Aspectos neurobiológicos del Síndrome de Rett

El Síndrome de Rett es un trastorno monogénico ligado al cromosoma X, de carácter progresivo que afecta el neurodesarrollo principalmente de niñas durante las primeras etapas del ciclo vital. Su etiología se debe principalmente a las mutaciones de cambio de nucleótido único con pérdida de función del gen MECP2. Este gen codifica para la proteína del mismo nombre cuya principal función es actuar como un represor global de la transcripción mediante el reconocimiento de zonas metiladas de islas CpG y el reclutamiento de factores correpresores que modulan la expresión génica desacetilando histonas. Dentro de las principales alteraciones estructurales asociadas al síndrome se encuentran una morfología neuronal atípica con tamaño del soma neuronal y número de espinas dendríticas reducido, además de alteraciones neuroquímicas sobre todo en la señalización GABAérgica llevando a una desregulación entre señales excitatorias e inhibitorias, causando epilepsia. También se han descrito una serie de alteraciones metabólicas, oxidativas e inflamatorias. El tratamiento hasta ahora se ha enfocado más en buscar un alivio sintomático para las manifestaciones del síndrome pero se ha desarrollado recientemente terapia génica con el objetivo de tratar desde sus bases neurogenéticas la patología y evitar así el desarrollo alterado durante la niñez.

Rett Syndrome is a monogenic disorder linked to the X chromosome, of a progressive nature that affects neurodevelopment mainly in girls during the first stages of the life cycle. Its etiology is mainly due to loss-of-function single nucleotide change mutations of the MECP2 gene. This gene codes for the protein of the same name whose main function is to act as a global repressor of transcription through the recognition of methylated areas of CpG islands and the recruitment of corepressor factors that modulate gene expression by deacetylating histones. Among the main structural alterations associated with the syndrome are an atypical neuronal morphology with a size of the neuronal soma and a reduced number of dendritic spines, in addition to neurochemical alterations, especially in the GABAergic signal, leading to dysregulation between excitatory and inhibitory signals, causing epilepsy. A series of metabolic, oxidative, and inflammatory disorders have also been described. Until now, treatment has focused more on seeking symptomatic relief for the manifestations of the syndrome, but gene therapy has recently been developed with the aim of treating the pathology from its neurogenetic bases and thus avoiding altered development during childhood.

A recurrent de novo mutation in ATP1A3 gene in a Mexican patient with alternating hemiplegia of childhood detected by massively parallel sequencing / Mutación de novo recurrente en el gen ATP1A3 en una paciente mexicana con hemiplejia alternante de la infancia detectada por secuenciación masiva en paralelo

Abstract Background: Pediatric movement disorders represent a diagnostic challenge for pediatricians and pediatric neurologists due to their high clinical heterogeneity and shared common features. Therefore, specific diagnoses require different approaches including metabolic work-up and specific tests for frequent genetic conditions. Alternating hemiplegia of childhood (AHC) is an ultra-rare pediatric movement disorder, characterized by paroxysmal alternating hemiplegia, dystonia, and seizure-like episodes that can be misleading during the evaluation of a child with a movement disorder. Case report: We present a Mexican patient with abnormal movements referred to the Genetics clinic because of hyperammonemia and a possible organic acidemia. Our assessment did not find clinical features compatible with an inborn error of metabolism. A massively parallel sequencing approach with targeted panel sequencing was used to get a final diagnosis. A missense variant c.2839G>A (p.Gly947Arg) located at exon 21 of ATP1A3 gene was demonstrated. This variant (rs398122887) has been previously reported as de novo producing alternating hemiplegia of childhood (AHC). Conclusions: AHC is an ultra-rare syndrome presented as a movement disorder with seizure-like episodes and a unique facial phenotype. Clinicians should be aware of this combination in order to diagnose this condition in a timely manner. Massive parallel sequencing panels are emerging as the best approach to diagnose rare movement disorders and simultaneously rule out metabolic disorders and common epileptic syndromes.

