Publications by authors named "Henna Tyynismaa"

67 Publications

De novo SPTAN1 mutation in axonal sensorimotor neuropathy and developmental disorder.

Brain 2020 12;143(12):e104

Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland.

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http://dx.doi.org/10.1093/brain/awaa344DOI Listing
December 2020

Dominant mutations in ITPR3 cause Charcot-Marie-Tooth disease.

Ann Clin Transl Neurol 2020 10 19;7(10):1962-1972. Epub 2020 Sep 19.

Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland.

Objective: ITPR3, encoding inositol 1,4,5-trisphosphate receptor type 3, was previously reported as a potential candidate disease gene for Charcot-Marie-Tooth neuropathy. Here, we present genetic and functional evidence that ITPR3 is a Charcot-Marie-Tooth disease gene.

Methods: Whole-exome sequencing of four affected individuals in an autosomal dominant family and one individual who was the only affected individual in his family was used to identify disease-causing variants. Skin fibroblasts from two individuals of the autosomal dominant family were analyzed functionally by western blotting, quantitative reverse transcription PCR, and Ca imaging.

Results: Affected individuals in the autosomal dominant family had onset of symmetrical neuropathy with demyelinating and secondary axonal features at around age 30, showing signs of gradual progression with severe distal leg weakness and hand involvement in the proband at age 64. Exome sequencing identified a heterozygous ITPR3 p.Val615Met variant segregating with the disease. The individual who was the only affected in his family had disease onset at age 4 with demyelinating neuropathy. His condition was progressive, leading to severe muscle atrophy below knees and atrophy of proximal leg and hand muscles by age 16. Trio exome sequencing identified a de novo ITPR3 variant p.Arg2524Cys. Altered Ca -transients in p.Val615Met patient fibroblasts suggested that the variant has a dominant-negative effect on inositol 1,4,5-trisphosphate receptor type 3 function.

Interpretation: Together with two previously identified variants, our report adds further evidence that ITPR3 is a disease-causing gene for CMT and indicates altered Ca homeostasis in disease pathogenesis.
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http://dx.doi.org/10.1002/acn3.51190DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7545616PMC
October 2020

ALS and Parkinson's disease genes CHCHD10 and CHCHD2 modify synaptic transcriptomes in human iPSC-derived motor neurons.

Neurobiol Dis 2020 07 11;141:104940. Epub 2020 May 11.

Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland; Neuroscience Center, Helsinki Institute of Life Science, University of Helsinki, Helsinki, Finland; Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland. Electronic address:

Mitochondrial intermembrane space proteins CHCHD2 and CHCHD10 have roles in motor neuron diseases such as amyotrophic lateral sclerosis, spinal muscular atrophy and axonal neuropathy and in Parkinson's disease. They form a complex of unknown function. Here we address the importance of these two proteins in human motor neurons. We show that gene edited human induced pluripotent stem cells (iPSC) lacking either CHCHD2 or CHCHD10 are viable and can be differentiated into functional motor neurons that fire spontaneous and evoked action potentials. Mitochondria in knockout iPSC and motor neurons sustain ultrastructure but show increased proton leakage and respiration, and reciprocal compensatory increases in CHCHD2 or CHCHD10. Knockout motor neurons have largely overlapping transcriptome profiles compared to isogenic control line, in particular for synaptic gene expression. Our results show that the absence of either CHCHD2 or CHCHD10 alters mitochondrial respiration in human motor neurons, inducing similar compensatory responses. Thus, pathogenic mechanisms may involve loss of synaptic function resulting from defective energy metabolism.
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http://dx.doi.org/10.1016/j.nbd.2020.104940DOI Listing
July 2020

Attitudes towards genetic testing and information: does parenthood shape the views?

J Community Genet 2020 Oct 4;11(4):461-473. Epub 2020 Apr 4.

Research Programs Unit, Stem Cells and Metabolism, University of Helsinki, Helsinki, Finland.

This study examines how parents of pediatric patients might differ in their views and attitudes towards genetic technology and information when compared to adult patients. There is surprisingly little evidence on how parents compare to other parts of population in their attitudes. Previous empirical studies often relate health-related preferences and attitudes to factors such as age, education, and income instead of parental status, thus evading comparison of parents to others as health-related decision makers. Findings related to the parental status can be useful when implementing genetic technology in clinical practice. We conducted a survey of views on genetic technology and information for groups of adult neurology patients (n = 68) and parents of pediatric neurology patients (n = 31) to shed some light on this issue. In addition to our own survey instrument, we conducted other surveys to gain insight on psychosocial factors that might affect these attitudes. The results suggest that parents are more concerned about their children's genetic risk factors when compared to the attitudes of adult patients about their own risk. For both groups, negative emotional state was associated with more concerns towards genetic information. Our study provides insights on how parental views might affect the acceptance of genetic technology and information.
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http://dx.doi.org/10.1007/s12687-020-00462-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7475141PMC
October 2020

Distinct effects on mRNA export factor GANP underlie neurological disease phenotypes and alter gene expression depending on intron content.

Hum Mol Genet 2020 Jun;29(9):1426-1439

Stem Cells and Metabolism Research Program, Research Programs Unit, University of Helsinki, 00290 Helsinki, Finland.

