Publications by authors named "Pirjo Isohanni"

51 Publications

Vegan diet in young children remodels metabolism and challenges the statuses of essential nutrients.

EMBO Mol Med 2021 Feb 20;13(2):e13492. Epub 2021 Jan 20.

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

Vegan diets are gaining popularity, also in families with young children. However, the effects of strict plant-based diets on metabolism and micronutrient status of children are unknown. We recruited 40 Finnish children with a median age 3.5 years-vegans, vegetarians, or omnivores from same daycare centers-for a cross-sectional study. They enjoyed nutritionist-planned vegan or omnivore meals in daycare, and the full diets were analyzed with questionnaires and food records. Detailed analysis of serum metabolomics and biomarkers indicated vitamin A insufficiency and border-line sufficient vitamin D in all vegan participants. Their serum total, HDL and LDL cholesterol, essential amino acid, and docosahexaenoic n-3 fatty acid (DHA) levels were markedly low and primary bile acid biosynthesis, and phospholipid balance was distinct from omnivores. Possible combination of low vitamin A and DHA status raise concern for their visual health. Our evidence indicates that (i) vitamin A and D status of vegan children requires special attention; (ii) dietary recommendations for children cannot be extrapolated from adult vegan studies; and (iii) longitudinal studies on infant-onset vegan diets are warranted.
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http://dx.doi.org/10.15252/emmm.202013492DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7863396PMC
February 2021

MED27 Variants Cause Developmental Delay, Dystonia, and Cerebellar Hypoplasia.

Ann Neurol 2021 Apr 8;89(4):828-833. Epub 2021 Feb 8.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX.

The Mediator multiprotein complex functions as a regulator of RNA polymerase II-catalyzed gene transcription. In this study, exome sequencing detected biallelic putative disease-causing variants in MED27, encoding Mediator complex subunit 27, in 16 patients from 11 families with a novel neurodevelopmental syndrome. Patient phenotypes are highly homogeneous, including global developmental delay, intellectual disability, axial hypotonia with distal spasticity, dystonic movements, and cerebellar hypoplasia. Seizures and cataracts were noted in severely affected individuals. Identification of multiple patients with biallelic MED27 variants supports the critical role of MED27 in normal human neural development, particularly for the cerebellum. ANN NEUROL 2021;89:828-833.
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http://dx.doi.org/10.1002/ana.26019DOI Listing
April 2021

SUCLA2 mutations cause global protein succinylation contributing to the pathomechanism of a hereditary mitochondrial disease.

Nat Commun 2020 11 23;11(1):5927. Epub 2020 Nov 23.

Gladstone Institutes and University of California, San Francisco, CA, 94158, USA.

Mitochondrial acyl-coenzyme A species are emerging as important sources of protein modification and damage. Succinyl-CoA ligase (SCL) deficiency causes a mitochondrial encephalomyopathy of unknown pathomechanism. Here, we show that succinyl-CoA accumulates in cells derived from patients with recessive mutations in the tricarboxylic acid cycle (TCA) gene succinyl-CoA ligase subunit-β (SUCLA2), causing global protein hyper-succinylation. Using mass spectrometry, we quantify nearly 1,000 protein succinylation sites on 366 proteins from patient-derived fibroblasts and myotubes. Interestingly, hyper-succinylated proteins are distributed across cellular compartments, and many are known targets of the (NAD)-dependent desuccinylase SIRT5. To test the contribution of hyper-succinylation to disease progression, we develop a zebrafish model of the SCL deficiency and find that SIRT5 gain-of-function reduces global protein succinylation and improves survival. Thus, increased succinyl-CoA levels contribute to the pathology of SCL deficiency through post-translational modifications.
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http://dx.doi.org/10.1038/s41467-020-19743-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7684291PMC
November 2020

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

The impact of gender, puberty, and pregnancy in patients with POLG disease.

Ann Clin Transl Neurol 2020 10 18;7(10):2019-2025. Epub 2020 Sep 18.

Department of Clinical Medicine (K1), University of Bergen, Bergen, Norway.

Objective: To study the impact of gender, puberty, and pregnancy on the expression of POLG disease, one of the most common mitochondrial diseases known.

Methods: Clinical, laboratory, and genetic data were collected retrospectively from 155 patients with genetically confirmed POLG disease recruited from seven European countries. We used the available data to study the impact of gender, puberty, and pregnancy on disease onset and deterioration.

Results: We found that disease onset early in life was common in both sexes but there was also a second peak in females around the time of puberty. Further, pregnancy had a negative impact with 10 of 14 women (71%) experiencing disease onset or deterioration during pregnancy.

Interpretation: Gender clearly influences the expression of POLG disease. While onset very early in life was common in both males and females, puberty in females appeared associated both with disease onset and increased disease activity. Further, both disease onset and deterioration, including seizure aggravation and status epilepticus, appeared to be associated with pregnancy. Thus, whereas disease activity appears maximal early in life with no subsequent peaks in males, both menarche and pregnancy appear associated with disease onset or worsening in females. This suggests that hormonal changes may be a modulating factor.
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http://dx.doi.org/10.1002/acn3.51199DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7545595PMC
October 2020

Diagnostic value of serum biomarkers FGF21 and GDF15 compared to muscle sample in mitochondrial disease.

