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Ophthalmological manifestations are common in mitochondrial diseases. All parts of the eye can be affected, and symptoms can appear at any age making diagnostics challenging. The aims of this thesis were to study a prevalence of a genetically defined Leber hereditary optic neuropathy (LHON) in Northern Finland among adult and child populations and to identify novel genetic aetiologies and risk factors for ophthalmological manifestations of childhood-onset mitochondrial diseases. The study population comprised two retrospective patient cohorts: 42 adult patients with aetiologically undefined bilateral optic atrophy, and 355 children with at least one of five common mitochondrial ocular symptoms: optic neuropathy, retinal degeneration, nystagmus, ophthalmoplegia or ptosis. Only children without specific syndromes or genetically verified diseases were eligible (98 patients), and 38 participated in further studies on mitochondrial DNA and targeted nuclear genes. Furthermore, whole exome sequencing and studies on patient-derived tissue samples were performed to identify genetic aetiology of an infantile-onset, fatal multiorgan disease with optic neuropathy, pigmentary retinopathy, and nystagmus. The study revealed that LHON prevalence in Northern Finland is the same as in other western countries. In all, 73% of paediatric patients (n= 257 / 355) had defined diseases or syndromes related to chromosomal alterations or known pathogenic nDNA variants. In 38 patients, the association between retinal degeneration and MT-ATP6 variants was revealed. Nystagmus, optic neuropathy and retinal degeneration were found to be possible signs of mitochondrial diseases, especially when developmental problems or a positive family history were also present. Furthermore, genetic and functional data on an early-onset progressive encephalomyopathy with ocular defects suggested a phenotype associated with DHX16 variant. This thesis highlights the increasing role of genetic analyses and, Tiivistelmä Mitokondriotaudeissa silmäoireet voivat olla itsenäisiä tai osa monielinoireyhtymää. Mitokondriotautien diagnosointi on haastavaa, sillä oireita voi ilmetä missä tahansa silmän rakenteessa kaikissa ikäryhmissä. Väitöskirjatyön tavoitteina oli selvittää Leberin perinnöllisen näköhermorappeuman (LHON) yleisyyttä Pohjois-Suomen aikuis- ja lapsiväestössä sekä tunnistaa uusia geneettisiä etiologioita ja riskitekijöitä lapsuusiällä ilmaantuville mitokondriotautien silmäoireille. Näköhermorappeuman yleisyyttä selvitettiin tutkimalla kahta retrospektiivistä potilaskohorttia. Aikuiskohorttiin kuuluneella 42 potilaalla oli avoin näköhermorappeuman etiologia ja lapsikohorttiin kuuluneella 355 potilaalla oli vähintään yksi viidestä mitokondriotaudeille tyypillisistä silmäoireista: näköhermon tai verkkokalvon rappeuma, silmävärve, silmänliikuttajalihaksen halvaus tai riippuluomi. Lapsipotilaista tutkimuskohorttiin hyväksyttiin vain ne 98 potilasta, joilla ei ollut todettu tunnettua oireyhtymää tai geneettisesti varmennettua tautia. Potilaista 38 osallistui mitokondrio DNA:n (mtDNA) sekä tiettyjen tuman geenien jatkotutkimuksiin, joissa eksomin sekvensointi (WES) ja proteiinitason tutkimukset tehtiin potilasperäisillä kudosnäytteillä. Tutkimuksen tavoitteena oli tunnistaa geneettinen syy imeväisiässä alkaneelle ja menehtymiseen johtaneelle monielintaudille, johon kuului näköhermon ja verkkokalvon rappeuma sekä silmävärve. Tutkimuksen mukaan LHON-silmäsairauden yleisyys Pohjois-Suomessa vastaa länsimaista tasoa. Lapsikohortin potilaista 73 prosentilla (257/355) oli jokin tunnettu oireyhtymä, kromosomimuutos tai taudinkuvan aiheuttava tuman geenimuutos. Jatkotutkimuksiin osallistuneen 38 potilaan aineistossa havaittiin yhteys verkkokalvon rappeuman ja mtDNA:n ATP6-geenivarianttien välillä. Silmävärve, näköhermon ja verkkokalvon rappeuma viittaavat mitokondriotaudin mahdollisuuteen, kun ne esiintyvät yhdessä kehityshäiriön tai positiivisen sukuanamneesin kanssa. Väitöski

Background: Large-scale mitochondrial DNA deletions (LMD) are a common genetic cause of mitochondrial disease and give rise to a wide range of clinical features. Lack of longitudinal data means the natural history remains unclear. This study was undertaken to describe the clinical spectrum in a large cohort of patients with paediatric disease onset. Methods: A retrospective multicentre study was performed in patients with clinical onset <16 years of age, diagnosed and followed in seven European mitochondrial disease centres. Results: A total of 80 patients were included. The average age at disease onset and at last examination was 10 and 31 years, respectively. The median time from disease onset to death was 11.5 years. Pearson syndrome was present in 21%, Kearns-Sayre syndrome spectrum disorder in 50% and progressive external ophthalmoplegia in 29% of patients. Haematological abnormalities were the hallmark of the disease in preschool children, while the most common presentations in older patients were ptosis and external ophthalmoplegia. Skeletal muscle involvement was found in 65% and exercise intolerance in 25% of the patients. Central nervous system involvement was frequent, with variable presence of ataxia (40%), cognitive involvement (36%) and stroke-like episodes (9%). Other common features were pigmentary retinopathy (46%), short stature (42%), hearing impairment (39%), cardiac disease (39%), diabetes mellitus (25%) and renal disease (19%). Conclusion: Our study provides new insights into the phenotypic spectrum of childhood-onset, LMD-associated syndromes. We found a wider spectrum of more prevalent multisystem involvement compared with previous studies, most likely related to a longer time of follow-up.

Scanning transmission X-ray microscopy (STXM) in the soft X-ray range is well-suited to study ultrastructural features of mammalian soft tissues. Especially at the carbon 1s edge, the imaging contrast varies drastically across the edge due to rapid changes in the X-ray absorption cross-section of functional groups present in the tissue samples enabling label-free soft X-ray spectromicroscopic studies. We present STXM spectromicroscopic imaging of mouse kidney and liver tissues. We especially concentrate on ultrastructural abnormalities in genetically modified Slc17a5 mice. STXM is a promising technique to study storage diseases without chemical alteration due to staining agents, but sample preparation poses a challenge.

Hepatotoxicity is a frequent complication during maintenance therapy of acute lymphoblastic leukemia (ALL) with 6-mercaptopurine and methotrexate. Elevated levels of methylated 6-mercaptopurine metabolites (MeMP) are associated with hepatotoxicity. However, not all mechanisms are known that lead to liver failure in patients with ALL. Variants in the POLG gene, which encodes the catalytic subunit of mitochondrial DNA polymerase gamma (POLG1), have been related to drug-induced hepatotoxicity, for example, by sodium valproate. The association of common POLG variants with hepatotoxicity during maintenance therapy was studied in 34 patients with childhood ALL. Of the screened POLG variants, four different variants were detected in 12 patients. One patient developed severe hepatotoxicity without elevated MeMP levels and harbored a heterozygous POLG p.G517V variant, which was not found in the other patients.