Defects in the mRNA export scaffold protein GANP, encoded by the MCM3AP gene, cause autosomal recessive early-onset peripheral neuropathy with or without intellectual disability. We extend here the phenotypic range associated with MCM3AP variants, by describing a severely hypotonic child and a sibling pair with a progressive encephalopathic syndrome. In addition, our analysis of skin fibroblasts from affected individuals from seven unrelated families indicates that disease variants result in depletion of GANP except when they alter critical residues in the Sac3 mRNA binding domain. GANP depletion was associated with more severe phenotypes compared with the Sac3 variants. Patient fibroblasts showed transcriptome alterations that suggested intron content-dependent regulation of gene expression. For example, all differentially expressed intronless genes were downregulated, including ATXN7L3B, which couples mRNA export to transcription activation by association with the TREX-2 and SAGA complexes. Our results provide insight into the molecular basis behind genotype-phenotype correlations in MCM3AP-associated disease and suggest mechanisms by which GANP defects might alter RNA metabolism.
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http://dx.doi.org/10.1093/hmg/ddaa051DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7297229PMC
June 2020

A patient with pontocerebellar hypoplasia type 6: Novel RARS2 mutations, comparison to previously published patients and clinical distinction from PEHO syndrome.

Eur J Med Genet 2020 Mar 16;63(3):103766. Epub 2019 Sep 16.

Folkhälsan Research Center, Helsinki, Finland; Department of Medical and Clinical Genetics, Medicum, University of Helsinki, Finland. Electronic address:

Pontocerebellar hypoplasia type 6 (PCH6) is a rare infantile-onset progressive encephalopathy caused by biallelic mutations in RARS2 that encodes the mitochondrial arginine-tRNA synthetase enzyme (mtArgRS). The clinical presentation overlaps that of PEHO syndrome (Progressive Encephalopathy with edema, Hypsarrhythmia and Optic atrophy). The proband presented with severe intellectual disability, epilepsy with varying seizure types, optic atrophy, axial hypotonia, acquired microcephaly, dysmorphic features and progressive cerebral and cerebellar atrophy and delayed myelination on MRI. The presentation had resemblance to PEHO syndrome but sequencing of ZNHIT3 did not identify pathogenic variants. Subsequent whole genome sequencing revealed novel compound heterozygous variants in RARS2, a missense variant affecting a highly conserved amino acid and a frameshift variant with consequent degradation of the transcript resulting in decreased mtArgRS protein level confirming the diagnosis of PCH6. Features distinguishing the proband's phenotype from PEHO syndrome were later appearance of hypotonia and elevated lactate levels in blood and cerebrospinal fluid. On MRI the proband presented with more severe supratentorial atrophy and lesser degree of abnormal myelination than PEHO syndrome patients. The study highlights the challenges in clinical diagnosis of patients with neonatal and early infantile encephalopathies with overlapping clinical features and brain MRI findings.
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http://dx.doi.org/10.1016/j.ejmg.2019.103766DOI Listing
March 2020

A Metabolic Vulnerability of Vision.

Authors:
Henna Tyynismaa

N Engl J Med 2019 10 11;381(15):1474-1476. Epub 2019 Sep 11.

From the Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland.

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http://dx.doi.org/10.1056/NEJMe1910322DOI Listing
October 2019

TRIM2, a novel member of the antiviral family, limits New World arenavirus entry.

PLoS Biol 2019 02 6;17(2):e3000137. Epub 2019 Feb 6.

Department of Microbiology and Immunology, UIC College of Medicine, Chicago, Illinois, United States of America.

Tripartite motif (TRIM) proteins belong to a large family with many roles in host biology, including restricting virus infection. Here, we found that TRIM2, which has been implicated in cases of Charcot-Marie-Tooth disease (CMTD) in humans, acts by blocking hemorrhagic fever New World arenavirus (NWA) entry into cells. We show that Trim2-knockout mice, as well as primary fibroblasts from a CMTD patient with mutations in TRIM2, are more highly infected by the NWAs Junín and Tacaribe virus than wild-type mice or cells are. Using mice with different Trim2 gene deletions and TRIM2 mutant constructs, we demonstrate that its antiviral activity is uniquely independent of the RING domain encoding ubiquitin ligase activity. Finally, we show that one member of the TRIM2 interactome, signal regulatory protein α (SIRPA), a known inhibitor of phagocytosis, also restricts NWA infection and conversely that TRIM2 limits phagocytosis of apoptotic cells. In addition to demonstrating a novel antiviral mechanism for TRIM proteins, these studies suggest that the NWA entry and phagocytosis pathways overlap.
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http://dx.doi.org/10.1371/journal.pbio.3000137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6380604PMC
February 2019

Recessive PYROXD1 mutations cause adult-onset limb-girdle-type muscular dystrophy.

J Neurol 2019 Feb 4;266(2):353-360. Epub 2018 Dec 4.

Research Programs Unit, Molecular Neurology, University of Helsinki, Helsinki, Finland.

Objective: To describe adult-onset limb-girdle-type muscular dystrophy caused by biallelic variants in the PYROXD1 gene, which has been recently linked to early-onset congenital myofibrillar myopathy.

Methods: Whole exome sequencing was performed for adult-onset neuromuscular disease patients with no molecular diagnosis. Patients with PYROXD1 variants underwent clinical characterization, lower limb muscle MRI, muscle biopsy and spirometry. A yeast complementation assay was used to determine the biochemical consequences of the genetic variants.

Results: We identified four patients with biallelic PYROXD1 variants. Three patients, who had symptom onset in their 20s or 30s, were homozygous for the previously described p.Asn155Ser. The fourth patient, with symptom onset at age 49, was compound heterozygous for p.Asn155Ser variant and previously unknown p.Tyr354Cys. All patients presented with a LGMD-type phenotype of symmetric muscle weakness and wasting. Symptoms started in proximal muscles of the lower limbs, and progressed slowly to involve also upper limbs in a proximal-predominant fashion. All patients remained ambulant past the age of 60. They had restrictive lung disease but no cardiac impairment. Muscle MRI showed strong involvement of anterolateral thigh muscles. Muscle biopsy displayed chronic myopathic changes. Yeast complementation assay demonstrated the p.Tyr354Cys mutation to impair PYROXD1 oxidoreductase ability.

