Assessment of FMR1 triplet repeats in patients affected with mental retardation, fragile X syndrome and primary ovarian insufficiency

The CGG repeats in the FMR1 gene expand in patients with fragile X syndrome, fragile X-associated tremour/ataxia syndrome and fragile X-associated primary ovarian failure. In this study, the CGG repeats in the FMR1 gene were studied in 449 males and 207 females using traditional polymerase chain reaction and triplet repeat primed PCR methods, also 18 CVS samples (six males and 12 females) were tested for prenatal diagnosis. Further, methylation sensitive multiplexed ligation dependent probe amplification was performed on some samples to confirm the results. Regarding the male patients, 1.1% and 9.7% had premutation (PM) and full mutation (FM) alleles, respectively. Also three (0.66%) male patients were mosaic for PM and FM alleles. Among females, 1.9% were GZ carriers and 5.8% were PM carriers. Prenatal diagnosis resulted in detection of two PM and one FM males as well as one FM carrier female. Our results were in concordance with the previously published results.

Analysis of fragilex mental retardation 1 and fragilex mental retardation 2 gene mutations in intellectually disabled population of unknown causes in Southern China / 中华神经医学杂志

Objective To screen the fragilex mental retardation 1 (FMR1) gene mutations and explore the frequency of FMR1 gene mutation in the population with mental retardation in South China.Methods Seventy-two patients (65 males and 7 females) with suspected fragile X syndrome (FXS) in South China were enrolled in our hospitals from October 2009 to April 2014.The CGG trinucleotide repeats in 5'UTR of FMR1 gene and CCG trinucleotide repeats in FMR2 gene were screened respectively by PCR.Southern blotting and capillary electrophoresis sequencing were performed in male patients without normal target bands and suspected female patients;patients with normal CGG alleles were,then,performed exons and 3'-UTR ofFMR1 gene amplification and sequencing.The frequency of FMR1 gene mutation in patients with mental retardation in different countries and regions was compared with statistical analysis.Results Six pedigrees with full mutation (one female and five males being the probands),one pedigree (mother and son) with FMR1 gene deletion and one pedigree (mother and son) with mutation in the transition region were identified in 72 patients with mental retardation.The prevalence of total mutation was 9.7％ (7/72) and that in male patients was 9.2％ (6/65).These results showed significant differences in prevalence as compared with the results from different countries and areas (P＜0.05);there were no variations in 3'UTR ofFMR1 gene and FMR2 gene mutation in the patients with FXS-like phenotype.Conclusions FMR1 mutation frequency may be higher in mental retardation population in southem China as compared with that in developed countries or areas.Targeted screening on the unexplained mental retardation pedigrees (family history) can improve the diagnosis of FXS.Importantly,deletion mutations screening should also be performed in suspected FXS subjects with normal CGG repeats.

Fragile X screening for FRAXA and FRAXE mutations using PCR based studies: Results of a five year study.

Background: Fragile X syndrome is the most common cause of inherited X-linked mental retardation. It is due to a mutation in a gene on X chromosome leading to hyper-expansion of a trinucleotide repeat sequence. The two most common Fragile sites with clinical significance are FRAXA at Xq27.3 comprising CGG repeat and a more distal FRAXE associated with amplification of a GCC repeat, located at Xq28. The frequency of occurrence of Fragile X syndrome is estimated to be 1/4000 male births. Screening of referrals for the mutations associated with the Fragile X syndrome constitutes a significant workload in many genetic laboratories. Aims: The aim of the present study was to establish the use of PCR based simple and rapid method of initial screening of samples, so that only a minority of samples tested positive with the above methods need to be screened by Southern blotting which is more time consuming and involves use of radioactive material. materials and Methods: Study includes 294 patients with mental retardation. DNA extracted from blood was used for simultaneous amplification of the triplet repeat sequences at the FRAXA and FRAXE loci. Secondly samples from females were analyzed for heterozygosity of normal FRAXA allele. For confirmation of the presence of an expanded FRAXA allele in all the male positive cases, Southern blot hybridization was carried out. PCR based assay was done to detect methylation of the CpG island upstream of the FMR-1 gene. Results: Out of the 294 cases 23 (7.8%) were found to be having full mutation (FM) for FRAXA (21 males, 1 female & 1 male with mosaic FM/PM) and 13 females as having premutation (PM). All these 36 cases were confirmed by Southern blotting using appropriate probes. Among the females the heterozygosity for FRAXA allele was found to be 46%. Conclusion: Non-radioactive PCR methods are efficient and rapid test for intial screening of samples for the presence of FRAXA and FRAXE mutations. Since a large majority of referrals do not have Fragile X, this economical and reliable method reduces the number of samples needing Southern blotting.