A study of 10 million military personnel revealed last year that the ubiquitous Epstein-Barr virus, which infects 94% of people and causes kissing disease, is also the leading cause of multiple sclerosis, a rare disorder that, in the most severe cases, causes those affected to have problems speaking and walking. In 36 out of every 100,000 citizens, the virus triggers a process in which the human body's own defenses destroy the envelope of neurons, as if the wires of the brain and spinal cord were peeled. Some patients need a wheelchair, but others are able to reach the summit of Everest, such as American professor Lori Schneider. A new investigation, with 22,000 patients, identifies on Wednesday the first genetic variant associated with a more aggressive evolution of the disease. The researchers believe the discovery opens a path to treatments that stave off disability.
The authors, from two international consortia with a total of about 150 scientists, have examined seven million genetic variants, to identify a key region between two genes: DYSF, involved in repairing damaged cells in muscles, and ZNF638, involved in the control of virus infections. Neurologist Sara Llufriu, from the Hospital Clínic of Barcelona, explains that if a person inherits this variant, both from his mother and father, "he needs the support of a cane more than three and a half years before." The Clinic has contributed the data of some 300 patients to the macro-study, which is published this Wednesday in the journal Nature, a benchmark of the best world science.
Alberto Ascherio, doctor: "If you do not have the kissing disease virus, your risk of developing multiple sclerosis is practically zero"
The scientific community had already found some 200 genetic variants associated with the risk of suffering from multiple sclerosis, but this is the first linked to the rapid progression of the disease, according to neurologist Manuel Comabella, from the Multiple Sclerosis Center of Catalonia. "The disease is very heterogeneous. Many patients need first a crutch to walk, then two crutches, and finally rely on a wheelchair. But there are also more benign forms. There are patients who even stay very physically active and run miles and miles. Obviously, this must be due to possibly genetic factors," says Comabella. His center, belonging to the Vall d'Hebron Hospital in Barcelona, has provided information on 173 patients.
Multiple sclerosis has no cure, but in recent decades there has been a "therapeutic revolution" that has allowed to reduce and even avoid outbreaks of the disease, according to the authors of the new study. The disorder is characterized by an inflammatory process, key at first, and a neurodegenerative component, responsible for the progression of the disease. Current treatments only act on inflammation, so they do not slow the progression of multiple sclerosis in the long term. Comabella stresses that the discovery of the genetic variant points to a new Achilles heel. "The finding illuminates a possible mechanism involved in the progression of the disease, which in the future could be susceptible to being blocked with drugs," says the neurologist.
Researchers Sara Llufriu, Albert Saiz and Yolanda Blanco, co-authors of the study at Hospital Clínic de Barcelona.Hospital Clínic / IDIBAPS
Data from the 22,000 patients also suggest that educational attainment plays a protective role against multiple sclerosis, while smoking aggravates the disease. British neurologist Stephen Sawcer, one of the lead authors of the research, acknowledges that it is difficult to quantify these effects. "We have seen that, on average, each extra year of studies reduces severity by about 0.05 points, on a scale of 0 to 10, which is equivalent to 0.5%," says Sawcer, from the University of Cambridge. Educational level also has a protective role in other neurodegenerative diseases, such as Alzheimer's.
The work includes data from patients from Europe, Australia, the United States and Canada. Neurologist Luis Querol, from the Hospital de la Santa Creu i Sant Pau in Barcelona, highlights the limitations of the study, in which he has not participated. "There are many factors involved in the rapid progression to disability: the age of the patients, the habits, the treatments used, even geographical variants," Querol told the Science Media Centre portal. "Some of these factors do not seem to have been taken into account, so new cohorts would be needed to control these differences, to see if the results are replicated," he stressed.
The team of Italian epidemiologist Alberto Ascherio of Harvard University (USA) discovered last year that the Epstein-Barr virus, culprit of the kissing disease, is also "the main cause" of multiple sclerosis. "Probably, multiple sclerosis does not develop if a person is not infected with the virus," he explained in an interview with this newspaper. For Ascherio, the disease is "a rare complication of infection." The new work will serve to illuminate what happens once this complex inflammatory autoimmune process is unleashed.
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