• What is MS?

• Symptoms

• Causes of MS

• What Virus Causes MS?

• Is MS contagious?

• Signs and tests

• Genetics of multiple sclerosis: linkage and association studies

What is Multiple Sclerosis

Multiple sclerosis is a chronic, often disabling disease of the central nervous system. Symptoms may be mild such as numbness in the limbs or severe -- paralysis or loss of vision.

Most people with MS are diagnosed between the ages of 20 and 40 but the unpredictable physical and emotional effects can be lifelong. The progress, severity and specific symptoms of MS in any one person cannot yet be predicted, but advances in research and treatment are giving hope to those affected by the disease.

Symptoms

The symptoms of MS are highly variable, depending on the areas of the central nervous system that have been affected. Not only do the symptoms vary from one person to another, but from day to day for any given individual. 

Causes of MS

Many people with MS ask if their disease is caused by a virus or other infectious agent. Much research has focused on trying to answer this question.

It is tempting to speculate on a viral cause for MS because viruses are known to cause demyelinating disease in animals and humans. Demyelination (destruction of myelin—the fatty sheath the surrounds and insulates nerve fibers in the central nervous system), causes nerve impulses to be slowed or halted and produces the symptoms of MS.

Data from epidemiological studies—those that analyze variations in geographical, socioeconomic, genetic, and other factors—suggest that exposure to an infectious agent may be involved in causing MS. Some viruses are known to have a long latency period between time of infection and appearance of clinical symptoms, as is thought to be the case in multiple sclerosis.

No Definitive Evidence to Link Any One Virus to MS

Although many different viruses have been suggested to cause MS, there has not yet been definitive evidence linking any one virus to the autoimmune reaction that is believed to be the process responsible for the demyelination seen in MS.  At one time or another, canine distemper virus, measles virus, herpes virus (HHV-6), rubella (or German measles) virus, HTLV-1 virus, and others have been reported to be associated with MS. With the possible exception of HHV-6, later studies have not substantiated these reports, and there is no proof that any of them causes MS.

Increased antibodies to many different viruses have been found in

the sera and cerebrospinal fluid of people with MS. This may not necessarily represent disease-causing infection by these viruses. It is more is likely to be the result of non-specific immune activation. The role of a virus as a causative or triggering agent of MS remains speculative.

MS is not Contagious

Currently, there is no evidence at all to suggest that MS is infectious or contagious. The role of a virus or viruses, if there is one, affects only people with a genetic predisposition to develop MS.

Source of information: National MS Society

Genetics of multiple sclerosis: linkage and association studies

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system caused by an interplay of environmental and genetic factors. The only genetic region that has been clearly demonstrated by linkage and association studies to contribute to MS genetic susceptibility is the human leukocyte antigen (HLA) system. The majority of HLA population studies in MS have focused on Caucasians of Northern European descent, where the predisposition to disease has been consistently associated with the class II DRB1*1501-DQA1*0102-DQB1*0602 haplotype. A positive association with DR4 was detected in Sardinians and in other Mediterranean populations. Moreover DR1, DR7, DR11 have been found to be protective in several populations. Systematic searches aimed at identifying non-HLA susceptibility genes were undertaken in several populations by means of linkage studies with microsatellite markers distributed across the whole genome. The conclusion of these studies was that there is no major MS locus, and genetic susceptibility to the disease is most likely explained by the presence of different genes each conferring a small contribution to the overall familial aggregation. The involvement of several candidate genes was tested by association studies, utilising either a population-based (case control) or a family-based (transmission disequilibrium test) approach. Candidate genes were selected mainly on the basis of their involvement in the autoimmune pathogenesis and include immunorelevant molecules such as cytokines, cytokine receptors, immunoglobulin, T cell receptor subunits and myelin antigens. With the notable exception of HLA, association studies met only modest success. This failure may result from the small size of the tested samples and the small number of markers considered for each gene. New tools for large scale screening are needed to identify genetic determinants with a low phenotypic effect. Large collaborative studies are planned to screen several thousands of patients with MS with several thousands of genetic markers. The tests are increasingly based on the DNA pooling procedure.