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      A expressão neurológica e o diagnóstico genético nas síndromes de Angelman, de Rett e do X-Frágil Translated title: Neurological manifestation and genetic diagnosis of Angelman, Rett and Fragile-X syndromes

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          Objetivo: discutir os aspectos clínicos, eletroencefalográficos e os mecanismos genéticos de três síndromes neurogenéticas, que se identificam como entidades nosológicas no grupo heterogêneo de patologias que cursam com retardo mental e autismo. Fontes dos dados: os autores realizaram revisão literária sobre cada síndrome do estudo, atualizando as informações, correlacionando e caracterizando as manifestações neurológicas, assim como a descrição dos mecanismos genéticos e a identificação dos marcadores biológicos. Síntese dos dados: houve a confirmação de que a síndrome de Rett é uma doença genética, conseqüente à mutação no gene MECP2, com variações clínicas que podem ser explicadas por diferentes mutações nesse gene. A síndrome de Angelman tem quatro mecanismos genéticos responsáveis pela variação fenotípica e pelos diferentes riscos de recorrência. Na síndrome do X-Frágil, o grau de comprometimento cognitivo está relacionado com o número de repetições dos trinucleotídeos. Conclusões: os diferentes mecanismos genéticos das três síndromes são responsáveis pela variabilidade clínica. Com a identificação de marcadores biológicos, o diagnóstico será mais precoce, ademais, poderão ser identificadas novas e mais sutis formas de expressão.

          Translated abstract

          Objective: to discuss clinical and electroencephalographic aspects and the genetic mechanisms of three neurogenic syndromes that can be related to nosologic entities in the heterogenic pathological group presenting symptoms of mental retardation and autism. Sources: the authors carried out a bibliographic review on each syndrome involved, correlating and characterizing the neurological manifestations, as well as describing genetic mechanisms and identifying biological markers. Summary of the findings: the authors were able to confirm that Rett Sydrome is a genetic disease resulting from the mutation of the MECP2 gene and clinical variations can be explained by different mutations in this gene. Angelman syndrome has four genetic mechanisms responsible for phenotypic variations and different risks of recurrence. In Fragile-X syndrome, the degree of cognitive impairment is related to the number of trinucleotide repeats. Conclusions: different genetic mechanisms of the three syndromes are responsible for clinical variability. By identifying the biological markers, the diagnosis will be performed earlier and it will be possible to identify new subtle expressions of the disease.

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          Most cited references 51

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          Fragile sites on human chromosomes: demonstration of their dependence on the type of tissue culture medium.

          The observation of heritable fragile sites on human chromosomes prepared for lymphocyte cultures has been shown to depend on the type of tissue culture medium in which the lymphocytes are grown. The sites are observed at a much greater frequency when medium 199 is used than when RPMI 1640, Ham's F10, Eagle's (basal), and CMRL 1969 are used. One site on the X chromosome is of clinical significance in that it is a marker for X-linked mental retardation.
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            Two affected boys in a Rett syndrome family: clinical and molecular findings.

            The authors report a family in which two boys had severe neonatal encephalopathy of unknown origin. They both presented with the same condition and died of severe apnea before they were 1 year old. Their sister has a classic form of Rett syndrome. Because mutations in the methyl-CpG-binding protein 2 (MECP2) gene have been identified in 70 to 80% of the sporadic cases of Rett syndrome, the authors looked for a mutation in the MECP2 gene in this family. The authors identified a missense mutation (T158M) in the affected girl and subsequently showed that one of her affected brothers, for whom DNA was available, carried the same mutation. The mother of the patients is a carrier of the T158M mutation. X-chromosome inactivation studies showed that the mother has a completely skewed X-chromosome inactivation pattern that favors the expression of the normal allele; this explains why she does not exhibit any phenotypic manifestation. In addition, the MECP2 mutation appeared on the grandpaternal X chromosome in this family. An MECP2 mutation can be identified in boys, even though they do not present a Rett syndrome phenotype.
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              Developmental implications of changing trajectories of IQ in males with fragile X syndrome.

              This study examined the trajectories of cognitive development in boys under the age of 21 years with fragile X syndrome. By combining information from three centers, data from 66 boys were analyzed; only children who had been tested two or more times with the same psychometric instrument at one or more year intervals were included in this study. Results demonstrated that males with fragile X syndrome show a decline in IQ scores, with the most marked declines seen during the early pubertal period. All 22 children retested during the 11- to 15-year period showed IQ declines, suggesting a slowing of development associated with the onset of puberty. Before age 10 years, males with higher (as opposed to lower) pretest IQs were more likely to decline at subsequent testings. A single etiological factor may not be sufficient to account for the observed findings, as both changes in neurobiological- and task-related factors seem implicated in the slowing intellectual development of this population.

                Author and article information

                Role: ND
                Role: ND
                Jornal de Pediatria
                J. Pediatr. (Rio J.)
                Sociedade Brasileira de Pediatria (Porto Alegre )
                August 2002
                : 78
                : suppl 1
                : S55-S62
                [1 ] Universidade Federal de São Paulo
                [2 ] SBNC
                [3 ] Universidade Federal da Bahia Brazil
                [4 ] Universidade Federal da Bahia Brazil
                [5 ] Universidade Federal da Bahia Brazil
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