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Scholarly Works (187 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2014)
Fragile X syndrome (FXS), caused by a trinucleotide expansion (>200 CGG repeats) in the fragile X mental retardation gene (FMR1), is currently not included in newborn screening (NBS) panels in the United States as it does not meet the standards for recommendation. Although in the past few years FXS has met many of the criteria for population screening and studies have shown that NBS for FXS is feasible, the idea is still controversial and the debate is open. The recent advances in genomic testing as well as groundbreaking advances in targeted treatment for FXS have been challenging the dogma and principle of the national NBS program: screen only if you can intervene. Arguments in favor of NBS include benefits of early intervention and follow-up for the identified baby, which would justify NBS even in the absence of medical benefit to the child. In addition, the extended family members may benefit from genetic and reproductive counseling, informed decision making before a subsequent pregnancy, and access to treatment and services. However, communicating the results and the potential consequences to families is a challenge and could lead to a heavy psychosocial burden. A controversial issue is the identification of premutation carriers (55-200 CGG repeats), because it not only can lead to information on the reproductive possibility of having a child with FXS but also leads to information about personal health risks associated with the premutation. Yet, knowledge of carrier status could stimulate and encourage lifestyle changes and preventive measures likely to reduce the risk of medical problems reported in premutation carriers. If NBS for FXS is developed, it must be carried out with clear awareness of the potential impact on the lives of the children, and it should be done after counseling and parents' informed consent. Importantly, the infrastructure to support testing, counseling, treatment, and follow-up will have to be made available to the families.
    Cover page: Newborn Screening for Fragile X Syndrome
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2015)
    Fragile X syndrome (FXS), a trinucleotide repeat disorder, is the most common heritable form of cognitive impairment. Since the discovery of the FMR1 gene in 1991, great strides have been made in the field of molecular diagnosis for FXS. Cytogenetic analysis, which was the method of diagnosis in the early 1990, was replaced by Southern blot and PCR analysis albeit with some limitations. In the past few years many PCR-based methodologies, able to amplify large full mutation expanded alleles, with or without methylation, have been proposed. Reviewed here are the advantages, disadvantages and limitations of the most recent developments in the field of FXS diagnosis.
      Cover page: Advanced technologies for the molecular diagnosis of fragile X syndrome
      • Thesis
      • Peer Reviewed
      UC Davis Electronic Theses and Dissertations (2021)

      The Fragile X-associated disorders are a group of genetic diseases resulting from the expansion of the CGG repeats in the 5’ untranslated region (5’ UTR) of the FMR1 gene, located on the X chromosome. Individuals with an expansion of greater than 200 CGG repeats have the full mutation, which leads to silencing of the gene and lack of the encoded protein, FMRP, causing Fragile X syndrome (FXS), the most common inherited form of intellectual disability. Individual carriers of a premutation allele (55-200 CGG repeat) are at risk of developing Fragile X-associated tremor/ataxia syndrome (FXTAS), a late onset neurodegenerative condition, which affects both males and females. Currently, there is no approved therapy or reliable biomarkers to determine therapeutic efficacy in FXS and associated disorders, in particular of FXTAS.The first part of my dissertation (Chapters 2, 3 and 4) investigates the development of a potential biomarker for early diagnosis and progression of FXTAS. The second part of my dissertation (Chapters 5 and 6), reports on the development of a protocol to derive epithelial cells from urine samples of FXS patients and on the molecular methods to study and diagnose FXTAS. Chapter 1 is a detailed introduction to the genetics of FXS, its pathophysiology and on currently available molecular biomarkers. In Chapter 2, I report on an investigation of the alternative splicing landscape at the FMR1 locus in conjunction with brain measures. I show that increased levels of specific FMR1 mRNA isoforms, those that encode truncated proteins, are present in premutation carriers who developed symptoms of FXTAS, relative to non-carrier healthy controls, suggesting a potential role in the development of the disorder. Chapter 3 reports on the identification of biomarkers for early diagnosis and progression of FXTAS. Interestingly, lipid metabolism and, specifically, the sub-pathways involved in mitochondrial bioenergetics as observed in other neurodegenerative disorders; were found to be significantly altered in FXTAS. Further, in Chapter 4, I demonstrate that differential expression levels of some of the previously-identified metabolites are linked with areas within the pons. In addition, we observed a significant correlation of these metabolic signatures with the FXTAS stage, strengthening the likelihood that they contribute to the progression and pathogenesis of FXTAS. In the second part of my thesis, which begins with Chapter 5, I describe a cost-effective and straightforward method to derive epithelial cell lines from urine samples collected from participants with FXS and healthy controls (TD). These cell lines can be used as a new model to study the molecular mechanisms behind FXS, including the expression of surface markers, inter and the intra-tissue CGG mosaicism, FMR1 mRNA and FMRP expression levels. Finally, in Chapter 6, I provide the protocols for FXTAS diagnostic tools, in both humans and mouse.

