BMI-associated alleles do not constitute risk alleles for polycystic ovary syndrome independently of BMI: a case-control study.

INTRODUCTION: Polycystic Ovary Syndrome (PCOS) has a strong genetic background and the majority of patients with PCOS have elevated BMI levels. The aim of this study was to determine to which extent BMI-increasing alleles contribute to risk of PCOS when contemporaneous BMI is taken into consideration. METHODS: Patients with PCOS and controls were recruited from the United Kingdom (563 cases and 791 controls) and The Netherlands (510 cases and 2720 controls). Cases and controls were of similar BMI. SNPs mapping to 12 BMI-associated loci which have been extensively replicated across different ethnicities, i.e., BDNF, FAIM2, ETV5, FTO, GNPDA2, KCTD15, MC4R, MTCH2, NEGR1, SEC16B, SH2B1, and TMEM18, were studied in association with PCOS within each cohort using the additive genetic model followed by a combined analysis. A genetic allelic count risk score model was used to determine the risk of PCOS for individuals carrying increasing numbers of BMI-increasing alleles. RESULTS: None of the genetic variants, including FTO and MC4R, was associated with PCOS independently of BMI in the meta-analysis. Moreover, no differences were observed between cases and controls in the number of BMI-risk alleles present and no overall trend across the risk score groups was observed. CONCLUSION: In this combined analysis of over 4,000 BMI-matched individuals from the United Kingdom and the Netherlands, we observed no association of BMI risk alleles with PCOS independent of BMI.

MicroRNA expression in abdominal and gluteal adipose tissue is associated with mRNA expression levels and partly genetically driven.

To understand how miRNAs contribute to the molecular phenotype of adipose tissues and related traits, we performed global miRNA expression profiling in subcutaneous abdominal and gluteal adipose tissue of 70 human subjects and characterised which miRNAs were differentially expressed between these tissues. We found that 12% of the miRNAs were significantly differentially expressed between abdominal and gluteal adipose tissue (FDR adjusted p<0.05) in the primary study, of which 59 replicated in a follow-up study of 40 additional subjects. Further, 14 miRNAs were found to be associated with metabolic syndrome case-control status in abdominal tissue and three of these replicated (primary study: FDR adjusted p<0.05, replication: p<0.05 and directionally consistent effect). Genome-wide genotyping was performed in the 70 subjects to enable miRNA expression quantitative trait loci (eQTL) analysis. Candidate miRNA eQTLs were followed-up in the additional 40 subjects and six significant, independent cis-located miRNA eQTLs (primary study: p<0.001; replication: p<0.05 and directionally consistent effect) were identified. Finally, global mRNA expression profiling was performed in both tissues to enable association analysis between miRNA and target mRNA expression levels. We find 22% miRNAs in abdominal and 9% miRNAs in gluteal adipose tissue with expression levels significantly associated with the expression of corresponding target mRNAs (FDR adjusted p<0.05). Taken together, our results indicate a clear difference in the miRNA molecular phenotypic profile of abdominal and gluteal adipose tissue, that the expressions of some miRNAs are influenced by cis-located genetic variants and that miRNAs are associated with expression levels of their predicted mRNA targets.

Genetics and epigenetics of obesity.

Obesity results from interactions between environmental and genetic factors. Despite a relatively high heritability of common, non-syndromic obesity (40-70%), the search for genetic variants contributing to susceptibility has been a challenging task. Genome wide association (GWA) studies have dramatically changed the pace of detection of common genetic susceptibility variants. To date, more than 40 genetic variants have been associated with obesity and fat distribution. However, since these variants do not fully explain the heritability of obesity, other forms of variation, such as epigenetics marks, must be considered. Epigenetic marks, or "imprinting", affect gene expression without actually changing the DNA sequence. Failures in imprinting are known to cause extreme forms of obesity (e.g. Prader-Willi syndrome), but have also been convincingly associated with susceptibility to obesity. Furthermore, environmental exposures during critical developmental periods can affect the profile of epigenetic marks and result in obesity. We review the most recent evidence for genetic and epigenetic mechanisms involved in the susceptibility and development of obesity. Only a comprehensive understanding of the underlying genetic and epigenetic mechanisms, and the metabolic processes they govern, will allow us to manage, and eventually prevent, obesity.