J Inherit Metab Dis 2021 Mar 21;44(2):469-480. Epub 2020 Sep 21.

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

The aim of this study was to compare the value of serum biomarkers, fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), with histological analysis of muscle in the diagnosis of mitochondrial disease. We collected 194 serum samples from patients with a suspected or known mitochondrial disease. Biomarkers were analyzed blinded using enzyme-labeled immunosorbent assay. Clinical data were collected using a structured questionnaire. Only 39% of patients with genetically verified mitochondrial disease had mitochondrial pathology in their muscle histology. In contrast, biomarkers were elevated in 62% of patients with genetically verified mitochondrial disease. Those with both biomarkers elevated had a muscle manifesting disorder and a defect affecting mitochondrial DNA expression. If at least one of the biomarkers was induced and the patient had a myopathic disease, a mitochondrial DNA expression disease was the cause with 94% probability. Among patients with biomarker analysis and muscle biopsy taken <12 months apart, a mitochondrial disorder would have been identified in 70% with analysis of FGF21 and GDF15 compared to 50% of patients whom could have been identified with muscle biopsy alone. Muscle findings were nondiagnostic in 72% (children) and 45% (adults). Induction of FGF21 and GDF15 suggest a mitochondrial etiology as an underlying cause of a muscle manifesting disease. Normal biomarker values do not, however, rule out a mitochondrial disorder, especially if the disease does not manifest in muscle. We suggest that FGF21 and GDF15 together should be first-line diagnostic investigations in mitochondrial disease complementing muscle biopsy.
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http://dx.doi.org/10.1002/jimd.12307DOI Listing
March 2021

Genetic background of ataxia in children younger than 5 years in Finland.

Neurol Genet 2020 Aug 5;6(4):e444. Epub 2020 Jun 5.

Department of Child Neurology (E.I., P.I., T.L.), Children's Hospital, University of Helsinki and Helsinki University Hospital; Research Programs Unit, Stem Cells and Metabolism, Faculty of Medicine (E.I., P.I., M.P., S.O., V.B., E.P., A.S.), Institute for Molecular Medicine Finland (FIMM) (P.L.), Neuroscience Center (A.S.), HiLife, University of Helsinki, Finland; and Genetics Research Centre (C.J.C.), Molecular and Clinical Sciences Research Institute, St. George's, University of London, United Kingdom.

Objective: To characterize the genetic background of molecularly undefined childhood-onset ataxias in Finland.

Methods: This study examined a cohort of patients from 50 families with onset of an ataxia syndrome before the age of 5 years collected from a single tertiary center, drawing on the advantages offered by next generation sequencing. A genome-wide genotyping array (Illumina Infinium Global Screening Array MD-24 v.2.0) was used to search for copy number variation undetectable by exome sequencing.

Results: Exome sequencing led to a molecular diagnosis for 20 probands (40%). In the 23 patients examined with a genome-wide genotyping array, 2 additional diagnoses were made. A considerable proportion of probands with a molecular diagnosis had de novo pathogenic variants (45%). In addition, the study identified a de novo variant in a gene not previously linked to ataxia: MED23. Patients in the cohort had medically actionable findings.

Conclusions: There is a high heterogeneity of causative mutations in this cohort despite the defined age at onset, phenotypical overlap between patients, the founder effect, and genetic isolation in the Finnish population. The findings reflect the heterogeneous genetic background of ataxia seen worldwide and the substantial contribution of de novo variants underlying childhood ataxia.
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http://dx.doi.org/10.1212/NXG.0000000000000444DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7323479PMC
August 2020

Using urine to diagnose large-scale mtDNA deletions in adult patients.

Ann Clin Transl Neurol 2020 08 7;7(8):1318-1326. Epub 2020 Jul 7.

Department of Clinical Medicine (K1), University of Bergen, Bergen, Norway.

Objective: The aim of this study was to evaluate if urinary sediment cells offered a robust alternative to muscle biopsy for the diagnosis of single mtDNA deletions.

Methods: Eleven adult patients with progressive external ophthalmoplegia and a known single mtDNA deletion were investigated. Urinary sediment cells were used to isolate DNA, which was then subjected to long-range polymerase chain reaction. Where available, the patient`s muscle DNA was studied in parallel. Breakpoint and thus deletion size were identified using both Sanger sequencing and next generation sequencing. The level of heteroplasmy was determined using quantitative polymerase chain reaction.

Results: We identified the deletion in urine in 9 of 11 cases giving a sensitivity of 80%. Breakpoints and deletion size were readily detectable in DNA extracted from urine. Mean heteroplasmy level in urine was 38% ± 26 (range 8 - 84%), and 57% ± 28 (range 12 - 94%) in muscle. While the heteroplasmy level in urinary sediment cells differed from that in muscle, we did find a statistically significant correlation between these two levels (R = 0.714, P = 0.031(Pearson correlation)).

