Sistemes de neurotransmissió en trastorns neuropediàtrics

[cat] La neurotransmissió és el procés funcional bàsic de comunicació neuronal, i té lloc a través de l’alliberament dels neurotransmissors a l’espai sinàptic. Els defectes clàssics monogènics dels neurotransmissors inclouen els trastorns del metabolisme, degradació i transport de les monoamines (o el seu cofactor la tetrahidrobiopterina –BH4-), el GABA, la glicina i la serina, majoritàriament. Recentment també s’inclouen altres neurotransmissors com l’acetilcolina o l’ATP, i els trastorns astrocitaris o dels gliotransmissors. Les manifestacions clíniques es troben dins de l’espectre de les sinaptopaties, i es solen caracteritzar per discapacitat intel·lectual, epilèpsia, trastorns del moviment o símptomes neuropsiquiàtrics. Poden debutar en qualsevol edat de la vida, però característicament solen ser malalties neuropediàtriques que repercuteixen en el neurodesenvolupament, i que per tant, debuten en els primers anys de la vida. El treball que es presenta en aquesta tesi fa referència a: A) els defectes monogènics clàssics dels neurotransmissors, i B) els defectes de la fisologia sinàptica. A. En el primer treball es realitza una presentació del primer grup internacional dedicat a l’estudi de les malalties dels neurotransmissors, l’International Working Group on Neurotransmitter Related Disorders (iNTD), s’actualitza quina ha estat la seva activitat aquests darrers anys i el resultat principal en forma del primer registre internacional de pacients. En el següent treball, es presenta la segona guia de pràctica clínica d’un grup de defectes dels neurotransmissors: els defectes síntesi o reciclatge de la tetrahidrobiopterina (BH4). B. Els defectes de la fisiologia sinàptica implicarien totes aquelles malalties responsables d’alterar el procés de neurotransmissió i la biodisponibilitat/homeòstasi del neurotransmissor a l’espai sinàptic. En el següent treball es proposa una nova categoria de malaltia basada en el cicle biològic de la vesícula sinàptica, centrades en el terminal presinàptic de la neurona. Inclouria defectes en la formació de novo de la vesícula sinàptica al soma neuronal, el transport, maduració, exocitosi i reciclatge. Es proposa una categorització en quatre grups fenotípics: encefalopatia epilèptica, trastorns del moviment, discapacitat intel·lectual sindròmica i no-sindròmica, i trastorns neuromusculars. A propòsit de les malalties de la vesícula sinàptica, el següent treball presenta diferents pacients amb mutació en el gen DNAJC6, que codifica per l’auxilina 1 i participa en l’endocitosi de la vesícula sinàptica. El fenotip d’aquests pacients és en forma de discapacitat intel·lectual i distonia-parkinsonisme juvenil progressiva. S’estudia el líquid cefalorraquidi i fibroblasts, i s’analitzen l’auxilina 1, la ciclina-G associada a quinasa (GAK), i diferents proteïnes sinàptiques. Es conclou que hi ha una especial vulnerabiliat de l’homeòstasi dopaminèrgica, amb un augment probablement compensatori de la GAK. El següent treball descriu una pacient amb mutació en el gen DLP1, que també implica la neurotransmissió dopaminèrgica, tot codificant una proteïna que participa de l’endocitosi de la vesícula sinàptica i la fissió mitocondrial. El darrer treball amplia els defectes de la neurotransmissió centrant-se en el GABA. Es presenta una cohort de 85 pacients amb diferents malalties neuropediàtriques, i s’analitza la fracció de GABA lliure i monoamines en líquid cefalorraquidi. Es reporta una especial vulnerabilitat de la neurotransmissió GABAèrgica en tota la cohort en fins a un 44% dels casos (davant del 20% de defectes de les monoamines), i especialment en els errors congènits del metabolisme. Finalment, els annexos presenten la feina realitzada al llarg de tots aquests anys i amb la difusió d’aquests grups de malalties a través de les reunions amb famílies i amb professionals, i de la creació d’una pàgina web. D’aquesta manera, s’aconsegueix tancar el cercle que va des del pacient, a l’estudi de la seva malaltia de base i el defecte molecular, i el retorn al pacient a través del contacte estret amb les associacions de famílies i la comunitat científica.[eng] Neurotrasmission is the basic functional process devoted to neuronal communication, that takes place in the synaptic cleft. Classical neurotransmitter defects include disorders of the synthesis, metabolism or transport of monoamines (mainly dopamine and serotonin, but also adrenalin and noradrenalin), aminoacids (such as GABA and glutamate, but also serine and glycine, among others), or other molecules identified in the last decades as having a role in neurotransmission (i.e. ATP, lactate or acetylcholine). Main clinical symptoms manifest in the form of global developmental delay and intellectual disability, movement disorders, neuropsychiatric symptoms and epilepsy, all in the spectrum of synaptopathies. The current thesis encompasses: A) 2 publications related to the classical neurotransmitter defects; and B) 4 publications related to disorders of the synaptic physiology and neurotransmission (that influence the process of neurotransmission, its homeostasis and the biodisponibility of the neurotransmitter in the synaptic cleft, not directly related to synthesis, transport or metabolism defects), all of them focused in the presynaptic terminal. A. The former include: 1) the first publication of the International Working Group for Neurotransmitter Related Disorders (iNTD: http://intd-online.org/) and the initiation of the international registry for patients with neurotransmitter defects, as well as 2) the first clinical guidelines related to tetrahydrobiopterin synthesis and regeneration disorders. B. The latter include: 1) a proposal for a new category of presynaptic disorder, focused on the synaptic vesicle cycle; 2) a cohort of patients carrying DNAJC6 mutations, that encode the protein auxilin 1 (implicated in the endocytosis of the synaptic vesicle), and the secondary dopaminergic disruption in these patients, studied in cerebrospinal fluid (CSF) and fibroblasts; 3) a patient with DLP1 mutation, that encodes dynamin-like protein 1, implicated in the mitochondrial and peroxisomal fission, as well as the endocytosis of the synaptic vesicle; and finally, 4) a cohort of 85 patients with different neuropediatric disorders, in whom free GABA levels were studied in CSF, revealing a special vulnerability of GABA levels compared to monoamine levels, especially in the group of inborn errors of metabolism. Finally, the annexes of the thesis reveal the dissemination of the work among the scientific communities and the empowering of families

