These model cells of Fragile X-associated tremor/ataxia syndrome
(FXTAS), show defects, in orange, that cause tremor ataxia.
(Image courtesy of the Disney lab, The Scripps Research Institute).
Molecule Reverses Some Fragile X Syndrome Defects
Scientists have designed a compound that shows promise as a potential therapy for one of the diseases closely linked to fragile X syndrome, a genetic condition that causes mental retardation, infertility, and memory impairment, and is the only known single-gene cause of autism
Scientists at the Florida campus of The Scripps Research Institute generated the study, published in the journal ACS Chemical Biology September 4, 2012, which focuses on tremor ataxia syndrome - usually affecting men over the age of 50 and resulting in Parkinson’s like-symptomstrembling, balance problems, muscle rigidity, as well as some neurological difficulties, including short-term memory loss and severe mood swings.
Tremor Ataxia Syndrome
Physical symptoms of FXTAS include
an intention tremor, ataxia, and parkinsonism
( small, shuffling steps, muscle rigidity and slowed
speech), as well as neuropathic symptoms.
As the disease progresses to the more advanced stages,
a person with FXTAS is at risk of autonomic dysfunction.
This includes hypertension, bowel and bladder
dysfunction, and impotence.
Individuals with FXTAS may also exhibit:
a decrease in cognition, including diminishing
short-term memory and executive function skills,
declining math and spelling abilities
and decision-making abilities.
FXTAS may also result in changes in personality,
due to alterations of the limbic area in the brain.
This includes increased irritability, angry outbursts,
and impulsive behaviour.
Hagerman, PJ; Hagerman RJ (2004). "Fragile X-associated tremor/ataxia
syndrome (FXTAS)". Mental Retardation and Developmental Disabilities
Research Reviews 10 (1): 2530.
With fragile X syndrome, tremor ataxia syndrome, and related diseases, the root of the problem is a structural motif known as an “expanded triplet repeat”in which a series of three nucleotides are repeated more times than normal in the genetic code of affected individuals. This defect, located in the fragile X mental retardation 1 (FMR1) gene, causes serious problems with the processing of RNA.
“While there is an abundance of potential RNA drug targets in disease, no one has any idea how to identify or design small molecules to target these RNAs,” said Mathew Disney, a Scripps Research associate professor who led the study. “We have designed a compound capable of targeting the right RNA and reversing the defects that cause fragile X-associated tremor ataxia.”
In tremor ataxia syndrome, the expanded triplet repeat leads to the expression of aberrant proteins that wreak widespread havoc. The repeats actually force the normal proteins that regulate RNA splicingnecessary for production of the right kind of proteinsinto hiding.
The compound designed by Disney
and his colleagues not only improves
the RNA splicing process,
but also minimizes the ability
of repeats to wreak havoc on a cell.
Disney: “It stops the repeat-associated defects in cell culture, and at fairly high concentrations, it completely reverses the defects. More importantly, the compound is non-toxic to the cells. It looks like a very good candidate for development, but we’re still in the early stages of testing.”
Overall, this study reinforces Disney’s earlier findings showing it is possible to identify and develop small molecules that target these traditionally recalcitrant RNA defects.
In March of this year, Disney published a study in the Journal of the American Chemical Society that described a small molecule that inhibited defects in myotonic dystrophy type 1 RNA in both cellular and animal models of disease.
“We’ve gotten very good at targeting RNA
with small molecules, something a lot of people
said couldn’t be done. Our approach is evolving
into a general method that can be used to target
any disease associated with an RNA, including,
perhaps, fragile X syndrome itself.”
Mathew Disney, Ph.D.
The new compound also works as a probe to better understand how these repeats cause fragile X syndrome and how they contribute to tremor ataxia, Disney added.
In addition to Disney, authors of the study, “Small Molecule That Targets r(CGG) and Improves Defects in 2 Fragile X-Associated Tremor Ataxia Syndrome,” include Biao Liu, Wang-Yong Yang, Tuan Tran, and Jessica L. Childs-Disney of Scripps Research; and Nicolas Charlet-Berguerand and Chantal Sellier of the Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut National de la Santé et de la Recherche Médicale (INSERM), the Centre National de la Recherche Scientifique (CNRS), and University of Strasbourg, Illkirch, France. For more information on the paper, see http://pubs.acs.org/doi/full/10.1021/cb300135h.
The study was funded by the National Institutes of Health (award numbers 3R01GM079235-02S1 and 1R01GM079235-01A2), INSERM, the French National Research Agency, and The Scripps Research Institute.
About The Scripps Research Institute
The Scripps Research Institute is one of the world's largest independent, not-for-profit organizations focusing on research in the biomedical sciences. Over the past decades, Scripps Research has developed a lengthy track record of major contributions to science and health, including laying the foundation for new treatments for cancer, rheumatoid arthritis, hemophilia, and other diseases. The institute employs about 3,000 people on its campuses in La Jolla, CA, and Jupiter, FL, where its renowned scientistsincluding three Nobel laureateswork toward their next discoveries. The institute's graduate program, which awards Ph.D. degrees in biology and chemistry, ranks among the top ten of its kind in the nation. For more information, see www.scripps.edu.
Original article: http://www.scripps.edu/news/press/2012/20120904disney.html