Enrichment for Northern European-derived multiple sclerosis risk alleles in Sardinia

BACKGROUND: The list of genomic loci associated with multiple sclerosis (MS) susceptibility outside the major histocompatibility complex (MHC) in patients of Northern European (NE) ancestry has increased to 103. Despite the extraordinarily high MS prevalence in the isolated Sardinian population, the contribution of genetic risk factors to MS in Sardinia is largely not understood. OBJECTIVE: The objective of this paper is to examine the relevance of non-MHC MS susceptibility variants in Sardinia. METHODS: We examined a log-additive MS-specific genetic burden score (MSGB) using 110 NE-derived risk alleles in a dataset of 75 Sardinian cases, 346 Sardinian controls and 177 cases and 1967 controls from the United States (US). RESULTS: Sardinian cases demonstrate a heavier non-MHC MSGB load than Sardinian controls and US cases (p = 2E-06, p = 1E-06, respectively). Furthermore, Sardinian controls carry a heavier burden than US controls (p = 2E-14). Our results confirm the limited ability of the 110-SNP MSGB to predict disease status in Sardinia (AUROC = 0.629). CONCLUSIONS: Risk alleles discovered in samples of NE ancestry are relevant to MS in Sardinia. Our results suggest a general enrichment of MS susceptibility alleles in Sardinians, encouraging the pursuit of further studies of MS in this population

Homozygosity haplotype and whole-exome sequencing analysis to identify potentially functional rare variants involved in multiple sclerosis among sardinian families

Multiple Sclerosis (MS) is a complex multifactorial autoimmune disease, whose sex-and age-adjusted prevalence in Sardinia (Italy) is among the highest worldwide. To date, 233 loci were associated with MS and almost 20% of risk heritability is attributable to common genetic variants, but many low-frequency and rare variants remain to be discovered. Here, we aimed to contribute to the understanding of the genetic basis of MS by investigating potentially functional rare variants. To this end, we analyzed thirteen multiplex Sardinian families with Immunochip genotyping data. For five families, Whole Exome Sequencing (WES) data were also available. Firstly, we performed a nonparametric Homozygosity Haplotype analysis for identifying the Region from Common Ancestor (RCA). Then, on these potential disease-linked RCA, we searched for the presence of rare variants shared by the affected individuals by analyzing WES data. We found: (i) a variant (43181034 T > G) in the splicing region on exon 27 of CUL9; (ii) a variant (50245517 A > C) in the splicing region on exon 16 of ATP9A; (iii) a non-synonymous variant (43223539 A > C), on exon 9 of TTBK1; (iv) a nonsynonymous variant (42976917 A > C) on exon 9 of PPP2R5D; and v) a variant (109859349-109859354) in 3′UTR of MYO16

Clinical Expression of Multiple Sclerosis in Hispanic Whites of Primarily Caribbean Ancestry

Objective: The clinical characteristics of multiple sclerosis (MS) are not well defined in Hispanic populations. We hypothesized that disease presentation in Hispanic white (HW) patients will be different from non-Hispanic white (NHW) patients given their ancestral background and reported lower disease prevalence. This study was undertaken to compare HW of primarily Caribbean ancestry to NHW on clinical characteristics of MS. Methods: We assessed 312 HW and 312 NHW patients with definite MS for clinical disease characteristics obtained through consented review of medical records. In order to assess the relationship between age-related phenotypes and ethnicity, linear regression was used. Logistic regression was used to assess the relationship between ethnicity and descriptors of disease presentation and severity as well as presence of neurological symptoms. Results: We observed a significantly younger age at diagnosis (p = 1.38E-02) and age at exam (p = 2.36E-05) in HW. However, age at first symptom did not differ significantly between the two groups. Furthermore, within HW, the mean age at first symptom and age at diagnosis was significantly younger in those born in the United States (p < 1.00E-03 for both). Interestingly, we noted an increase in ambulatory disability in HW patients, primarily among those with relapsing disease (p = 4.18E-03). Conclusions: We found several differences in age-related phenotypes and disease severity between HW of primarily Caribbean origin and NHW patients. To our knowledge, this is the largest study to date that examined the clinical characteristics of MS in Hispanic patients of largely Caribbean origin

