Abstract 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.

Mitochondrial disorders are considered to be the most common cause of metabolic abnormalities in the paediatric neurology population (Zeviani et al., 1996). These authors reported that the phenotypes observed in 25-30% of the paediatric patients in their neurology clinics were due to a mitochondrial aetiology. The genetic aetiology in an equivalently affected paediatric population in South Africa is currently unknown. This study investigated the possibility that reported mutations could account for the mitochondrial phenotypes observed in the South African population. It focussed on the most frequent paediatric mitochondrial disorders namely: Leigh Syndrome (LS), mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), and myoclonic epilepsy and ragged red muscle fibres (MERRF). A clinically well characterised group of 25 patients with mitochondrial disorders was included in this study. The molecular analysis of the mitochondrial genome was initially based on a restriction fragment length polymorphism (RFLP) screening strategy for the ten most common mitochondrial DNA (mtDNA) mutations associated with the above¬mentioned three disorders. However, during the study the mutation analysis strategy was modified to a sequencing strategy as this provided more information than the RFLP approach. The modified sequencing strategy extended the study to incorporate fifteen additional mtDNA mutations, associated with other mitochondrial disorders, and individuals included in the study were thus investigated for the presence of 25 mtDNA mutations. Moreover, the modified strategy provided additional information of the regions encompassing the reported mutations. A single patient was observed to harbour the reported A3243G MELAS mutation. This mutation was noted to be heteroplasmic in the proband and two of her maternal relatives. None of the other 24 reported mutations were observed in this patient population. One novel mtDNA alteration in the tRNALeu(UUR) gene was observed in a single patient, although the pathogenicity of this mutation remains to be investigated. Novel and reported polymorph isms, some of which are associated with specific haplogroups, were also observed when comparing sequencing data against the Cambridge reference sequence. The data generated during this study contributed towards the understanding of the uniqueness of the South African population in the global context. This was apparent from the fact that only one of the reported mutations was observed in our patient population who were clinically well characterised and displayed phenotypes similar to those reported internationally. Results form this study underlined the complexity of mitochondrial disorders and argues in favour of whole mitochondrial genome sequence information to be used for diagnostic purposes. Moreover, the results confer with the hypothesis that novel mitochondrial mutations may account for the majority of mitochondrial phenotypes observed in the South African population. / Dissertation (MSc (Human Genetics))--University of Pretoria, 2007. / Genetics / unrestricted

Mitochondrial diseases are caused by gene mutations in either mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) and they are among one of the most common forms of inherited disorders. It is estimated that 1 out of every 5000 individuals will develop a mitochondrial disease in their lifetime. Due to the crucial and widespread functionality of mitochondria in human cells, prolonged diseases of the mitochondria affect cells of the brain, heart, liver, muscles and kidneys and can lead to multi-organ failure in some patients. Inherited or acquired mitochondrial diseases can present at any stage of life, affecting both children and adults. Since its discovery, the mitochondrial genome has been analyzed and sequenced with increasing ease and this process has helped recognize various mitochondrial disorders as the root of genetic diseases. This paper will explore the unique properties of the mitochondrion and its genome, examine the relationship between mtDNA and some common myopathies such as Leigh syndrome (LS) or maternally inherited Leigh syndrome (MILS), mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) in order to explore commonalities and differences in their inheritance patterns and their effect on mitochondrial function. Although studies have shown that these conditions generally affect the process of oxidative phosphorylation in mitochondria, because of the wide variety of presentations of this disease, further research is needed to understand the different etiologies, as well as to explore novel therapies to treat them.