Interpretation: Our findings suggest that urine can be used to screen patients suspected clinically of having a single mtDNA deletion. Based on our data, the use of urine could considerably reduce the need for muscle biopsy in this patient group.
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http://dx.doi.org/10.1002/acn3.51119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7448145PMC
August 2020

Simplifying the clinical classification of polymerase gamma (POLG) disease based on age of onset; studies using a cohort of 155 cases.

J Inherit Metab Dis 2020 07 23;43(4):726-736. Epub 2020 Jan 23.

Department of Clinical Medicine (K1), University of Bergen, Bergen, Norway.

Background: Variants in POLG are one of the most common causes of inherited mitochondrial disease. Phenotypic classification of POLG disease has evolved haphazardly making it complicated and difficult to implement in everyday clinical practise. The aim of our study was to simplify the classification and facilitate better clinical recognition.

Methods: A multinational, retrospective study using data from 155 patients with POLG variants recruited from seven European countries.

Results: We describe the spectrum of clinical features associated with POLG variants in the largest known cohort of patients. While clinical features clearly form a continuum, stratifying patients simply according to age of onset-onset prior to age 12 years; onset between 12 and 40 years and onset after the age of 40 years, permitted us to identify clear phenotypic and prognostic differences. Prior to 12 years of age, liver involvement (87%), seizures (84%), and feeding difficulties (84%) were the major features. For those with onset between 12 and 40 years, ataxia (90%), peripheral neuropathy (84%), and seizures (71%) predominated, while for those with onset over 40 years, ptosis (95%), progressive external ophthalmoplegia (89%), and ataxia (58%) were the major clinical features. The earlier the onset the worse the prognosis. Patients with epilepsy and those with compound heterozygous variants carried significantly worse prognosis.

Conclusion: Based on our data, we propose a simplified POLG disease classification, which can be used to guide diagnostic investigations and predict disease course.
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http://dx.doi.org/10.1002/jimd.12211DOI 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

An unusual ryanodine receptor 1 (RYR1) phenotype: Mild calf-predominant myopathy.

Neurology 2019 04 6;92(14):e1600-e1609. Epub 2019 Mar 6.

From the Neuromuscular Research Center (M. Jokela, S.L., J.P., B.U.), Department of Neurology, University Hospital and University of Tampere; Division of Clinical Neurosciences (M. Jokela), Department of Neurology, Turku University Hospital and University of Turku; Kiinamyllynkatu 4-8 (M. Jokela), Turku, Finland; Unità Operativa Complessa di Neurologia (G.T.), Dipartimento di Scienze dell'Invecchiamento, Neurologiche, Ortopediche e della Testa-Collo, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy; Folkhälsan Institute of Genetics and Department of Medical Genetics (A.V., P.-H.J., S.V., M. Johari, M.S.), Haartman Institute, University of Helsinki, Finland; Institute of Pediatric Neurology (E.M., M.P.), Catholic University School of Medicine, Rome, Italy; Department of Pathology (S.H.), Fimlab Laboratories, Tampere University Hospital, Finland; Metabolic and Neuromuscular Unit (M.D.), Meyer Hospital, Florence, Italy; Department of Pediatric Neurology (P.I.), Children's Hospital, University of Helsinki and Helsinki University Hospital; Department of Neurology (P.H.), Kuopio University Hospital and University of Eastern Finland; and Department of Neurology (B.U.), Vasa Central Hospital, Finland.

Objective: To identify the genetic defect causing a distal calf myopathy with cores.

Methods: Families with a genetically undetermined calf-predominant myopathy underwent detailed clinical evaluation, including EMG/nerve conduction studies, muscle biopsy, laboratory investigations, and muscle MRI. Next-generation sequencing and targeted Sanger sequencing were used to identify the causative genetic defect in each family.

Results: A novel deletion-insertion mutation in ryanodine receptor 1 () was found in the proband of the index family and segregated with the disease in 6 affected relatives. Subsequently, we found 2 more families with a similar calf-predominant myopathy segregating with unique -mutated alleles. All patients showed a very slowly progressive myopathy without episodes of malignant hyperthermia or rhabdomyolysis. Muscle biopsy showed cores or core-like changes in all families.

Conclusions: Our findings expand the spectrum of -related disorders to include a calf-predominant myopathy with core pathology and autosomal dominant inheritance. Two families had unique and previously unreported mutations, while affected persons in the third family carried 2 previously known mutations in the same dominant allele.
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http://dx.doi.org/10.1212/WNL.0000000000007246DOI Listing
April 2019

Elevated cerebrospinal fluid protein in POLG-related epilepsy: Diagnostic and prognostic implications.

Epilepsia 2018 08 19;59(8):1595-1602. Epub 2018 Jun 19.

Department of Clinical Medicine (K1), University of Bergen, Bergen, Norway.