Fabry Disease and Central Nervous System Involvement : From Big to Small, from Brain to Synapse

Fabry disease (FD) is an X-linked lysosomal storage disorder (LSD) secondary to mutations in the GLA gene that causes dysfunctional activity of lysosomal hydrolase α-galactosidase A and results in the accumulation of globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3). The endothelial accumulation of these substrates results in injury to multiple organs, mainly the kidney, heart, brain and peripheral nervous system. The literature on FD and central nervous system involvement is scarce when focusing on alterations beyond cerebrovascular disease and is nearly absent in regard to synaptic dysfunction. In spite of that, reports have provided evidence for the CNS' clinical implications in FD, including Parkinson's disease, neuropsychiatric disorders and executive dysfunction. We aim to review these topics based on the current available scientific literature

Unraveling Molecular Pathways Altered in MeCP2-Related Syndromes, in the Search for New Potential Avenues for Therapy

Methyl-CpG-binding protein 2 (MeCP2) is an X-linked epigenetic modulator whose dosage is critical for neural development and function. Loss-of-function mutations in MECP2 cause Rett Syndrome (RTT, OMIM #312750) while duplications in the Xq28 locus containing MECP2 and Interleukin-1 receptor-associated kinase 1 (IRAK1) cause MECP2 duplication syndrome (MDS, OMIM #300260). Both are rare neurodevelopmental disorders that share clinical symptoms, including intellectual disability, loss of speech, hand stereotypies, vasomotor deficits and seizures. The main objective of this exploratory study is to identify novel signaling pathways and potential quantitative biomarkers that could aid early diagnosis and/or the monitoring of disease progression in clinical trials. We analyzed by RT-PCR gene expression in whole blood and microRNA (miRNA) expression in plasma, in a cohort of 20 females with Rett syndrome, 2 males with MECP2 duplication syndrome and 28 healthy controls, and correlated RNA expression with disease and clinical parameters. We have identified a set of potential biomarker panels for RTT diagnostic and disease stratification of patients with microcephaly and vasomotor deficits. Our study sets the basis for larger studies leading to the identification of specific miRNA signatures for early RTT detection, stratification, disease progression and segregation from other neurodevelopmental disorders. Nevertheless, these data will require verification and validation in further studies with larger sample size including a whole range of ages

The International Working Group on Neurotransmitter related Disorders (iNTD): A worldwide research project focused on primary and secondary neurotransmitter disorders

INTRODUCTION: Neurotransmitters are chemical messengers that enable communication between the neurons in the synaptic cleft. Inborn errors of neurotransmitter biosynthesis, breakdown and transport are a group of very rare neurometabolic diseases resulting in neurological impairment at any age from newborn to adulthood. METHODS AND RESULTS: The International Working Group on Neurotransmitter related Disorders (iNTD) is the first international network focusing on the study of primary and secondary neurotransmitter disorders. It was founded with the aim to foster exchange and improve knowledge in the field of these rare diseases. The newly established iNTD patient registry for neurotransmitter related diseases collects longitudinal data on the natural disease course, approach to diagnosis, therapeutic strategies, and quality of life of affected patients. The registry forms the evidence base for the development of consensus guidelines for patients with neurotransmitter related disorders. CONCLUSION: The iNTD network and registry will improve knowledge and strengthen research capacities in the field of inborn neurotransmitter disorders. The evidence-based guidelines will facilitate standardized diagnostic procedures and treatment approaches

Discovery of biomarker panels for neural dysfunction in inborn errors of amino acid metabolism.