Investigating Multiple Sclerosis genetic susceptibility on the founder population of east-central Sardinia via association and linkage analysis of immune-related loci

Background: A wealth of single-nucleotide polymorphisms (SNPs) responsible for multiple sclerosis (MS) susceptibility have been identified; however, they explain only a fraction of MS heritability. Objectives: We contributed to discovery of new MS susceptibility SNPs by studying a founder population with high MS prevalence. Methods: We analyzed ImmunoChip data from 15 multiplex families and 94 unrelated controls from the Nuoro Province, Sardinia, Italy. We tested each SNP for both association and linkage with MS, the linkage being explored in terms of identity-by-descent (IBD) sharing excess and using gene dropping to compute a corresponding empirical p-value. By targeting regions that are both associated and in linkage with MS, we increase chances of identifying interesting genomic regions. Results: We identified 486 MS-associated ( p &lt; 1 × 10–4) and 18,426 MS-linked ( p &lt; 0.05) SNPs. A total of 111 loci were both linked and associated with MS, 18 of them pointing to 14 non-major histocompatibility complex (MHC) genes, and 93 of them located in the MHC region. Conclusion: We discovered new suggestive signals and confirmed some previously identified ones. We believe this to represent a significant step toward an understanding of the genetic basis of MS. </jats:sec

Supplementary Material for: Clinical Expression of Multiple Sclerosis in Hispanic Whites of Primarily Caribbean Ancestry

<b><i>Objective:</i></b> The clinical characteristics of multiple sclerosis (MS) are not well defined in Hispanic populations. We hypothesized that disease presentation in Hispanic white (HW) patients will be different from non-Hispanic white (NHW) patients given their ancestral background and reported lower disease prevalence. This study was undertaken to compare HW of primarily Caribbean ancestry to NHW on clinical characteristics of MS. <b><i>Methods:</i></b> We assessed 312 HW and 312 NHW patients with definite MS for clinical disease characteristics obtained through consented review of medical records. In order to assess the relationship between age-related phenotypes and ethnicity, linear regression was used. Logistic regression was used to assess the relationship between ethnicity and descriptors of disease presentation and severity as well as presence of neurological symptoms. <b><i>Results:</i></b> We observed a significantly younger age at diagnosis (p = 1.38E-02) and age at exam (p = 2.36E-05) in HW. However, age at first symptom did not differ significantly between the two groups. Furthermore, within HW, the mean age at first symptom and age at diagnosis was significantly younger in those born in the United States (p < 1.00E-03 for both). Interestingly, we noted an increase in ambulatory disability in HW patients, primarily among those with relapsing disease (p = 4.18E-03). <b><i>Conclusions:</i></b> We found several differences in age-related phenotypes and disease severity between HW of primarily Caribbean origin and NHW patients. To our knowledge, this is the largest study to date that examined the clinical characteristics of MS in Hispanic patients of largely Caribbean origin

Investigating multiple sclerosis genetic susceptibility on the founder population of east-central Sardinia via association and linkage analysis of immune-related loci

Background: A wealth of single-nucleotide polymorphisms (SNPs) responsible for multiple sclerosis (MS) susceptibility have been identified; however, they explain only a fraction of MS heritability. Objectives: We contributed to discovery of new MS susceptibility SNPs by studying a founder population with high MS prevalence. Methods: We analyzed ImmunoChip data from 15 multiplex families and 94 unrelated controls from the Nuoro Province, Sardinia, Italy. We tested each SNP for both association and linkage with MS, the linkage being explored in terms of identity-by-descent (IBD) sharing excess and using gene dropping to compute a corresponding empirical p-value. By targeting regions that are both associated and in linkage with MS, we increase chances of identifying interesting genomic regions. Results: We identified 486 MS-associated (p < 1 × 10-4) and 18,426 MS-linked (p < 0.05) SNPs. A total of 111 loci were both linked and associated with MS, 18 of them pointing to 14 non-major histocompatibility complex (MHC) genes, and 93 of them located in the MHC region. Conclusion: We discovered new suggestive signals and confirmed some previously identified ones. We believe this to represent a significant step toward an understanding of the genetic basis of MS

