New research shows gene therapy could treat Pitt-Hopkins syndrome

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DNA Gene Therapy Concept

A new study has shown that gene therapy may be able to prevent or reverse many adverse effects of Pitt-Hopkins syndrome

New research from the UNC Neuroscience Center lab of Ben Philpot, Ph.D., shows that restoring lost gene activity prevents many signs of disease in an animal model of Pitt-Hopkins syndrome, a rare single-gene neurodevelopmental disorder.

Pitt-Hopkins syndrome is a rare genetic disorder caused by a mutation in the TCF4 gene on chromosome 18. Pitt-Hopkins syndrome is characterized by developmental delay, potential breathing difficulties such as episodic hyperventilation and/or waking breath holding, recurrent seizures/epilepsy, gastrointestinal distress, speech disorders, and distinctive facial features. Children diagnosed with Pitt-Hopkins syndrome often have a happy and lively disposition, with frequent smiles and laughter.

The prevalence of Pitt-Hopkins syndrome in the general population is unclear. However, some estimates place the incidence of Pitt-Hopkins syndrome between 1 in 34,000 and 1 in 41,000. The disorder affects both men and women and is not limited to a single ethnic group.

Pitt-Hopkins syndrome is classified as an autism spectrum disorder, and some people who have it have been diagnosed with autism, “atypical” autistic traits, and/or sensory integration disorder. Many researchers believe that treating Pitt-Hopkins syndrome will lead to treatments for similar conditions because of its genetic link to autism and other disorders.

Researchers at the University of North Carolina School of Medicine have shown for the first time that postnatal gene therapy may be able to prevent or reverse many of the adverse effects of Pitt-Hopkins syndrome, a rare genetic disorder. Severe developmental delay, intellectual disability, breathing and movement abnormalities, anxiety, epilepsy, and moderate but characteristic facial abnormalities are all symptoms of this autism spectrum disorder.

The scientists who published their findings in the journal eLife, developed an experimental, gene therapy-like technique to restore normal functioning of the gene deficiency in people with Pitt-Hopkins syndrome. The drug prevented the emergence of disease indicators such as anxiety-like behaviors, impaired memory and abnormal gene expression patterns in affected brain cells in newborn mice that would otherwise model the syndrome.

“This first demonstration of proof-of-principle suggests that restoring normal levels of the Pitt-Hopkins syndrome gene is a viable therapy for Pitt-Hopkins syndrome, for which there is otherwise no specific treatment,” he said senior author Ben Philpot, Ph.D. , Kenan Distinguished Professor of Cell Biology and Physiology at the UNC School of Medicine and Associate Director of the UNC Neuroscience Center.

brain protein Cre

Brain cross-section: protein Cre (green) delivered to cells via AAV as gene therapy. Photo credit: Philpot Lab (UNC School of Medicine)

Most genes are inherited in pairs, one copy from the mother and one from the father. Pitt-Hopkins syndrome occurs in a child when one copy of the TCF4 gene is missing or mutated, resulting in insufficient TCF4 protein levels. Typically, this deletion or mutation occurs spontaneously in the parental egg or sperm prior to conception or in the earliest stages of embryonic life after conception.

Since it was first described by Australian researchers in 1978, only about 500 cases of the syndrome have been reported worldwide. But nobody knows the true prevalence of the syndrome; Some estimates suggest there could be more than 10,000 cases in the United States alone.

Because TCF4 is a “transcription factor” gene, a master switch that controls the activities of at least a hundred other genes, its disruption leads to numerous developmental abnormalities from the onset of development. In principle, the best treatment strategy is to prevent these abnormalities by restoring normal TCF4 expression as early as possible – but this has not yet been tested.

Philpot’s team, led by first author Hyojin (Sally) Kim, Ph.D., a graduate student in the Philpot lab during the study, developed a mouse model of Pitt-Hopkins syndrome in which the level of the mouse version of TCF4 could be reliably halved . This mouse model showed many typical signs of the disorder. Restoring the full activity of the gene from the beginning of embryonic life completely prevented these signs. The researchers also found evidence in these initial experiments that gene activity had to be restored in virtually all types of neurons to prevent the appearance of Pitt-Hopkins signs.

Next, the researchers set up a proof-of-concept experiment that models a real-world gene therapy strategy. In engineered mice that had about half of the expression of the mouse version of Tcf4 turned off, the researchers used a virus-transmitted enzyme to turn the missing expression back on in neurons right after the mice were born. Analysis of the brain showed this restoration of activity over the next few weeks.

Although the treated mice had moderately smaller brains and bodies compared to normal mice, they did not develop many of the abnormal behaviors seen in untreated Pitt-Hopkins model mice. The exception was innate nest-building behavior, in which the treated mice appeared abnormal at first, although their abilities returned to normal within a few weeks.

The treatment at least partially reversed two other abnormalities observed in untreated mice: altered levels of TCF4-regulated genes and altered patterns of neuronal activity as measured in electroencephalographic (EEG) recordings.

“These results give hope that future gene therapy will bring significant benefits to people with Pitt-Hopkins syndrome, even if they deliver postnatally; it doesn’t require diagnosis and treatment in the womb,” Kim said.

Philpot and his lab now plan to study the effectiveness of their strategy when applied to Pitt-Hopkins mice later in life. They also plan to develop an experimental gene therapy in which the human TCF4 gene itself is delivered by a virus into a Pitt-Hopkins mouse model — a therapy that could eventually be tested in children with Pitt-Hopkins syndrome.

“We will be working on gene therapy, but our results here suggest that there are other TCF4-restoring approaches that might work, including treatments that increase the activity of the remaining good copy of TCF4,” Philpot said.

The research was supported by the Ann D. Bornstein Grant from the Pitt-Hopkins Research Foundation, the National Institute of Neurological Disorders and Stroke (R01NS114086), the Estonian Research Council, and the Orphan Disease Center at the Perelman School of Medicine at the University of Pennsylvania ( MDBR-21-105-Pitt Hopkins).

Reference: “Rescuing Behavioral and Electrophysiological Phenotypes in a Pitt-Hopkins Syndrome Mouse Model by Genetically Restoring Tcf4 Expression” by Hyojin Kim, Eric B. Gao, Adam Draper, Noah C. Berens, Hanna Vihma, Xinyuan Zhang, Alexandra Higashi-Howard, Kimberly D Ritola, Jeremy M Simon, Andrew J Kennedy and Benjamin D Philpot, May 10, 2022, eLife.
DOI: 10.7554/eLife.72290

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