The fragile X mental retardation (FMR1) gene contains an expansion-prone CGG repeat within its 5' UTR. Alleles with 55-200 repeats are known as premutation (PM) alleles and confer risk for one or ...more of the FMR1 premutation (PM) disorders that include Fragile X-associated Tremor/Ataxia Syndrome (FXTAS), Fragile X-associated Primary Ovarian Insufficiency (FXPOI), and Fragile X-Associated Neuropsychiatric Disorders (FXAND). PM alleles expand on intergenerational transmission, with the children of PM mothers being at risk of inheriting alleles with > 200 CGG repeats (full mutation FM) alleles) and thus developing Fragile X Syndrome (FXS). PM alleles can be somatically unstable. This can lead to individuals being mosaic for multiple size alleles. Here, we describe a detailed evaluation of somatic mosaicism in a large cohort of female PM carriers and show that 94% display some evidence of somatic instability with the presence of a series of expanded alleles that differ from the next allele by a single repeat unit. Using two different metrics for instability that we have developed, we show that, as with intergenerational instability, there is a direct relationship between the extent of somatic expansion and the number of CGG repeats in the originally inherited allele and an inverse relationship with the number of AGG interruptions. Expansions are progressive as evidenced by a positive correlation with age and by examination of blood samples from the same individual taken at different time points. Our data also suggests the existence of other genetic or environmental factors that affect the extent of somatic expansion. Importantly, the analysis of candidate single nucleotide polymorphisms (SNPs) suggests that two DNA repair factors, FAN1 and MSH3, may be modifiers of somatic expansion risk in the PM population as observed in other repeat expansion disorders.
Carriers of a premutation allele (PM) in the FMR1 gene are at risk of developing a number of Fragile X premutation asssociated disorders (FXPAC), including Fragile X-associated Tremor/Ataxia Syndrome ...(FXTAS), Fragile X-associated Primary Ovarian Insufficiency (FXPOI), and Fragile X-associated neuropsychiatric disorders (FXAND). We have recently reported somatic CGG allele expansion in female PM; however, its clinical significance remains unclear. The aim of this study was to examine the potential clinical association between somatic FMR1 allele instability and PM associated disorders. Participants comprised of 424 female PM carriers age 0.3- 90 years. FMR1 molecular measures and clinical information on the presence of medical conditions, were determined for all subjects for primary analysis. Two sub-groups of participants (age ≥ 25, N = 377 and age ≥ 50, N = 134) were used in the analysis related to presence of FXPOI and FXTAS, respectively. Among all participants (N = 424), the degree of instability (expansion) was significantly higher (median 2.5 vs 2.0, P = 0.026) in participants with a diagnosis of attention deficit hyperactivity disorder (ADHD) compared to those without. FMR1 mRNA expression was significantly higher in subjects with any psychiatric disorder diagnosis (P = 0.0017); specifically, in those with ADHD (P = 0.009), and with depression (P = 0.025). Somatic FMR1 expansion was associated with the presence of ADHD in female PM and FMR1 mRNA levels were associated with the presence of mental health disorders. The findings of our research are innovative as they suggest a potential role of the CGG expansion in the clinical phenotype of PM and may potentially guide clinical prognosis and management.
Carriers of the
premutation (PM) allele are at risk of one or more clinical conditions referred to as FX premutation-associated conditions (FXPAC). Since the
gene is on the X chromosome, the ...activation ratio (AR) may impact the risk, age of onset, progression, and severity of these conditions. The aim of this study was to evaluate the reliability of AR measured using different approaches and to investigate potential correlations with clinical outcomes. Molecular and clinical assessments were obtained for 30 PM female participants, and AR was assessed using both Southern blot analysis (AR-Sb) and methylation PCR (AR-mPCR). Higher ARs were associated with lower
transcript levels for any given repeat length. The higher AR-Sb was significantly associated with performance, verbal, and full-scale IQ scores, confirming previous reports. However, the AR-mPCR was not significantly associated (
> 0.05) with these measures. Similarly, the odds of depression and the number of medical conditions were correlated with higher AR-Sb but not correlated with a higher AR-mPCR. This study suggests that AR-Sb may be a more reliable measure of the AR in female carriers of PM alleles. However, further studies are warranted in a larger sample size to fully evaluate the methylation status in these participants and how it may affect the clinical phenotype.