Resumen Introducción: Los trastornos pediátricos del movimiento representan un reto diagnóstico para pediatras y neurólogos pediatras debido a su gran heterogeneidad clínica y características comunes compartidas. Por lo tanto, los diagnósticos específicos requieren de diferentes abordajes que incluyen la búsqueda de desórdenes metabólicos y pruebas específicas para condiciones genéticas frecuentes. La hemiplejia alternante de la infancia (AHC) es un trastorno pediátrico del movimiento poco común, caracterizado por cuadros paroxísticos de hemiplejia alternante, distonía y episodios semejantes a crisis epilépticas, que pueden resultar desorientadores durante el abordaje diagnóstico de un infante con un desorden del movimiento. Caso clínico: Presentamos una paciente mexicana con movimientos anormales referida a la Clínica de Genética por hiperamonemia y una posible acidemia orgánica. Nuestro abordaje no identificó características clínicas compatibles con un error innato del metabolismo. Se utilizó un abordaje basado en secuenciación masiva en paralelo para obtener un diagnóstico final. Se demostró una variante de sentido equivocado c.2839G>A (p.Gly947Arg) localizada en el exón 21 del gen ATP1A3. Esta variante (rs398122887) ha sido previamente reportada como de novo, ocasionando AHC. Conclusiones: La AHC es un síndrome excepcionalmente raro que se presenta con un trastorno del movimiento con cuadros semejantes a crisis epilépticas y un fenotipo facial particular. Los médicos deben ser conscientes de esta combinación con el fin de diagnosticar oportunamente esta condición. Los paneles de secuenciación masiva están emergiendo como el mejor abordaje para diagnosticar trastornos del movimiento raros y, simultáneamente, descartar trastornos metabólicos y síndromes epilépticos comunes.

Recent Advances in the Genetic Dissection of Neural Circuits in Drosophila / 神经科学通报·英文版

Nervous systems endow animals with cognition and behavior. To understand how nervous systems control behavior, neural circuits mediating distinct functions need to be identified and characterized. With superior genetic manipulability, Drosophila is a model organism at the leading edge of neural circuit analysis. We briefly introduce the state-of-the-art genetic tools that permit precise labeling of neurons and their interconnectivity and investigating what is happening in the brain of a behaving animal and manipulating neurons to determine how behaviors are affected. Brain-wide wiring diagrams, created by light and electron microscopy, bring neural circuit analysis to a new level and scale. Studies enabled by these tools advances our understanding of the nervous system in relation to cognition and behavior.

Clinical and genetic basis of familial amyotrophic lateral sclerosis / Bases clínicas e genéticas da esclerose lateral amiotrófica familiar

Amyotrophic lateral sclerosis represents the most common neurodegenerative disease leading to upper and lower motor neuron compromise. Although the vast majority of cases are sporadic, substantial gain has been observed in the knowledge of the genetic forms of the disease, especially of familial forms. There is a direct correlation between the profile of the mutated genes in sporadic and familial forms, highlighting the main role ofC9orf72 gene in the clinical forms associated with frontotemporal dementia spectrum. The different genes related to familial and sporadic forms represent an important advance on the pathophysiology of the disease and genetic therapeutic perspectives, such as antisense therapy. The objective of this review is to signal and summarize clinical and genetic data related to familial forms of amyotrophic lateral sclerosis.

A esclerose lateral amiotrófica representa a forma mais comum de doença neurodegenerativa com comprometimento do neurônio motor superior e inferior. Embora a maioria dos casos seja esporádica, ganho impressionante referente ao conhecimento das formas genética da doença foi observado, em especial das formas familiares. Há uma correlação direta entre o perfil de genes mutados nas formas familiares e esporádicas, destacando-se o papel principal do geneC9orf72 nas formas clínicas associadas com espectro da demência frontotemporal. Os diferentes genes relacionados às formas familiares e esporádicas representam um importante avanço na fisiopatologia da doença e perespectivas terapêuticas genéticas, como a terapia antisense. O objetivo desta revisão é apontar e resumir os principais dados clínicos e genéticos relacionados às formas familiares da esclerose lateral amiotrófica.