Objective: Epilepsy is common in individuals with mutations in POLG, the gene encoding the catalytic subunit of the mitochondrial DNA polymerase gamma. Early recognition and aggressive seizure management are crucial for patient survival. Disruption of the blood-brain barrier (BBB) is implicated in various neurological disorders including epilepsy. The aim of this study was to assess whether POLG-related disease is associated with BBB dysfunction and what clinical implications this has for patients.

Methods: Our retrospective study used data from 83 patients with pathogenic POLG mutations from 4 countries--Norway, Sweden, Finland, and the United Kingdom. Data were collected using a structured questionnaire. We used the presence of raised cerebrospinal fluid (CSF) protein and a raised CSF/serum ratio of albumin (Q-alb) to evaluate the integrity of the blood-CSF barrier.

Results: Raised CSF protein was found in 70% of patients (n = 58/83) and appeared to be associated with the most severe phenotypes. In those in whom it was measured, the Q-alb ratio was markedly elevated (n = 18). The majority of those with epilepsy (n = 50/66, 76%) had raised CSF protein, and this preceded seizure debut in 75% (n = 15/20). The median survival time from symptom onset for those with raised CSF protein was decreased (13 months) compared to those with normal CSF protein (32 months).

Significance: Our results indicate that there is disruption of the BBB in POLG-related disease, as evidenced by a raised CSF protein and Q-alb ratio. We also find that raised CSF protein is a common finding in patients with POLG disease. Our data suggest that the presence of BBB dysfunction predicts a poorer outcome, and elevated CSF protein may therefore be an additional biomarker both for early diagnosis and to identify those at high risk of developing epilepsy.
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http://dx.doi.org/10.1111/epi.14459DOI Listing
August 2018

Retrospective natural history of thymidine kinase 2 deficiency.

J Med Genet 2018 08 30;55(8):515-521. Epub 2018 Mar 30.

Department of Neurology, Columbia University Medical Center, New York City, New York, USA.

Background: Thymine kinase 2 (TK2) is a mitochondrial matrix protein encoded in nuclear DNA and phosphorylates the pyrimidine nucleosides: thymidine and deoxycytidine. Autosomal recessive mutations cause a spectrum of disease from infantile onset to adult onset manifesting primarily as myopathy.

Objective: To perform a retrospective natural history study of a large cohort of patients with TK2 deficiency.

Methods: The study was conducted by 42 investigators across 31 academic medical centres.

Results: We identified 92 patients with genetically confirmed diagnoses of TK2 deficiency: 67 from literature review and 25 unreported cases. Based on clinical and molecular genetics findings, we recognised three phenotypes with divergent survival: (1) infantile-onset myopathy (42.4%) with severe mitochondrial DNA (mtDNA) depletion, frequent neurological involvement and rapid progression to early mortality (median post-onset survival (POS) 1.00, CI 0.58 to 2.33 years); (2) childhood-onset myopathy (40.2%) with mtDNA depletion, moderate-to-severe progression of generalised weakness and median POS at least 13 years; and (3) late-onset myopathy (17.4%) with mild limb weakness at onset and slow progression to respiratory insufficiency with median POS of 23 years. Ophthalmoparesis and facial weakness are frequent in adults. Muscle biopsies show multiple mtDNA deletions often with mtDNA depletion.

Conclusions: In TK2 deficiency, age at onset, rate of weakness progression and POS are important variables that define three clinical subtypes. Nervous system involvement often complicates the clinical course of the infantile-onset form while extraocular muscle and facial involvement are characteristic of the late-onset form. Our observations provide essential information for planning future clinical trials in this disorder.
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http://dx.doi.org/10.1136/jmedgenet-2017-105012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6073909PMC
August 2018

Reply to 'Letter to Editor by Finsterer J and Zarrouk-Mahjoub S: Phenotypic manifestations of the m.8969G>A variant'.

Neurogenetics 2018 05 26;19(2):133-134. Epub 2018 Feb 26.

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

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http://dx.doi.org/10.1007/s10048-018-0542-zDOI Listing
May 2018

Defective mitochondrial ATPase due to rare mtDNA m.8969G>A mutation-causing lactic acidosis, intellectual disability, and poor growth.

Neurogenetics 2018 01 19;19(1):49-53. Epub 2018 Jan 19.

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

Mutations in mitochondrial ATP synthase 6 (MT-ATP6) are a frequent cause of NARP (neurogenic muscle weakness, ataxia, and retinitis pigmentosa) or Leigh syndromes, especially a point mutation at nucleotide position 8993. M.8969G>A is a rare MT-ATP6 mutation, previously reported only in three individuals, causing multisystem disorders with mitochondrial myopathy, lactic acidosis, and sideroblastic anemia or IgA nephropathy. We present two siblings with the m.8969G>A mutation and a novel, substantially milder phenotype with lactic acidosis, poor growth, and intellectual disability. Our findings expand the phenotypic spectrum and show that mtDNA mutations should be taken account also with milder, stable phenotypes.
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http://dx.doi.org/10.1007/s10048-018-0537-9DOI Listing
January 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

Progressive deafness-dystonia due to SERAC1 mutations: A study of 67 cases.