Purpose: FINCA disease (Fibrosis, Neurodegeneration and Cerebral Angiomatosis, OMIM 618278) is an infantile-onset neurodevelopmental and multiorgan disease. Since our initial report in 2018, additional patients have been described. FINCA is the first human disease caused by recessive variants in the highly conserved NHLRC2 gene. Our previous studies have shown that Nhlrc2-null mouse embryos die during gastrulation, indicating the essential role of the protein in embryonic development. Defect in NHLRC2 leads to cerebral neurodegeneration and severe pulmonary, hepatic and cardiac fibrosis. Despite having a structure suggestive of an enzymatic role and the clinical importance of NHLRC2 in multiple organs, the specific physiological role of the protein is unknown. Methods: The clinical histories of five novel FINCA patients diagnosed with whole exome sequencing were reviewed. Segregation analysis of the biallelic, potentially pathogenic NHLRC2 variants was performed using Sanger sequencing. Studies on neuropathology and NHLRC2 expression in different brain regions were performed on autopsy samples of three previously described deceased FINCA patients. Results: One patient was homozygous for the pathogenic variant c.442G > T, while the other four were compound heterozygous for this variant and two other pathogenic NHLRC2 gene variants. All five patients presented with multiorgan dysfunction with neurodevelopmental delay, recurrent infections and macrocytic anemia as key features. Interstitial lung disease was pronounced in infancy but often stabilized. Autopsy samples revealed widespread, albeit at a lower intensity than the control, NHLRC2 expression in the brain. Conclusion: This report expands on the characteristic clinical features of FINCA disease. Presentation is typically in infancy, and although patients can live to late adulthood, the key clinical and histopathological features are fibrosis, infection susceptibility/immunodeficiency/intellectual disa

Background and Objective: The objective of this study was to better delineate the genetic landscape and key clinical characteristics of complex, early-onset, monogenic hyperkinetic movement disorders. Methods: Patients were recruited from 14 international centers. Participating clinicians completed standardized proformas capturing demographic, clinical, and genetic data. Two pediatric movement disorder experts reviewed available video footage, classifying hyperkinetic movements according to published criteria. Results: One hundred forty patients with pathogenic variants in 17 different genes (ADCY5, ATP1A3, DDC, DHPR, FOXG1, GCH1, GNAO1, KMT2B, MICU1, NKX2.1, PDE10A, PTPS, SGCE, SLC2A1, SLC6A3, SPR, and TH) were identified. In the majority, hyperkinetic movements were generalized (77%), with most patients (69%) manifesting combined motor semiologies. Parkinsonism-dystonia was characteristic of primary neurotransmitter disorders (DDC, DHPR, PTPS, SLC6A3, SPR, TH); chorea predominated in ADCY5-, ATP1A3-, FOXG1-, NKX2.1-, SLC2A1-, GNAO1-, and PDE10A-related disorders; and stereotypies were a prominent feature in FOXG1- and GNAO1-related disease. Those with generalized hyperkinetic movements had an earlier disease onset than those with focal/segmental distribution (2.5 ± 0.3 vs. 4.7 ± 0.7 years; P = 0.007). Patients with developmental delay also presented with hyperkinetic movements earlier than those with normal neurodevelopment (1.5 ± 2.9 vs. 4.7 ± 3.8 years; P < 0.001). Effective disease-specific therapies included dopaminergic agents for neurotransmitters disorders, ketogenic diet for glucose transporter deficiency, and deep brain stimulation for SGCE-, KMT2B-, and GNAO1-related hyperkinesia. Conclusions: This study highlights the complex phenotypes observed in children with genetic hyperkinetic movement disorders that can lead to diagnostic difficulty. We provide a comprehensive analysis of motor semiology to guide physicians in the genetic investigation of thes

Background and Objective: The objective of this study was to better delineate the genetic landscape and key clinical characteristics of complex, early-onset, monogenic hyperkinetic movement disorders. Methods: Patients were recruited from 14 international centers. Participating clinicians completed standardized proformas capturing demographic, clinical, and genetic data. Two pediatric movement disorder experts reviewed available video footage, classifying hyperkinetic movements according to published criteria. Results: One hundred forty patients with pathogenic variants in 17 different genes (ADCY5, ATP1A3, DDC, DHPR, FOXG1, GCH1, GNAO1, KMT2B, MICU1, NKX2.1, PDE10A, PTPS, SGCE, SLC2A1, SLC6A3, SPR, and TH) were identified. In the majority, hyperkinetic movements were generalized (77%), with most patients (69%) manifesting combined motor semiologies. Parkinsonism-dystonia was characteristic of primary neurotransmitter disorders (DDC, DHPR, PTPS, SLC6A3, SPR, TH); chorea predominated in ADCY5-, ATP1A3-, FOXG1-, NKX2.1-, SLC2A1-, GNAO1-, and PDE10A-related disorders; and stereotypies were a prominent feature in FOXG1- and GNAO1-related disease. Those with generalized hyperkinetic movements had an earlier disease onset than those with focal/segmental distribution (2.5 ± 0.3 vs. 4.7 ± 0.7 years; P = 0.007). Patients with developmental delay also presented with hyperkinetic movements earlier than those with normal neurodevelopment (1.5 ± 2.9 vs. 4.7 ± 3.8 years; P < 0.001). Effective disease-specific therapies included dopaminergic agents for neurotransmitters disorders, ketogenic diet for glucose transporter deficiency, and deep brain stimulation for SGCE-, KMT2B-, and GNAO1-related hyperkinesia. Conclusions: This study highlights the complex phenotypes observed in children with genetic hyperkinetic movement disorders that can lead to diagnostic difficulty. We provide a comprehensive analysis of motor semiology to guide physicians in the genetic investigatio

Objective: Paediatric movement disorder patients can benefit from deep brain stimulation (DBS) treatment and it should be offered in a timely manner. In this paper we describe our experience establishing a DBS service for paediatric patients. Methods: We set out to establish a paediatric DBS (pDBS) procedure in Oulu University Hospital in northern Finland, where up to this point DBS treatment for movement disorders had been available for adult patients. Collaboration with experienced centres aided in the process. Results: A multidisciplinary team was assembled and a systematic protocol for patient evaluation and treatment was created, with attention to special features of the regional health care system. All of our first paediatric patients had very severe movement disorders, which is typical for a new DBS centre. The patients benefitted from pDBS treatment despite variable aetiologies of movement disorders, which included cerebral palsy and rare genetic disorders with variants in PDE10A, TPK1 and ARX. We also present our high-quality paediatric MR-imaging protocol with tractography. Conclusions: Establishment of a pDBS centre requires expertise in classification of paediatric movement disorders, longstanding experience in adult DBS and a committed multidisciplinary team. Besides high-quality imaging and a skilled neurosurgery team, careful patient selection, realistic treatment goals and experience in rehabilitation are imperative in pDBS treatment.