The course of pathophysiological mechanisms involved in fragile X-associated tremor/ataxia syndrome (FXTAS) remains largely unknown. Previous proteomics and metabolomics studies conducted in blood ...samples collected from FMR1 premutation carriers with FXTAS reported abnormalities in energy metabolism, and precursors of gluconeogenesis showed significant changes in plasma expression levels in FMR1 premutation carriers who developed FXTAS. We conducted an analysis of postmortem human brain tissues from 44 donors, 25 brains with FXTAS, and 19 matched controls. We quantified the metabolite relative abundance in the inferior temporal gyrus and the cerebellum using untargeted mass spectrometry (MS)-based metabolomics. We investigated how the metabolite type and abundance relate to the number of cytosine-guanine-guanine (CGG) repeats, to markers of neurodegeneration, and to the symptoms of FXTAS. A metabolomic analysis identified 191 primary metabolites, the data were log-transformed and normalized prior to the analysis, and the relative abundance was compared between the groups. The changes in the relative abundance of a set of metabolites were region-specific with some overlapping results; 22 metabolites showed alterations in the inferior temporal gyrus, while 21 showed differences in the cerebellum. The relative abundance of cytidine was decreased in the inferior temporal gyrus, and a lower abundance was found in the cases with larger CGG expansions; oleamide was significantly decreased in the cerebellum. The abundance of 11 metabolites was influenced by changes in the CGG repeat number. A histological evaluation found an association between the presence of microhemorrhages in the inferior temporal gyrus and a lower abundance of 2,5-dihydroxypyrazine. Our study identified alterations in the metabolites involved in the oxidative-stress response and bioenergetics in the brains of individuals with FXTAS. Significant changes in the abundance of cytidine and oleamide suggest their potential as biomarkers and therapeutic targets for FXTAS.
Fragile X (FMR1) premutation is a common mutation that affects about 1 in 200 females and 1 in 450 males and can lead to the development of fragile-X-associated tremor/ataxia syndrome (FXTAS). ...Although there is no targeted, proven treatment for FXTAS, research suggests that sulforaphane, an antioxidant present in cruciferous vegetables, can enhance mitochondrial function and maintain redox balance in the dermal fibroblasts of individuals with FXTAS, potentially leading to improved cognitive function. In a 24-week open-label trial involving 15 adults aged 60-88 with FXTAS, 11 participants successfully completed the study, demonstrating the safety and tolerability of sulforaphane. Clinical outcomes and biomarkers were measured to elucidate the effects of sulforaphane. While there were nominal improvements in multiple clinical measures, they were not significantly different after correction for multiple comparisons. PBMC energetic measures showed that the level of citrate synthase was higher after sulforaphane treatment, resulting in lower ATP production. The ratio of complex I to complex II showed positive correlations with the MoCA and BDS scores. Several mitochondrial biomarkers showed increased activity and quantity and were correlated with clinical improvements.
The fragile X-related disorders (FXDs) are a group of clinical conditions that result primarily from an unusual mutation, the expansion of a CGG-repeat tract in exon 1 of the
gene. Mouse models are ...proving useful for understanding many aspects of disease pathology in these disorders. There is also reason to think that such models may be useful for understanding the molecular basis of the unusual mutation responsible for these disorders. This review will discuss what has been learnt to date about mechanisms of repeat instability from a knock-in FXD mouse model and what the implications of these findings may be for humans carrying expansion-prone
alleles.