The genetics of obesity.

Obesity is a result of excess body fat accumulation. This excess is associated with adverse health effects such as CVD, type 2 diabetes, and cancer. The development of obesity has an evident environmental contribution, but as shown by heritability estimates of 40% to 70%, a genetic susceptibility component is also needed. Progress in understanding the etiology has been slow, with findings largely restricted to monogenic, severe forms of obesity. However, technological and analytical advances have enabled detection of more than 20 obesity susceptibility loci. These contain genes suggested to be involved in the regulation of food intake through action in the central nervous system as well as in adipocyte function. These results provide plausible biological pathways that may, in the future, be targeted as part of treatment or prevention strategies. Although the proportion of heritability explained by these genes is small, their detection heralds a new phase in understanding the etiology of common obesity.

Parent-of-origin effects at the major histocompatibility complex in multiple sclerosis.

Multiple sclerosis (MS) susceptibility is characterized by maternal parent-of-origin effects and increased female penetrance. In 7796 individuals from 1797 MS families (affected individuals n = 2954), we further implicate epigenetic modifications within major histocompatibility complex (MHC) class II haplotypes as mediating these phenomena. Affected individuals with the main MS-associated allele HLA-DRB1*15 had a higher female-to-male ratio versus those lacking it (P = 0.00023). Distorted transmission of MHC haplotypes by both parent-of-origin and gender-of-affected-offspring was most evident in the maternal HLA-DRB1*15 transmission to affected female offspring (OR = 3.31, 95% CI = 2.59-4.24) contrasting with similarity among maternal transmission to affected male offspring (OR = 2.13, 95% CI = 1.44-3.14), paternal transmissions to affected female (OR = 2.14, 95% CI = 1.64-2.78) and male (OR = 2.16, 95% CI = 1.37-3.39) offspring. Significant parent-of-origin effects were observed in affected females (maternal: P = 9.33 x 10(-42); paternal: P = 1.12 x 10(-15); comparison: P = 0.0014), but not in affected males (maternal: P = 6.70 x 10(-8); paternal: P = 2.54 x 10(-6); comparison: P = 0.95). Conditional logistic regression analysis revealed further differential risk of HLA diplotypes. Risks for HLA-DRB1*15 and likely for other HLA-DRB1 haplotypes were restricted by (i) parent-of-origin, (ii) gender-of-offspring and (iii) trans epistasis in offspring. These findings may illuminate the gender bias characterizing autoimmunity overall. They raise questions about the concept of restricted antigen presentation in autoimmunity and suggest that gender-specific epigenetic interactions may be the driving forces behind the MHC haplotypic associations. Haplotype-specific epigenetic modifications at MHC class II and their decay appear to be at the heart of MS pathogenesis and inheritance of risk, providing the focus for gene-environment interactions that determine susceptibility and resistance.

MicroRNA-125a is over-expressed in insulin target tissues in a spontaneous rat model of Type 2 Diabetes.