HIDEA syndrome is caused by biallelic pathogenic variants in P4HTM. The phenotype is characterized by muscular and central hypotonia, hypoventilation including obstructive and central sleep apneas, intellectual disability, dysautonomia, epilepsy, eye abnormalities, and an increased tendency to develop respiratory distress during pneumonia. Here, we report six new patients with HIDEA syndrome caused by five different biallelic P4HTM variants, including three novel variants. We describe two Finnish enriched pathogenic P4HTM variants and demonstrate that these variants are embedded within founder haplotypes. We review the clinical data from all previously published patients with HIDEA and characterize all reported P4HTM pathogenic variants associated with HIDEA in silico. All known pathogenic variants in P4HTM result in either premature stop codons, an intragenic deletion, or amino acid changes that impact the active site or the overall stability of P4H-TM protein. In all cases, normal P4H-TM enzyme function is expected to be lost or severely decreased. This report expands knowledge of the genotypic and phenotypic spectrum of the disease.

Isolated populations have been valuable for the discovery of rare monogenic diseases and their causative genetic variants. Finnish disease heritage (FDH) is an example of a group of hereditary monogenic disorders caused by single major, usually autosomal-recessive, variants enriched in the population due to several past genetic drift events. Interestingly, distinct subpopulations have remained in Finland and have maintained their unique genetic repertoire. Thus, FDH diseases have persisted, facilitating vigorous research on the underlying molecular mechanisms and development of treatment options. This Review summarizes the current status of FDH, including the most recently discovered FDH disorders, and introduces a set of other recently identified diseases that share common features with the traditional FDH diseases. The Review also discusses a new era for population-based studies, which combine various forms of big data to identify novel genotype–phenotype associations behind more complex conditions, as exemplified here by the FinnGen project. In addition to the pathogenic variants with an unequivocal causative role in the disease phenotype, several risk alleles that correlate with certain phenotypic features have been identified among the Finns, further emphasizing the broad value of studying genetically isolated populations.

Aims: This study aimed to investigate associations between renal and extrarenal manifestations of mitochondrial diseases and their natural history as well as predictors of renal disease severity and overall disease outcome. The secondary aim was to generate a protocol of presymptomatic assessment and monitoring of renal function in patients with a defined mitochondrial disease. Methods: A multicenter, retrospective cohort study was performed by the Mitochondrial Clinical and Research Network (MCRN). Patients of any age with renal manifestations associated with a genetically verified mitochondrial disease were included from 8 expert European centers specializing in mitochondrial diseases: Gothenburg, Oulu, Copenhagen, Bergen, Helsinki, Stockholm, Rotterdam, and Barcelona. Results: Of the 36 patients included, two-thirds had mitochondrial DNA-associated disease. Renal manifestations were the first sign of mitochondrial disease in 19%, and renal involvement was first identified by laboratory tests in 57% of patients. Acute kidney injury occurred in 19% of patients and was the first sign of renal disease in the majority of these. The most common renal manifestation was chronic kidney disease (75% with stage 2 or greater), followed by tubulopathy (44.4%), the latter seen mostly among patients with single large-scale mitochondrial DNA deletions. Acute kidney injury and tubulopathy correlated with worse survival outcome. The most common findings on renal imaging were increased echogenicity and renal dysplasia/hypoplasia. Renal histology revealed focal segmental glomerulosclerosis, nephrocalcinosis, and nephronophthisis. Conclusion: Acute kidney injury is a distinct renal phenotype in patients with mitochondrial disease. Our results highlight the importance to recognize renal disease as a sign of an underlying mitochondrial disease. Acute kidney injury and tubulopathy are 2 distinct indicators of poor survival in patients with mitochondrial diseases.

Cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) deficiency due to the homozygous PCK1 variant has recently been associated with childhood-onset hypoglycemia with a recognizable pattern of abnormal urine organic acids. In this study, 21 children and 3 adult patients with genetically confirmed PEPCK-C deficiency were diagnosed during the years 2016 to 2019 and the available biochemical and clinical data were collected. All patients were ethnic Finns. Most patients (22 out of 24) had a previously published homozygous PCK1 variant c.925G>A. Two patients had a novel compound heterozygous PCK1 variant c.925G>A and c.716C>T. The laboratory results showed abnormal urine organic acid profile with increased tricarboxylic acid cycle intermediates and inadequate ketone body production during hypoglycemia. The hypoglycemic episodes manifested predominantly in the morning. Infections, fasting or poor food intake, heavy exercise, alcohol consumption, and breastfeeding were identified as triggering factors. Five patients presented with neonatal hypoglycemia. Hypoglycemic seizures occurred in half of the patients (12 out of 24). The first hypoglycemic episode often occurred at the age of 1–2 years, but it sometimes presented at a later age, and could re-occur during school age or adulthood. This study adds to the laboratory data on PEPCK-C deficiency, confirming the recognizable urine organic acid pattern and identifying deficient ketogenesis as a novel laboratory finding. The phenotype is expanded suggesting that the risk of hypoglycemia may continue into adulthood if predisposing factors are present.

The loss of NHL repeat containing 2 (Nhlrc2) leads to early embryonic lethality in mice, but the exact timing is currently unknown. In this study, we determined the time of lethality for Nhlrc2 knockout (KO), C57BL/6NCrl-Nhlrc2tm1a(KOMP)Wtsi/Oulu, embryos and the in situ expression pattern of Nhlrc2 based on LacZ reporter gene expression during this period. Nhlrc2 KO preimplantation mouse embryos developed normally after in vitro fertilization. Embryonic stem (ES) cells established from KO blastocysts proliferated normally despite a complete loss of the NHLRC2 protein. Nhlrc2 KO embryos from timed matings implanted and were indistinguishable from their wildtype littermates on embryonic day (E) 6.5. On E7.5, Nhlrc2 KO embryo development was arrested, and on E8.5, only 6% of the genotyped embryos were homozygous for the Nhlrc2tm1a(KOMP)Wtsi allele. Nhlrc2 KO E8.5 embryos showed limited embryonic or extraembryonic tissue differentiation and remained at the cylinder stage. Nhlrc2 expression was ubiquitous but strongest in the epiblast/ectoderm and extraembryonic ectoderm on E6.5 and E7.5. NHLRC2 is essential for early postimplantation development, and its loss leads to failed gastrulation and amniotic folding in mice. Future studies on the evolutionarily conserved NHLRC2 will provide new insights into the molecular pathways involved in the early steps of postimplantation development.