        Cover page: Biomarkers of Prediction, Development, Progression and Severity of Fragile X Syndrome and FMR1 Associated Disorders
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2019)
        Fragile X syndrome (FXS) is the most common inherited form of intellectual disability (ID) and a known monogenic cause of autism spectrum disorder (ASD). It is a trinucleotide repeat disorder, in which more than 200 CGG repeats in the 5' untranslated region (UTR) of the fragile X mental retardation 1 (FMR1) gene causes methylation of the promoter with consequent silencing of the gene, ultimately leading to the loss of the encoded fragile X mental retardation 1 protein, FMRP. FMRP is an RNA binding protein that plays a primary role as a repressor of translation of various mRNAs, many of which are involved in the maintenance and development of neuronal synaptic function and plasticity. In addition to intellectual disability, patients with FXS face several behavioral challenges, including anxiety, hyperactivity, seizures, repetitive behavior, and problems with executive and language performance. Currently, there is no cure or approved medication for the treatment of the underlying causes of FXS, but in the past few years, our knowledge about the proteins and pathways that are dysregulated by the loss of FMRP has increased, leading to clinical trials and to the path of developing molecular biomarkers for identifying potential targets for therapies. In this paper, we review candidate molecular biomarkers that have been identified in preclinical studies in the FXS mouse animal model and are now under validation for human applications or have already made their way to clinical trials.
          Cover page: Molecular Biomarkers in Fragile X Syndrome
          • Thesis
          • Peer Reviewed
          UC Davis Electronic Theses and Dissertations (2022)

          I. Abstract

          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.

            Cover page: Genetic factors associated with CGG repeat instability in FMR1 Premutation Carriers with Various Degrees of Mosaicism
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2020)
            Fragile X syndrome (FXS) is an X-linked neurodevelopmental condition associated with intellectual disability and behavioral problems due to the lack of the Fragile X mental retardation protein (FMRP), which plays a crucial role in synaptic plasticity and memory. A desirable in vitro cell model to study FXS would be one that can be generated by simple isolation and culture method from a collection of a non-invasive donor specimen. Currently, the various donor-specific cells can be isolated mainly from peripheral blood and skin biopsy. However, they are somewhat invasive methods for establishing cell lines from the primary subject material. In this study, we characterized a cost-effective and straightforward method to derive epithelial cell lines from urine samples collected from participants with FXS and healthy controls (TD). The urine-derived cells expressed epithelial cell surface markers via fluorescence-activated cell sorting (FACS). We observed inter, and the intra-tissue CGG mosaicism in the PBMCs and the urine-derived cells from participants with FXS potentially related to the observed variations in the phenotypic and clinical presentation FXS. We characterized these urine-derived epithelial cells for FMR1 mRNA and FMRP expression and observed some expression in the lines derived from full mutation mosaic participants. Further, FMRP expression was localized in the cytoplasm of the urine-derived epithelial cells of healthy controls. Deficient FMRP expression was also observed in mosaic males, while, as expected, no expression was observed in cells derived from participants with a hypermethylated full mutation.
              Cover page: Urine-Derived Epithelial Cell Lines: A New Tool to Model Fragile X Syndrome (FXS)
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2024)

              Background

              Vestibular migraine (VM) is one of the most common causes of recurrent vertigo and presents with a history of spontaneous or positional vertigo with a history of migraine headaches. While research has identified a high prevalence of migraine headaches and vestibular deficits among fragile X premutation carriers, there has been no discussion about VM within this population.

              Objective

              This case series and review seeks to describe the clinical characteristics and pathophysiology of VM among individuals with the fragile X premutation. We also seek to discuss treatment and future steps in addressing VM in this population.