Evaluating Mitochondrial DNA Variation in Autism Spectrum Disorders

Despite the increasing speculation that oxidative stress and abnormal energy metabolism may play a role in Autism Spectrum Disorders (ASD), and the observation that patients with mitochondrial defects have symptoms consistent with ASD, there are no comprehensive published studies examining the role of mitochondrial variation in autism. Therefore, we have sought to comprehensively examine the role of mitochondrial DNA (mtDNA) variation with regard to ASD risk, employing a multi-phase approach. In phase 1 of our experiment, we examined 132 mtDNA single-nucleotide polymorphisms (SNPs) genotyped as part of our genome-wide association studies of ASD. In phase 2 we genotyped the major European mitochondrial haplogroup-defining variants within an expanded set of autism probands and controls. Finally in phase 3, we resequenced the entire mtDNA in a subset of our Caucasian samples (~400 proband-father pairs). In each phase we tested whether mitochondrial variation showed evidence of association to ASD. Despite a thorough interrogation of mtDNA variation, we found no evidence to suggest a major role for mtDNA variation in ASD susceptibility. Accordingly, while there may be attractive biological hints suggesting the role of mitochondria in ASD our data indicate that mtDNA variation is not a major contributing factor to the development of ASD

Analysis of immune-related loci identifies 48 new susceptibility variants for multiple sclerosis

Using the ImmunoChip custom genotyping array, we analyzed 14,498 subjects with multiple sclerosis and 24,091 healthy controls for 161,311 autosomal variants and identified 135 potentially associated regions (P < 1.0 × 10−4). In a replication phase, we combined these data with previous genome-wide association study (GWAS) data from an independent 14,802 subjects with multiple sclerosis and 26,703 healthy controls. In these 80,094 individuals of European ancestry, we identified 48 new susceptibility variants (P < 5.0 × 10−8), 3 of which we found after conditioning on previously identified variants. Thus, there are now 110 established multiple sclerosis risk variants at 103 discrete loci outside of the major histocompatibility complex. With high-resolution Bayesian fine mapping, we identified five regions where one variant accounted for more than 50% of the posterior probability of association. This study enhances the catalog of multiple sclerosis risk variants and illustrates the value of fine mapping in the resolution of GWAS signals

A gene pathway analysis highlights the role of cellular adhesion molecules in multiple sclerosis susceptibility

Genome-wide association studies (GWASs) perform per-SNP association tests to identify variants involved in disease or trait susceptibility. However, such an approach is not powerful enough to unravel genes that are not individually contributing to the disease/trait, but that may have a role in interaction with other genes as a group. Pathway analysis is an alternative way to highlight such group of genes. Using SNP association P-values from eight multiple sclerosis (MS) GWAS data sets, we performed a candidate pathway analysis for MS susceptibility by considering genes interacting in the cell adhesion molecule (CAMs) biological pathway using Cytoscape software. This network is a strong candidate, as it is involved in the crossing of the blood-brain barrier by the T cells, an early event in MS pathophysiology, and is used as an efficient therapeutic target. We drew up a list of 76 genes belonging to the CAM network. We highlighted 64 networks enriched with CAM genes with low P-values. Filtering by a percentage of CAM genes up to 50% and rejecting enriched signals mainly driven by transcription factors, we highlighted five networks associated with MS susceptibility. One of them, constituted of ITGAL, ICAM1 and ICAM3 genes, could be of interest to develop novel therapeutic targets