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Previous issue date: 2015-07-31 === As fendas labiopalatinas n?o-sindr?micas (FL/PNS) s?o defeitos cong?nitos
comuns em humanos, caracterizadas pelo desenvolvimento incompleto de
estruturas que separam a cavidade nasal da cavidade oral, e s?o causadas devido a
uma intera??o entre fatores gen?ticos e ambientais. Dados obtidos de estudos de
caso-controle e interven??o diet?tica indicam que a suplementa??o materna com
multivitaminas contendo ?cido f?lico previne o surgimento das fissuras orais. ?
conhecido que o ?cido f?lico participa de fun??es celulares essenciais, como a
s?ntese de nucleot?deos para o reparo do DNA, as quais contribuem para a prote??o
da integridade do genoma contra eventos de danos gerados por fatores end?genos
e/ou ex?genos. Inclusive, estudos revelam que a defici?ncia desta vitamina aumenta
a forma??o de micron?cleos, estruturas citogen?ticas indicadoras de danos no DNA.
Al?m disso, esta defici?ncia ? modulada pelos polimorfismos gen?ticos associados
ao metabolismo do ?cido f?lico, comprometendo o desempenho das fun??es de
estabilidade do genoma e, portanto, est?o sendo associados com o desenvolvimento
de v?rios dist?rbios, dentre eles as fissuras orais. A partir deste contexto, foi
conduzido um estudo transversal do tipo caso-controle n?o pareado com o objetivo
de avaliar a frequ?ncia de biomarcadores de instabilidade gen?mica, sua rela??o
com polimorfismos gen?ticos do metabolismo do folato, e se essas vari?veis est?o
associadas com o desenvolvimento das FL/PNS em crian?as do Rio Grande do
Norte, Brasil.
Foram recrutados 48 pacientes fissurados e 18 crian?as controles,
respectivamente, no Hospital de Pediatria Professor Heriberto Ferreira Bezerra
(HOSPED)/UFRN e em escolas estaduais da cidade de Natal, RN. Com o devido
consentimento dos participantes, realizou-se uma entrevista com os respons?veis
para obten??o de dados epidemiol?gicos, como tamb?m procedeu-se a coleta
sangu?nea das crian?as para a realiza??o dos testes. Foi executado o ensaio do
micron?cleo com bloqueio da citocinese para calcular a frequ?ncia de micron?cleos
(MN), pontes nucleoplasm?ticas (PN) e brotos nucleares (BN). A partir da extra??o
do DNA gen?mico, avaliou-se os polimorfismos da metilenotetrahidrofolato redutase
C677T e A1298C, metionina sintase A2756G, metionina sintase redutase A66G e do
receptor de folato reduzido A80G pela t?cnica de rea??o em cadeia da polimerase
associada ao polimorfismo de tamanho do fragmento de restri??o (PCR-RFLP).
As crian?as com FL/PNS apresentaram maior frequ?ncia basal de MN, PN e
BN que o grupo de crian?as controle (p < 0,001), e nenhum dos polimorfismos
avaliados modificaram significativamente a frequ?ncia destes biomarcadores. Al?m
disso, crian?as com FL/PNS apresentaram 2,3 vezes mais risco de exibir altas
frequ?ncias de MN (p = 0,043) segundo modelo de regress?o log?stica bin?ria. A alta
instabilidade do genoma nas crian?as com fissuras orais sugere que os eventos
genot?xicos, em particular os que promovem quebras na dupla fita do DNA e n?o
s?o devidamente reparados formando micron?cleos, representam fatores relevantes
no desenvolvimento das fendas labiopalatinas n?o-sindr?micas. === The non-syndromic clefts of the lip and/or palate (NSCL/P) are common birth
defects in humans characterized by an incomplete development of cellular structures
that separate the nasal cavity from the oral cavity, and they are caused due to an
interaction between genetic and environmental factors. Data from case-control and
dietary intervention studies indicates that maternal supplementation with
multivitamins containing folic acid prevents the formation of oral clefts. It is known
that folic acid plays a role in essential cellular functions, such as nucleotides
synthesis for DNA repair, which contribute to the protection of genome integrity from
damage events generated by endogenous and/or exogenous factors. In fact, studies
show that a deficiency in this vitamin increases micronuclei formation, a cytogenetic
structure that indicates misrepair of damaged DNA. Furthermore, this deficiency is
modulated by genetic polymorphisms associated with folic acid metabolism, affecting
the performance of genome stability functions and therefore, it has been associated
with the development of various disorders, including oral clefts.
From this context, it was planned a unpaired case-control cross-sectional
study in order to assess the frequency of genome instability biomarkers, their
relationship with genetic polymorphisms in folate metabolism, and if these variables
are associated with the development of NSCL/P in children from a Northeast region
at Brazil.
For this research, it was recruited 48 NSCL/P patients and 18 control children,
respectively, at the Pediatric Hospital Professor Heriberto Ferreira Bezerra
(HOSPED)/ UFRN and at schools in Natal city. With the participants consent, they
were interviewed with a standard questionnaire to obtain epidemiological data, and
the children underwent a blood sampling for the tests. It was performed the
cytokinesis-block micronucleus assay to estimate the frequency of micronuclei (MN),
nucleoplasmic bridges (NPB) and nuclear buds (NB). Also, from the genomic DNA
extraction, it was evaluated by PCR-RFLP the polymorphisms of
methylenetetrahydrofolate reductase C677T and A1298C, methionine synthase
A2756G, methionine synthase reductase A66G and reduced folate carrier A80G.
Children with NSCL/P had higher baseline frequency of MN, NPB and NB than
the control group (p < 0.001), and none of the evaluated polymorphisms significantly
modified the frequency of these biomarkers. In addition, children with clefts had 2.3
times more risk of displaying high frequency of MN (p = 0.043) according to the
binary logistic regression model. The high genomic instability in children with oral
clefts suggests that genotoxic events that promote double strand breaks on DNA and
are not properly repaired, thus originating micronuclei, represent significant factors in
the development of non-syndromic cleft lip/ palate.
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