Contribution of Rare and Low-Frequency Variants to Multiple Sclerosis Susceptibility in the Italian Continental Population

Genome-wide association studies identified over 200 risk loci for multiple sclerosis (MS) focusing on common variants, which account for about 50% of disease heritability. The goal of this study was to investigate whether low-frequency and rare functional variants, located in MS-established associated loci, may contribute to disease risk in a relatively homogeneous population, testing their cumulative effect (burden) with gene-wise tests. We sequenced 98 genes in 588 Italian patients with MS and 408 matched healthy controls (HCs). Variants were selected using different filtering criteria based on allelic frequency and in silico functional impacts. Genes showing a significant burden (n = 17) were sequenced in an independent cohort of 504 MS and 504 HC. The highest signal in both cohorts was observed for the disruptive variants (stop-gain, stop-loss, or splicing variants) located in EFCAB13, a gene coding for a protein of an unknown function (p < 10(-4)). Among these variants, the minor allele of a stop-gain variant showed a significantly higher frequency in MS versus HC in both sequenced cohorts (p = 0.0093 and p = 0.025), confirmed by a meta-analysis on a third independent cohort of 1298 MS and 1430 HC (p = 0.001) assayed with an SNP array. Real-time PCR on 14 heterozygous individuals for this variant did not evidence the presence of the stop-gain allele, suggesting a transcript degradation by non-sense mediated decay, supported by the evidence that the carriers of the stop-gain variant had a lower expression of this gene (p = 0.0184). In conclusion, we identified a novel low-frequency functional variant associated with MS susceptibility, suggesting the possible role of rare/low-frequency variants in MS as reported for other complex diseases

Association of Genetic Markers with CSF Oligoclonal Bands in Multiple Sclerosis Patients

OBJECTIVE: to explore the association between genetic markers and Oligoclonal Bands (OCB) in the Cerebro Spinal Fluid (CSF) of Italian Multiple Sclerosis patients. METHODS: We genotyped 1115 Italian patients for HLA-DRB1*15 and HLA-A*02. In a subset of 925 patients we tested association with 52 non-HLA SNPs associated with MS susceptibility and we calculated a weighted Genetic Risk Score. Finally, we performed a Genome Wide Association Study (GWAS) with OCB status on a subset of 562 patients. The best associated SNPs of the Italian GWAS were replicated in silico in Scandinavian and Belgian populations, and meta-analyzed. RESULTS: HLA-DRB1*15 is associated with OCB+: p\u200a=\u200a0.03, Odds Ratio (OR)\u200a=\u200a1.6, 95% Confidence Limits (CL)\u200a=\u200a1.1-2.4. None of the 52 non-HLA MS susceptibility loci was associated with OCB, except one SNP (rs2546890) near IL12B gene (OR: 1.45; 1.09-1.92). The weighted Genetic Risk Score mean was significantly (p\u200a=\u200a0.0008) higher in OCB+ (7.668) than in OCB- (7.412) patients. After meta-analysis on the three datasets (Italian, Scandinavian and Belgian) for the best associated signals resulted from the Italian GWAS, the strongest signal was a SNP (rs9320598) on chromosome 6q (p\u200a=\u200a9.4 710(-7)) outside the HLA region (65 Mb). DISCUSSION: genetic factors predispose to the development of OCB

Multiple sclerosis progression is not associated with birth timing in Italy

Background Month of birth has been associated in some studies with the susceptibility to develop Multiple Sclerosis (MS). However, only few studies have evaluated whether birth timing also affects disease progression. Objectives To assess whether season and month of birth are associated with disease progression in a large cohort of Italian patients. Methods Quantile regression was used to analyze the impact of each month and season of birth with all the others combined on the median Multiple Sclerosis Severity Score of 1866 MS patients. Results No significant temporal trend was found after adjustment for multiple comparisons. Conclusions Birth timing showed no association with MS progression in Italian patients

Inverse correlation of genetic risk score with age at onset in bout-onset and progressive-onset multiple sclerosis

We correlated the weighted genetic risk score measured using 107 established susceptibility variants for multiple sclerosis (MS) with the age at onset in bout-onset (BOMS, n=906) and progressive-onset MS Italian patients (PrMS) (n=544). We observed an opposite relationship in the two disease courses: a higher weighted genetic risk score was associated with an earlier age at onset in BOMS (rho= -0.1; p=5 7 10(-3)) and a later age at onset in PrMS cases (rho=0.07; p=0.15) (p of difference of regression=1.4 7 10(-2)). These findings suggest that established MS risk variants anticipate the onset of the inflammatory phase, while they have no impact on, or even delay, the onset of the progressive phase

Familial clustering in Italian progressive-onset and bout-onset multiple sclerosis.