Rapid development of molecular methods has led to the identification of an increasing number of disease-causing genes and variants, but their molecular function is often unknown. However, understanding their role in normal physiology and in disease is essential for the development of treatment options. In vitro and in vivo disease models are important tools for biomedical research. In vivo models enable the study of physiological processes in the context of a whole animal. Among animal models, mouse is the most used, and has been widely utilised to understand human biology and disease. In the current study, a novel rare multiorgan disease is characterised. Three patients with a previously undescribed early infantile-onset disease were discovered from two unrelated Finnish families. The patients presented with progressive cerebropulmonary and multiorgan symptoms leading to death before 2 years of age. The disease was named FINCA after its main histopathological findings: fibrosis, neurodegeneration, and cerebral angiomatosis. Whole-exome sequencing revealed hetero compound variants in a poorly characterised NHL repeat containing 2 (NHLRC2) gene of the patients. Both variants segregated from healthy heterozygous parents. Patient-derived skin fibroblasts showed a significant decrease in the amount of NHLRC2 protein. Zebrafish and knockout and knockin (KI) mouse models were generated to study the molecular function of the disease-causing gene and the pathogenesis of the disease in vitro and in vivo. Complete loss of Nhlrc2 resulted in early embryonic lethality in mouse revealing an important role for the gene in early embryogenesis. Further analysis showed Nhlrc2 to be essential for completion of gastrulation but not for the viability of embryonic stem cells. The FINCA KI mouse model showed a consistent decrease in NHLRC2 but lacked a severe phenotype. However, studies of the mouse model revealed altered proteins associated with endo- and autolysosomal pathways, Tiivistelmä Molekyylibiologian menetelmien nopea kehittyminen on mahdollistanut uusien, toiminnaltaan tuntemattomien tautigeenien ja varianttien tunnistamisen. Geenin toiminnan ymmärtäminen normaalissa fysiologiassa ja taudissa on välttämätöntä, jotta hoitojen kehittäminen on mahdollista. In vivo- ja in vitro -tautimallit ovat tärkeitä työkaluja biolääketieteen tutkimuksessa. Eläinmallit mahdollistavat fysiologisten toimintojen tutkimuksen koko eläimessä. Hiiri on malleista käytetyin, ja sitä on käytetty laajalti ihmisen biologian ja tautien tutkimuksessa. Tässä tutkimuksessa kuvattiin uusi, harvinainen monielintauti. Kolme potilasta, jotka olivat kahdesta suomalaisesta perheestä, sairastui ennestään tuntemattomaan tautiin ensimmäisten elinkuukausiensa aikana. Heille kehittyi etenevä keskushermosto- ja keuhko-oireisto sekä monielintauti, joka johti potilaiden menehtymiseen ennen kahden vuoden ikää. Tauti nimettiin FINCA-taudiksi kudostason päälöydösten eli fibroosin (fibrosis), hermostorappeuman (neurodegeneration) ja aivojen verisuonimuutosten (cerebral angiomatosis) mukaan. Koko eksomin sekvensointi paljasti potilailla yhdistelmän variantteja huonosti tunnetussa NHL repeat containing 2 (NHLRC2) -geenissä. Variantit periytyivät terveiltä heterotsygooteilta vanhemmilta. NHLRC2-proteiinin määrä oli merkittävästi alentunut potilaislähtöisissä fibroblasti-soluissa. Taudin taustalla olevan geenin molekyylitason toimintaa ja FINCA-taudin etenemistä tutkittiin in vitro ja in vivo hyödyntäen seeprakalaa, Nhlrc2-poistogeenistä hiirtä ja luotua FINCA-hiirimallia. Poistogeeniset hiiret menehtyivät aikaisin alkionkehityksen aikana. NHLRC2 paljastui välttämättömäksi gastrulaatiolle, mutta ei alkion kantasolujen elinkyvylle. FINCA-hiirimallin kudosten NHLRC2-taso laski merkittävästi, mutta hiirelle ei kehittynyt vakavaa ilmiasua. Hiirimallin tutkimukset paljastivat kuitenkin muutoksia endo- ja autolysosomaalisiin reaktioreitteihin sekä RNA-homeostaasiin yhdistetyissä proteiineis

The modification of genes in animal models has evidently and comprehensively improved our knowledge on proteins and signaling pathways in human physiology and pathology. In this review, we discuss almost 40 monogenic rare diseases that are enriched in the Finnish population and defined as the Finnish disease heritage (FDH). We will highlight how gene-modified mouse models have greatly facilitated the understanding of the pathological manifestations of these diseases and how some of the diseases still lack proper models. We urge the establishment of subsequent international consortiums to cooperatively plan and carry out future human disease modeling strategies. Detailed information on disease mechanisms brings along broader understanding of the molecular pathways they act along both parallel and transverse to the proteins affected in rare diseases, therefore also aiding understanding of common disease pathologies.

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.

Background: Homozygous loss of DIAPH1 results in seizures, cortical blindness, and microcephaly syndrome (SCBMS). We studied 5 Finnish and 2 Omani patients with loss of DIAPH1 presenting with SCBMS, mitochondrial dysfunction, and immunodeficiency. Objective: We sought to further characterize phenotypes and disease mechanisms associated with loss of DIAPH1. Methods: Exome sequencing, genotyping and haplotype analysis, B- and T-cell phenotyping, in vitro lymphocyte stimulation assays, analyses of mitochondrial function, immunofluorescence staining for cytoskeletal proteins and mitochondria, and CRISPR-Cas9 DIAPH1 knockout in heathy donor PBMCs were used. Results: Genetic analyses found all Finnish patients homozygous for a rare DIAPH1 splice-variant (NM_005219:c.684+1G>A) enriched in the Finnish population, and Omani patients homozygous for a previously described pathogenic DIAPH1 frameshift-variant (NM_005219:c.2769delT;p.F923fs). In addition to microcephaly, epilepsy, and cortical blindness characteristic to SCBMS, the patients presented with infection susceptibility due to defective lymphocyte maturation and 3 patients developed B-cell lymphoma. Patients’ immunophenotype was characterized by poor lymphocyte activation and proliferation, defective B-cell maturation, and lack of naive T cells. CRISPR-Cas9 knockout of DIAPH1 in PBMCs from healthy donors replicated the T-cell activation defect. Patient-derived peripheral blood T cells exhibited impaired adhesion and inefficient microtubule-organizing center repositioning to the immunologic synapse. The clinical symptoms and laboratory tests also suggested mitochondrial dysfunction. Experiments with immortalized, patient-derived fibroblasts indicated that DIAPH1 affects the amount of complex IV of the mitochondrial respiratory chain. Conclusions: Our data demonstrate that individuals with SCBMS can have combined immune deficiency and implicate defective cytoskeletal organization and mitochondrial dysfunction in

Aim: To examine the epidemiological, clinical, and genetic characteristics of paediatric patients with genetic white matter disorders (GWMDs) in Northern Finland. Method: A longitudinal population-based cohort study was conducted in the tertiary catchment area of Oulu University Hospital from 1990 to 2019. Patients were identified retrospectively by International Statistical Classification of Diseases and Related Health Problems codes in hospital records and prospectively by attending physicians. Inclusion criteria were children younger than 18 years with defined GWMDs or genetic disorders associated with white matter abnormalities (WMAs) on brain magnetic resonance imaging. Results: Eighty patients (mean age [SD] at the end of the study 11y [8y 6mo], range 0–35y; 45 males, 35 females) were diagnosed with a defined GWMD. The cumulative childhood incidence was 30 per 100 000 live births. Regarding those patients with 49 distinct GWMDs, 20% had classic leukodystrophies and 80% had genetic leukoencephalopathies. The most common leukodystrophies were cerebral adrenoleukodystrophy, Krabbe disease, and Salla disease. Additionally, 29 patients (36%) had genetic aetiologies not previously associated with brain WMAs or they had recently characterised GWMDs, including SAMD9L- and NHLRC2-related neurological disorders. Aetiology was mitochondrial in 21% of patients. The most common clinical findings were motor developmental delay, intellectual disability, hypotonia, and spasticity. Interpretation: The cumulative childhood incidence of childhood-onset GWMDs was higher than previously described. Comprehensive epidemiological and natural history data are needed before future clinical trials are undertaken.