Ann Neurol 2017 Dec;82(6):1004-1015

Institute of Human Genetics, Technische UniversitätMünchen, Munich, Germany.

Objective: 3-Methylglutaconic aciduria, dystonia-deafness, hepatopathy, encephalopathy, Leigh-like syndrome (MEGDHEL) syndrome is caused by biallelic variants in SERAC1.

Methods: This multicenter study addressed the course of disease for each organ system. Metabolic, neuroradiological, and genetic findings are reported.

Results: Sixty-seven individuals (39 previously unreported) from 59 families were included (age range = 5 days-33.4 years, median age = 9 years). A total of 41 different SERAC1 variants were identified, including 20 that have not been reported before. With the exception of 2 families with a milder phenotype, all affected individuals showed a strikingly homogeneous phenotype and time course. Severe, reversible neonatal liver dysfunction and hypoglycemia were seen in >40% of all cases. Starting at a median age of 6 months, muscular hypotonia (91%) was seen, followed by progressive spasticity (82%, median onset = 15 months) and dystonia (82%, 18 months). The majority of affected individuals never learned to walk (68%). Seventy-nine percent suffered hearing loss, 58% never learned to speak, and nearly all had significant intellectual disability (88%). Magnetic resonance imaging features were accordingly homogenous, with bilateral basal ganglia involvement (98%); the characteristic "putaminal eye" was seen in 53%. The urinary marker 3-methylglutaconic aciduria was present in virtually all patients (98%). Supportive treatment focused on spasticity and drooling, and was effective in the individuals treated; hearing aids or cochlear implants did not improve communication skills.

Interpretation: MEGDHEL syndrome is a progressive deafness-dystonia syndrome with frequent and reversible neonatal liver involvement and a strikingly homogenous course of disease. Ann Neurol 2017;82:1004-1015.
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http://dx.doi.org/10.1002/ana.25110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5847115PMC
December 2017

A complex genomic locus drives mtDNA replicase POLG expression to its disease-related nervous system regions.

EMBO Mol Med 2018 01;10(1):13-21

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

DNA polymerase gamma (POLG), the mtDNA replicase, is a common cause of mitochondrial neurodegeneration. Why POLG defects especially cause central nervous system (CNS) diseases is unknown. We discovered a complex genomic regulatory locus for , containing three functional CNS-specific enhancers that drive expression specifically in oculomotor complex and sensory interneurons of the spinal cord, completely overlapping with the regions showing neuronal death in POLG patients. The regulatory locus also expresses two functional RNAs, RNA and MIR9-3, which are coexpressed with The MIR9-3 targets include NR2E1, a transcription factor maintaining neural stem cells in undifferentiated state, and MTHFD2, the regulatory enzyme of mitochondrial folate cycle, linking POLG expression to stem cell differentiation and folate metabolism. Our evidence suggests that distant genomic non-coding regions contribute to regulation of genes encoding mitochondrial proteins. Such genomic arrangement of locus, driving expression to CNS regions affected in POLG patients, presents a potential mechanism for CNS-specific manifestations in POLG disease.
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http://dx.doi.org/10.15252/emmm.201707993DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5760859PMC
January 2018

Phenotype-genotype correlations in Leigh syndrome: new insights from a multicentre study of 96 patients.

J Med Genet 2018 01 3;55(1):21-27. Epub 2017 Nov 3.

Department of Pediatrics, The Queen Silvia Children's Hospital, University of Gothenburg, Gothenburg, Sweden.

Background: Leigh syndrome is a phenotypically and genetically heterogeneous mitochondrial disorder. While some genetic defects are associated with well-described phenotypes, phenotype-genotype correlations in Leigh syndrome are not fully explored.

Objective: We aimed to identify phenotype-genotype correlations in Leigh syndrome in a large cohort of systematically evaluated patients.

Methods: We studied 96 patients with genetically confirmed Leigh syndrome diagnosed and followed in eight European centres specialising in mitochondrial diseases.

Results: We found that ataxia, ophthalmoplegia and cardiomyopathy were more prevalent among patients with mitochondrial DNA defects. Patients with mutations in and genes with complex I deficiency shared common phenotypic features, such as early development of central nervous system disease, followed by high occurrence of cardiac and ocular manifestations. The cerebral cortex was affected in patients with mutations significantly more often than the rest of the cohort. Patients with the m.8993T>G mutation in gene had more severe clinical and radiological manifestations and poorer disease outcome compared with patients with the m.8993T>C mutation.

Conclusion: Our study provides new insights into phenotype-genotype correlations in Leigh syndrome and particularly in patients with complex I deficiency and with defects in the mitochondrial ATP synthase.
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http://dx.doi.org/10.1136/jmedgenet-2017-104891DOI Listing
January 2018

Mutations in GPAA1, Encoding a GPI Transamidase Complex Protein, Cause Developmental Delay, Epilepsy, Cerebellar Atrophy, and Osteopenia.