BACKGROUND: MicroRNAs (miRNAs) are non-coding RNA molecules involved in post-transcriptional control of gene expression of a wide number of genes, including those involved in glucose homeostasis. Type 2 diabetes (T2D) is characterized by hyperglycaemia and defects in insulin secretion and action at target tissues. We sought to establish differences in global miRNA expression in two insulin-target tissues from inbred rats of spontaneously diabetic and normoglycaemic strains. METHODS: We used a miRNA microarray platform to measure global miRNA expression in two insulin-target tissues: liver and adipose tissue from inbred rats of spontaneously diabetic (Goto-Kakizaki [GK]) and normoglycaemic (Brown-Norway [BN]) strains which are extensively used in genetic studies of T2D. MiRNA data were integrated with gene expression data from the same rats to investigate how differentially expressed miRNAs affect the expression of predicted target gene transcripts. RESULTS: The expression of 170 miRNAs was measured in liver and adipose tissue of GK and BN rats. Based on a p-value for differential expression between GK and BN, the most significant change in expression was observed for miR-125a in liver (FC = 5.61, P = 0.001, Padjusted = 0.10); this overexpression was validated using quantitative RT-PCR (FC = 13.15, P = 0.0005). MiR-125a also showed over-expression in the GK vs. BN analysis within adipose tissue (FC = 1.97, P = 0.078, Padjusted = 0.99), as did the previously reported miR-29a (FC = 1.51, P = 0.05, Padjusted = 0.99). In-silico tools assessing the biological role of predicted miR-125a target genes suggest an over-representation of genes involved in the MAPK signaling pathway. Gene expression analysis identified 1308 genes with significantly different expression between GK and BN rats (Padjusted < 0.05): 233 in liver and 1075 in adipose tissue. Pathways related to glucose and lipid metabolism were significantly over-represented among these genes. Enrichment analysis suggested that differentially expressed genes in GK compared to BN included more predicted miR-125a target genes than would be expected by chance in adipose tissue (FDR = 0.006 for up-regulated genes; FDR = 0.036 for down-regulated genes) but not in liver (FDR = 0.074 for up-regulated genes; FDR = 0.248 for down-regulated genes). CONCLUSION: MiR-125a is over-expressed in liver in hyperglycaemic GK rats relative to normoglycaemic BN rats, and our array data also suggest miR-125a is over-expressed in adipose tissue. We demonstrate the use of in-silico tools to provide the basis for further investigation of the potential role of miR-125a in T2D. In particular, the enrichment of predicted miR-125a target genes among differentially expressed genes has identified likely target genes and indicates that integrating global miRNA and mRNA expression data may give further insights into miRNA-mediated regulation of gene expression.

Genome-wide association scan meta-analysis identifies three Loci influencing adiposity and fat distribution.

To identify genetic loci influencing central obesity and fat distribution, we performed a meta-analysis of 16 genome-wide association studies (GWAS, N = 38,580) informative for adult waist circumference (WC) and waist-hip ratio (WHR). We selected 26 SNPs for follow-up, for which the evidence of association with measures of central adiposity (WC and/or WHR) was strong and disproportionate to that for overall adiposity or height. Follow-up studies in a maximum of 70,689 individuals identified two loci strongly associated with measures of central adiposity; these map near TFAP2B (WC, P = 1.9x10(-11)) and MSRA (WC, P = 8.9x10(-9)). A third locus, near LYPLAL1, was associated with WHR in women only (P = 2.6x10(-8)). The variants near TFAP2B appear to influence central adiposity through an effect on overall obesity/fat-mass, whereas LYPLAL1 displays a strong female-only association with fat distribution. By focusing on anthropometric measures of central obesity and fat distribution, we have identified three loci implicated in the regulation of human adiposity.

Epistasis among HLA-DRB1, HLA-DQA1, and HLA-DQB1 loci determines multiple sclerosis susceptibility.

Multiple sclerosis (MS), a common central nervous system inflammatory disease, has a major heritable component. Susceptibility is associated with the MHC class II region, especially HLA-DRB5*0101-HLA-DRB1*1501-HLA-DQA1*0102-HLA-DQB1*0602 haplotypes(hereafter DR2), which dominate genetic contribution to MS risk. Marked linkage disequilibrium (LD) among these loci makes identification of a specific locus difficult. The once-leading candidate, HLA-DRB1*15, localizes to risk, neutral, and protective haplotypes. HLA-DRB1*15 and HLA-DQB1*0602, nearly always located together on a small ancestral chromosome segment, are strongly MS-associated. One intervening allele on this haplotype, viz. HLA-DQA1*0102, shows no primary MS association. Two Canadian cohorts (n = 830 and n = 438 trios) genotyped for HLA-DRB1, HLA-DQA1 and HLA-DQB1 alleles were tested for association using TDT. To evaluate epistasis involving HLA-DRB1*15, transmissions from HLA-DRB1*15-negative parents were stratified by the presence/absence of HLA-DRB1*15 in affected offspring. All 3 alleles contribute to MS susceptibility through novel epistatic interactions. HLA-DQA1*0102 increased disease risk when combined with HLA-DRB1*1501 in trans, thereby unambiguously implicating HLA-DQ in MS susceptibility. Three-locus haplotypes demonstrated that HLA-DRB1*1501 and HLA-DQB1*0602 each influence risk. Transmissions of rare morcellated DR2 haplotypes showed no interaction with HLA-DQA1*0102. Incomplete haplotypes bearing only HLA-DRB1*1501 or HLA-DQB1*0602 did not predispose to MS. Balanced reciprocal transmission distortion can mask epistatic allelic association. These findings implicate epistasis among HLA class II alleles in human immune responses generally, provide partial explanation for intense linkage disequilibrium in the MHC, have relevance to animal models, and demonstrate key roles for DR2-specific interactions in MS susceptibility. MHC disease associations may be more generally haplotypic or diplotypic.

