O Gene MECP2 e a função neurocognitiva humana: rastreamento de mutações em pacientes com retardo mental de etiologia desconhecida / The MECP2 gene and the human neurocognitive function: mutation screening in patients with mental retardation of unknown etiology

O retardo mental (RM) é uma das doenças humanas mais comuns, com prevalência de aproximadamente 2%. Esta condição pode resultar de inúmeras causas genéticas, dificultando o seu diagnóstico e representando um desafio para os clínicos. Fatores genéticos possuem um papel importante na etiologia desta condição. Mais de 280 genes foram associados ao RM e, dentre eles, destaca-se o MECP2. Mutações pontuais neste gene, localizado em Xq28, são a principal causa da síndrome de Rett, uma desordem neurológica que, com raras exceções, acomete exclusivamente meninas. Em meninos, estas mutações estão associadas ao RM, mas suas frequências não se mostraram significativas para a aplicação no diagnóstico. Recentemente, microduplicações envolvendo o gene MECP2 foram observadas em meninos com RM, revelando um novo mecanismo mutacional associado a este gene. Este projeto teve como objetivo estudar a contribuição de mutações no gene MECP2 na etiologia do RM em amostra de 150 meninos brasileiros com RM idiopático. A análise de mutações pontuais foi realizada por sequenciamento direto dos produtos da PCR. Para o rastreamento de duplicações, estabelecemos um método de PCR quantitativo em tempo real capaz de dosar o número relativo de cópias do gene MECP2. O método foi otimizado e validado em controles saudáveis. Estudos de expressão foram realizados nos indivíduos com duplicações por PCR em tempo real e a extensão das duplicações foi inferida através da dosagem gênica de quatro regiões adicionais flanqueadoras do MECP2. Oito mutações pontuais foram encontradas, sendo uma variante intrônica, três variantes silenciosas e quatro variantes de sentido trocado. Destas, três são não patogênicas e uma (c.1214C>T), nunca descrita, afeta um aninoácido da proteína altamente conservado. Através de estudos de segregação, de amostra controle normal e de bioinformática, inferimos que esta variante é patogênica. A dosagem gênica do MECP2 por PCR quantitativo identificou três pacientes...

Mental retardation (MR) is one of the most common human disorders, with a prevalence of appoximately 2%. This condition may have several genetic causes, which difficults diagnosis, representing a challenge for clinicians. Genetic factors play a major role in the etiology of this condition. More then 280 genes were associated with MR and, among them, the MECP2. Point mutations in this gene, located in Xq28, are the major cause of Rett syndrome, a neurological disorder that, with rare exceptions, affects exclusively women. In males, these mutations are associated with MR, however their frequency is not supportive for diagnosis application. Recently, microduplications envolving the gene MECP2 were observed in males with MR, uncovering a new mutational mechanism associated with this gene. This project has the objective to study the contribution of mutations in the MECP2 gene in the MR etiology of 150 brazilian males with idiopathic MR. The analysis of point mutations was performed by direct sequencing of the PCR method to quantify the relative MECP2 copy number. The method was optimized and validated in normal controls. Expression studies were performed in the individuals with duplications by Real time PCR and the size of the duplications was accessed though the gene dosage of four additional regions flanking the MECP2. Eight point mutations were identifies, one intronic variant, three silent mutations and four misense mutations. From those, three were non-pathogenic and one (c.1214C>T), never described, affects a highly conserved aminoacid. Through segregation studies, control sample screening and bioinformatics analysis we believe that this variant is pathogenic. MECP2 gene dosage by quantitative PCR has identified three patients with duplications involving this gene (~2). The size of these rearranjements varied among the patients, including other genes in the duplication, what may explain the clinical variantions observed in the patients...

Neonatal seizures: the overlap between diagnosis of metabolic disorders and structural abnormalities. Case report

Inborn metabolic errors (IME) and cortical developmental malformations are uncommon etiologies of neonatal seizures, however they may represent treatable causes of refractory epilepsy and for this reason must be considered as possible etiological factors. This case report aims to demonstrate the importance of neuroimaging studies in one patient with neonatal seizures, even when there are clues pointing to a metabolic disorder. CASE REPORT: A previously healthy 14 day-old child started presenting reiterated focal motor seizures (FMS) which evolved to status epilepticus. Exams showed high serum levels of ammonia and no other abnormalities. A metabolic investigation was conducted with normal results. During follow-up, the patient presented developmental delay and left side hemiparesia. Seizures remained controlled with anti-epileptic drugs for four months, followed by relapse with repetitive FMS on the left side. Temporary improvement was obtained with anti-epileptic drug adjustment. At the age of 6 months, during a new episode of status epilepticus, high ammonia levels were detected. Other metabolic exams remained normal. The child was referred to a video-electroencephalographic monitoring and continuous epileptiform discharges were recorded over the right parasagittal and midline regions, with predominance over the posterior quadrant. A new neuroimaging study was performed and displayed a malformation of cortical development. Our case illustrates that because newborns are prone to present metabolic disarrangement, an unbalance such as hyperammonemia may be a consequence of acute events and conduct to a misdiagnosis of IME

Síndrome de Rett: reporte de 4 casos en Costa Rica / Rett syndrome: report of 4 cases in Costa Rica

Se reportan cuatro casos en Costa Rica de niñas con criterio diagnóstico de Síndrome de Rett clásico, comportando una regresión psicomotora al final del primer año de vida, una desaceleración del crecimiento cefálico y un trastorno conductual dentro del cual la habilidad de las manos es reemplazada por estereotipias.