Am J Hum Genet 2017 Nov;101(5):856-865

Centre Hospitalier Universitaire Sainte Justine Research Center, University of Montreal, Montreal, QC H3T1C5, Canada; Department of Pediatrics, University of Montreal, Montreal, QC H3T 1J4, Canada. Electronic address:

Approximately one in every 200 mammalian proteins is anchored to the cell membrane through a glycosylphosphatidylinositol (GPI) anchor. These proteins play important roles notably in neurological development and function. To date, more than 20 genes have been implicated in the biogenesis of GPI-anchored proteins. GPAA1 (glycosylphosphatidylinositol anchor attachment 1) is an essential component of the transamidase complex along with PIGK, PIGS, PIGT, and PIGU (phosphatidylinositol-glycan biosynthesis classes K, S, T, and U, respectively). This complex orchestrates the attachment of the GPI anchor to the C terminus of precursor proteins in the endoplasmic reticulum. Here, we report bi-allelic mutations in GPAA1 in ten individuals from five families. Using whole-exome sequencing, we identified two frameshift mutations (c.981_993del [p.Gln327Hisfs102] and c.920delG [p.Gly307Alafs11]), one intronic splicing mutation (c.1164+5C>T), and six missense mutations (c.152C>T [p.Ser51Leu], c.160_161delinsAA [p.Ala54Asn], c.527G>C [p.Trp176Ser], c.869T>C [p.Leu290Pro], c.872T>C [p.Leu291Pro], and c.1165G>C [p.Ala389Pro]). Most individuals presented with global developmental delay, hypotonia, early-onset seizures, cerebellar atrophy, and osteopenia. The splicing mutation was found to decrease GPAA1 mRNA. Moreover, flow-cytometry analysis of five available individual samples showed that several GPI-anchored proteins had decreased cell-surface abundance in leukocytes (FLAER, CD16, and CD59) or fibroblasts (CD73 and CD109). Transduction of fibroblasts with a lentivirus encoding the wild-type protein partially rescued the deficiency of GPI-anchored proteins. These findings highlight the role of the transamidase complex in the development and function of the cerebellum and the skeletal system.
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http://dx.doi.org/10.1016/j.ajhg.2017.09.020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5673666PMC
November 2017

PURA syndrome: clinical delineation and genotype-phenotype study in 32 individuals with review of published literature.

J Med Genet 2018 02 2;55(2):104-113. Epub 2017 Nov 2.

Department of Human Genetics and Genomic Medicine, Faculty of Medicine, University of Southampton, Southampton, UK.

Background: De novo mutations in have recently been described to cause PURA syndrome, a neurodevelopmental disorder characterised by severe intellectual disability (ID), epilepsy, feeding difficulties and neonatal hypotonia.

Objectives: To delineate the clinical spectrum of PURA syndrome and study genotype-phenotype correlations.

Methods: Diagnostic or research-based exome or Sanger sequencing was performed in individuals with ID. We systematically collected clinical and mutation data on newly ascertained PURA syndrome individuals, evaluated data of previously reported individuals and performed a computational analysis of photographs. We classified mutations based on predicted effect using 3D in silico models of crystal structures of -derived Pur-alpha homologues. Finally, we explored genotype-phenotype correlations by analysis of both recurrent mutations as well as mutation classes.

Results: We report mutations in (purine-rich element binding protein A) in 32 individuals, the largest cohort described so far. Evaluation of clinical data, including 22 previously published cases, revealed that all have moderate to severe ID and neonatal-onset symptoms, including hypotonia (96%), respiratory problems (57%), feeding difficulties (77%), exaggerated startle response (44%), hypersomnolence (66%) and hypothermia (35%). Epilepsy (54%) and gastrointestinal (69%), ophthalmological (51%) and endocrine problems (42%) were observed frequently. Computational analysis of facial photographs showed subtle facial dysmorphism. No strong genotype-phenotype correlation was identified by subgrouping mutations into functional classes.

Conclusion: We delineate the clinical spectrum of PURA syndrome with the identification of 32 additional individuals. The identification of one individual through targeted Sanger sequencing points towards the clinical recognisability of the syndrome. Genotype-phenotype analysis showed no significant correlation between mutation classes and disease severity.
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http://dx.doi.org/10.1136/jmedgenet-2017-104946DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5800346PMC
February 2018

Defective mitochondrial RNA processing due to PNPT1 variants causes Leigh syndrome.

