New research from the UNC Neuroscience Center laboratory of Ben Philpot, Ph.D., reveals that restoring lost gene activity prevents many signs of disease in an animal model of Pitt-Hopkins syndrome, a rare monogenic 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 problems such as episodic hyperventilation and/or apnea while awake, recurrent seizures/epilepsy, gastrointestinal difficulties, lack of speech and distinctive facial features. Children diagnosed with Pitt-Hopkins syndrome often have a cheerful and lively demeanor with frequent smiles and laughter.
The prevalence of Pitt-Hopkins syndrome in the general population is unclear. However, some estimates place the frequency of Pitt-Hopkins syndrome between 1 in 34,000 and 1 in 41,000. The disease affects both men and women equally and is not restricted to one 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 features, and/or sensory integration dysfunction. Many researchers believe that treating Pitt Hopkins syndrome will lead to treatments for similar disorders because of its genetic link to autism and other conditions.
For the first time, researchers at the University of North Carolina School of Medicine have shown that postnatal gene therapy could prevent or reverse many of the negative effects of Pitt-Hopkins syndrome, a rare genetic disorder. Severe developmental delay, intellectual disability, respiratory and motor abnormalities, anxiety, epilepsy, and mild but distinctive facial abnormalities are all symptoms of this autism spectrum disorder.
The scientists, who published their findings in the journal eLife, created an experimental gene therapy-like technique to restore normal function of the deficient gene in people with Pitt-Hopkins syndrome. The drug prevented disease indicators such as anxious behavior, memory impairment and abnormal gene expression patterns from occurring in affected brain cells in newborn mice that would otherwise model the syndrome.
“This early proof-of-principle demonstration suggests that restoring normal levels of the Pitt-Hopkins syndrome gene is a viable therapy for Pitt-Hopkins syndrome, which otherwise has no specific treatment,” the author said. Principal 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.
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 an insufficient level of TCF4 protein. Typically, this deletion or mutation occurs spontaneously in the parental egg or sperm before conception, or in the early stages of embryonic life after conception.
Only around 500 cases of the syndrome have been reported worldwide since it was first described by Australian researchers in 1978. But no one knows the true prevalence of the syndrome; some estimates suggest there could be more than 10,000 cases in the United States alone.
Since TCF4 is a “transcription factor” gene, a general switch that controls the activities of at least hundreds of other genes, its disruption from the start of development leads to numerous developmental anomalies. In principle, preventing these abnormalities by restoring normal TCF4 expression as soon as possible is the best treatment strategy, but it 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 the TCF4 could be reliably halved. This mouse model showed many typical signs of the disease. The restoration of 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 emergence of Pitt-Hopkins signs.
Next, the researchers set up a proof-of-concept experiment modeling a real-world gene therapy strategy. In engineered mice in which about half the expression of the mouse version of Tcf4 was turned off, the researchers used a virus-delivered enzyme to reactivate the missing expression in neurons just after the mice were born. Brain scans showed this restoration of activity over the following weeks.
Even though the treated mice had moderately smaller brains and bodies than 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 treated mice appeared abnormal at first, although their abilities returned to normal within weeks.
The treatment at least partially reversed two other abnormalities seen in untreated mice: altered levels of genes regulated by TCF4 and altered patterns of neuronal activity as measured in electroencephalographic (EEG) recordings.
“These findings raise hope that future gene therapy will provide significant benefits to people with Pitt-Hopkins syndrome, even when delivered after birth; it will not require in utero diagnosis and treatment,” said Kim.
Philpot and his lab now plan to explore the effectiveness of their strategy when applied to Pitt-Hopkins mice at later life stages. They also plan to develop an experimental gene therapy in which the human TCF4 gene itself will be delivered by a virus into a Pitt-Hopkins mouse model – a therapy that could ultimately be tested in children with Pitt-Hopkins syndrome.
“We will be working on a gene therapy, but our results here suggest that there are other approaches to restoring TCF4 that could work, including treatments that stimulate the activity of the remaining good copy of TCF4,” said Philpot.
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 Center for Orphan Diseases of the University’s Perelman School of Medicine. of Pennsylvania (MDBR-21-105-Pitt Hopkins).
Reference: “Rescue of Behavioral and Electrophysiological Phenotypes in a Mouse Model of Pitt-Hopkins Syndrome by Genetic Restoration of 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.