| Qin Ba mountain region was very closed in the past, thus forming a relative separated population. There are many mental retardation (MR) children in the region and familial aggregation is common. This suggests that genetic factors may also be involved except environmental factors.The method of methylation-sensitive restriction endomucleasea(MSRE) BssHlIand PCR technique was used to test the CpG island of the Fragile X mental retardation 1(FMR1) gene among the male MR children in Zhashui and Ankang. The CpG island methylation of gene may lead to the transcriptional silencing of gene. Fragil X syndrome results from the absent of FMR1 gene expression and CGG repeats at the 5' untranslation region (UTR) of the gene expand to full mutation is strong associated with the methylation. Abnormal methylation was observed in Zhashui indicating fragile X syndrome may be one of the genetic factors for MR.To investigate the relation between the abnormal methylatin and CGG repeats, we studied the CGG short tandem repeats (STR) in 5' untranslation region of FMR1 gene, using case-control sample of children of Qin Ba mountain region. The result reveal that the expansion of CGG repeats is not the only reason leading to the methylation of the CpG island of FMR1 gene.We also performed an association study of CGG repeats and samples. Significant difference between case and control was found in Zhashui ( x2=30. 15, 18df, P=0. 036) indicating that there may exist susceptibility genes of MR near the locus. We also found significant difference for allele 31 between case and control ( x2=4.11, 1df, P=0.043) revealing mutation for MR may be exist near this allele.Overall, our result show there may be other cause for the methylation of the CpG island of FMR1 gene and the absent expression of FMR1 gene maybe a factor for MR. Other gene mutation may exist near the allele of 31 CGG repeats for MR in Zhashui. Our findings provide more evidence for the further study in the future. |
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