Multiple sclerosis (MS) is a T-cell-mediated disease of the central nervous system, characterized by damage to myelin and axons, resulting in progressive neurological disability. Genes may influence susceptibility to MS, but results of association studies are inconsistent, aside from the identification of HLA class II haplotypes. Whole-genome linkage screens in MS have both confirmed the importance of the HLA region and uncovered non-HLA loci that may harbor susceptibility genes. In this twostage analysis, we determined genotypes, in up to 672 MS patients and 672 controls, for 123 single-nucleotide polymorphisms (SNPs) in 66 genes. Genes were chosen based on their chromosomal positions or biological functions. In stage one, 22 genes contained at least one SNP for which the carriage rate for one allele differed significantly (Po0.08) between patients and controls. After additional genotyping in stage two, two genes-each containing at least three significantly (Po0.05) associated SNPs-conferred susceptibility to MS: LAG3 on chromosome 12p13, and IL7R on 5p13. LAG3 inhibits activated T cells, while IL7R is necessary for the maturation of T and B cells. These results imply that germline allelic variation in genes involved in immune homeostasis-and, by extension, derangement of immune homeostasis-influence the risk of MS.

Apolipoprotein E (opoE) is involved in the transport of lipids necessary for membrane repair and is encoded by a gene on chromosome 19q13, a region positive for linkage in two multiple sclerosis (MS) genome-wide screens. The APOE epsilon4 allele confers susceptibility to both familial and sporadic Alzheimer's disease (AD). Carriage of epsilon4 is associated with defective dendritic remodeling in AD, and with unfavorable clinical outcome in head trauma and cerebrovascular disease. According to the results of previous studies, APOE epsilon4 does not increase the risk of developing MS, but it may influence disease progression and ultimate disability. From a total cohort of over 900 MS patients, we compared APOE epsilon2-4 genotypes in, roughly, the cohort's least disabled and most disabled septiles. 'Benign MS' (n=124) was defined as an Expanded Disability Status Scale (EDSS) score of 3.0 or less, despite at least 10 years of disease duration, and 'severe MS' (n=140) as the attainment of an EDSS score of 6.0 within 8 years of disease onset. We found no significant differences in genotype or phenotype frequencies between the benign-MS and severe-MS septiles; however, the risk conferred by epsilon4 rose progressively upon comparison of carriage rates in more narrowly defined anti-podal quantiles.