Genetic white matter disorders (GWMD), leukodystrophies and genetic leukoencephalopathies, are a major cause of neurodevelopmental disorders. Over a hundred related genes are recognised. The recent implementation of next-generation sequencing has facilitated the frequent characterisation of novel disorders seen today. This study was intended to evaluate the current epidemiology, genetic aetiologies, clinical phenotypes, and natural history of childhood-onset GWMDs. Additional aims were to characterise novel and rare phenotypes and to examine the effect of Finnish disease heritage on the distribution of specific disorders. This population-based cohort study consisted of 80 children diagnosed with a genetically defined white matter disorder in Northern Finland between 1990 and 2019. The cumulative childhood incidence was 30/100,000 live births, and it was higher in the later study period. In total, 49 distinct disorders were identified, of which 20% were leukodystrophies and 80% were genetic leukoencephalopathies. Mitochondrial aetiology was noted in 21% of the cases. Disorders belonging to the Finnish disease heritage constituted 10% of the cases. Motor developmental delay (79%), intellectual disability (56%), hypotonia (60%), and spasticity (49%) were the most frequent clinical findings. The study identified 20 disorders that were either recently characterised or not previously associated with white matter abnormalities. These included a novel TAF1C related phenotype. Additionally, a rare neonatal Alexander disease with a novel GFAP variant was described, consolidating the recently proposed neonatal phenotype. These findings provide comprehensive data on the current epidemiology and clinical features of GWMDs, benefitting future clinical trials. In addition to enabling genetic counselling, genetic phenotype data guide clinicians and researchers studying the pathomechanisms of GWMDs., Tiivistelmä Geneettiset valkean aivoaineen sairaudet, leukodystrofiat ja geneettiset leukoenkefalopatiat, ovat merkittäviä neurologisten kehityshäiriöiden aiheuttajia. Taudinaiheuttajageenejä tunnetaan yli sata, ja eksomi- ja genomisekvensoinnin yleistyminen on mahdollistanut uusien tautien löytämisen aiempaa tehokkaammin. Tämän tutkimuksen tavoitteena oli selvittää lapsuusiän geneettisten valkean aivoaineen sairauksien epidemiologiaa, geneettisiä etiologioita, kliinisiä ilmiasuja ja tautien luonnollista kulkua. Lisäksi tavoitteena oli löytää uusia ja harvinaisia fenotyyppejä sekä tarkastella suomalaisen tautiperinnön vaikutusta tautikirjoon. Tämän väestöpohjaisen kohortti-tutkimuksen aineistona oli 80 Pohjois-Suomessa asunutta lasta, joilla diagnosoitiin geneettinen valkean aivoaineen sairaus vuosina 1990–2019. Tautien kumulatiivinen ilmaantuvuus lapsuudessa oli 30/100 000 elävänä syntynyttä lasta, ja insidenssi oli suurempi myöhempinä vuosikymmeninä. Löydetyistä 49 taudista 20 % oli leukodystrofioita ja 80 % geneettisiä enkefalopatioita. Mitokondriaalinen tausta liittyi 21 %:iin tapauksista. Kymmenellä prosentilla oli suomalaiseen tautiperintöön kuuluva sairaus. Yleisimpiä kliinisiä löydöksiä olivat motoriikan kehityshäiriöt (49 %), älyllinen kehitysvammaisuus (56 %), heikko lihasjäntevyys (60 %) ja spastisuus (49 %). Aineistoon kuului 20 viime vuosina löydettyä sairautta tai sairautta, joita ei ole aiemmin pidetty valkean aivoaineen sairauksina. Yksi näistä oli aiemmin kuvaamaton TAF1C-geeniin liittyvä neurologinen sairaus. Toisessa osatyössä kuvattiin uusi GFAP-geenin muutos ja harvinainen Alexanderin taudin vastasyntyneisyyskauden tautimuoto, mikä tukee tämän olemassaoloa muista ikäkausista erillisenä tautimuotona. Tutkimustulokset muodostavat kokonaisvaltaisen kuvauksen geneettisten valkean aivoaineen sairauksien epidemiologiasta ja kliinisistä piirteistä. Löydökset auttavat tulevaisuudessa kliinisten tutkimusten suunnittelua ja perinnöllisyysneuvontaa sekä oh

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.

Reversible infantile respiratory chain deficiency (RIRCD) is a rare mitochondrial myopathy leading to severe metabolic disturbances in infants, which recover spontaneously after 6‐months of age. RIRCD is associated with the homoplasmic m.14674T>C mitochondrial DNA mutation; however, only ~ 1/100 carriers develop the disease. We studied 27 affected and 15 unaffected individuals from 19 families and found additional heterozygous mutations in nuclear genes interacting with mt‐tRNAGlu including EARS2 and TRMU in the majority of affected individuals, but not in healthy carriers of m.14674T>C, supporting a digenic inheritance. Our transcriptomic and proteomic analysis of patient muscle suggests a stepwise mechanism where first, the integrated stress response associated with increased FGF21 and GDF15 expression enhances the metabolism modulated by serine biosynthesis, one carbon metabolism, TCA lipid oxidation and amino acid availability, while in the second step mTOR activation leads to increased mitochondrial biogenesis. Our data suggest that the spontaneous recovery in infants with digenic mutations may be modulated by the above described changes. Similar mechanisms may explain the variable penetrance and tissue specificity of other mtDNA mutations and highlight the potential role of amino acids in improving mitochondrial disease.

Background: FINCA disease is a pediatric cerebropulmonary disease caused by variants in the NHL repeat-containing 2 (NHLRC2) gene. Neurological symptoms are among the first manifestations of FINCA disease, but the consequences of NHLRC2 deficiency in the central nervous system are currently unexplored. Methods: The orthologous mouse gene is essential for development, and its complete loss leads to early embryonic lethality. In the current study, we used CRISPR/Cas9 to generate an Nhlrc2 knockin (KI) mouse line, harboring the FINCA patient missense mutation (c.442G > T, p.Asp148Tyr). A FINCA mouse model, resembling the compound heterozygote genotype of FINCA patients, was obtained by crossing the KI and Nhlrc2 knockout mouse lines. To reveal NHLRC2-interacting proteins in developing neurons, we compared cortical neuronal precursor cells of E13.5 FINCA and wild-type mouse embryos by two-dimensional difference gel electrophoresis. Results: Despite the significant decrease in NHLRC2, the mice did not develop severe early onset multiorgan disease in either sex. We discovered 19 altered proteins in FINCA neuronal precursor cells; several of which are involved in vesicular transport pathways and actin dynamics which have been previously reported in other cell types including human to have an association with dysfunctional NHLRC2. Interestingly, isoform C2 of hnRNP C1/C2 was significantly increased in both developing neurons and the hippocampus of adult female FINCA mice, connecting NHLRC2 dysfunction with accumulation of RNA binding protein. Conclusions: We describe here the first NHLRC2-deficient mouse model to overcome embryonic lethality, enabling further studies on predisposing and causative mechanisms behind FINCA disease. Our novel findings suggest that disrupted RNA metabolism may contribute to the neurodegeneration observed in FINCA patients.

Summary 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. Conclusions: Based on our data, we propose a simplified POLG disease classification, which can be used to guide diagnostic investigations and predict disease course.