Conclusion: PYROXD1 variants can cause an adult-onset slowly progressive LGMD-type phenotype.
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http://dx.doi.org/10.1007/s00415-018-9137-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6373352PMC
February 2019

Instability of the mitochondrial alanyl-tRNA synthetase underlies fatal infantile-onset cardiomyopathy.

Hum Mol Genet 2019 01;28(2):258-268

Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK.

Recessively inherited variants in AARS2 (NM_020745.2) encoding mitochondrial alanyl-tRNA synthetase (mt-AlaRS) were first described in patients presenting with fatal infantile cardiomyopathy and multiple oxidative phosphorylation defects. To date, all described patients with AARS2-related fatal infantile cardiomyopathy are united by either a homozygous or compound heterozygous c.1774C>T (p.Arg592Trp) missense founder mutation that is absent in patients with other AARS2-related phenotypes. We describe the clinical, biochemical and molecular investigations of two unrelated boys presenting with fatal infantile cardiomyopathy, lactic acidosis and respiratory failure. Oxidative histochemistry showed cytochrome c oxidase-deficient fibres in skeletal and cardiac muscle. Biochemical studies showed markedly decreased activities of mitochondrial respiratory chain complexes I and IV with a mild decrease of complex III activity in skeletal and cardiac muscle. Using next-generation sequencing, we identified a c.1738C>T (p.Arg580Trp) AARS2 variant shared by both patients that was in trans with a loss-of-function heterozygous AARS2 variant; a c.1008dupT (p.Asp337*) nonsense variant or an intragenic deletion encompassing AARS2 exons 5-7. Interestingly, our patients did not harbour the p.Arg592Trp AARS2 founder mutation. In silico modelling of the p.Arg580Trp substitution suggested a deleterious impact on protein stability and folding. We confirmed markedly decreased mt-AlaRS protein levels in patient fibroblasts, skeletal and cardiac muscle, although mitochondrial protein synthesis defects were confined to skeletal and cardiac muscle. In vitro data showed that the p.Arg580Trp variant had a minimal effect on activation, aminoacylation or misaminoacylation activities relative to wild-type mt-AlaRS, demonstrating that instability of mt-AlaRS is the biological mechanism underlying the fatal cardiomyopathy phenotype in our patients.
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http://dx.doi.org/10.1093/hmg/ddy294DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6321959PMC
January 2019

Screening for Fabry disease and Hereditary ATTR amyloidosis in idiopathic small-fiber and mixed neuropathy.

Muscle Nerve 2019 03 4;59(3):354-357. Epub 2018 Dec 4.

Department of Neurology, Tampere University Hospital and Faculty of Medical and Life Sciences, University of Tampere, Tampere, Finland.

Introduction: In this study we assessed the value of genetic screening for Fabry disease (FD) and hereditary ATTR amyloidosis in patients with idiopathic small-fiber neuropathy (SFN) or mixed neuropathy in a clinical setting.

Methods: This was a Nordic multicenter study with 9 participating centers. Patients with idiopathic SFN or mixed neuropathy were included. Genetic sequencing of the TTR and GLA genes was performed.

Results: There were 172 patients enrolled in the study. Genetic screening was performed in 155 patients. No pathogenic mutations in the TTR gene were found. A single patient had a possible pathogenic variant, R118C, in the GLA gene, but clinical investigation showed no firm signs of FD.

Discussion: Screening for hereditary ATTR amyloidosis and FD in patients with idiopathic SFN or mixed neuropathy without any additional disease-specific symptoms or clinical characteristics in a Nordic population appears to be of little value in a clinical setting. Muscle Nerve 59:354-357, 2019.
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http://dx.doi.org/10.1002/mus.26348DOI Listing
March 2019

Redox regulation of GRPEL2 nucleotide exchange factor for mitochondrial HSP70 chaperone.

Redox Biol 2018 10 4;19:37-45. Epub 2018 Aug 4.

Research Programs Unit, Molecular Neurology, University of Helsinki, Helsinki, Finland; Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland. Electronic address:

Mitochondria are central organelles to cellular metabolism. Their function relies largely on nuclear-encoded proteins that must be imported from the cytosol, and thus the protein import pathways are important for the maintenance of mitochondrial proteostasis. Mitochondrial HSP70 (mtHsp70) is a key component in facilitating the translocation of proteins through the inner membrane into the mitochondrial matrix. Its protein folding cycle is regulated by the nucleotide-exchange factor GrpE, which triggers the release of folded proteins by ATP rebinding. Vertebrates have two mitochondrial GrpE paralogs, GRPEL1 and 2, but without clearly defined roles. Using BioID proximity labeling to identify potential binding partners of the GRPELs in the mitochondrial matrix, we obtained results supporting a model where both GRPELs regulate mtHsp70 as homodimers. We show that GRPEL2 is not essential in human cultured cells, and its absence does not prevent mitochondrial protein import. Instead we find that GRPEL2 is redox regulated in oxidative stress. In the presence of hydrogen peroxide, GRPEL2 forms dimers through intermolecular disulfide bonds in which Cys87 is the thiol switch. We propose that the dimerization of GRPEL2 may activate the folding machinery responsible for protein import into mitochondrial matrix or enhance the chaperone activity of mtHSP70, thus protecting mitochondrial proteostasis in oxidative stress.
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http://dx.doi.org/10.1016/j.redox.2018.07.024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6089081PMC
October 2018

Loss of MICOS complex integrity and mitochondrial damage, but not TDP-43 mitochondrial localisation, are likely associated with severity of CHCHD10-related diseases.

