Two ethnic Chinese men with clinico-radiologic features of Fragile X-associated tremor-ataxia syndrome (FXTAS) were found on genetic testing to have neuronal intranuclear inclusion disease (NIID), highlighting that NIID should be considered in the differential diagnosis of FXTAS. NIID may also be much more common than FXTAS in certain Asian populations.
Matched MeSH terms: Fragile X Syndrome/diagnosis*; Fragile X Syndrome/physiopathology
An Indian family with all 3 sons having the fragile X syndrome is reported. The frequency of fragile X cells observed ranged from 4·16%. The phenotypically normal mother, although an obligate carrier, did not express any fragile X chromosomes in her Iymphocyte cultures. The range of mental retardation in affected
hemizygous males and heterozygous females as well as the significance of the fragile X chromosome in prenatal diagnosis are discussed.
Matched MeSH terms: Fragile X Syndrome/complications; Fragile X Syndrome/genetics*
Fragile X Syndrome (FXS) is the most common form of inherited mental retardation in men. It is caused by abnormalities in the FMR1 gene that are associated with CGG repeat expansion and the hypermethylation status of its promoter. Methylated alleles lead to transcriptional inhibition and consequent loss of Fragile X Mental Retardation Protein. Chemical modification of cytosine to uracil by bisulfite treatment has proved to be an attractive method for DNA methylation studies that precludes labor-intensive Southern blot analysis, which is the gold standard test for FXS. In this report, bisulfite-treated DNA samples were amplified using real-time multiplex methylation-specific polymerase chain reaction followed by melting curve analysis. Our results show that all control samples with known CGG repeat numbers and methylation statuses were correctly diagnosed. The samples from 43 male patients were also successfully diagnosed, which were in complete agreement with the results of Southern blotting. By such means, 39 patients were found to have an unmethylated allele; 3, a fully mutated allele; and 1, both methylated and unmethylated alleles, thus implying a diagnosis of mosaicism. In conclusion, we find our method to be convenient for screening a large number of male patients with FXS, because it is rapid and easy to perform, especially when there is a low quantity of DNA that must be sensitively and accurately assayed.
Matched MeSH terms: Fragile X Syndrome/diagnosis*; Fragile X Syndrome/genetics
Noncoding repeat expansions cause various neuromuscular diseases, including myotonic dystrophies, fragile X tremor/ataxia syndrome, some spinocerebellar ataxias, amyotrophic lateral sclerosis and benign adult familial myoclonic epilepsies. Inspired by the striking similarities in the clinical and neuroimaging findings between neuronal intranuclear inclusion disease (NIID) and fragile X tremor/ataxia syndrome caused by noncoding CGG repeat expansions in FMR1, we directly searched for repeat expansion mutations and identified noncoding CGG repeat expansions in NBPF19 (NOTCH2NLC) as the causative mutations for NIID. Further prompted by the similarities in the clinical and neuroimaging findings with NIID, we identified similar noncoding CGG repeat expansions in two other diseases: oculopharyngeal myopathy with leukoencephalopathy and oculopharyngodistal myopathy, in LOC642361/NUTM2B-AS1 and LRP12, respectively. These findings expand our knowledge of the clinical spectra of diseases caused by expansions of the same repeat motif, and further highlight how directly searching for expanded repeats can help identify mutations underlying diseases.
Matched MeSH terms: Fragile X Syndrome/genetics*; Fragile X Syndrome/pathology
Neurodevelopmental disorders are defined as a set of abnormal brain developmental conditions marked by the early childhood onset of cognitive, behavioral, and functional deficits leading to memory and learning problems, emotional instability, and impulsivity. Autism spectrum disorder, attention-deficit/hyperactivity disorder, Tourette syndrome, fragile X syndrome, and Down's syndrome are a few known examples of neurodevelopmental disorders. Although they are relatively common in both developed and developing countries, very little is currently known about their underlying molecular mechanisms. Both genetic and environmental factors are known to increase the risk of neurodevelopmental disorders. Current diagnostic and screening tests for neurodevelopmental disorders are not reliable; hence, individuals with neurodevelopmental disorders are often diagnosed in the later stages. This negatively affects their prognosis and quality of life, prompting the need for a better diagnostic biomarker. Recent studies on microRNAs and their altered regulation in diseases have shed some light on the possible role they could play in the development of the central nervous system. This review attempts to elucidate our current understanding of the role that microRNAs play in neurodevelopmental disorders with the hope of utilizing them as potential biomarkers in the future.