Background: Mitochondrial diabetes is primarily caused by β-cell failure, a cell type whose unique properties are important in pathogenesis. Methods: By reducing glucose, we induced energetic stress in two rodent β-cell models to assess effects on cellular function. Results: Culturing rat insulin-secreting INS-1 cells in low glucose conditions caused a rapid reduction in whole cell respiration, associated with elevated mitochondrial reactive oxygen species production, and an altered glucose-stimulated insulin secretion profile. Prolonged exposure to reduced glucose directly impaired mitochondrial function and reduced autophagy. Conclusions: Insulinoma cell lines have a very different bioenergetic profile to many other cell lines and provide a useful model of mechanisms affecting β-cell mitochondrial function.

Purpose: A new syndrome with hypotonia, intellectual disability, and eye abnormalities (HIDEA) was previously described in a large consanguineous family. Linkage analysis identified the recessive disease locus, and genome sequencing yielded three candidate genes with potentially pathogenic biallelic variants: transketolase (TKT), transmembrane prolyl 4-hydroxylase (P4HTM), and ubiquitin specific peptidase 4 (USP4). However, the causative gene remained elusive. Methods: International collaboration and exome sequencing were used to identify new patients with HIDEA and biallelic, potentially pathogenic, P4HTM variants. Segregation analysis was performed using Sanger sequencing. P4H-TM wild-type and variant constructs without the transmembrane region were overexpressed in insect cells and analyzed using sodium dodecyl sulfate–polyacrylamide gel electrophoresis and western blot. Results: Five different homozygous or compound heterozygous pathogenic P4HTM gene variants were identified in six new and six previously published patients presenting with HIDEA. Hypoventilation, obstructive and central sleep apnea, and dysautonomia were identified as novel features associated with the phenotype. Characterization of three of the P4H-TM variants demonstrated yielding insoluble protein products and, thus, loss-of-function. Conclusions: Biallelic loss-of-function P4HTM variants were shown to cause HIDEA syndrome. Our findings enable diagnosis of the condition, and highlight the importance of assessing the need for noninvasive ventilatory support in patients.

Various genetic aetiologies — including mitochondrial diseases, chromosomal disorders, and other monogenic diseases — are involved in status epilepticus (SE), a common neurologic emergency occurring in children and adults that exhibits high rates of morbidity and mortality. The exact frequency of mitochondrial SE is currently undefined. Furthermore, patients with pathogenic variants of POLG1 encoding mitochondrial DNA polymerase gamma have an increased risk of acute liver failure (ALF) induced by the common antiepileptic drug, valproic acid (VPA), which is problematic due to these patients also often experiencing drug-resistant seizures. Overall, the role of liver transplantation (LT) in VPA-ALF due to mitochondrial disease has been controversial. In the present work, large retrospective cohort studies were conducted for two main purposes: (1) to determine the genetic aetiologies of SE among Finnish paediatric and adult patients by specifically focusing on the common mitochondrial genetic defects associated with an increased risk of SE and (2) to examine whether common POLG1 p.Q1236H and p.E1143G variants are connected to liver or pancreatic toxicity upon exposure to VPA monotherapy. This thesis also describes the characteristics of VPA-ALF associated with the pathogenic POLG1 variant p.W748S and the prognosis of LT in a retrospective case series. Mitochondrial diseases explained 4.5% of SE cases in the study cohort. Patients with mitochondrial SE suffered from refractory SE significantly more often than patients with other forms of genetic or non-genetic SE. Additionally, mortality rates were higher in patients with mitochondrial or chromosomal disorders compared with the other groups, reflecting the severity of the underlying condition and the higher frequency of refractory SE. POLG1 variants p.Q1236H and p.E1143G could not be identified as risk factors for VHT or pancreatic toxicity, implying that VPA treatment might be suitable for patients harbouring t, Tiivistelmä Useita perinnöllisiä syitä, kuten mitokondriotauteja, kromosomihäiriöitä ja muita geenimuutoksia on tunnistettu status epilepticuksen (SE) eli pitkittyneen epileptisen kohtauksen taustalla. SE on yleinen neurologinen hätätilanne, johon liittyy merkittävää oheissairastavuutta ja kuolleisuutta sekä lapsilla että aikuisilla. Mitokondriotauteihin liittyvän SE:n tarkkaa esiintyvyyttä ei tiedetä. Potilailla, joilla on patogeenisia variantteja mitokondrioiden DNA-polymeraasia koodaavassa tuman POLG1-geenissä, on todettu kohonnut riski yleisesti käytetyn epilepsialääkkeen valproaatin (VPA) aiheuttaman akuutin maksavaurion kehittymiselle. Tämä tekee lääkehoidon valinnasta ongelmallista, koska näillä potilailla on usein epilepsialääkkeille resistenttejä kohtauksia. Maksansiirron merkitys akuutin maksavaurion hoidossa mitokondriotauteja sairastavilla potilailla on ollut kiistanalainen. Tutkimuksen tavoitteena oli selvittää SE:n perinnöllisiä syitä suomalaisilla lapsi- ja aikuispotilailla retrospektiivisesti kerätyssä laajassa potilasaineistossa. Tutkimuksessa keskityttiin yleisimpiin mitokondriaalisiin perinnöllisiin muutoksiin, joiden on aiemmin todettu liittyvän SE:n lisääntyneeseen riskiin. Tutkimuksen toisena päätavoitteena oli selvittää väestössä yleisten POLG1-geenin muutosten eli varianttien p.Q1236H ja p.E1143G yhteyttä maksatoksisuuteen tai haimatoksisuuteen VPA-monoterapian aikana. Lisäksi tutkittiin VPA:n aiheuttaman maksavaurion kliinisiä erityispiirteitä patogeeniseen POLG1-varianttiin p.W748S liittyen sekä mutaatiostatuksen vaikutusta maksansiirron jälkeiseen ennusteeseen. Mitokondriotaudit selittivät 4,5 % SE-tapauksista tämän väitöskirjatyön potilasaineistossa ja näillä potilailla SE pitkittyi hoitoresistentiksi tai erittäin resistentiksi merkitsevästi muita potilasryhmiä useammin. Kuolleisuus oli suurin potilailla, joilla todettiin mitokondriotauti tai kromosomihäiriö, liittyen todennäköisimmin vakavaan taustasairauteen ja hoitoresistentin SE:n suu

