Fragile X Syndrome
March 04, 2015
Waisman Center investigators Xinyu Zhao, PhD, and Anita Bhattacharyya, PhD, were awarded an $750,000 grant, over three years, from the John Merck Fund to explore a new treatment for fragile X syndrome (FXS) using gene editing. Zhao and Bhattacharyya received a $100,000 pilot grant from John Merck Fund in 2014 to begin this study and the new funding took effect February 1.
Fragile X syndrome—an intellectual disability— causes learning difficulties, hyperactivity, social anxiety, hypersensitivity to sensory stimuli, and autism and autism-related behaviors. Fragile X is caused by a repetitive genetic error on the X chromosome. The mutation is in a single gene called FMR1. A small set of nucleotides—the building blocks of DNA—are repeated excessively, disrupting the structure of the gene and preventing the production of its normally encoded protein called FMRP.
“Fragile X syndrome is caused by mutation of a single gene resulting in gene shuts down. If we can find a way to reactivate this gene, we can treat the disease,” says Zhao.
Zhao and Bhattacharyya’s grant is part of the Merck Fund’s developmental disabilities translational research program that supports research with potential for immediate impact on people with developmental disabilities and their families.
The FXS study at the Waisman Center is comprised of three phases. During phase 1, Bhattacharyya’s lab derived several pluripotent stem (iPS) cell lines from individuals with FXS and performed initial analysis of these lines. In phase 2, the Zhao and Bhattacharyya combined their expertise to explore methods that could reactivate the gene that shut down in FXS. Using a new genetic editing tool, a reporter cell line—with a reporter gene insertion into the human FXS gene—was created to monitor gene activation.
With a reliable cell reporter line in use and new funding, Zhao and Bhattacharyya began the third phase that is a drug screen for FXS gene reactivation.
“The main thing that we’re doing that other people have not done before is make human reporter cell lines. Before, scientists looked into the cells to find the gene expression. We can do it by using relevant human cells and a really sensitive reporter,” says Bhattacharyya. “We’re right at the beginning of this new process of gene editing in humans.”
A parallel aspect of this project is to explore how FXS mutation affects neuronal development. Zhao’s lab will take the FXS iPS cell-derived neurons and transplant them into mouse brains to study development “If you really want to study neurodevelopment, you have to study it in the brain, not a in a culture dish,” says Zhao. “The basis for this grant is using a mouse model to study human development in the brain and eventually use this model to test drugs for gene reactivation in neurons in the brain.”
The goals of the study are two-fold: to create a human reporter line for reactivation screen and create a living model to determine the cause of FXS and to test potential therapeutics.
Both Bhattacharyya and Zhao contributed to the understanding of the causes, consequences, and treatments of FXS. Zhao, a professor of neuroscience, has been working on FMRP regulation and how FMRP deficiency leads to learning deficits in individuals with FXS. Her findings suggest that promoting neurogenesis—the process of generating neurons—after birth may have therapeutic potential for people with FXS and other neurological disorders.
Bhattacharyya, a senior scientist, uses iPS cells from individuals with FXS to investigate the process of how nerve cells develop in FXS. She is also interested in how cell communication and cell signaling is affected by the lack of the FMRP protein. Bhattacharyya’s lab works with other Waisman Center investigators to distinguish attributes between FXS and autism with the goal to develop iPS cell lines to address questions about FXS.
More than one in 4,000 males and one in 8,000 females have the fragile X gene mutation. Many more people, however, have the premutation – an unstable version of the FMR1 gene that can transform into the full mutation in future generations. Carriers of the premutation are at greater risk for a neurodegenerative disorder resembling Parkinson’s disease called Fragile X-associated Tremor Ataxia Syndrome. There is evidence that the premutation may increase vulnerability to stress and affective challenges. As many as one in 250 women and one in 500 men in the general population carry the premutation.
Bhattacharyya hopes this study will advance knowledge about FXS and open doors to future treatment options.
“We’re not only going to learn a lot about how the FMR1 gene is silenced and how to reactivate it, we’re going to learn about the process to develop better treatments.”