Age at Epstein-Barr virus infection and Epstein-Barr virus nuclear antigen-1 antibodies in Swedish children.

There is strong evidence supporting a role for Epstein-Barr virus (EBV) in the etiopathogenesis of multiple sclerosis (MS). Because of the strong association between antibody (Ab) titer against EBV nuclear antigen 1 (EBNA1) and late age at EBV infection, manifested as infectious mononucleosis (IM), and MS risk, we sought to determine whether age at primary EBV infection was associated with subsequent anti-EBNA1 Ab titer in a longitudinal study of Swedish children with EBV seropositivity and anti-EBNA1 Ab titers measured at ages 2, 5, and 10.

Vitamin D and multiple sclerosis.

The hypothesis that adequate vitamin D nutrition can contribute to the prevention of multiple sclerosis (MS) was originally proposed to explain the geographical distribution of MS, but only recently has the relation between various measures of vitamin D (eg, sun exposure, dietary sources, and serum concentrations of 25-hydroxyvitamin D) and risk of developing MS been rigorously investigated. Overall, the results of these studies support a protective effect of vitamin D, but there are uncertainties and many unanswered questions, including how vitamin D exerts a protective effect, how genetic variations modify the effect, and whether vitamin D can influence the course of MS progression.

Genome-wide association study of circulating vitamin D levels.

The primary circulating form of vitamin D, 25-hydroxy-vitamin D [25(OH)D], is associated with multiple medical outcomes, including rickets, osteoporosis, multiple sclerosis and cancer. In a genome-wide association study (GWAS) of 4501 persons of European ancestry drawn from five cohorts, we identified single-nucleotide polymorphisms (SNPs) in the gene encoding group-specific component (vitamin D binding) protein, GC, on chromosome 4q12-13 that were associated with 25(OH)D concentrations: rs2282679 (P=2.0x10(-30)), in linkage disequilibrium (LD) with rs7041, a non-synonymous SNP (D432E; P=4.1x10(-22)) and rs1155563 (P=3.8x10(-25)). Suggestive signals for association with 25(OH)D were also observed for SNPs in or near three other genes involved in vitamin D synthesis or activation: rs3829251 on chromosome 11q13.4 in NADSYN1 [encoding nicotinamide adenine dinucleotide (NAD) synthetase; P=8.8x10(-7)], which was in high LD with rs1790349, located in DHCR7, the gene encoding 7-dehydrocholesterol reductase that synthesizes cholesterol from 7-dehydrocholesterol; rs6599638 in the region harboring the open-reading frame 88 (C10orf88) on chromosome 10q26.13 in the vicinity of ACADSB (acyl-Coenzyme A dehydrogenase), involved in cholesterol and vitamin D synthesis (P=3.3x10(-7)); and rs2060793 on chromosome 11p15.2 in CYP2R1 (cytochrome P450, family 2, subfamily R, polypeptide 1, encoding a key C-25 hydroxylase that converts vitamin D3 to an active vitamin D receptor ligand; P=1.4x10(-5)). We genotyped SNPs in these four regions in 2221 additional samples and confirmed strong genome-wide significant associations with 25(OH)D through meta-analysis with the GWAS data for GC (P=1.8x10(-49)), NADSYN1/DHCR7 (P=3.4x10(-9)) and CYP2R1 (P=2.9x10(-17)), but not C10orf88 (P=2.4x10(-5)).

Polymorphisms in vitamin D metabolism related genes and risk of multiple sclerosis.

The extent to which potential genetic determinants of vitamin D levels may be related to multiple sclerosis (MS) risk has not been thoroughly explored. The objective of this study was to determine whether polymorphisms in VDR, CYP27B1, CYP24A1, CYP2R1 and DBP are associated with the risk of MS and whether these variants may modify associations between environmental or dietary vitamin D on MS risk. A nested case-control study was conducted in two, large cohorts of US nurses, including 214 MS cases and 428 age-matched controls. Conditional logistic regression models were used to calculate relative risks (RR) and 95% confidence intervals (CIs) and to assess the significance of gene-environment interactions. No associations were observed for any of the single-nucleotide polymorphisms (SNPs) in VDR, CYP27B1, CYP24A1, CYP2R1 or DBP (p > 0.05 for all). The authors did observe an interaction (p = 0.04) between dietary intake of vitamin D and the vitamin D receptor FokI polymorphism on MS risk. The protective effect of increasing vitamin D was evident only in individuals with the 'ff ' genotype (RR = 0.2, 95% CI: 0.06, 0.78; p = 0.02 for 400 IU/day increase). It was concluded that this does not support a role for the selected SNPs involved in vitamin D metabolism in the etiology of MS. The finding of a marginally significant gene-environment interaction requires replication in larger datasets, but suggests future genetic studies may benefit from considering relevant environmental context.

Integration of genetic risk factors into a clinical algorithm for multiple sclerosis susceptibility: a weighted genetic risk score.

BACKGROUND: Prediction of susceptibility to multiple sclerosis (MS) might have important clinical applications, either as part of a diagnostic algorithm or as a means to identify high-risk individuals for prospective studies. We investigated the usefulness of an aggregate measure of risk of MS that is based on genetic susceptibility loci. We also assessed the added effect of environmental risk factors that are associated with susceptibility for MS. METHODS: We created a weighted genetic risk score (wGRS) that includes 16 MS susceptibility loci. We tested our model with data from 2215 individuals with MS and 2189 controls (derivation samples), a validation set of 1340 individuals with MS and 1109 controls taken from several MS therapeutic trials (TT cohort), and a second validation set of 143 individuals with MS and 281 controls from the US Nurses' Health Studies I and II (NHS/NHS II), for whom we also have data on smoking and immune response to Epstein-Barr virus (EBV). FINDINGS: Individuals with a wGRS that was more than 1.25 SD from the mean had a significantly higher odds of MS in all datasets. In the derivation sample, the mean (SD) wGRS was 3.5 (0.7) for individuals with MS and 3.0 (0.6) for controls (p<0.0001); in the TT validation sample, the mean wGRS was 3.4 (0.7) for individuals with MS versus 3.1 (0.7) for controls (p<0.0001); and in the NHS/NHS II dataset, the mean wGRS was 3.4 (0.8) for individuals with MS versus 3.0 (0.7) for controls (p<0.0001). In the derivation cohort, the area under the receiver operating characteristic curve (C statistic; a measure of the ability of a model to discriminate between individuals with MS and controls) for the genetic-only model was 0.70 and for the genetics plus sex model was 0.74 (p<0.0001). In the TT and NHS cohorts, the C statistics for the genetic-only model were both 0.64; adding sex to the TT model increased the C statistic to 0.72 (p<0.0001), whereas adding smoking and immune response to EBV to the NHS model increased the C statistic to 0.68 (p=0.02). However, the wGRS does not seem to be correlated with the conversion of clinically isolated syndrome to MS. INTERPRETATION: The inclusion of 16 susceptibility alleles into a wGRS can modestly predict MS risk, shows consistent discriminatory ability in independent samples, and is enhanced by the inclusion of non-genetic risk factors into the algorithm. Future iterations of the wGRS might therefore make a contribution to algorithms that can predict a diagnosis of MS in a clinical or research setting.