Hum Mol Genet 2017 09;26(17):3352-3361

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

Leigh syndrome is a severe infantile encephalopathy with an exceptionally variable genetic background. We studied the exome of a child manifesting with Leigh syndrome at one month of age and progressing to death by the age of 2.4 years, and identified novel compound heterozygous variants in PNPT1, encoding the polynucleotide phosphorylase (PNPase). Expression of the wild type PNPT1 in the subject's myoblasts functionally complemented the defects, and the pathogenicity was further supported by structural predictions and protein and RNA analyses. PNPase is a key enzyme in mitochondrial RNA metabolism, with suggested roles in mitochondrial RNA import and degradation. The variants were predicted to locate in the PNPase active site and disturb the RNA processing activity of the enzyme. The PNPase trimer formation was not affected, but specific RNA processing intermediates derived from mitochondrial transcripts of the ND6 subunit of Complex I, as well as small mRNA fragments, accumulated in the subject's myoblasts. Mitochondrial RNA processing mediated by the degradosome consisting of hSUV3 and PNPase is poorly characterized, and controversy on the role and location of PNPase within human mitochondria exists. Our evidence indicates that PNPase activity is essential for the correct maturation of the ND6 transcripts, and likely for the efficient removal of degradation intermediates. Loss of its activity will result in combined respiratory chain deficiency, and a classic respiratory chain-deficiency-associated disease, Leigh syndrome, indicating an essential role for the enzyme for normal function of the mitochondrial respiratory chain.
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http://dx.doi.org/10.1093/hmg/ddx221DOI Listing
September 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

Absence of Hikeshi, a nuclear transporter for heat-shock protein HSP70, causes infantile hypomyelinating leukoencephalopathy.

Eur J Hum Genet 2017 02 21;25(3):366-370. Epub 2016 Dec 21.

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

Genetic leukoencephalopathies are a heterogeneous group of central nervous system disorders with white matter involvement. In a Finnish patient, we identified a novel homozygous disease-causing variant in HIKESHI, c.11G>C, p.(Cys4Ser), leading to hypomyelinating leukoencephalopathy with periventricular cysts and vermian atrophy. A founder Ashkenazi-Jewish disease-causing variant recently linked Hikeshi and its heat-shock protective function to leukoencephalopathy. In our patient, clinical features of lower limb spasticity, optic atrophy, nystagmus, and severe developmental delay were similar to reported patients. Additional features included vermian atrophy, epileptic seizures, and an ovarian tumor. Structural modeling and protein analyses revealed that modified interactions inside Hikeshi's hydrophobic pockets induce protein instability. The patient's cells showed impaired nuclear translocation of HSP70 during heat shock, and decreased ERO1-Lα, an endoplasmic reticulum (ER) oxidoreductase. Overall, we show that: (1) the clinical spectrum associated with Hikeshi deficiency extends to leukoencephalopathy with vermian atrophy and epilepsy; (2) the cellular disease process involves both nuclear chaperone and ER functions.
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http://dx.doi.org/10.1038/ejhg.2016.189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5315520PMC
February 2017

Modified Atkins diet induces subacute selective ragged-red-fiber lysis in mitochondrial myopathy patients.

EMBO Mol Med 2016 11 2;8(11):1234-1247. Epub 2016 Nov 2.

Research Program of Molecular Neurology, Biomedicum Helsinki University of Helsinki, Helsinki, Finland

Mitochondrial myopathy (MM) with progressive external ophthalmoplegia (PEO) is a common manifestation of mitochondrial disease in adulthood, for which there is no curative therapy. In mice with MM, ketogenic diet significantly delayed progression of the disease. We asked in this pilot study what effects high-fat, low-carbohydrate "modified Atkins" diet (mAD) had for PEO/MM patients and control subjects and followed up the effects by clinical, morphological, transcriptomic, and metabolomic analyses. All of our five patients, irrespective of genotype, showed a subacute response after 1.5-2 weeks of diet, with progressive muscle pain and leakage of muscle enzymes, leading to premature discontinuation of the diet. Analysis of muscle ultrastructure revealed selective fiber damage, especially in the ragged-red-fibers (RRFs), a MM hallmark. Two years of follow-up showed improvement of muscle strength, suggesting activation of muscle regeneration. Our results indicate that (i) nutrition can modify mitochondrial disease progression, (ii) dietary counseling should be part of MM care, (iii) short mAD is a tool to induce targeted RRF lysis, and (iv) mAD, a common weight-loss method, may induce muscle damage in a population subgroup.
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http://dx.doi.org/10.15252/emmm.201606592DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090657PMC
November 2016

FGF21 is a biomarker for mitochondrial translation and mtDNA maintenance disorders.

Neurology 2016 Nov 28;87(22):2290-2299. Epub 2016 Oct 28.