Neurobiol Dis 2018 11 6;119:159-171. Epub 2018 Aug 6.

Université Côte d'Azur, Inserm, CNRS, IRCAN, CHU de Nice, France. Electronic address:

Following the involvement of CHCHD10 in FrontoTemporal-Dementia-Amyotrophic Lateral Sclerosis (FTD-ALS) clinical spectrum, a founder mutation (p.Gly66Val) in the same gene was identified in Finnish families with late-onset spinal motor neuronopathy (SMAJ). SMAJ is a slowly progressive form of spinal muscular atrophy with a life expectancy within normal range. In order to understand why the p.Ser59Leu mutation, responsible for severe FTD-ALS, and the p.Gly66Val mutation could lead to different levels of severity, we compared their effects in patient cells. Unlike affected individuals bearing the p.Ser59Leu mutation, patients presenting with SMAJ phenotype have neither mitochondrial myopathy nor mtDNA instability. The expression of CHCHD10 mutant allele leads to disassembly of mitochondrial contact site and cristae organizing system (MICOS) with mitochondrial dysfunction and loss of cristae in patient fibroblasts. We also show that G66V fibroblasts do not display the loss of MICOS complex integrity and mitochondrial damage found in S59L cells. However, S59L and G66V fibroblasts show comparable accumulation of phosphorylated mitochondrial TDP-43 suggesting that the severity of phenotype and mitochondrial damage do not depend on mitochondrial TDP-43 localization. The expression of the CHCHD10 allele is responsible for mitochondrial network fragmentation and decreased sensitivity towards apoptotic stimuli, but with a less severe effect than that found in cells expressing the CHCHD10 allele. Taken together, our data show that cellular phenotypes associated with p.Ser59Leu and p.Gly66Val mutations in CHCHD10 are different; loss of MICOS complex integrity and mitochondrial dysfunction, but not TDP-43 mitochondrial localization, being likely essential to develop a severe motor neuron disease.
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http://dx.doi.org/10.1016/j.nbd.2018.07.027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7015038PMC
November 2018

Analysis of Mitochondrial Protein Synthesis: De Novo Translation, Steady-State Levels, and Assembled OXPHOS Complexes.

Curr Protoc Toxicol 2018 Aug 31;77(1):e56. Epub 2018 Jul 31.

Research Programs Unit, Molecular Neurology, University of Helsinki, Helsinki, Finland.

Mitochondria are multifunctional organelles with their own genome and protein synthesis machinery. The 13 proteins encoded by mitochondrial DNA (mtDNA) are core subunits of the oxidative phosphorylation (OXPHOS) system producing the majority of cellular ATP. Yet most mitochondrial proteins are encoded by nuclear genes, synthesized by cytosolic ribosomes, and imported into mitochondria. Therefore, disturbances in cytosolic proteostasis have consequences on the gene expression and synthesis of mtDNA-encoded proteins and overall on mitochondrial function. Internal and environmental factors such as mutations, aging, oxidative stress, and toxic agents can affect the translation and the stability of mitochondrial proteins and lead to OXPHOS dysfunction. Here, methods for analysis of mitochondrial translation rate and protein stability using radioactive and non-radioactive technique as well as the methods for studying steady-state levels and assembly of OXPHOS complexes are described. © 2018 by John Wiley & Sons, Inc.
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http://dx.doi.org/10.1002/cptx.56DOI Listing
August 2018

Reply: A novel MCM3AP mutation in a Lebanese family with recessive Charcot-Marie-Tooth neuropathy.

Brain 2018 09;141(9):e67

Research Programs Unit, Molecular Neurology, University of Helsinki, Helsinki, Finland.

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http://dx.doi.org/10.1093/brain/awy185DOI Listing
September 2018

Absence of NEFL in patient-specific neurons in early-onset Charcot-Marie-Tooth neuropathy.

Neurol Genet 2018 Jun 5;4(3):e244. Epub 2018 Jun 5.

Research Programs Unit (M.T.S., E.Y., L.M., M.A., H.T.), Molecular Neurology, University of Helsinki; Clinical Neurosciences, Neurology (E.Y., M.A.), University of Helsinki and Helsinki University Hospital; Institute for Molecular Medicine Finland (FIMM) (J.L., P.M.), University of Helsinki; Neuromuscular Research Center (J.P.), Tampere University Hospital and University of Tampere; and Department of Medical and Clinical Genetics (H.T.), University of Helsinki, Finland.

Objective: We used patient-specific neuronal cultures to characterize the molecular genetic mechanism of recessive nonsense mutations in neurofilament light () underlying early-onset Charcot-Marie-Tooth (CMT) disease.

Methods: Motor neurons were differentiated from induced pluripotent stem cells of a patient with early-onset CMT carrying a novel homozygous nonsense mutation in . Quantitative PCR, protein analytics, immunocytochemistry, electron microscopy, and single-cell transcriptomics were used to investigate patient and control neurons.

Results: We show that the recessive nonsense mutation causes a nearly total loss of messenger RNA (mRNA), leading to the complete absence of NEFL protein in patient's cultured neurons. Yet the cultured neurons were able to differentiate and form neuronal networks and neurofilaments. Single-neuron gene expression fingerprinting pinpointed as the most downregulated gene in the patient neurons and provided data of intermediate filament transcript abundancy and dynamics in cultured neurons. Blocking of nonsense-mediated decay partially rescued the loss of mRNA.

