Researchers exploring Rett syndrome have uncovered a new mechanical driver behind its hallmark breathing abnormalities, identifying peripheral chemoreceptors as a key culprit. Simultaneously, clinical trials are underway to test a Parkinson’s medication aimed at reducing distressing breath-holding episodes in patients.
Disordered Breathing and the Search for Root Causes
For families managing Rett syndrome, a rare genetic disease affecting girls almost exclusively, the physical toll is terrifying. The condition, caused by the mutation or deletion of the single MECP2 gene on the X chromosome, brings intellectual disabilities, seizures, and limited hand use. Yet among its most alarming hallmarks are profound respiratory disruptions. Children experience extreme cycles of disordered breathing, alternating between periods of apnea where breathing stops entirely, followed by gasping and rapid hyperventilation.
While Rett is not a degenerative disease and individuals frequently live into adulthood, these breathing episodes remain deeply distressing. Historically, researchers classified Rett strictly as a central nervous system disorder, locating the core problem in the brain. However, past investigations into how the brain controlled these breathing symptoms remained inconclusive. A team at the University of Connecticut set out to untangle the precise mechanics.
Uncovering the Carotid Body Connection in Mouse Models
The human body normally regulates respiration through two distinct sensors. One is a cluster of carbon dioxide-sensing cells in the brainstem, while the other sits around the carotid artery in the neck, monitoring oxygen levels. To see how the brain operated independently, researchers initiated experiments using a mouse model lacking the MECP2 gene. By having the mice breathe pure oxygen, investigators effectively took the peripheral oxygen sensors in the neck offline to observe pure brain-driven respiration.
To the surprise of the research team, exposure to pure oxygen stabilized the breathing patterns of the deficient mice. This unexpected result pointed away from a purely central origin and suggested that over-activation of the peripheral chemoreceptors around the carotid artery was driving the instability. Proving this hypothesis required isolating the gene deletion exclusively within the tiny carotid body of normal mice, a delicate structure roughly the size of two grains of sand.
Collaborating with specialists at George Washington University, the research team used a specialized viral gel injection to block MECP2 only in the oxygen-sensing peripheral chemoreceptors while leaving the brain’s carbon dioxide sensors untouched. The targeted maneuver succeeded: normal mice began displaying the classic Rett breathing pattern of apnea and hyperventilation. Subsequent gene expression analysis revealed that dopamine-expressing genes were less active in the carotid bodies of Rett models. Because dopamine acts as an inhibitory signal in that region, its reduction effectively removes the system’s brakes, leading to erratic breathing.
Targeting Breath-Holding in Clinical Trials
While laboratory researchers trace the cellular roots of respiratory instability, clinical investigators are pursuing active treatments for the symptoms families face daily. An international effort designated as the STARS study is evaluating whether sarizotan, a medication originally developed for Parkinson’s disease, can mitigate severe breath-holding.
In patients with Rett syndrome, these breath-holding spells can persist for up to 30 seconds at a time and repeat across hours. Experts note that the behavior forces patients to swallow large amounts of air, which severely compromises nutrition—a major issue for individuals with the condition.
Although breath-holding often subsides as patients reach early adulthood, it remains highly disruptive during youth. The multisite trial represents the first multisite trial of a potential therapy addressing this specific symptom. Investigators suggest the drug may act by activating serotonin 1a receptors in the brain stem, though its precise mechanism remains unclear.
Multisite Enrollment and Disease-Modifying Stakes
Sponsored by Newron Pharmaceuticals U.S., Inc., the clinical trial spans four domestic sites alongside several international locations. Participating domestic centers include the University of Alabama at Birmingham, the Altman Clinical and Translation Research Institute at the University of California San Diego, Rush Medical University Center in Chicago, and Texas Children’s Hospital in Houston.
The study specifically targets patients aged 13 and older who weigh at least 55 pounds and experience multiple daily episodes of waking breath-holding. Local teams, such as the cohort at UAB, aim to enroll 10 to 15 participants for a one-year follow-up period.
By combining new mechanistic insights into peripheral chemoreceptor dysfunction with ongoing pharmacological trials, researchers hope to build a clearer path toward easing the respiratory burden carried by patients and their families.