Undefined severe neurological and multi-organ diseases are rare as single diseases, but as a group of diseases, they are responsible for significant morbidity, impaired quality of life and mortality, emphasizing the importance of neuroscience research and its translation into novel diagnostic and treatment strategies. Molecular karyotyping and whole-exome sequencing were used to identify three novel disease-causing genes, GLE1, NHLRC2 and MYH7B, in Northem Finnish families having children with undefined progressive neuromuscular diseases. Functional studies on GLE1, NHLRC2, and MYH7B were conducted in order to understand better the impact of these mutations. The studies revealed that the cellular localization of GLE1 was impaired due to a mutation in the coding gene. The NHLRC2 is involved in many biological processes and its dysfunction has a role in the development of a novel FINCA disease and in fibrosis. Furthermore, mutations in MYH7B in the myosin family have now been connected to encephalomyopathies. Mutations in GLE1, NHLRC2 and MYH7B are involved in encephalomyopathies and neurodegeneration, stressing the important role of these genes in normal psychomotor development Analyses of these previously uncharacterized disease-causing gene mutations provided new insights into the etiologies behind these diseases, representing a relevant starting point for resolving the pathomechanisms underpinning these disorders. The newly-discovered human disease-causing genes and the novel phenotypes of childhood onset neuromuscular diseases provide the possibility for offering the relevant families preclinical diagnostics and may be beneficial in the identification of similar clinical phenotypes all around the world., Tiivistelmä Yksittäiset, määrittelemättömät, vaikeat neurologiset monielinsairaudet ovat harvinaisia. Sen sijaan neurologisten ja monielinsairauksien alle ryhmittyvät taudit ovat merkittävä syy useisiin sairauksiin, jotka heikentävät elämänlaatua ja aiheuttavat kuolleisuutta. Tästä johtuen neurotieteiden tutkimus ja saatujen tulosten soveltaminen diagnostiikassa ja hoitomuotojen kehittämisessä on hyvin tärkeää. Molekyylikaryotyypitys- ja eksomisekvensointi-menetelmiä hyödynnettiin etsittäessä taudin syytä eteneville neuromuskulaarisairauksille pohjoissuomalaisissa perheissä. Tutkimuksessa tehtiin lisäksi funktionaalisia kokeita GLE1-, NHLRC2- ja MYH7B-proteiineilla, jotta ymmärrettäisiin paremmin löydettyjen mutaatioiden vaikutus potilaiden sairauksiin. Havaittiin, että GLE1-mutaatio vaikutti proteiinin solunsisäiseen paikantumiseen. NHLRC2-proteiini puolestaan on mukana useissa solun biologisissa prosesseissa ja sen toiminnanhäiriö vaikuttaa FINCA-taudin ja fibroosin kehittymiseen. MYH7B-myosiinigeenimutaatio puolestaan yhdistettiin ensimmäistä kertaa enkefalomyopatiaan. Havaittujen tautigeenien; GLE1, NHLRC2 ja MYH7B, vaikutus enkefalomyopatioissa ja neurodegeneraatiossa kertoo, että kyseisillä geeneillä on hyvin todennäköisesti tärkeä rooli ihmisen kehityksessä. Kyseisten, aiemmin tuntemattomien sairautta-aiheuttavien geenimutaatioiden analysointi lisäsi tietoa sairauksien etiologiasta ja loi pohjan tautimekanismien ratkaisemiselle tulevaisuudessa. Työssä esitettyjä uusia sairautta-aiheuttavia geenejä ja uusia karakterisoituja lapsuusiän neuromuskulaarisairauksien ilmiasuja voidaan hyödyntää perheille tarjotun sikiödiagnostiikan lisäksi myös muiden potilaiden samankaltaisen taudinkuvan diagnosoinnissa maailmanlaajuisesti.

Novel genetic aetiologies for epileptic encephalopathies and movement disorders have been discovered by using next-generation sequencing methods. The phenotypic and genotypic variability in these conditions is very wide. The aim of this study was to discover novel genetic causes and phenotypes of childhood-onset drug-resistant epilepsy and epileptic or developmental encephalopathies that occur separately or together with movement disorders, and familial movement disorders. Furthermore, the use of whole-exome sequencing (WES) as a diagnostic tool in clinical practice was evaluated. Altogether, 12 children with undefined aetiology, who fulfilled the inclusion criteria, were included in the study. GABRG2 gene was identified as a genetic cause of epileptic encephalopathies. Novel GABRG2-associated phenotypes included progressive neurodegeneration, epilepsy in infancy with migrating focal seizures, and autism spectrum disorder. New pathogenic variants, GABRG2 p.P282T and p.S306F, were discovered. The pathogenic NACC1 variant caused focal epilepsy, developmental disability, bilateral cataracts, and dysautonomia. The novel phenotype associated with the NACC1 p.R298W variant included hyperkinetic movement disorder. SAMD9L was found to be the genetic cause for the familial movement disorder. The phenotype associated with the novel SAMD9L p.I891T variant was very variable. Neuroradiological findings included cerebellar atrophy and periventricular white matter changes. After publication of these results, SAMD9L was reported to be one of the most common genetic aetiologies of childhood bone marrow failure and myelodysplastic syndrome. The pathogenic homozygous MTR variant was found to cause early-onset epileptic encephalopathy that occurred together with movement disorder and haematological disturbances. Drug resistant seizures responded to cofactor and vitamin treatments. Whole-exome sequencing for 10 patients with drug-resistant epilepsy or epileptic or developmental, Tiivistelmä Uusien sekvensointimenetelmien käyttöönotto on mahdollistanut epileptisten enkefalopatioiden ja liikehäiriöiden uusien geneettisten syiden löytymisen. Näissä sairausryhmissä geenien ja ilmiasujen vaihtelevuus on suurta. Tutkimuksen tarkoituksena oli löytää uusia geneettisiä syitä ja ilmiasuja lapsuusiällä alkavissa vaikeahoitoisissa epilepsioissa ja epileptisissä tai kehityksellisissä joko itsenäisesti tai yhdessä liikehäiriön kanssa esiintyvissä enkefalopatioissa sekä perheittäin esiintyvissä liikehäiriöissä. Lisäksi selvitettiin eksomisekvensoinnin käyttökelpoisuutta kliinisessä diagnostiikassa näiden potilasryhmien kohdalla. Tutkimukseen osallistui yhteensä 12 sisäänottokriteerit täyttävää lasta, joiden sairauden syy oli jäänyt tuntemattomaksi. GABRG2-geenin mutaatiot aiheuttivat epileptisiä enkefalopatioita, joiden uutena ilmiasuna oli etenevä taudinkuva, johon liittyivät aivojen rappeutuminen, migroiva imeväisiän paikallisalkuinen epilepsia sekä autismikirjon häiriö. Tutkimuksessa löydettiin uusia GABRG2-mutaatioita: p.P282T ja p.S306F. NACC1-geenin mutaatio aiheutti epilepsian, kehitysvammaisuuden, molemminpuolisen kaihin ja autonomisen hermoston toiminnan häiriön. Hyperkineettinen liikehäiriö oli uusi NACC1 p.R298W -mutaatioon liittyvä ilmiasu. SAMD9L-geenin mutaatio aiheutti perheessä esiintyvän liikehäiriön. Neurologinen ja hematologinen ilmiasu olivat hyvin vaihtelevia. Aivojen kuvantamislöydöksiin sisältyi pikkuaivojen rappeutumista ja valkoisen aivoaineen muutoksia aivokammioiden ympärillä. Näiden tutkimustulosten julkaisemisen jälkeen SAMD9L-geenin mutaatioiden on todettu olevan yksi yleisimmistä perinnöllisistä luuytimen vajaatoiminnan ja myelodysplasian syistä. Homotsygoottinen MTR-geenin mutaatio aiheutti varhain alkaneen epileptisen enkefalopatian, liikehäiriön ja hematologisen häiriön. Kofaktori- ja vitamiini hoidot vähensivät epileptisiä kohtauksia, joihin tavanomainen lääkitys ei tehonnut. Geneettiset syyt ja ilmiasut ovat epileptisis