Conclusions: The strict neuronal specificity of neurofilament has hindered the mechanistic studies of recessive nonsense mutations. Here, we show that such mutation leads to the absence of NEFL, causing childhood-onset neuropathy through a loss-of-function mechanism. We propose that the neurofilament accumulation, a common feature of many neurodegenerative diseases, mimics the absence of NEFL seen in recessive CMT if aggregation prevents the proper localization of wild-type NEFL in neurons. Our results suggest that the removal of NEFL as a proposed treatment option is harmful in humans.
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http://dx.doi.org/10.1212/NXG.0000000000000244DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5991776PMC
June 2018

Clinical, biochemical, and genetic features associated with VARS2-related mitochondrial disease.

Hum Mutat 2018 04 7;39(4):563-578. Epub 2018 Feb 7.

Unit of Neuromuscular and Neurodegenerative Disorders, Laboratory of Molecular Medicine, 'Bambino Ges.' Children's Research Hospital, Rome, Italy.

In recent years, an increasing number of mitochondrial disorders have been associated with mutations in mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs), which are key enzymes of mitochondrial protein synthesis. Bi-allelic functional variants in VARS2, encoding the mitochondrial valyl tRNA-synthetase, were first reported in a patient with psychomotor delay and epilepsia partialis continua associated with an oxidative phosphorylation (OXPHOS) Complex I defect, before being described in a patient with a neonatal form of encephalocardiomyopathy. Here we provide a detailed genetic, clinical, and biochemical description of 13 patients, from nine unrelated families, harboring VARS2 mutations. All patients except one, who manifested with a less severe disease course, presented at birth exhibiting severe encephalomyopathy and cardiomyopathy. Features included hypotonia, psychomotor delay, seizures, feeding difficulty, abnormal cranial MRI, and elevated lactate. The biochemical phenotype comprised a combined Complex I and Complex IV OXPHOS defect in muscle, with patient fibroblasts displaying normal OXPHOS activity. Homology modeling supported the pathogenicity of VARS2 missense variants. The detailed description of this cohort further delineates our understanding of the clinical presentation associated with pathogenic VARS2 variants and we recommend that this gene should be considered in early-onset mitochondrial encephalomyopathies or encephalocardiomyopathies.
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http://dx.doi.org/10.1002/humu.23398DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5873438PMC
April 2018

Adrenomyeloneuropathy due to mutation in the ABCD1 gene as underlying factor in spastic paraparesis.

Duodecim 2017;133(7):683-7

We present a Finnish family in which adrenomyeloneuropathy (AMN) caused by the mutation in the ABCD1 gene was revealed as the cause of spastic paraparesis. . Two patients had hypoadrenalism, which is in some cases some associated with the disease . AMN is a hereditary disease manifested both in men and women. but owing to the location of the gene in the X chromosome the symptoms are usually more severe in male patients. . Diagnoses was trucked down with gene-panel sequencing and confirmed through detection of an elevated level of very long-chain fatty acids in the serum of the patients. Specific molecular genetic diagnosis is beneficial, because it enables precise genetic counseling as well as recognition and treatment of associated symptoms, such as severe cortisol deficiency.
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January 2018

Editing activity for eliminating mischarged tRNAs is essential in mammalian mitochondria.

Nucleic Acids Res 2018 01;46(2):849-860

Research Programs Unit, Molecular Neurology, University of Helsinki, 00290 Helsinki, Finland.

Accuracy of protein synthesis is enabled by the selection of amino acids for tRNA charging by aminoacyl-tRNA synthetases (ARSs), and further enhanced by the proofreading functions of some of these enzymes for eliminating tRNAs mischarged with noncognate amino acids. Mouse models of editing-defective cytoplasmic alanyl-tRNA synthetase (AlaRS) have previously demonstrated the importance of proofreading for cytoplasmic protein synthesis, with embryonic lethal and progressive neurodegeneration phenotypes. Mammalian mitochondria import their own set of nuclear-encoded ARSs for translating critical polypeptides of the oxidative phosphorylation system, but the importance of editing by the mitochondrial ARSs for mitochondrial proteostasis has not been known. We demonstrate here that the human mitochondrial AlaRS is capable of editing mischarged tRNAs in vitro, and that loss of the proofreading activity causes embryonic lethality in mice. These results indicate that tRNA proofreading is essential in mammalian mitochondria, and cannot be overcome by other quality control mechanisms.
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http://dx.doi.org/10.1093/nar/gkx1231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5778596PMC
January 2018

Clinical and metabolic consequences of L-serine supplementation in hereditary sensory and autonomic neuropathy type 1C.

Cold Spring Harb Mol Case Stud 2017 Nov 21;3(6). Epub 2017 Nov 21.

Research Programs Unit, Molecular Neurology, University of Helsinki, Helsinki 00014, Finland.

Hereditary sensory neuropathy type 1 (HSAN1) may be the first genetic neuropathy amenable to a specific mechanism-based treatment, as L-serine supplementation can be used to lower the neurotoxic levels of 1-deoxysphingolipids (1-deoxySL) that cause the neurodegeneration. The treatment is so far untested in HSAN1C caused by variants in the serine palmitoyl transferase subunit 2 () gene. The aim of this study was to establish whether oral L-serine lowers 1-deoxySL in a patient with HSAN1C, to perform a dose escalation to find the minimal effective dose, and to assess the safety profile and global metabolic effects of the treatment. Our patient underwent a 52-wk treatment in which the L-serine dose was titrated up to 400 mg/kg/day. She was followed up by repeated clinical examination, nerve conduction testing, and skin biopsies to document effects on small nerve fibers. Serum was assayed for 1-deoxySL and metabolomics analysis of 111 metabolites. We found a robust lowering of 1-deoxySL, which correlated in a near-linear fashion with increased serum L-serine levels. Metabolomics analysis showed a modest elevation in glycine and a marked reduction in the level of cytosine, whereas most of the other assayed metabolites did not change. There were no direct side effects from the treatment, but the patient developed a transitory toe ulceration during the course of the study. The Charcot-Marie-Tooth neuropathy score increased by 1 point. We conclude that oral supplementation of L-serine decreases 1-deoxySL in HSAN1C without major global effects on metabolism. L-serine is therefore a potential treatment for HSAN1C.
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http://dx.doi.org/10.1101/mcs.a002212DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5701299PMC
November 2017

MCM3AP in recessive Charcot-Marie-Tooth neuropathy and mild intellectual disability.

