The late onset of multiple sclerosis—being diagnosed after age 50—appears to be more common than previously thought. In a study among 838 individuals with MS, the peak age of onset was between the ages of 20 and 25, but 9.4% experienced their first symptoms after the age of 50.

Because of other medical problems which affect older people, MS may be overlooked, accounting for a large number of misdiagnosed cases.

Whether there is a difference in prognosis¾predicted course of the disease¾for those with late onset of MS is still controversial.

Childhood MS:

MS is usually thought of as a disease of adults, with the highest incidence of new diagnosis among people in their 20s and 30s.  Its onset generally occurs between the ages of 15 and 55.  But, uncommonly, MS is diagnosed between the ages of 10 and 15.  A diagnosis before the age of 10 is even rarer, although there have been isolated reports of infants as young as 18 months diagnosed with MS. Children with MS generally experience the same types of symptoms as adults, including possible cognitive dysfunction that may affect school performance.

A recent study of 149 individuals with early onset MS revealed no significant difference in the course of the disease compared with adults.  The majority of children in this study had relapsing-remitting MS.  However, there was a slightly greater number of males among those diagnosed before the age of 12.  After that age there was a higher number of females, suggesting a possible hormonal effect related to puberty.

There appear to be multiple causes in MS, possibly including viruses and environmental, genetic, and immune system factors. Among the well-established epidemiological observations on MS are:

1.      Worldwide, MS occurs with much greater frequency in higher latitudes (above 40° latitude) away from the equator, than in lower latitudes, closer to the equator.

2.      In the U.S., MS occurs more frequently in states that are above the 37^th parallel than in states below it.  From east to west, the 37^th parallel extends from Newport News, VA, to Santa Cruz, CA—running along the northern border of North Carolina to the northern border of Arizona and including most of California.  The MS prevalence rate for the region below the 37^th parallel is 57 to 78 cases per 100,000 people. The prevalence rate for those above the 37^th parallel is 110 to 140 cases per 100,000 people.  Nationwide, there are an estimated 250,000 to 350,000 people with MS.

3.      An individual who is born in an area with a higher risk of developing MS and moves to an area of lower risk, acquires the risk of the new home if the move occurs prior to adolescence.

4.      MS is more common among Caucasians (particularly those of northern European ancestry) than other races, and is almost unheard of in some populations, such as Inuit.

5.      MS is 2-3 times as common in women than in men.

6.      Certain outbreaks or clusters of MS have been identified, but their significance is not known.

7.      In certain populations, a genetic marker has been linked to MS. A particular genetic trait occurs more frequently in people with MS than in those who do not have the disease.

These and other studies have contributed to the opinion that early exposure to an environmental agent might be a triggering factor in people who are predisposed by genetic factors to develop MS.  

Genetics:

The genes a person inherits help determine whether that person is at increased risk for developing MS. While there is evidence from studies that this genetic component exists, it appears to be only one factor among several. Most likely an individual’s genetic blueprint ultimately determines if that individual will be susceptible to a triggering factor, which in turn initiates the autoimmune process that leads to the development of MS.

What Population Studies Show

Epidemiologic surveys have determined that an individual's risk of developing MS increases several-fold if a close family member has MS. But the risk is still relatively low. While the average person in the United States has about 1 chance in 1,000 of developing MS, close relatives of people with MS, such as children or siblings, have a 1 in 100 to 1 in 50 chance of developing MS. The identical twin of a person with MS has a 1 in 3 chance of developing the disease. 

The fact that identical twins of people with MS¾who share all the same genes¾don’t always get MS and that more than 80% of people with MS do not have a first-degree relative with MS, show that genes are not the only factors involved and that MS is not directly inherited.

New Techniques Help Pinpoint Genetic Factors

In the past few years, scientists have developed a set of tools that gives them the ability to pinpoint the genetic factors that make a person susceptible to MS. These tools are the methods of molecular genetics—techniques used to isolate and determine the chemical structure of genes.

In the 1980s, scientists began to apply the tools of molecular genetics to human diseases caused by defects in single genes. This work led to major advances in understanding diseases such as Duchenne muscular dystrophy and cystic fibrosis. The situation for diseases such as multiple sclerosis is more complicated.  Scientists now believe that a person is susceptible to multiple sclerosis only if he or she inherits an unlucky combination of alterations in several genes.

Advances in molecular genetics and the identification of large families in which several members have MS—“multiplex” MS families—have made possible research to uncover MS susceptibility genes.  Since 1991, the National MS Society has supported an international project searching for these genes.

Scientists Are Searching for ‘DNA Markers’

Many multiplex families from throughout the world have agreed to participate in these studies. The researchers are looking for patterns of genetic material that are consistently inherited by people with MS. These recognizable patterns are called “DNA markers.”

When one of these markers is identified, scientists focus on that area, seeking additional markers closer to that gene. Eventually the location of that gene can be identified. This process of moving closer to the gene until it is identified has to be repeated for each of the marker regions from the multiplex families.

By 1996, as many as 20 locations that may contain genes contributing to MS were identified, but no single gene was shown to have a major influence on susceptibility to MS.  Research will likely find that other, as yet unidentified, genes contribute to MS.

After the location of each susceptibility gene is identified, the role that the gene plays in the immune system and neurologic aspects of people with MS will have to be determined. Because the immune system is so involved in MS, many scientists think at least some of the susceptibility genes are related to the immune system.  Already there have been reports linking some immune system genes to MS.

How This Research Could Help People With MS

Finding the genes responsible for susceptibility to MS may lead to the development of new and more effective ways to treat the disease.  Such research could also uncover the basic cause of the disease and help predict the course of the disease in an individual. This would make it easier for physicians to tailor therapies and provide information to help people make life decisions.

Another possible benefit might be the early diagnosis of people in families where one or more member already has MS. Many physicians believe that the earlier MS is diagnosed and treatment begun, the better the outcome will be.

This information is taken with permission from the NMSS.org