From the Research Programs Unit, Molecular Neurology (J.M.L., S.F., H.L., M.A., P.I.), Faculty of Medicine/Clinicum, Oncology (P.O.), and Finland Genome Scale Biology Program (S.L.), University of Helsinki, Finland; Mitochondrial Medicine Group (E.B., C.V., M.Z.), Medical Research Council Mitochondrial Biology Unit, Cambridge, UK; Center for Physiology and Pathophysiology (O.R.B., R.J.W.), Institute of Vegetative Physiology, University of Köln, Germany; Transplantation and Liver Surgery Clinic (H.I., K.H.), Department of Oncology (P.O., S.L.), and Heart and Lung Center, Department of Cardiology (T.H.), Helsinki University Hospital; School of Medicine (M.H., J.J., R.L.), University of Tampere; Anaesthesiology, Intensive Care and Pain Medicine (R.M.), Clinical Neurosciences, Neurology (H.L., M.A., A.S.), and Child Neurology, Children's Hospital (P.I.), University of Helsinki and Helsinki University Hospital, Finland; Dyslipidemia Center (G.M.), Cardiotoracovascular Department, Niguarda Hospital, Milan, Italy; PEDEGO Research Unit (J.U.) and Biocenter Oulu (J.U.), University of Oulu; Finnish Clinical Biobank Tampere (R.L.), Tampere University Hospital, Finland; Nijmegen Centre for Mitochondrial Disorders (J.S.), Radboud University Medical Centre, Nijmegen, the Netherlands; Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD) (R.J.W.), Köln; Center for Molecular Medicine Cologne (R.J.W.), CMMC, University of Köln, Germany; Faculty of Life and Environmental Sciences (K.N.), University of Tsukuba, Japan; and Medical Research Center Oulu (J.U.), Oulu University Hospital and University of Oulu, Finland.

Objective: To validate new mitochondrial myopathy serum biomarkers for diagnostic use.

Methods: We analyzed serum FGF21 (S-FGF21) and GDF15 from patients with (1) mitochondrial diseases and (2) nonmitochondrial disorders partially overlapping with mitochondrial disorder phenotypes. We (3) did a meta-analysis of S-FGF21 in mitochondrial disease and (4) analyzed S-Fgf21 and skeletal muscle Fgf21 expression in 6 mouse models with different muscle-manifesting mitochondrial dysfunctions.

Results: We report that S-FGF21 consistently increases in primary mitochondrial myopathy, especially in patients with mitochondrial translation defects or mitochondrial DNA (mtDNA) deletions (675 and 347 pg/mL, respectively; controls: 66 pg/mL, p < 0.0001 for both). This is corroborated in mice (mtDNA deletions 1,163 vs 379 pg/mL, p < 0.0001). However, patients and mice with structural respiratory chain subunit or assembly factor defects showed low induction (human 335 pg/mL, p < 0.05; mice 335 pg/mL, not significant). Overall specificities of FGF21 and GDF15 to find patients with mitochondrial myopathy were 89.3% vs 86.4%, and sensitivities 67.3% and 76.0%, respectively. However, GDF15 was increased also in a wide range of nonmitochondrial conditions.

Conclusions: S-FGF21 is a specific biomarker for muscle-manifesting defects of mitochondrial translation, including mitochondrial transfer-RNA mutations and primary and secondary mtDNA deletions, the most common causes of mitochondrial disease. However, normal S-FGF21 does not exclude structural respiratory chain complex or assembly factor defects, important to acknowledge in diagnostics.

Classification Of Evidence: This study provides Class III evidence that elevated S-FGF21 accurately distinguishes patients with mitochondrial myopathies from patients with other conditions, and FGF21 and GDF15 mitochondrial myopathy from other myopathies.
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http://dx.doi.org/10.1212/WNL.0000000000003374DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5270510PMC
November 2016

Recurrent De Novo Dominant Mutations in SLC25A4 Cause Severe Early-Onset Mitochondrial Disease and Loss of Mitochondrial DNA Copy Number.

Am J Hum Genet 2016 10 29;99(4):860-876. Epub 2016 Sep 29.

Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, UK. Electronic address:

Mutations in SLC25A4 encoding the mitochondrial ADP/ATP carrier AAC1 are well-recognized causes of mitochondrial disease. Several heterozygous SLC25A4 mutations cause adult-onset autosomal-dominant progressive external ophthalmoplegia associated with multiple mitochondrial DNA deletions, whereas recessive SLC25A4 mutations cause childhood-onset mitochondrial myopathy and cardiomyopathy. Here, we describe the identification by whole-exome sequencing of seven probands harboring dominant, de novo SLC25A4 mutations. All affected individuals presented at birth, were ventilator dependent and, where tested, revealed severe combined mitochondrial respiratory chain deficiencies associated with a marked loss of mitochondrial DNA copy number in skeletal muscle. Strikingly, an identical c.239G>A (p.Arg80His) mutation was present in four of the seven subjects, and the other three case subjects harbored the same c.703C>G (p.Arg235Gly) mutation. Analysis of skeletal muscle revealed a marked decrease of AAC1 protein levels and loss of respiratory chain complexes containing mitochondrial DNA-encoded subunits. We show that both recombinant AAC1 mutant proteins are severely impaired in ADP/ATP transport, affecting most likely the substrate binding and mechanics of the carrier, respectively. This highly reduced capacity for transport probably affects mitochondrial DNA maintenance and in turn respiration, causing a severe energy crisis. The confirmation of the pathogenicity of these de novo SLC25A4 mutations highlights a third distinct clinical phenotype associated with mutation of this gene and demonstrates that early-onset mitochondrial disease can be caused by recurrent de novo mutations, which has significant implications for the application and analysis of whole-exome sequencing data in mitochondrial disease.
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http://dx.doi.org/10.1016/j.ajhg.2016.08.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5065686PMC
October 2016