Large expansions (>200 CGG repeats;full mutation) of a CGG-repeat in the FMR1 gene cause the leading heritable form of intellectual disability (fragile X syndrome) and are associated with the leading known single- gene form of autism. Smaller expansions (55-200 CGG repeats;premutation) give rise to one of the most common known single-gene neurodegenerative disorders, fragile X-associated tremor/ataxia syndrome (FXTAS), and also result in the leading single-gene form of primary ovarian failure. Therefore, the consequences of CGG-repeat expansions are of great societal impact, with over one-hundred thousand individuals in the United States affected by one or more of the fragile X-associated disorders. In both premutation and full-mutation disorders, disease pathogenesis is due to altered levels of expression - reduced/absent protein for fragile X syndrome and elevated mRNA for FXTAS. In the proposed research, we will exploit a novel method for single-molecule genomic (SMRT) sequencing, coupled with the generation of single-allele fibroblast sub-clones, to determine at the sequence-level the CGG-repeat lengths and complexity (i.e., size mosaicism) of expanded CGG-repeat FMR1 alleles (Specific Aim 1) and to define the dependence of FMR1 protein (FMRP) levels on CGG-repeat length and to identify at least some of the factors that control FMRP expression (Specific Aim 2). In addition, we will further define the basis for increased mRNA levels for FMR1 alleles within the premutation range (Specific Aim 3), and will exploit our earlier observation that the start of transcription shifts upstream as the CGG-repeat expands, with much of the excess mRNA being produced by the additional, upstream initiator. We hypothesize that targeting the region of the mRNA between the normal and upstream initiators will effectively lower mRNA levels toward the normal range, without excess reduction. This proposal, representing another potential therapeutic approach to FXTAS, will be evaluated as part of Specific Aim 3.

Public Health Relevance

Expansions of a CGG-repeat in the FMR1 gene cause the leading heritable form of intellectual disability (fragile X syndrome) and are associated with the leading known single-gene form of autism. Smaller expansions give rise to the neurodegenerative disorder, FXTAS. In the proposed research, we propose to identify the origins of altered expression of the gene (low protein, fragile X syndrome;elevated RNA, FXTAS) to facilitate the development of targeted therapeutic approaches to these disorders.

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Research Project (R01)
Project #
Application #
Study Section
Developmental Brain Disorders Study Section (DBD)
Program Officer
Urv, Tiina K
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Davis
Schools of Medicine
United States
Zip Code
Ludwig, Anna Lisa; Espinal, Glenda M; Pretto, Dalyir I et al. (2014) CNS expression of murine fragile X protein (FMRP) as a function of CGG-repeat size. Hum Mol Genet 23:3228-38
Pretto, Dalyir I; Kumar, Madhur; Cao, Zhengyu et al. (2014) Reduced excitatory amino acid transporter 1 and metabotropic glutamate receptor 5 expression in the cerebellum of fragile X mental retardation gene 1 premutation carriers with fragile X-associated tremor/ataxia syndrome. Neurobiol Aging 35:1189-97
Juang, Bi-Tzen; Ludwig, Anna L; Benedetti, Kelli L et al. (2014) Expression of an expanded CGG-repeat RNA in a single pair of primary sensory neurons impairs olfactory adaptation in Caenorhabditis elegans. Hum Mol Genet 23:4945-59
Sahdeo, Sunil; Tomilov, Alexey; Komachi, Kelly et al. (2014) High-throughput screening of FDA-approved drugs using oxygen biosensor plates reveals secondary mitofunctional effects. Mitochondrion 17:116-25
Loomis, Erick W; Sanz, Lionel A; Chédin, Frédéric et al. (2014) Transcription-associated R-loop formation across the human FMR1 CGG-repeat region. PLoS Genet 10:e1004294
Pretto, Dalyir I; Hunsaker, Michael R; Cunningham, Christopher L et al. (2013) Intranuclear inclusions in a fragile X mosaic male. Transl Neurodegener 2:10
Hagerman, Paul (2013) Fragile X-associated tremor/ataxia syndrome (FXTAS): pathology and mechanisms. Acta Neuropathol 126:1-19
Sorensen, Page L; Gane, Louise W; Yarborough, Mark et al. (2013) Newborn screening and cascade testing for FMR1 mutations. Am J Med Genet A 161A:59-69
Hoem, Gry; Raske, Christopher R; Garcia-Arocena, Dolores et al. (2011) CGG-repeat length threshold for FMR1 RNA pathogenesis in a cellular model for FXTAS. Hum Mol Genet 20:2161-70
Ludwig, Anna L; Hershey, John W B; Hagerman, Paul J (2011) Initiation of translation of the FMR1 mRNA Occurs predominantly through 5'-end-dependent ribosomal scanning. J Mol Biol 407:21-34

Showing the most recent 10 out of 15 publications