The active ingredient in the erectile dysfunction drug Viagra has shown striking potential as a treatment for a devastating and rare childhood disease, offering new hope where no approved therapy exists.
Researchers from Charité – Universitätsmedizin Berlin report that sildenafil significantly improved symptoms in patients with Leigh syndrome, a severe genetic disorder. The findings, based on a pilot study and supported by preclinical research, have prompted plans for a Europe-wide clinical trial and have already secured Orphan Drug Designation from the European Medicines Agency to fast-track its development.
Promising Results in Patients and Animals
In the initial study, six patients aged between nine months and 38 years received daily, low-dose sildenafil for periods of up to seven years. The doses, ranging from 0.66 to 3 milligrams, are a fraction of a standard Viagra pill. The results, described by lead author Professor Markus Schuelke, were marked. One child’s walking distance increased tenfold, from 500 to 5,000 metres. Another patient saw the complete suppression of near-monthly metabolic crises, while epileptic seizures ceased in a third.
The researchers observed improved muscle strength, neurological function, and metabolic symptoms. These human findings were mirrored in laboratory tests on cell cultures and animal models. Studies in rodents and pigs with fatal cases of Leigh syndrome showed that sildenafil helped them live longer; two of seven treated pigs survived for over two months, with one remaining stable for six months.
How a Vasodilator Targets a Cellular Energy Crisis
The connection between a drug for erectile dysfunction and a neurodegenerative disease lies in addressing a fundamental energy deficit. Leigh syndrome is a mitochondrial disease, where genetic mutations disrupt the mitochondria—the cell’s power plants. This leads to crippling energy shortages, particularly in the brain and muscles.
Sildenafil’s primary known action is vasodilation—increasing blood flow. Researchers believe this improved circulation may help alleviate a dangerous complication of Leigh syndrome: high blood pressure in the arteries of the lungs. Furthermore, evidence from the study of lab-grown nerve cells and brain organoids suggests sildenafil may directly improve cellular energy metabolism and nerve cell function, offering a dual potential benefit for patients.
Professor Schuelke, while cautioning that these initial observations require confirmation in a larger study, stated the team was “very pleased to have found a promising drug candidate for the treatment of this serious hereditary disease.”
The Devastating Reality of Leigh Syndrome
The urgent need for a treatment is underscored by the disease’s severity. Leigh syndrome affects approximately one in 36,000 children globally, though incidence spikes in isolated populations like parts of Quebec, Canada. Caused by mutations in over 100 different genes, it typically manifests in infancy or early childhood with symptoms like feeding difficulties, loss of motor skills, vomiting, and seizures.
As it progresses, the disease can cause muscle weakness, movement disorders, vision loss, breathing difficulties, and impaired heart and kidney function. According to the US National Institutes of Health, half of children born with the condition die before the age of three. The Child Neurology Foundation notes that while some individuals have a milder, stable course, others experience rapid neurological decline.
Diagnosis involves MRI scans and blood tests, and current management is limited to supportive care. This includes thiamine (Vitamin B1) supplementation, dietary approaches like the ketogenic diet for specific genetic forms, and medications to manage lactic acidosis—a build-up of acid in the blood due to faulty energy production.
The research collaboration, which also involves the Heinrich Heine University Düsseldorf and the Fraunhofer Institute for Translational Medicine and Pharmacology, stresses that sildenafil must not be used without clinical supervision. The genetic complexity of Leigh syndrome also means not every form may respond to the same treatment. Nevertheless, the repurposing of this well-known drug offers a significant and tangible glimmer of hope for affected families.