Análisis molecular de familias uruguayas con Enfermedad de Huntington / Molecular analysis of the Uruguayan families with Huntington’s Disease

Introducción: La Enfermedad de Huntington (EH) es un trastorno neurodegenerativo; autosómico dominante, con expresividad variable y penetrancia completa. La prevalencia estimada es entre 1-4 cada 100.000 habitantes. Es causada por expansión de tripletes CAG en el exón 1 del gen IT-15 que conduce a la síntesis de una proteína con una región de poliglutaminas expandidas que forman agregados en el núcleo celular induciendo a la apoptosis. Los alelos normales presentan un número menor a 26 tripletes CAG, y aquellos con más de 40 conducirán siempre a la enfermedad. Alelos de entre 26 a 36 repetidos se consideran normales “mutables” y de 36 a 39 repetidos generan un riesgo aumentado de desarrollar la enfermedad. Objetivo: Poner a punto el diagnóstico molecular en una población uruguaya, mediante la determinación del tamaño exacto de la mutación en personas afectadas o con sospecha clínica de EH, mediante el uso de técnicas de biología molecular. Métodos: Pacientes de la Policlínica de Enfermedad de Parkinson y Movimientos Anormales del Hospital de Clínicas. La determinación del número de repetidos se realizó mediante técnicas de amplificación del ADN por PCR y posterior análisis en geles de poliacrilamida y secuenciación. Resultados: Realizamos el diagnóstico molecular de 16 pacientes, 15 con un diagnóstico clínico previo, y uno asintomático. Se descartó el diagnóstico de EH en otros dos individuos analizados. Conclusiones: Hemos logrado la puesta a punto del estudio molecular para la enfermedad de EH por primera vez en nuestro país. Esta prueba es de gran utilidad como diagnóstico confirmatorio, etiológico o diferencial de EH.

Introduction: Huntington disease (HD) is a neurodegenerative disorder with an autosomal dominant inheritance mode, complete penetrance and variable clinical expressivity. The estimated prevalence is 1 to 4 per 100.000 individuals. It is caused by a CAG triplet expansion in exon 1 of the IT-15 gene which codes for a protein with an enlarged polyglutamine region. This leads to the formation of protein aggregates in the cell nucleus and induces apoptosis. Normal alleles show less than 26 CAG repeats, and those over 40 always lead to the disease. Alleles with 26 to 36 repeats are considered normal “mutable” alleles and those between 36 to 39, are considered in a gray zone with increased risk of developing the disease. Aims: To develop a diagnosis of HD in a uruguayan population and determine the exact size of the mutation in clinically affected subjects using molecular biology techniques. Methods: Patients were derived from Neurology Clinic of the “Hospital de Clínicas”. The determination of the CAG repeat number was done using polymerase chain reaction (PCR) technique, subsequent analysis on polyacrilamide gels and sequencing. Results: We performed the molecular diagnosis in 18 patients with clinical suspicion of HD. Fifteen of them had a previous clinical diagnosis and one had no symptoms. Besides, in two additional individuals this test allowed us to discard HD. Conclusions: A molecular diagnostic for HD disease was developed for the first time in our country. This test is of great clinical utility as a confirmatory, etiological, or differential diagnosis.

Remembering Obaid Siddiqi, a pioneer in the study of temperature-sensitive paralytic mutants in Drosophila.

Although Obaid Siddiqi’s major research focus in neurogenetics was on chemosensation and olfaction in Drosophila, he made seminal contributions to the study of temperature-sensitive paralytic mutants that paved the way for research that we and many other investigators have continued to pursue. Here we recount Siddiqi’s investigation and the impact it had on our own studies especially at a formative stage of our careers. We acknowledge our debt to Obaid Siddiqi and remember him fondly as an inspired and inspiring scientist, mentor, role model and human being.