Brain 2017 Aug;140(8):2093-2103

Research Programs Unit, Molecular Neurology, University of Helsinki, 00290 Helsinki, Finland.

Defects in mRNA export from the nucleus have been linked to various neurodegenerative disorders. We report mutations in the gene MCM3AP, encoding the germinal center associated nuclear protein (GANP), in nine affected individuals from five unrelated families. The variants were associated with severe childhood onset primarily axonal (four families) or demyelinating (one family) Charcot-Marie-Tooth neuropathy. Mild to moderate intellectual disability was present in seven of nine affected individuals. The affected individuals were either compound heterozygous or homozygous for different MCM3AP variants, which were predicted to cause depletion of GANP or affect conserved amino acids with likely importance for its function. Accordingly, fibroblasts of affected individuals from one family demonstrated severe depletion of GANP. GANP has been described to function as an mRNA export factor, and to suppress TDP-43-mediated motor neuron degeneration in flies. Thus our results suggest defective mRNA export from nucleus as a potential pathogenic mechanism of axonal degeneration in these patients. The identification of MCM3AP variants in affected individuals from multiple centres establishes it as a disease gene for childhood-onset recessively inherited Charcot-Marie-Tooth neuropathy with intellectual disability.
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http://dx.doi.org/10.1093/brain/awx138DOI Listing
August 2017

ATPase-deficient mitochondrial inner membrane protein ATAD3A disturbs mitochondrial dynamics in dominant hereditary spastic paraplegia.

Hum Mol Genet 2017 04;26(8):1432-1443

Research Programs Unit, Molecular Neurology, University of Helsinki, Helsinki, Finland.

De novo mutations in ATAD3A (ATPase family AAA-domain containing protein 3A) were recently found to cause a neurological syndrome with developmental delay, hypotonia, spasticity, optic atrophy, axonal neuropathy, and hypertrophic cardiomyopathy. Using whole-exome sequencing, we identified a dominantly inherited heterozygous variant c.1064G > A (p.G355D) in ATAD3A in a mother presenting with hereditary spastic paraplegia (HSP) and axonal neuropathy and her son with dyskinetic cerebral palsy, both with disease onset in childhood. HSP is a clinically and genetically heterogeneous disorder of the upper motor neurons. Symptoms beginning in early childhood may resemble spastic cerebral palsy. The function of ATAD3A, a mitochondrial inner membrane AAA ATPase, is yet undefined. AAA ATPases form hexameric rings, which are catalytically dependent on the co-operation of the subunits. The dominant-negative patient mutation affects the Walker A motif, which is responsible for ATP binding in the AAA module of ATAD3A, and we show that the recombinant mutant ATAD3A protein has a markedly reduced ATPase activity. We further show that overexpression of the mutant ATAD3A fragments the mitochondrial network and induces lysosome mass. Similarly, we observed altered dynamics of the mitochondrial network and increased lysosomes in patient fibroblasts and neurons derived through differentiation of patient-specific induced pluripotent stem cells. These alterations were verified in patient fibroblasts to associate with upregulated basal autophagy through mTOR inactivation, resembling starvation. Mutations in ATAD3A can thus be dominantly inherited and underlie variable neurological phenotypes, including HSP, with intrafamiliar variability. This finding extends the group of mitochondrial inner membrane AAA proteins associated with spasticity.
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http://dx.doi.org/10.1093/hmg/ddx042DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5393146PMC
April 2017

mutations and motor neuron disease: the distribution in Finnish patients.

J Neurol Neurosurg Psychiatry 2017 03 3;88(3):272-277. Epub 2016 Nov 3.

Neuromuscular Research Center, Tampere University and University Hospital, Tampere, Finland.

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http://dx.doi.org/10.1136/jnnp-2016-314154DOI Listing
March 2017

Unique Exercise Lactate Profile in Muscle Phosphofructokinase Deficiency (Tarui Disease); Difference Compared with McArdle Disease.

Front Neurol 2016 30;7:82. Epub 2016 May 30.

Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland; Clinical Neurosciences, Neurology, Helsinki University Hospital, University of Helsinki, Helsinki, Finland.

Introduction: Glycogen storage disease V (GSDV, McArdle disease) and GSDVII (Tarui disease) are the most common of the rare disorders of glycogen metabolism. Both are associated with low lactate levels on exercise. Our aim was to find out whether lactate response associated with exercise testing could distinguish between these disorders.

Methods: Two siblings with Tarui disease, two patients with McArdle disease and eight healthy controls were tested on spiroergometric exercise tests with follow-up of venous lactate and ammonia.

Results: A late increase of lactate about three times the basal level was seen 10-30 min after exercise in patients with Tarui disease being higher than in McArdle disease and lower than in the controls. Ammonia was increased in Tarui disease.