Multiple sclerosis (MS) is a complex disease triggered by environmental and genetic agents, and clinically characterized by bout onset (BOMS) or progressive onset (PrMS). We collected clinical and familial aggregation data in a cohort of 518 Italian PrMS patients, and compared with 400 BOMS cases. An increased prevalence of MS in first-degree relatives of Italian PrMS was found. Familial aggregation is not influenced by probands' clinical course, and there is no disease course concordance within MS families. These data are useful in counseling MS patients affected with different clinical courses of the disease

Familial clustering in Italian progressive-onset and bout-onset multiple sclerosis

Multiple sclerosis (MS) is a complex disease triggered by environmental and genetic agents, and clinically characterized by bout onset (BOMS) or progressive onset (PrMS). We collected clinical and familial aggregation data in a cohort of 518 Italian PrMS patients, and compared with 400 BOMS cases. An increased prevalence of MS in first-degree relatives of Italian PrMS was found. Familial aggregation is not influenced by probands' clinical course, and there is no disease course concordance within MS families. These data are useful in counseling MS patients affected with different clinical courses of the disease

Genetic burden of common variants in progressive and bout-onset multiple sclerosis

Background: The contribution of genetic variants underlying the susceptibility to different clinical courses of multiple sclerosis (MS) is still unclear. Objective: The aim of the study is to evaluate and compare the proportion of liability explained by common SNPs and the genetic burden of MS-associated SNPs in progressive onset (PrMS) and bout-onset (BOMS) cases. Methods: We estimated the proportion of variance in disease liability explained by 296,391 autosomal SNPs in cohorts of Italian PrMS and BOMS patients using the genome-wide complex trait analysis (GCTA) tool, and we calculated a weighted genetic risk score (wGRS) based on the known MS-associated loci. Results: Our results identified that common SNPs explain a greater proportion of phenotypic variance in BOMS (36.5%±10.1%) than PrMS (20.8%±6.0%) cases, and a trend of decrease was observed when testing primary progressive (PPMS) without brain MRI inflammatory activity (p = 7.9 × 10−3). Similarly, the wGRS and the variance explained by MS-associated SNPs were higher in BOMS than PPMS in males (wGRS: 6.63 vs 6.51, p = 0.04; explained variance: 4.8%±1.5% vs 1.7%±0.6%; p = 0.05). Conclusions: Our results suggest that the liability of disease is better captured by common genetic variants in BOMS than PrMS cases. The absence of inflammatory activity and male gender further raise the difference between clinical courses

Association of genetic markers with CSF oligoclonal bands in multiple sclerosis patients.

to explore the association between genetic markers and Oligoclonal Bands (OCB) in the Cerebro Spinal Fluid (CSF) of Italian Multiple Sclerosis patients.We genotyped 1115 Italian patients for HLA-DRB1*15 and HLA-A*02. In a subset of 925 patients we tested association with 52 non-HLA SNPs associated with MS susceptibility and we calculated a weighted Genetic Risk Score. Finally, we performed a Genome Wide Association Study (GWAS) with OCB status on a subset of 562 patients. The best associated SNPs of the Italian GWAS were replicated in silico in Scandinavian and Belgian populations, and meta-analyzed.HLA-DRB1*15 is associated with OCB+: p = 0.03, Odds Ratio (OR) = 1.6, 95\% Confidence Limits (CL) = 1.1-2.4. None of the 52 non-HLA MS susceptibility loci was associated with OCB, except one SNP (rs2546890) near IL12B gene (OR: 1.45; 1.09-1.92). The weighted Genetic Risk Score mean was significantly (p = 0.0008) higher in OCB+ (7.668) than in OCB- (7.412) patients. After meta-analysis on the three datasets (Italian, Scandinavian and Belgian) for the best associated signals resulted from the Italian GWAS, the strongest signal was a SNP (rs9320598) on chromosome 6q (p = 9.4×10(-7)) outside the HLA region (65 Mb).genetic factors predispose to the development of OCB