              Methods

              A review of the literature regarding vestibular migraine and presentation of migraine headaches and vestibular deficits among premutation carriers was performed. A detailed clinical history of migraine headaches and vertigo was obtained from three patients with the fragile X premutation seen by the senior author (RJH).

              Results

              All three cases first developed symptoms of migraine headaches earlier in life, with the development of VM near menopause. Two of the three cases developed progressive balance issues following the development of VM. All three cases found that their VM episodes were improved or resolved with pharmacological and/or lifestyle interventions.

              Conclusions

              It is important to recognize VM among premutation carriers because beneficial treatments are available. Future studies are needed regarding the prevalence of VM and the relationship to subsequent FXTAS. The pathophysiology of VM remains uncertain but possibilities include mitochondrial abnormalities, cranial nerve VIII toxicity secondary to neurotoxic protein accumulation, and calcitonin gene-related peptide (CGRP) signaling dysfunction due to altered levels of fragile X messenger ribonucleoprotein (FMRP).
                Cover page: Case Series: Vestibular Migraines in Fragile X Premutation Carriers
                • Article
                Pediatrics (2024)
                This case series plus review seeks to describe the clinical characteristics and pathophysiology of VM among individuals with the fragile X premutation. We also seek to discuss treatment and future steps in addressing VM in this population.
                  Cover page: Case Series of Vestibular Migraine in Fragile X Premutation Carriers
                  • Article
                  • Peer Reviewed
                  UC Davis Previously Published Works (2011)
                  Recent data from a national survey highlighted a significant difference in obesity rates in young fragile X males (31%) compared to age matched controls (18%). Fragile X syndrome (FXS) is the most common cause of intellectual disability in males and the most common single gene cause of autism. This X-linked disorder is caused by an expansion of a trinucleotide CGG repeat (>200) on the promotor region of the fragile X mental retardation 1 gene (FMR1). As a result, the promotor region often becomes methylated which leads to a deficiency or absence of the FMR1 protein (FMRP). Common characteristics of FXS include mild to severe cognitive impairments in males but less severe cognitive impairment in females. Physical features of FXS include an elongated face, prominent ears, and post-pubertal macroorchidism. Severe obesity in full mutation males is often associated with the Prader-Willi phenotype (PWP) which includes hyperphagia, lack of satiation after meals, and hypogonadism or delayed puberty; however, there is no deletion at 15q11-q13 nor uniparental maternal disomy. Herein, we discuss the molecular mechanisms leading to FXS and the Prader-Willi phenotype with an emphasis on mouse FMR1 knockout studies that have shown the reversal of weight increase through mGluR antagonists. Finally, we review the current medications used in treatment of FXS including the atypical antipsychotics that can lead to weight gain and the research regarding the use of targeted treatments in FXS that will hopefully have a significantly beneficial effect on cognition and behavior without weight gain.
                    Cover page: Fragile X Syndrome
                    • Article
                    • Peer Reviewed
                    UC Davis Previously Published Works (2015)
                    Premutation alleles in fragile X mental retardation 1 (FMR1) can cause the late-onset neurodegenerative disorder, fragile X-associated tremor ataxia syndrome (FXTAS) and/or the fragile X-associated primary ovarian insufficiency in approximately 20% of heterozygotes. Heterozygotes of the FMR1 premutation have a higher incidence of immune mediated disorders such as autoimmune thyroid disorder, especially when accompanied by FXTAS motor signs. We describe the time course of symptoms of immune mediated disorders and the subsequent development of FXTAS in four women with an FMR1 CGG expansion, including three with the premutation and one with a gray zone expansion. These patients developed an immune mediated disorder followed by neurological symptoms that become consistent with FXTAS. In all patients we observed a pattern involving an initial appearance of disease symptoms-often after a period of heightened stress (depression, anxiety, divorce, general surgery) followed by the onset of tremor and/or ataxia. Immune mediated diseases are associated with the manifestations of FXTAS temporally, although further studies are needed to clarify this association. If a cause and effect relationship can be established, treatment of pre-existing immune mediated disorders may benefit patients with pathogenic FMR1 mutations.
                      Cover page: Immune mediated disorders in women with a fragile X expansion and FXTAS
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