Discussion: Our results suggest that follow-up of lactate associated with exercise testing can be utilized in diagnostics to distinguish between different GSD diseases.
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http://dx.doi.org/10.3389/fneur.2016.00082DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4885106PMC
June 2016

Splicing Defect in Mitochondrial Seryl-tRNA Synthetase Gene Causes Progressive Spastic Paresis Instead of HUPRA Syndrome.

Hum Mutat 2016 09 27;37(9):884-8. Epub 2016 Jun 27.

Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland.

Mitochondrial aminoacyl-tRNA synthetases are an important group of disease genes typically underlying either a disorder affecting an isolated tissue or a distinct syndrome. Missense mutations in the mitochondrial seryl-tRNA synthetase gene, SARS2, have been identified in HUPRA syndrome (hyperuricemia, pulmonary hypertension, renal failure in infancy, and alkalosis). We report here a homozygous splicing mutation in SARS2 in a patient with progressive spastic paresis. We show that the mutation leads to diminished levels of the synthetase in patient's fibroblasts. This has a destabilizing effect on the tRNASer(AGY) isoacceptor, but to a lesser degree than in HUPRA syndrome patients. tRNASer(UCN) is largely unaffected in both phenotypes. In conclusion, the level of tRNASer(AGY) instability may be a factor in determining tissue manifestation in patients with SARS2 mutations. This finding exemplifies the sensitivity of the nervous system to partially reduced aminoacylation, which is sufficient in other tissues to maintain respiratory chain function.
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http://dx.doi.org/10.1002/humu.23021DOI Listing
September 2016

PFKM gene defect and glycogen storage disease GSDVII with misleading enzyme histochemistry.

Neurol Genet 2015 Jun 4;1(1):e7. Epub 2015 Jun 4.

Research Programs Unit (M.A., E.Y., H.T.), Molecular Neurology, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland; Clinical Neurosciences (M.A.), Neurology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Neuromuscular Research Center (J.P., S.S., K.V., B.U.), Tampere University Hospital and University of Tampere, Tampere, Finland; Department of Pathology (S.H., H.H.), Fimlab Laboratories, University Hospital and University of Tampere, Tampere, Finland; Department of Pathology (A.P.), HUSLAB, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Department of Neurology (S.S.), Seinäjoki Central Hospital, Seinäjoki, Finland; and Unit of Clinical Physiology (P.P.), HUS Medical Imaging Center, Helsinki University Hospital, Helsinki, Finland.

Objective: To elaborate the diagnostic methods used as "gold standard" in one of the most common glycogen storage diseases (GSDs), Tarui disease (GSDVII).

Methods: Two siblings with disease suggestive of GSD underwent thorough clinical analysis, including muscle biopsy, muscle MRI, exercise tests, laboratory examinations, and whole-exome sequencing (WES).

Results: Both siblings had juvenile-onset exercise intolerance with cramping and infrequent myoglobinuria. Muscle biopsy showed extralysosomal glycogen accumulation, but because of normal phosphofructokinase histochemistry, GSDVII was thought to be excluded. However, WES revealed a causative homozygous PFKM gene defect, R39Q, in both siblings, establishing the diagnosis of GSDVII, which was confirmed by very low residual phosphofructo-1-kinase (PFK) enzyme activity in biochemical studies.

Conclusions: We suggest that in patients with suspicion of GSD and extralysosomal glycogen accumulation, biochemical activity assay of PFK followed by molecular genetics should be performed even when enzyme histochemistry is normal.
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http://dx.doi.org/10.1212/NXG.0000000000000007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4821086PMC
June 2015

CHCHD10 variant p.(Gly66Val) causes axonal Charcot-Marie-Tooth disease.

Neurol Genet 2015 Jun 26;1(1):e1. Epub 2015 Mar 26.

Research Programs Unit (M.A., E.Y., M.S., H.T.), Molecular Neurology, University of Helsinki; Clinical Neurosciences, Neurology (M.A., S.K.-E.), University of Helsinki and Helsinki University Hospital; Department of Pathology (A.P.), HUSLAB & University of Helsinki; Department of Clinical Neurophysiology (J.P.T.), Medical Imaging Center, Helsinki University Hospital; and Department of Medical Genetics (H.T.), Haartman Institute, University of Helsinki, Finland.

Objective: We describe the phenotype consistent with axonal Charcot-Marie-Tooth disease type 2 (CMT2) in 4 families with a c.197G>T (p.(Gly66Val)) variant in CHCHD10.

Methods: We sequenced the CHCHD10 gene in a cohort of 107 families with CMT2 of unknown etiology. The patients were characterized by clinical examination and electroneuromyography. Muscle MRI and biopsy of the muscle or nerve were performed in selected cases. Neuropathologic autopsy was performed in 1 case.

Results: The c.197G>T variant in CHCHD10 was found in 6 families, 4 of which included multiple individuals available for detailed clinical study. Variants in this gene have recently been associated with amyotrophic lateral sclerosis-frontotemporal dementia, mitochondrial myopathy, or spinal muscular atrophy Jokela type (SMAJ), but not with CMT2. Our patients had a late-onset distal axonal neuropathy with motor predominance, progressing to involve sensory nerves. Neurophysiologic and neuropathologic studies confirmed the diagnosis of sensorimotor axonal neuropathy with no loss of anterior horn neurons. Muscle biopsies showed occasional cytochrome c oxidase-negative fibers, combined with small amounts of mitochondrial DNA deletions.

Conclusions: CHCHD10 c.197G>T (p.(Gly66Val)) is a cause of sensorimotor axonal neuropathy. This gene should be considered in patients presenting with a pure CMT2 phenotype, particularly when motor symptoms predominate.
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http://dx.doi.org/10.1212/NXG.0000000000000003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4821082PMC
June 2015

Mitochondrial DNA Replication Defects Disturb Cellular dNTP Pools and Remodel One-Carbon Metabolism.

