A new drug has corrected the defect behind the neurodegenerative disease Huntington's for the first time in a patient trial, according to researchers at University College London.
The experiment drug effectively decreased toxic proteins in the brain, giving hope that the deadly disease's progression might be halted.
"I really think this is, potentially, the biggest breakthrough in neurodegenerative disease in the past 50 years," said Alzheimer's researcher John Hardy about the results of the first clinical trial.
Huntington's is a devastating disease that slowly breaks down the nerve cells in the patient's brain, resulting in losing the ability to walk, talk and think, ultimately causing death. Symptoms usually begin to show between ages 30 and 40, and patients die within 10 to 20 years as the disease kills more and more brain cells.
"You end up in almost a vegetative state, it's a horrible end," said Peter Allen, a 51-year-old in the early stages of the disease who participated in the drug trial.
It's perhaps even harder to live with knowing that the disease is inherited, with 90 percent of sufferers receiving the gene from a parent.
Allen has seen his mother, uncle and grandmother all succumb to the disease, and tests show his sister and brother are also living with the disease in latent form.
The next generation, the three siblings' eight children, all have a high risk of developing it.
"It's so difficult to have that degenerative thing in you," Allen told the BBC. "You know the last day was better than the next one's going to be."
Along with Allen, 45 other patients participated in the clinical trial held at London's Leonard Wolfson Experimental Neurology Centre at the National Hospital for Neurology and Neurosurgery.
The treatment, injected into the spinal cord, was tolerated well by all patients and showed to critically reduce harmful levels of the huntingtin protein.
"I've been seeing patients in clinic for nearly 20 years, I've seen many of my patients over that time die," said lead researcher Sarah Tabrizi.
"For the first time we have the potential, we have the hope, of a therapy that one day may slow or prevent Huntington's disease. This is of groundbreaking importance for patients and families."
Doctors hesitate to call the treatment a cure at this stage in testing. Long-term data will show whether the effects of the drug in lowering harmful huntingtin protein can change the course of the disease.
Allen and the other patients will continue to take the drug to monitor its long-term effects.
Allen hopes the treatment will be able to save the lives of his family members and children.
"Hopefully that will be made available to everybody, to my brothers and sisters and fundamentally my children," said Allen, describing himself as "the luckiest person in the world."