ABSTRACT
Objective@#To determine the CGG repeat number and methylation status of FMR1 gene for fetuses whose mothers have carried a FMR1 mutation.@*Methods@#For 30 pregnant women, the fetal CGG repeat number was determined with a GC-rich PCR system by using chorionic villus, amniotic fluid or umbilical blood samples. The methylation status of the FMR1 gene was confirmed with Southern blotting.@*Results@#In total 30 prenatal diagnoses were performed for 29 carriers of FMR1 gene mutations and 1 with FMR1 gene deletion mosaicism. Three fetuses were found to carry premutations, 9 were with full mutations and 1 with mosaicism of premutation and full mutations. Eighteen fetuses were normal.@*Conclusion@#Considering the genetic complexity of Fragile X syndrome (FXS), single method may not suffice accurate determination of their genetic status. The pitfalls and technical limitations of protocols requires adoption of personalized strategy for its prenatal diagnosis.
ABSTRACT
Fragile X syndrome (FXS) is a neurodevelopmental disorder commonly found worldwide, caused by the silencing of fragile X mental retardation 1 (FMR1) gene on the X-chromosome. Most of the patients lost FMR1 function due to an expansion of cytosine-guanine-guanine (CGG) repeat at the 5’ untranslated region (5’UTR) of the gene. The purpose of this study is to identify the prevalence of FXS and characterize the FMR1 gene CGG repeats distribution among children with developmental disability in Malaysia. Genomic DNA of 2201 samples from different ethnicities (Malays, Chinese, Indian and others) of both genders were PCR-amplified from peripheral blood leukocytes based on specific primers at 5’UTR of FMR1 gene. Full mutations and mosaics were successfully identified by triple methylation specific PCR (ms-PCR) and subsequently verified with FragilEase kit. The findings revealed for the first time the prevalence of FXS full mutation in children with developmental disability in Malaysia was 3.5%, a slightly higher figure as compared to other countries. Molecular investigation also identified 0.2% and 0.4% probands have permutation and intermediate alleles, respectively. The CGG repeats length observation showed 95% of patients had normal alleles within 11 to 44 CGG repeats; with 29 repeats found most common among Malays and Indians while 28 repeats were most common among Chinese. In conclusion, this is the first report of prevalence and characterisation of CGG repeats that reflects genetic variability among Malaysian ethnic grouping.
ABSTRACT
BACKGROUND: Fragile X syndrome is one of the most common causes of mental retardation. For its prevention, detection of premutation range CGG repeat in FMR1 gene is necessary. The aim of our study was to determine the prevalence of premutation range of CGG repeat in neonate, and to evaluate the possibility of screening test. METHODS: DNA were extracted from Guthrie paper blood spot, referred for neonatal metabolic screening test, collected during the period of March 1996 through August 1996, at Chunchon Sacred Heart Hospital. Then FMR1 gene involving CGG repeat was amplified by polymerase chain reaction, and then abnormal expansion of CGG were analyzed by agarose gel electrophoresis and digoxigenin labelled chemiluminescent detection method. RESULTS: Four cases among 669 PCR product were appeared to have abnormal CGG expansion and 3 out of the 4 cases were confirmed to have abnormal CGG repeat by chemiluminescent detection method. CONCLUSION: We found 3 premutation range CGG expansion with a prevalence of 1/233 in neonate. Although PCR based agarose gel electrophoresis alone is not suitable for screening test, it could be a useful tool for fragile X screening test in combination with chemiluminescent detection method.