Patients with inborn errors of amino acid metabolism frequently show neuropsychiatric symptoms despite accurate metabolic control. This study aimed to gain insight into the underlying mechanisms of neural dysfunction. Here we analyzed the expression of brain-derived neurotrophic factor (BDNF) and 10 genes required for correct brain functioning in plasma and blood of patients with Urea Cycle Disorders (UCD), Maple Syrup Urine Disease (MSUD) and controls. Receiver-operating characteristic (ROC) analysis was used to evaluate sensitivity and specificity of potential biomarkers. CACNA2D2 (α2δ2 subunit of voltage-gated calcium channels) and MECP2 (methyl-CpG binding protein 2) mRNA and protein showed an excellent neural function biomarker signature (AUC ≥ 0,925) for recognition of MSUD. THBS3 (thrombospondin 3) mRNA and AABA gave a very good biomarker signature (AUC 0,911) for executive-attention deficits. THBS3, LIN28A mRNA, and alanine showed a perfect biomarker signature (AUC 1) for behavioral and mood disorders. Finally, a panel of BDNF protein and at least two large neural AAs showed a perfect biomarker signature (AUC 1) for recognition of psychomotor delay, pointing to excessive protein restriction as central causative of psychomotor delay. To conclude, our study has identified promising biomarker panels for neural function evaluation, providing a base for future studies with larger samples

Brain MR patterns in inherited disorders of monoamine neurotransmitters: An analysis of 70 patients

Inherited monoamine neurotransmitter disorders (iMNDs) are rare disorders with clinical manifestations ranging from mild infantile hypotonia, movement disorders to early infantile severe encephalopathy. Neuroimaging has been reported as non-specific. We systematically analysed brain MRIs in order to characterize and better understand neuroimaging changes and to re-evaluate the diagnostic role of brain MRI in iMNDs

Assessment of intellectual impairment, health-related quality of life, and behavioral phenotype in patients with neurotransmitter related disorders: Data from the iNTD registry

Inherited disorders of neurotransmitter metabolism are a group of rare diseases, which are caused by impaired synthesis, transport, or degradation of neurotransmitters or cofactors and result in various degrees of delayed or impaired psychomotor development. To assess the effect of neurotransmitter deficiencies on intelligence, quality of life, and behavior, the data of 148 patients in the registry of the International Working Group on Neurotransmitter Related Disorders (iNTD) was evaluated using results from standardized age-adjusted tests and questionnaires. Patients with a primary disorder of monoamine metabolism had lower IQ scores (mean IQ 58, range 40-100) within the range of cognitive impairment (<70) compared to patients with a BH4 deficiency (mean IQ 84, range 40-129). Short attention span and distractibility were most frequently mentioned by parents, while patients reported most frequently anxiety and distractibility when asked for behavioral traits. In individuals with succinic semialdehyde dehydrogenase deficiency, self-stimulatory behaviors were commonly reported by parents, whereas in patients with dopamine transporter deficiency, DNAJC12 deficiency, and monoamine oxidase A deficiency, self-injurious or mutilating behaviors have commonly been observed. Phobic fears were increased in patients with 6-pyruvoyltetrahydropterin synthase deficiency, while individuals with sepiapterin reductase deficiency frequently experienced communication and sleep difficulties. Patients with BH4 deficiencies achieved significantly higher quality of life as compared to other groups. This analysis of the iNTD registry data highlights: (a) difference in IQ and subdomains of quality of life between BH4 deficiencies and primary neurotransmitter-related disorders and (b) previously underreported behavioral traits.Dietmar Hopp Stiftung (DE); Medical Faculty of the University of Heidelberg

Severity-adjusted evaluation of liver transplantation on health outcomes in urea cycle disorders

Purpose: Liver transplantation (LTx) is performed in individuals with urea cycle disorders when medical management (MM) insufficiently prevents the occurrence of hyperammonemic events. However, there is a paucity of systematic analyses on the effects of LTx on health-related outcome parameters compared to individuals with comparable severity who are medically managed. Methods: We investigated the effects of LTx and MM on validated health-related outcome parameters, including the metabolic disease course, linear growth, and neurocognitive outcomes. Individuals were stratified into “severe” and “attenuated” categories based on the genotype-specific and validated in vitro enzyme activity. Results: LTx enabled metabolic stability by prevention of further hyperammonemic events after transplantation and was associated with a more favorable growth outcome compared with individuals remaining under MM. However, neurocognitive outcome in individuals with LTx did not differ from the medically managed counterparts as reflected by the frequency of motor abnormality and cognitive standard deviation score at last observation. Conclusion: Whereas LTx enabled metabolic stability without further need of protein restriction or nitrogen-scavenging therapy and was associated with a more favorable growth outcome, LTx—as currently performed—was not associated with improved neurocognitive outcomes compared with long-term MM in the investigated urea cycle disorders.</p