By: Daniel Kantor, M.D.
Genes are more than what you wear, they make us what we are. We are all created from two sets of genetic blueprints, strings of amino acids (the basic building blocks that make up DNA) that tell our cells what proteins to produce in order to make our bodies work. One set of chromosomes comes from your mother and one set comes from your father.
Our genes make us unique. If we all had the same genetic make-up, we would all be identical twins – we would all be the same sex, the same race, the same everything. Luckily, the genes from our parents combine to form a unique mixture which determines every-thing from our eye and hair color to, in some cases, whether we will be susceptible to certain diseases.
Some health conditions, like Huntington’s disease, a genetic neurological disorder, are inherited if you have even one gene telling your body to develop the disease. This is called an autosomal dominant disorder. Other diseases, such as sickle cell anemia, develop only if you have both genes for the condition, one from each parent. This is known as an autosomal recessive disorder.
MS isn’t like either of those conditions, though.
MS is thought to be an autoimmune disease, where the body gets confused and instead of attacking foreign invaders, it attacks itself. While MS is linked to our genes, it is not defined by them. Scientists first proved this by looking at identical twins.
Identical twins have the same genetic makeup, but they experience life differently. This means that while their features may look identical, their likelihood of developing some diseases, such as diabetes, may be different. One twin may be heavier than the other, for instance, and may thereby place themselves at greater risk for developing a condition related to weight. So even though their genetic programming is identical, their environmental exposure is not.
Studies have shown that if one identical twin has MS, the other has only a 30 percent chance of developing the condition. If MS were completely genetic, then the other twin would have a 100 percent chance of having it, because both identical twins have exactly the same genes. If it were not genetic at all, then the other twin’s risk of MS would be 0.1 percent, the odds seen in the general population. So we believe that MS is partially genetic and partially caused by our surroundings.
Knowing exactly where that genetic susceptibility lies or what exactly the environmental exposure, is one of the great mysteries of MS. Still, we know a lot more about MS and genetics than we did 20, 10, or even five years ago. We now recognize that there are certain parts of our genetic code that make us more or less susceptible to developing MS, just as there are genes which make us more or less susceptible to developing other autoimmune diseases, such as lupus or rheumatoid arthritis. If a person has these genes, and then gets exposed to a certain environmental condition, then MS could develop.
Researchers currently think that the environmental condition could be an early viral infection that the body tries to fight off. Instead of attacking the foreign invader, – the virus – the body gets confused and learns to attack itself.
No matter what the “trigger,” however, other people are exposed to that same environment and don’t develop MS. Is that because they don’t have the genes to be susceptible? Scientists are still working on finding out.
People who are related often share both genes and their environment, and so we sometimes find families that have multiple members with MS. These families seem to have a greater likelihood of inheriting the MS “susceptibility genes” than others. Most people with MS, however, have a very low likelihood of passing down MS to their children.
The child of a person with MS has an approximately 2 percent chance of having the condition. To put this into perspective, the risk of having a heart attack in the American population is more than 2 percent. This means that if you have MS, your child is more likely to have a heart attack as an adult than to have MS.
Since researchers now believe that there is a string of genetic code that makes people more susceptible to developing MS, a natural question is if there is some test that can tell us if you carry that gene. That is a difficult problem, since people with MS have many of the same genes as those people without it (for example, the twins where one has MS and the other does not). So, in order for us to get closer to answering the question of which genes place a person at a greater likelihood of developing MS, scientists need to collect blood from as many people with the condition as possible.
The goal of this research is not simply to know what genes make a person more likely to develop MS, but to eventually figure out what treatments will be most effective for an individual. This will allow for more personalized medicine, and will ensure that MS is treated in the best way.
There also is hope that genetic research will help us to predict who is at risk for developing MS, allowing doctors to try to prevent the condition before it starts. There is a lot of hope invested in genetic research of MS. Although much hard work is needed to figure it all out, in the future, genes may be not what we wear or who we are, but what we can be.
Daniel Kantor, M.D. is Assistant Professor of Neurology and Director of the Comprehensive Multiple Sclerosis Center at the University of Florida in Jacksonville, Florida. He also serves on the ethics committee of Shands Jacksonville Hospital and recently was elected to serve as a board member of the Duval County Medical Society and as an alternate delegate to the Florida Medical Society. He is the President-Elect of the Florida Society of Neurology and is a member of the Clinical Advisory Committee of the North Florida chapter of the National Multiple Sclerosis Society. He is a principal investigator in several multiple sclerosis studies and a member of an international collaboration studying the genetics of MS.
(Last reviewed 7/2009)