial translation elongation factor Ts (EFTs), with high carrier frequency in Finland and expand the manifestations of this disease group from infantile cardiomyopathy to juvenile neuropathy/encephalopathy disorders.<h4>Methods</h4>DNA analysis, whole-exome analysis, protein biochemistry, and protein modeling.<h4>Results</h4>We used whole-exome sequencing to find the genetic cause of infantile-onset mitochondrial cardiomyopathy, progressing to ...[more]

PMID: 25037205

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Project description:OBJECTIVES/BACKGROUND: Ataxia with oculomotor apraxia defines a group of genetically distinct recessive ataxias including ataxia-telangectasia (A-T, ATM gene), ataxia with oculomotor apraxia type 1 (AOA1, APTX gene) and type 2 (AOA2, SETX gene). Although, a few unique clinical features differentiate each of these forms, the patients also share common clinical signs, such as the presence of cerebellar atrophy, sensorimotor axonal neuropathy, and elevated alpha-fetoprotein (AFP) serum level. MATERIALS AND METHODS: We selected 22 Italian patients from 21 families, presenting progressive cerebellar ataxia, axonal neuropathy, and elevated serum AFP. We screened the coding regions of ATM, APTX and SETX genes for point mutations by direct sequencing or DHPLC, and searched genomic rearrangements in SETX by MLPA analysis. In selected cases, quantification of ATM and senataxin proteins was performed by Western blot. Clinical, neurophysiological, and neuroimaging data were collected. RESULTS: Thirteen patients (12 families) carried SETX mutations (AOA2, 57%), two were mutated in ATM (A-T), and three in APTX (AOA1). In three remaining patients, we could not find pathogenic mutations, and in one case we found, in homozygosis, the SETX p.K992R polymorphism (population frequency 1-2%). In AOA2 cases, we identified 14 novel and three reported SETX mutations. Signs at onset were gait ataxia and facial dyskinesia, and the age ranged between 11 and 18 years. None had obvious oculomotor apraxia at the latest examination (age 14-45 years). The patient carrying the p.K992R SETX polymorphism had a phenotype similar to that of the diagnosed AOA2 patients, while the other three undiagnosed subjects had a very late onset and a few distinguishing clinical features. DISCUSSION AND CONCLUSIONS: We describe a large series of 13 AOA2 Italian patients. The phenotype was consistent with previous descriptions of AOA2, except for a higher frequency of strabism, and for the absence of oculomotor apraxia. In our survey ~60% of juvenile-to-adult cases with cerebellar ataxia, sensorimotor neuropathy and increased AFP are due to mutations in the SETX gene, and a smaller percentage to APTX and ATM gene mutations.

Project description:To define the phenotype and elucidate the molecular basis for an autosomal recessively inherited optic atrophy and auditory neuropathy in a consanguineous family with two affected children.Family members underwent detailed ophthalmologic, electrophysiological, and audiological assessments. An autozygosity mapping strategy using high-density single nucleotide polymorphism microarrays and microsatellite markers was used to detect regions of genome homozygosity that might contain the disease gene. Candidate genes were then screened for mutations by direct sequencing.Both affected subjects had poor vision from birth and complained of progressive visual loss over time. Current visual acuity ranged from 6/60 to 6/120. Fundus examination revealed bilateral temporal optic nerve pallor in both patients with otherwise normal retinal findings. International-standard full-field electroretinograms were normal in both individuals, with no evidence of generalized retinal dysfunction. Pattern cortical visual evoked potentials were grossly abnormal bilaterally in both cases. The pattern electroretinogram N95:P50 ratio was subnormal, and the P50 was of shortened peak time bilaterally in both patients. The electrophysiological findings were consistent with bilateral retinal ganglion cell/optic nerve dysfunction. Audiological investigation in both siblings revealed abnormalities falling within the auditory neuropathy/dysynchrony spectrum. There were no auditory symptoms and good outer hair cell function (as demonstrated by transient evoked otoacoustic emissions) but impaired inner hair cell/neural function with abnormal stapedial reflex thresholds and abnormal or absent auditory brainstem-evoked responses. The single nucleotide polymorphism microarray data demonstrated a 24.17 Mb region of homozygosity at 11q14.1-11q22.3, which was confirmed by microsatellite marker analysis. The candidate target region contained the transmembrane protein 126A (TMEM126A) gene, and direct sequencing identified a previously described nonsense mutation (c.163C>T; p.Arg55X).We describe the first detailed phenotyping of patients with autosomal recessive TMEM126A-associated optic atrophy and auditory neuropathy. These findings will facilitate the identification of individuals with this recently described disorder.

Dataset Information

Mitochondrial EFTs defects in juvenile-onset Leigh disease, ataxia, neuropathy, and optic atrophy.

Publications

Mitochondrial EFTs defects in juvenile-onset Leigh disease, ataxia, neuropathy, and optic atrophy.

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