Sofia Ahola1, Pirjo Isohanni1, Liliya Euro1, Virginia Brilhante1, Aarno Palotie1, Helena Pihko1, Tuula Lönnqvist1, Tanita Lehtonen1, Jukka Laine1, Henna Tyynismaa1, Anu Suomalainen2. 1. From the Research Programs Unit, Molecular Neurology, Biomedicum Helsinki (S.A., P.I., L.E., V.B., H.T., A.S.), Institute for Molecular Medicine Finland (A.P.), Department of Medical Genetics, Haartman Institute (H.T.), and Neuroscience Center (A.S.), University of Helsinki; Department of Child Neurology, Children's Hospital (P.I., H.P., T. Lönnqvist), and Department of Neurology (A.S.), Helsinki University Central Hospital, Finland; Analytic and Translational Genetics Unit, Department of Medicine (A.P.), and Psychiatric & Neurodevelopmental Genetics Unit, Department of Psychiatry (A.P.), Massachusetts General Hospital, Boston; Program in Medical and Population Genetics (A.P.), Broad Institute of MIT and Harvard, Cambridge, MA; and Department of Pathology (T. Lehtonen, J.L.), University of Turku, Finland. 2. From the Research Programs Unit, Molecular Neurology, Biomedicum Helsinki (S.A., P.I., L.E., V.B., H.T., A.S.), Institute for Molecular Medicine Finland (A.P.), Department of Medical Genetics, Haartman Institute (H.T.), and Neuroscience Center (A.S.), University of Helsinki; Department of Child Neurology, Children's Hospital (P.I., H.P., T. Lönnqvist), and Department of Neurology (A.S.), Helsinki University Central Hospital, Finland; Analytic and Translational Genetics Unit, Department of Medicine (A.P.), and Psychiatric & Neurodevelopmental Genetics Unit, Department of Psychiatry (A.P.), Massachusetts General Hospital, Boston; Program in Medical and Population Genetics (A.P.), Broad Institute of MIT and Harvard, Cambridge, MA; and Department of Pathology (T. Lehtonen, J.L.), University of Turku, Finland. anu.wartiovaara@helsinki.fi.
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.
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 diseasepatient 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.
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