Human TRMU encoding the mitochondrial 5-methylaminomethyl-2-thiouridylate-methyltransferase is a putative nuclear modifier gene for the phenotypic expression of the deafness-associated 12S rRNA mutations
ABSTRACT Nuclear modifier genes have been proposed to modulate the phenotypic manifestation of human mitochondrial 12S rRNA A1491G mutation associated with deafness in many families world-wide. Here we identified and characterized the putative nuclear modifier gene TRMU encoding a highly conserved mitochondrial protein related to tRNA modification. A 1937bp TRMU cDNA has been isolated and the genomic organization of TRMU has been elucidated. The human TRMU gene containing 11 exons encodes a 421 residue protein with a strong homology to the TRMU-like proteins of bacteria and other homologs. TRMU is ubiquitously expressed in various tissues, but abundantly in tissues with high metabolic rates including heart, liver, kidney, and brain. Immunofluorescence analysis of human 143B cells expressing TRMU-GFP fusion protein demonstrated that the human Trmu localizes and functions in mitochondrion. Furthermore, we show that in families with the deafness-associated 12S rRNA A1491G mutation there is highly suggestive linkage and linkage disequilibrium between microsatellite markers adjacent to TRMU and the presence of deafness. These observations suggest that human TRMU may modulate the phenotypic manifestation of the deafness-associated mitochondrial 12S rRNA mutations.
- SourceAvailable from: Hanns Lochmuller
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- "A very similar clinical presentation was detected recently with mutations in a mitochondrial tRNA synthetase gene (YARS2, OMIM *610957) (Riley et al. 2010). A missense change in the gene encoding the mt-tRNA modifying enzyme tRNA 5-methylaminomethyl-2-thiouri- dylate methyltransferase (TRMU, OMIM *610230) have been postulated as a modifier in patients with sensorineural deafness, carrying the homoplasmic m.1555G > A mutation in the mtDNA (OMIM *561000) (Yan et al. 2006; Guan et al. 2006). More recently, autosomal recessive missense, splice and frameshift mutations were described in 13 cases of infantile reversible hepatopathy (Zeharia et al. 2009). "
ABSTRACT: Combined respiratory chain deficiency accounts for about 30% of mitochondrial respiratory chain deficiencies and is frequently associated with mtDNA depletion, deletions or point mutations. However combined respiratory chain deficiency may also be caused by mutations in nuclear genes affecting mitochondrial translation. Here we describe a 2-year-old girl, who developed an acute, isolated, severe liver failure with mitochondrial pathology and decreased respiratory chain enzyme activities both in liver and skeletal muscle at 4 months of age. Her liver function improved significantly within a month, liver function tests returned to normal. Liver cirrhosis remained without any further complications so far. Pathogenic compound heterozygous mutations were identified in the TRMU gene. This condition is one of the few mitochondrial disorders with a life-threatening onset showing recovery later in life, therefore a prompt diagnosis and treatment of these patients has great importance in clinical practice. We suggest that TRMU deficiency should be considered in infants with acute liver disease.Journal of Inherited Metabolic Disease 02/2011; 34(1):197-201. DOI:10.1007/s10545-010-9250-z · 3.37 Impact Factor
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ABSTRACT: We explored the clinical and molecular characterization of a Chinese family with non-syndromic hearing impairment. Clinical evaluations revealed a possible maternal inheritance pattern, and showed an extremely similar phenotype of hearing loss including the age of onset, severity, and audiometric configuration. Sequence analysis of the mitochondrial 12S rRNA and tRNA(Ser(UCN)) genes led to the identification of a homoplasmic A827G mutation in all maternal relatives, which was absent in other family members and 40 Chinese controls. This mutation has previously been reported sporadically in a few individuals with aminoglycoside-induced and non-syndromic hearing loss. The A827G mutation is located at the A-site of the mitochondrial 12S rRNA gene which is highly evolutionarily conserved in mammals. The occurrence of the A827G mutation in these genetically unrelated subjects strongly suggests that this mutation is involved in the pathogenesis of hearing impairment. However, incomplete penetrance of hearing loss indicates that the A827G mutation alone is not sufficient to produce clinical phenotype but requires the involvement of modifier factors for the phenotypic expression, even though aminoglycosides and GJB2 gene may not contribute to the penetrance of the A827G mutation in this Chinese family. In contrast with the variable phenotype of hearing loss associated with other mitochondrial mutations, all of the patients in our family exhibited strikingly similar clinical features. This discrepancy likely reflects the difference of genetic backgrounds between this pedigree and others.Biochemical and Biophysical Research Communications 07/2006; 344(4):1253-7. DOI:10.1016/j.bbrc.2006.04.033 · 2.30 Impact Factor
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ABSTRACT: The human mitochondrial 12S ribosomal RNA (rRNA) A1555G mutation has been associated with aminoglycoside-induced and nonsyndromic deafness in many families worldwide. Our previous investigation revealed that the A1555G mutation is a primary factor underlying the development of deafness but is not sufficient to produce a deafness phenotype. However, it has been proposed that nuclear-modifier genes modulate the phenotypic manifestation of the A1555G mutation. Here, we identified the nuclear-modifier gene TRMU, which encodes a highly conserved mitochondrial protein related to transfer RNA (tRNA) modification. Genotyping analysis of TRMU in 613 subjects from 1 Arab-Israeli kindred, 210 European (Italian pedigrees and Spanish pedigrees) families, and 31 Chinese pedigrees carrying the A1555G or the C1494T mutation revealed a missense mutation (G28T) altering an invariant amino acid residue (A10S) in the evolutionarily conserved N-terminal region of the TRMU protein. Interestingly, all 18 Arab-Israeli/Italian-Spanish matrilineal relatives carrying both the TRMU A10S and 12S rRNA A1555G mutations exhibited prelingual profound deafness. Functional analysis showed that this mutation did not affect importation of TRMU precursors into mitochondria. However, the homozygous A10S mutation leads to a marked failure in mitochondrial tRNA metabolisms, specifically reducing the steady-state levels of mitochondrial tRNA. As a consequence, these defects contribute to the impairment of mitochondrial-protein synthesis. Resultant biochemical defects aggravate the mitochondrial dysfunction associated with the A1555G mutation, exceeding the threshold for expressing the deafness phenotype. These findings indicate that the mutated TRMU, acting as a modifier factor, modulates the phenotypic manifestation of the deafness-associated 12S rRNA mutations.The American Journal of Human Genetics 09/2006; 79(2):291-302. DOI:10.1086/506389 · 10.93 Impact Factor