Wednesday, July 09, 2008
The use of MRIs to map the condition of the central nervous system has been helpful in identifying the illness.
By Susan J. Landers, AMNews staff. July 14, 2008.
Washington -- Multiple sclerosis is beginning to reveal some of its secrets to the researchers who study the disease that plays havoc with the central nervous systems of about 400,000 Americans.
Although its cause remains elusive, a possible scenario for its development includes a genetic predisposition that may be influenced by infectious agents and environmental factors, said researchers at a June 24 Capitol Hill briefing.
The event was sponsored by the Society for Women's Health Research and the National Multiple Sclerosis Society.
About 20% of people with MS have a family history of the disease, said Henry McFarland, MD, chief of neuroimmunology at the National Institute of Neurological Disorders and Stroke.
Studies comparing identical twins and fraternal twins have offered evidence of the disease's genetic component. According to researchers from the University of California, San Francisco, the risk for developing MS when one twin has the disease is 2% for an unaffected fraternal twin and between 25% and 30% for an identical twin. But findings also point to a strong environmental influence because only a minority of genetically identical twins are both affected with MS.
The disease is generally more common among people of Northern European descent, and some populations have a very low incidence. For example, although MS is rare among Hungarian Gypsies, it is relatively common among other Hungarians, Dr. McFarland said.
Research indicates that a complex interaction of genes, perhaps between 50 and 100, is at work in the development of MS, Dr. McFarland said. A consortium of researchers in the U.S. and the United Kingdom have joined together to try to unravel the genetic influences, he noted. Last year two more genes were identified.
A diagnostic advance
Until recently, the disease has been difficult to diagnose, since its symptoms, which are many and varied, are shared with other conditions. But this ambiguity also can be a diagnostic clue: "The more difficulty people have in trying to explain the symptoms, the greater the likelihood that it is MS," said Heidi Crayton, MD, medical director of the MS Center of Greater Washington and an assistant professor of neurology at Georgetown University Medical Center in Washington, D.C.
Muscle rigidity is probably among the most widely recognized, but other systems can include bladder and bowel problems, numbness and tingling, pain and vision problems. "For years people with MS have been told there is no pain involved, but that's just not true," she added.
20% of people with multiple sclerosis have a family history of the disease.
Among the most troubling symptoms is the cognitive difficulty that comes from loss of brain tissue in some patients, Dr. Crayton said. "This symptom is common, especially in untreated patients."
The 45% to 65% of patients who will develop cognitive impairments within 10 years is a "huge issue now," she said. It also is the focus of treatment.
Detection of the disease has become easier with the use of MRIs, which can make the "invisible visible," she said. Brain atrophy and spinal cord lesions are clearly seen in scans. But the link between MRI findings and the clinical status of a patient is not clear, she noted.
A number of possible triggering infectious agents have been studied, including the herpes virus and the Epstein-Barr virus, Dr. Crayton said. "We're starting to see that many people who have MS have also had mono infections in the past."
In addition, advances have been made in understanding the environmental factors involved in the disease, Dr. McFarland said. Ongoing studies are looking at exposure to ultraviolet light and the relationship of vitamin D levels before MS onset.
A "hygiene hypothesis" also is being investigated, he said. The thought behind this notion is that people with good hygiene are more vulnerable to the disease.
The 4 courses of MS
People with multiple sclerosis typically experience one of four disease courses, each of which might be mild, moderate or severe.
Relapsing-remitting: Marked by clearly defined attacks of worsening neurologic function -- also termed relapses, flare-ups or exacerbations -- that are followed by partial or complete periods of recovery. During this time, no disease progression occurs. Approximately 85% of initial diagnoses involve this form of the disease.
Primary-progressive: Characterized by slowly worsening neurologic function from the beginning with no distinct relapses. The rate of progression may vary, with occasional plateaus and temporary minor improvements. About 10% of diagnoses are this form.
Secondary-progressive: After an initial period of relapsing-remitting MS, this course is marked by a steadily worsening condition, with or without occasional flare-ups, minor recoveries or plateaus. Before disease-modifying medications became available, about 50% of relapsing-remitting MS cases evolved into this form within 10 years. Long-term data are not yet available to determine if treatment has delayed this transition.
Progressive-relapsing: This relatively rare (about 5%of cases) course is marked by a steadily worsening disease from the beginning, with clear attacks of worsening neurologic function. The disease continues to progress without remissions.
Source: National Multiple Sclerosis Society
Facts on MS
* Approximately 400,000 people in the United States currently have multiple sclerosis.
* An estimated 200 additional people are diagnosed with the disease each week.
* Worldwide, MS affects more than 2.5 million people.
* Researchers have identified factors in the distribution of MS cases that eventually may help pinpoint the causes of the disease.
* These factors include gender, genetics, age, geography and ethnic background.
Source: National Multiple Sclerosis Society