An examination of the Apo-1/Fas promoter Mva I polymorphism in Japanese patients with multiple sclerosis

Apoptosis is a physiologic process that regulates normal homeostasis and is likely to contribute to the pathogenesis of autoimmune diseases by impairing elimination of autoreactive T and B cells [1]. Physiologic regulation of cell death is essential for removal of potentially autoreactive lymphocytes during development and excess cells after the completion of an immune response. Apo-1/Fas, also known as CD95, is a 36-kDa transmembrane glycoprotein expressed on the surface of many cell types, such as lymphocytes, epithelial cells, fibroblasts, and certain endothelial cells. Apo-1/Fas mediates apoptosis of these cells [2], whereas Fas ligand (FasL) expression is tightly regulated and restricted to activated T cells, NK cells, and at sites of immune privilege [3]. Apo-1/Fas is considered to have an important role in the regulation of the immune system by deleting autoreactive lymphocytes. Inadequate co-stimulation of T cells by antigen-presenting glial cells might render T cells susceptible to activation-induced apoptosis. T cells expressing Apo-1/Fas might also die in an antigen-nonspecific manner after interacting with glial cells expressing Apo-1/FasL. T-cell apoptosis contributes to resolution of the central nervous system (CNS) inflammation and clinical recovery from attacks of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS) [4]. Apoptosis of autoreactive T cells in the CNS is likely to be important in preventing the development of MS [5]. On the other hand, Apo-1/Fas mRNA and protein are both induced after UV light exposure [6], indicating that the regulation of this gene is important in the cellular response to UV light. The geographic distribution of MS might be related to the degree of sunlight exposure, and exposure to UV light might have a protective effect in MS. Taken together, Apo-1/Fas is a candidate proapoptotic gene in MS.

Apo-1/Fas is a type I transmembrane protein that belongs to the tumor necrosis factor receptor superfamily (TNFRSF), and maps to the long arm of chromosome 10q23/10q24.1 in humans [7, 8]. Positive lod scores with microsatellite markers near this region were identified in the United States [9] and Canadian genome screens [10]. The gene encoding Apo-1/Fas, TNFRSF6, contains a single nucleotide polymorphism (SNP) in the promoter at position -670 that disrupts a gamma-activated sequence (GAS) transcription factor binding sequence [11]. This polymorphism creates an Mva I restriction fragment length polymorphism (RFLP), and abolishes the binding site of the nuclear transcription element, GAS. The function of the polymorphism remains unclear, but its location, on a consensus sequence of the GAS, implies that it might be associated with altered Fas gene transcription.

In the present study, we examined the association of the promoter -670 polymorphism in the Apo-1/Fas gene in Japanese patients with MS.

We analyzed a new genetic marker, Mva I polymorphism on the Fas promoter gene, in patients with MS. There were no differences in genotype or allele frequencies among MS patients and controls. Furthermore, our results indicated that Mva I polymorphisms are not associated with the clinical course (relapsing-remitting course or secondary progressive course). Patients with the A/A genotype tended to have a later onset than those with the G/G or G/A genotype but this difference was not statistically significant. To date, there has been one report regarding this Mva I polymorphism and MS [15]. In that report in Australian population, there were increases in the A allele in MS individuals overall, and in HLA-DRB1*1501 negative MS patients [15]. This tendency was not detected in the Japanese MS individuals in the present study.

Some studies reported an association between the Fas promoter -670 polymorphism and autoimmune diseases or degenerative diseases. Huang et al. demonstrated a skewed distribution of Mva I genotypes in the first cohort of 103 Australian patients with rheumatoid arthritis (RA), but this association was not confirmed in a second cohort [16]. The -670 polymorphism is associated with development of anti-RNP antibodies in systemic lupus erythematosus (SLE) [17]. The -670 polymorphism is also associated with Alzheimer's disease and interacts with the APO-E variant [18], indicating that it has potential biologic significance.

MS is considered to be an autoimmune disorder of unknown etiology. The pathogenesis of the disease remains obscure, but genetic factors are considered to be contributory. In the HLA, there was an association between DRB1*1501 and MS in our study as well as in Caucasian. With respect to the genetics of MS, it is possible that non-HLA genes have a pathogenetic role. Because a case-control study design might provide spurious results attributable to population stratification, including negative findings such as those reported in the present study, additional studies are necessary to exclude the possibility of type 2 errors. Population association studies that compare the frequency of variants between cases and controls might be particularly effective and might be a powerful assay for common genetic variants of weak effect [19]. While our results are not entirely consistent with those of another report examining other ethnicities [15], this inconsistency might be due, in part, to differences in the polymorphism background of the different ethnic group. Further research in gene polymorphisms present in other ethnic groups is needed, as well as further research in the Japanese patient group. In addition, susceptibility genes might provide a small individual contribution in MS, thus their identification might be important for providing clues to the pathogenesis of the different clinical forms of the disease and for designing the most effective therapy for each individual patient.

We investigated Mva I polymorphism on the Apo-1/Fas promoter gene from the DNA of 114 Japanese patients with conventional MS and 121 healthy controls. We found no evidence that the polymorphism contributes to susceptibility to MS. Furthermore, there was no association between Apo-1/Fas gene polymorphisms and clinical course (relapsing-remitting course or secondary-progressive course). No significant association was observed between Apo-1/Fas gene polymorphisms and the age at disease onset.