Childhood acute lymphoblastic leukemia (ALL) is the most common cancer in children. The overall survival rate has reached to 90%. However, ALL still presents a significant disease burden and is a major cause for deaths in children. Recently, both inherited germline variants related to ALL susceptibility and somatic genetic variants forming novel subgroups of ALL have been discovered. In this thesis two families with familial ALL were studied. Constitutional heterozygous microdeletion at chromosome 7p12.1p13, including IKZF1, was discovered in the first family with intellectual impairment, overgrowth, and susceptibility to childhood ALL. In the second family, constitutional chromosome translocation was revealed in two individuals with childhood ALL and, subsequently, in seven unaffected family members. The balanced reciprocal translocation t(12;14)(p13.2;q23.1) resulted in breakpoints on two genes; ETV6 on chromosome 12 and RTN1 on chromosome 14. Only a few familial and sporadic ALL cases with germline variants in either IKZF1 or ETV6 have been published, thus supporting the significant role of these constitutional variants in childhood ALL predisposition. Inherited bone marrow failure syndromes (IBMFS) may predispose to childhood leukemia, including ALL. Two unrelated patients were diagnosed with bone marrow failure without the symptoms of classical IBMFS. Neither patient had any signs of developmental delay or congenital anomalies. Exome sequencing revealed identical c.1457del(p.(Ile486fs)) mutation on the ERCC6L2 gene in both patients. A few patients with IBMFS and ERCC6L2 variants have been described in previous studies. Some of them also had congenital craniofacial anomalies and developmental delay that were not detected in the patients in this thesis. The ALL cohort study on genetic variation of mitochondrial DNA (mtDNA) included 36 children. Metabolic change where malignant cells uncouple energy production from oxidative phosphorylation (OXPHOS) is on, Tiivistelmä Akuutti lymfoblastileukemia (ALL) on lasten yleisin syöpä. Vaikka nykyisin noin 90 prosenttia paranee, ALL aiheuttaa huomattavan paljon sairastavuutta ja on merkittävä lasten kuolinsyy. Vastikään on löydetty perinnöllisiä geneettisiä muutoksia, jotka altistavat lapsuusiän ALL:lle. Tutkimuksen kohteena oli kaksi perhettä, joissa vähintään kaksi lasta on sairastunut ALL:aan. Ensimmäisessä perheessä havaittiin lapsuusiän ALL:aan sairastuneilla kehityshäiriöisillä sisaruksilla äidiltä periytyvä heterotsygoottinen deleetio kromosomissa 7p12.1p13, jossa sijaitsee IKZF1-geeni. Toisessa perheessä perinnöllinen kahden kromosomin translokaatio todettiin kahdella lapsuusiän ALL:aan sairastuneella sekä seitsemällä perheenjäsenellä. Balansoitu translokaatio t(12;14)(p13.2;q23.1) aiheuttaa katkaisukohdan ETV6-geeniin kromosomissa 12 ja RTN1-geeniin kromosomissa 14. Tähän mennessä on julkaistu vain muutamia tutkimuksia potilaista, joilla on ollut perinnöllinen muutos joko IKZF1- tai ETV6-geenissä. Näillä geeneillä oletetaan olevan tärkeä merkitys perinnöllisessä alttiudessa sairastua lapsuusiän ALL:aan. Perinnölliset luuytimen toimintahäiriöt voivat altistaa leukemialle, kuten ALL:lle. Kahdella lapsella todettiin luuytimen toimintahäiriö, mutta ei muita oireita, jotka voisivat liittyä tyypillisiin perinnöllisiin luuytimen toimintahäiriöihin. Eksomisekvensoinnissa todettiin identtinen, homotsygoottinen mutaatio c.1457del(p.(Ile486fs)) ERCC6L2-geenissä. Kirjallisuuslähteiden mukaan vain muutamalla potilaalla on todettu ERCC6L2-geenin muutoksesta johtuva luuytimen toimintahäiriö. Osalla heistä on ollut synnynnäisiä kallon ja kasvojen anomalioita sekä kehityshäiriö, jollaisia tähän tutkimukseen osallistuneilla potilailla ei todettu. Potilaskohorttitutkimuksessa tutkittiin mitokondriaalisen DNA:n (mtDNA) muutoksia ALL:aan sairastuneilla lapsilla. Syöpäsolut eivät hyödynnä mitokondrion elektroninsiirtoketjua energian tuotantoon, ja tämä aineenvaihdunnan muutos on tunnustettu

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Background: Mitochondrial cytochrome c oxidase 2, MT-CO2, encodes one of the three subunits, which form the catalytic core of cytochrome c oxidase (COX), complex IV. Mutations in MT-CO2 are rare and the associated phenotypes are variable including nonsyndromic and syndromic forms of mitochondrial diseases. Case presentation: We describe a 30-year-old man with cognitive decline, epilepsy, psychosis, exercise intolerance, sensorineural hearing impairment, retinitis pigmentosa, cataract and lactic acidosis. COX-deficient fibers and ragged red fibers were abundant in the muscle. Sequencing of mitochondrial DNA (mtDNA) revealed a novel frameshift mutation m.8156delG that was predicted to cause altered C-terminal amino acid sequence and to lead to truncation of the COX subunit 2. The deletion was heteroplasmic being present in 26% of the mtDNA in blood, 33% in buccal mucosa and 95% in muscle. Deletion heteroplasmy correlated with COX-deficiency in muscle histochemistry. The mother and the siblings of the proband did not harbor the deletion. Conclusions: The clinical features and muscle histology of the proband suggested a mitochondrial disorder. The m.8156delG deletion is a new addition to the short list of pathogenic mutations in the mtDNA-encoded subunits of COX. This case illustrates the importance of mtDNA sequence analysis in patients with an evident mitochondrial disorder.

Mitochondrial ribosomal 12S subunit gene (MTRNR1) is a hot spot for hearing loss mutations. Mutations such as m.1555A>G, m.1494C>T and m.1095C>T, cause sensitivity to aminoglycosides. Aminoglycoside treatment induces permanent hearing loss or deafness in the carriers and should therefore be avoided. The prevalence of these sensitivity mutations varies in different countries and populations. Over 90% of preterm children need aminoglycoside treatment during their first weeks of life. Infants who carry a mitochondrial sensitivity mutation can develop a life-long sensorineural hearing impairment as a side-effect of aminoglycoside treatment. Total of 813 Finnish preterm (born G, m.1494T>C and m.1095C>T mutations. The population prevalence of m.1555A>G was determined to be 0.12% in Finland. M.1494C>T and m.1095C>T mutations were absent. Out of the 813 infants, a term-born infant was found to harbor m.1555A>G at 81% heteroplasmy, while his mother’s heteroplasmy was 68%. Both had normal hearing and had not received aminoglycosides. Mothers with a family history of hearing loss who are at risk of preterm labor would benefit from antenatal genotyping of m.1555A>G mutation. The prevalence of m.1555A>G in Finns was close to other European countries. M.1494C>T and m.1095C>T mutations either do not occur in the Finnish population or they are very rare. This study highlights the importance of population-specific genotyping of MTRNR1 aminoglycoside sensitivity mutations, especially in countries with liberal aminoglycoside use.