Quantificação de diferentes microRNAs no sistema nervoso central: implicações nos mecanismos de desenvolvimento e processos fisiopatologicos / Quantification of microRNAs in the central nervoussystem: implications

MicroRNAs são moléculas recém-descobertas de RNA não-codificadores que possuem de 21 a 24 nucleotídeos e que regulam a expressão após a transcrição dos genes alvo. Essa regulação pode ser realizada através da inibição da tradução ou da degradação do RNA mensageiro. Os miRNAs estão envolvidos em vários processo biológicos como, diferenciação celular e desenvolvimento embrionário, além de apresentarem expressão tecido e tempo-específica. Eles podem regular a expressão de pelo menos 1/3 de todos os genes humanos e estão envolvidos com a regulação do metabolismo e da apoptose. Os miRNAs são a chave como reguladores pós-transcricionais da neurogênese; estudos mostram que eles possuem a expressão associada com a transição entre proliferação e diferenciação e também tem expressão constitutiva em neurônios maduros, evidenciando o envolvimento dessas moléculas com o desenvolvimento do sistema nervoso central (SNC). Outros miRNAs estão sendo estudados e verifica-se que eles agem como reguladores de genes envolvidos em doenças como Alzheimer, Parkinson e, provavelmente, também devam possuir um papel na regulação das epilepsias. No primeiro trabalho, apresentado no segundo capítulo, investigamos o papel dos miRNAs no desenvolvimento do SNC através da quantificação de 104 miRNAs em cérebros em desenvolvimento de camundongos. No segundo trabalho, apresentado no terceiro capítulo, para analisarmos o papel dos miRNAs na epilepsia de lobo temporal, verificamos se havia presença de miRNAs com expressão diferenciada entre tecidos removidos de pacientes que se submeteram a cirurgia de hipocampectomia e tecidos normais provenientes de autópsias. Para ambos os experimentos, foram extraídos os RNAs dos tecidos e quantificados por PCR em tempo real com o kit MicroRNA Assay baseado em iniciadores com estrutura em stem loop. Nos camundongos, análises de bioinformática encontraram quatro cluster de acordo com a expressão dos miRNAs...

MicroRNAs are a new class of small RNA molecules (21-24 nucleotide-long) that negatively regulate gene expression either by translational repression or target mRNA degradation. It is believed that about 30% of all human genes are targeted by these molecules. MiRNAs are involved in many important biological processes including cell differentiation, embryonic development and central nervous system formation, besides they showed specific temporal-space expression. They can regulate 1/3 of human genes and are involved in metabolism and apoptosis. miRNAs are the key as neurogenesis postranscriptional regulation; studies previous indicates miRNA expression associate with proliferation and differentiation in development of central nervous system (CNS) and housekeeping expression in mature neurons. They are involved in several diseases as Alzkeimer's and Parkinson and may have a role in epilepsy regulation. In second chapter, we analyze the miRNA expression in mouse brain during four stages of CNS development; in third chapter, we analyze hippocampal tissue of four patients who underwent selective resection of the mesial temporal structures for the treatment of clinically refractory seizures. In addition we used control samples from autopsy (n=4) for comparison. In both experiments, total RNA was isolated from tissues and used in real-time PCR reactions with TaqMan¿ microRNA assays (Applied Biosystems) to quantify 104 (mouse brain) or 157 (human tissue) different miRNAs...

Sugar-hydrolysing enzymes in gustatory mutants of Drosophila.

The distribution of the isozymes of α-glucosidase in different parts of Drosophila melanogaster was examined. Two of the eight glucosidase bands are associated with tarsi. The gustatory mutations in the genes gustB and gustC greatly reduce tarsal glucosidase activity, but the enzyme deficiency is not correlated with inability to taste sugars.