Matched MeSH terms: Fragile X Syndrome/diagnosis; Fragile X Syndrome/genetics
Hereditary or developmental neurological disorders (HNDs or DNDs) affect the quality of life and contribute to the high mortality rates among neonates. Most HNDs are incurable, and the search for new and effective treatments is hampered by challenges peculiar to the human brain, which is guarded by the near-impervious blood-brain barrier. Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR), a gene-editing tool repurposed from bacterial defense systems against viruses, has been touted by some as a panacea for genetic diseases. CRISPR has expedited the research into HNDs, enabling the generation of in vitro and in vivo models to simulate the changes in human physiology caused by genetic variation. In this review, we describe the basic principles and workings of CRISPR and the modifications that have been made to broaden its applications. Then, we review important CRISPR-based studies that have opened new doors to the treatment of HNDs such as fragile X syndrome and Down syndrome. We also discuss how CRISPR can be used to generate research models to examine the effects of genetic variation and caffeine therapy on the developing brain. Several drawbacks of CRISPR may preclude its use at the clinics, particularly the vulnerability of neuronal cells to the adverse effect of gene editing, and the inefficiency of CRISPR delivery into the brain. In concluding the review, we offer some suggestions for enhancing the gene-editing efficacy of CRISPR and how it may be morphed into safe and effective therapy for HNDs and other brain disorders.
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.
Fragile X syndrome is a result of an unstable expansion of (CGG)n trinucleotide sequences in the FMR-1 (Fragile X Mental Retardation 1) gene site at Xq27. In a normal person, n ranges from 6 to 40 repeats with an average of 30 repeats, whereas in a mutated FMR1 gene the sequence is repeated several times over (stuttering gene). Full mutation occurs when n equals 200 repeats or more. Where n equals 50 to 200 repeats, it is a premutation. Fragile X occurs when the FMR-1 gene is unable to make normal amounts of usable Fragile X Mental Retardation Protein, or FMRP. The amount of FMRP in the body is one factor that determines the severity of the Fragile X syndrome. A person with nearly normal levels of FMRP usually has mild or no symptoms, while a person with very little or no normal FMRP has more severe symptoms. The mechanism for the role of the FMRP gene is still being researched upon. However, it has been observed that large numbers of repeats (more than 200) inactivates the gene through a process of methylation and when the gene is inactivated, the cell may make little or none of the needed FMRP. Inheritance is X-linked with reduced penetrance and the frequency of occurrence goes up through generations. The phenotypic manifestations of fragile-X syndrome vary and are largely dependent on the size of the mutation or premutation. The identification of the fragile site on G banded metaphases is a time consuming and delicate process requiring experience and skill, however, molecular diagnosis using DNA analysis and Southern blotting, even though expensive, is more specific in determining the presence or absence of the gene. This study was aimed to establish a rapid polymerase chain reaction (PCR) based - touch down PCR, as a screening method for fragile X syndrome. A total of six cases were analysed. Of these, one was a known case of Fragile X (T1) diagnosed by conventional cytogenetics, two were from the latter’s family members namely, his mother (T2) and father (T3), and the other two (T4 and T5) were randomly selected from patients presenting with dysmorphic features and delayed development respectively. One normal control (TC) was included. Cytogenetic analyses for detection of the fragile site was carried out in all cases. Two culture systems were used, namely the synchronised lymphocyte culture and the folate - thymidine deficient culture. Stained metaphases from the fragile X cultures were screened for the presence of the fragile site on the X chromosome. G-banded karyotyping was done using an image analyser to exclude presence of chromosomal abnormalities. DNA was extracted from these samples and amplified by touch-down PCR. Cytogenetic analysis revealed a folate-sensitive fragile site in the affected male, but none in the other five samples. G-banded karyotyping exhibited no additional chromosomal abnormalities. All extracted DNA samples were successfully amplified. Five of the samples showed presence of the product at the expected band at 552bp, excluding the presence of an expansion of CGG segment of the FMR-1 gene. The absence of a band in an affected individual, suggested a fully mutated allele of FRAXA (Folate Sensitive Fragile Site at Xq28). We succeeded in establishing a slightly modified touch-down PCR analysis. Our study indicates that PCR testing offers a rapid and specific method for screening of normal allele and full mutation of the fragile X gene. We suggest this technique to be applied as a complementary tool for cytogenetic analysis to detect the FRAXA gene.