Allele instability in trinucleotides repeat disorders has been associated with many different physical and psychological conditions, including inherited forms of autism and neurodegenerative ...disorders. This form of instability is observed in Fragile X Syndrome, a trinucleotide disorder, in which a CGG repeat located in the 5’UTR of the fragile X messenger ribonucleoprotein 1 (FMR1) gene is greater than 200 CGG repeats. This leads to methylation of the gene, transcriptional silencing and consequent absence or reduction of the encoded protein, FMRP. In FMR1 premutation (PM) carriers, who have an allele containing between 55 – 200 CGG repeat length, a CGG repeat expansion during transmission to the offspring, leads to Fragile X Syndrome. Although allele instability has been observed mainly in full mutation alleles (>200 CGG repeats), it has been observed throughout the CGG range, and leading to somatic mosaicism.However, it is unclear what molecular factors are associated with the risk of FMR1 CGG repeat expansion and if instability correlates with clinical conditions throughout the lifespan of individuals carrying an expanded allele. Furthermore, it is unknown if these factors confer difference in the degrees of risk based on the individual’s biological sex, or age, or if instability or changes may occur over time within individuals.In this study, we investigated 426 PM female and 454 PM male carriers. Within these two cohorts, we observed that CGG repeat size correlates with FMR1 mRNA levels, and with the number of AGG interruptions, confirming previous reports. Interestingly, a lower number of AGG interruptions and higher CGG repeat size increases the risk of expansion from mother to offspring during transmission, relevant to the new observation here reported. When studying CGG instability over time, we found that eight PM females (n=24) underwent allele expansion as they aged, with three individuals displaying an increase of three or greater repeats in CGG repeat number. Likewise, in the PM male group (n=50), 19 individuals showed an increased CGG repeat number over time, with two undergoing CGG allele size decrease. We also found that the expanded unmethylated regions, significantly correlated with CGG repeat size and AGG interruptions in both females and males.Thus, CGG repeat size and AGG interruptions are significantly correlated with somatic instability, regardless of gender, although differences in allele expansion patterns between PM males and females exist. Trans molecular factors such as DNA repair-associated genes are also capable of affecting risk of expansion. Indeed, our preliminary observations found a significant correlation between allele in two genes, MSH3 and FAN1, both of which play a role in DNA repair.These findings carry the implications that molecular measures could be used to determine individuals with higher likelihood of allele instability, which may influence the phenotypic expression. Overall, this study can help future diagnostics in determining which PM individuals, both males and females, are more likely to experience allele expansion and be at risk of developing Fragile X associated conditions.
Carriers of the FMR1 premutation (PM) allele are at risk of one or more clinical conditions referred to as FX premutation-associated conditions (FXPAC). Since the FMR1 gene is on the X chromosome, ...the activation ratio (AR) may impact the risk, age of onset, progression, and severity of these conditions. The aim of this study was to evaluate the reliability of AR measured using different approaches and to investigate potential correlations with clinical outcomes. Molecular and clinical assessments were obtained for 30 PM female participants, and AR was assessed using both Southern blot analysis (AR-Sb) and methylation PCR (AR-mPCR). Higher ARs were associated with lower FMR1 transcript levels for any given repeat length. The higher AR-Sb was significantly associated with performance, verbal, and full-scale IQ scores, confirming previous reports. However, the AR-mPCR was not significantly associated (p > 0.05) with these measures. Similarly, the odds of depression and the number of medical conditions were correlated with higher AR-Sb but not correlated with a higher AR-mPCR. This study suggests that AR-Sb may be a more reliable measure of the AR in female carriers of PM alleles. However, further studies are warranted in a larger sample size to fully evaluate the methylation status in these participants and how it may affect the clinical phenotype.
A toxin produced by Pseudomonas tolaasii, tolaasin, causes brown blotch disease in mushrooms. Tolaasin forms pores on the cellular membrane and destroys cell structure. Inhibiting the ability of ...tolaasin to form ion channels may be an effective method to protect against attack by tolaasin. However, it is first necessary to elucidate the three-dimensional structure of the ion channels formed by tolaasin. In this study, the structure of the tolaasin ion channel was determined in silico based on data obtained from nuclear magnetic resonance experiments.
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