Cell Metab 2016 Apr 25;23(4):635-48. Epub 2016 Feb 25.

Research Programs Unit, Molecular Neurology, University of Helsinki, 00290 Helsinki, Finland; Department of Neurology, University of Helsinki, Helsinki University Hospital, 00290 Helsinki, Finland; Neuroscience Center, University of Helsinki, 00790 Helsinki, Finland. Electronic address:

Mitochondrial dysfunction affects cellular energy metabolism, but less is known about the consequences for cytoplasmic biosynthetic reactions. We report that mtDNA replication disorders caused by TWINKLE mutations-mitochondrial myopathy (MM) and infantile onset spinocerebellar ataxia (IOSCA)-remodel cellular dNTP pools in mice. MM muscle shows tissue-specific induction of the mitochondrial folate cycle, purine metabolism, and imbalanced and increased dNTP pools, consistent with progressive mtDNA mutagenesis. IOSCA-TWINKLE is predicted to hydrolyze dNTPs, consistent with low dNTP pools and mtDNA depletion in the disease. MM muscle also modifies the cytoplasmic one-carbon cycle, transsulfuration, and methylation, as well as increases glucose uptake and its utilization for de novo serine and glutathione biosynthesis. Our evidence indicates that the mitochondrial replication machinery communicates with cytoplasmic dNTP pools and that upregulation of glutathione synthesis through glucose-driven de novo serine biosynthesis contributes to the metabolic stress response. These results are important for disorders with primary or secondary mtDNA instability and offer targets for metabolic therapy.
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http://dx.doi.org/10.1016/j.cmet.2016.01.019DOI Listing
April 2016

Truncated HSPB1 causes axonal neuropathy and impairs tolerance to unfolded protein stress.

BBA Clin 2015 Jun 11;3:233-42. Epub 2015 Mar 11.

Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, Helsinki 00290, Finland ; Department of Medical Genetics, Haartman Institute, University of Helsinki, Helsinki 00290, Finland.

Background: HSPB1 belongs to the family of small heat shock proteins (sHSP) that have importance in protection against unfolded protein stress, in cancer cells for escaping drug toxicity stress and in neurons for suppression of protein aggregates. sHSPs have a conserved α-crystalline domain (ACD), flanked by variable N- and C-termini, whose functions are not fully understood. Dominant missense variants in HSPB1, locating mostly to the ACD, have been linked to inherited neuropathy.

Methods: Patients underwent detailed clinical and neurophysiologic characterization. Disease causing variants were identified by exome or gene panel sequencing. Primary patient fibroblasts were used to investigate the effects of the dominant defective HSPB1 proteins.

Results: Frameshift variant predicting ablation of the entire C-terminus p.(Met169Cfs2*) of HSPB1 and a missense variant p.(Arg127Leu) were identified in patients with dominantly inherited motor-predominant axonal Charcot-Marie-Tooth neuropathy. We show that the truncated protein is stable and binds wild type HSPB1. Both mutations impaired the heat stress tolerance of the fibroblasts. This effect was particularly pronounced for the cells with the truncating variant, independent of heat-induced nuclear translocation and induction of global transcriptional heat response. Furthermore, the truncated HSPB1 increased cellular sensitivity to protein misfolding.

Conclusion: Our results suggest that truncation of the non-conserved C-terminus impairs the function of HSPB1 in cellular stress response.

General Significance: sHSPs have important roles in prevention of protein aggregates that induce toxicity. We showed that C-terminal part of HSPB1 is critical for tolerance of unfolded protein stress, and when lacking causes axonal neuropathy in patients.
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http://dx.doi.org/10.1016/j.bbacli.2015.03.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4661565PMC
June 2015

The Variant p.(Arg183Trp) in SPTLC2 Causes Late-Onset Hereditary Sensory Neuropathy.

Neuromolecular Med 2016 Mar 16;18(1):81-90. Epub 2015 Nov 16.

Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, Haartmaninkatu 8, 00290, Helsinki, Finland.

Hereditary sensory and autonomic neuropathy 1 (HSAN1) is an autosomal dominant disorder that can be caused by variants in SPTLC1 or SPTLC2, encoding subunits of serine palmitoyl-CoA transferase. Disease variants alter the enzyme's substrate specificity and lead to accumulation of neurotoxic 1-deoxysphingolipids. We describe two families with autosomal dominant HSAN1C caused by a new variant in SPTLC2, c.547C>T, p.(Arg183Trp). The variant changed a conserved amino acid and was not found in public variant databases. All patients had a relatively mild progressive distal sensory impairment, with onset after age 50. Small fibers were affected early, leading to abnormalities on quantitative sensory testing. Sural biopsy revealed a severe chronic axonal neuropathy with subtotal loss of myelinated axons, relatively preserved number of non-myelinated fibers and no signs for regeneration. Skin biopsy with PGP9.5 labeling showed lack of intraepidermal nerve endings early in the disease. Motor manifestations developed later in the disease course, but there was no evidence of autonomic involvement. Patients had elevated serum 1-deoxysphingolipids, and the variant protein produced elevated amounts of 1-deoxysphingolipids in vitro, which proved the pathogenicity of the variant. Our results expand the genetic spectrum of HSAN1C and provide further detail about the clinical characteristics. Sequencing of SPTLC2 should be considered in all patients presenting with mild late-onset sensory-predominant small or large fiber neuropathy.
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http://dx.doi.org/10.1007/s12017-015-8379-1DOI Listing
March 2016