A latest genetic strategy that boosts production of the protein disrupted in Rett syndrome has shown promising results in laboratory studies, offering a potential path toward treatments that address the root cause of the debilitating neurological disorder. The research, published earlier this month in Science Translational Medicine, centers on manipulating how cells process genetic information to increase levels of the MECP2 protein.
Rett syndrome, primarily affecting girls, is caused by mutations in the MECP2 gene, located on the X chromosome. This gene is crucial for regulating thousands of other genes essential for brain function. While some mutations completely halt MECP2 production, others result in a defective protein or reduced quantities. The condition is characterized by a period of normal development followed by a rapid regression in motor skills, language and cognitive abilities. Boys with Rett syndrome typically experience a more severe course and often die in early childhood, according to the National Institutes of Health.
Currently, the only FDA-approved drug for Rett syndrome, trofinetide, manages some of the condition’s symptoms but doesn’t correct the underlying genetic defect. Researchers have long sought ways to increase MECP2 protein levels, as studies have demonstrated that restoring these levels in mice can reverse many of the syndrome’s traits and extend lifespan. However, achieving the right balance is critical; too little MECP2 causes Rett syndrome, while too much can lead to MECP2 duplication syndrome, another neurological disorder.
Existing gene therapy approaches utilize viral vectors to deliver a functional copy of the MECP2 gene, aiming to self-regulate production and prevent overproduction. However, these vectors have limited reach, only affecting brain cells near the injection site. “Because MECP2 is active throughout the brain, researchers are exploring other strategies that can safely boost protein levels more broadly,” explained Huda Zoghbi, professor of molecular and human genetics at Baylor College of Medicine and a lead investigator on the study.
Zoghbi and her team focused on the cell’s splicing machinery – the process that removes non-coding segments from genes. They devised a method to encourage this machinery to “skip” a modest segment within the MECP2 gene. This adjustment increased MECP2 protein production in mice. In neurons derived from individuals with Rett syndrome, removing the same segment partially corrected several hallmarks of the condition.
“It’s a very clever study,” said Walter Kaufmann, an adjunct professor of human genetics at Emory University School of Medicine, who was not involved in the research.
The research builds on the understanding that the MECP2 gene produces two versions of messenger RNA, known as e1 and e2. The key difference lies in the presence of a short segment, exon 2, which is included in the e2 form but absent in e1. The e1 version is more efficiently translated into protein.
To favor the e1 version, the researchers deleted exon 2 in MECP2 in wildtype mice. This resulted in increased production of the e1 form, raising MECP2 protein levels by up to 60 percent in the brains of the modified mice. Male mice, carrying only one X chromosome, tolerated the increase with only minor increases in anxiety-like behavior. Female mice, with a mix of cells expressing either normal or altered MECP2, showed no obvious behavioral changes.
Testing the approach in neurons grown from stem cells of people with different Rett-associated variants yielded further encouraging results. In neurons carrying the G118E variant – which reduces both the stability and DNA-binding ability of MECP2 – deleting exon 2 restored protein levels to near normal, improving neuronal function and structure. Up to 65 percent of disrupted genes in these neurons showed partial recovery after MECP2 levels increased. Even in neurons with a more disruptive variant, where MECP2 levels only rose slightly, gene activity across hundreds of affected genes shifted closer to normal.
“It told us something about the protein itself—that even small levels of change can make a significant difference,” said Harini Tirumala, a former graduate student in Zoghbi’s lab and a study investigator.
The team likewise developed a molecule resembling an antisense oligonucleotide, designed to bind near exon 2 and prevent its inclusion in the final mRNA. This exon-skipping approach also increased levels of the e1 form of MECP2 in wildtype mice.
Kaufmann likened the strategy to exon-skipping antisense oligonucleotides used for Duchenne muscular dystrophy, which don’t cure the condition but convert a severe form into a milder one by producing a shorter, yet functional, protein. He suggested the Rett approach could similarly improve the functionality of many MECP2 variants.
However, Zoghbi cautioned that the strategy would only be effective for individuals whose variants allow for some residual MECP2 protein function. It would not benefit those with variants that completely eliminate the protein or its activity. “There, we can’t help,” she said. She estimates that approximately 65 percent of people with Rett syndrome still produce some functional protein and could potentially benefit from this approach.
Zoghbi also suggested the principle could extend beyond Rett syndrome, potentially applicable to other genetic conditions where different versions of a gene produce proteins with varying efficiencies.
Mriganka Sur, professor of neuroscience at the Massachusetts Institute of Technology, who was not involved in the study, acknowledged the strength of the proof-of-concept data in human neurons and mice, justifying further investigation. “It’s a very creative approach,” he said. However, Sur noted that the results come from experiments in healthy animals, not established Rett models, leaving it unclear how effective the exon-skipping approach would be in people with the condition. He also pointed out that other strategies, including those using small RNA switches to regulate MECP2 levels, are already in clinical trials and showing promise, while the new approach “has a longer way to go.”
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