Expression of the multiple sclerosis-associated MHC class II Allele HLA-DRB1*1501 is regulated by vitamin D.

Multiple sclerosis (MS) is a complex trait in which allelic variation in the MHC class II region exerts the single strongest effect on genetic risk. Epidemiological data in MS provide strong evidence that environmental factors act at a population level to influence the unusual geographical distribution of this disease. Growing evidence implicates sunlight or vitamin D as a key environmental factor in aetiology. We hypothesised that this environmental candidate might interact with inherited factors and sought responsive regulatory elements in the MHC class II region. Sequence analysis localised a single MHC vitamin D response element (VDRE) to the promoter region of HLA-DRB1. Sequencing of this promoter in greater than 1,000 chromosomes from HLA-DRB1 homozygotes showed absolute conservation of this putative VDRE on HLA-DRB1*15 haplotypes. In contrast, there was striking variation among non-MS-associated haplotypes. Electrophoretic mobility shift assays showed specific recruitment of vitamin D receptor to the VDRE in the HLA-DRB1*15 promoter, confirmed by chromatin immunoprecipitation experiments using lymphoblastoid cells homozygous for HLA-DRB1*15. Transient transfection using a luciferase reporter assay showed a functional role for this VDRE. B cells transiently transfected with the HLA-DRB1*15 gene promoter showed increased expression on stimulation with 1,25-dihydroxyvitamin D3 (P = 0.002) that was lost both on deletion of the VDRE or with the homologous "VDRE" sequence found in non-MS-associated HLA-DRB1 haplotypes. Flow cytometric analysis showed a specific increase in the cell surface expression of HLA-DRB1 upon addition of vitamin D only in HLA-DRB1*15 bearing lymphoblastoid cells. This study further implicates vitamin D as a strong environmental candidate in MS by demonstrating direct functional interaction with the major locus determining genetic susceptibility. These findings support a connection between the main epidemiological and genetic features of this disease with major practical implications for studies of disease mechanism and prevention.

Epigenetics in multiple sclerosis susceptibility: difference in transgenerational risk localizes to the major histocompatibility complex.

Multiple sclerosis (MS) susceptibility demonstrates a complex pattern of inheritance. Haplotypes containing HLA-DRB1*1501 carry most of the genetic risk. Epidemiological evidence implicating epigenetic factors includes complex distortion of disease transmission seen in aunt/uncle-niece/nephew (AUNN) pairs. Unexpectedly, in AUNN families we found that allele frequencies for HLA-DRB1*1501 were different between the first and second generations affected. Affected aunts had significantly lower HLA-DRB1*15 frequency compared with their affected nieces (chi(2) = 9.90, P = 0.0016), whereas HLA-DRB1*15 frequency in affected males remains unaltered across the two generations (chi(2) = 0.23, P = 0.63). We compared transmissions for the HLA-DRB1*15 allele using a family-based transmission disequilibrium test approach in 1690 individuals from 350 affected sibling pair (ASP) families and 960 individuals from 187 AUNN families. Transmissions differed between the ASP and the AUNN families (chi(2) = 6.92; P = 0.0085). The risk carried by HLA-DRB1*15 was increased in families with affected second-degree relatives (AUNN: OR = 4.07) when compared with those consisting only first-degree relatives (ASP: OR = 2.17), establishing heterogeneity of risk among HLA-DRB1*15 haplotypes based on whether collateral parental relatives are affected. These observations strongly implicate gene-environment interactions in susceptibility and more specifically, that epigenetic modifications differentiate among human leukocyte antigen class II risk haplotypes and are involved in the determination of the gender bias in MS. These data strongly suggest that the female-specific increasing risk of MS is mediated through these alleles or adjacent variation. The comparison of transmission of the same allele in vertically affected pedigrees (AUNN) to collinear sibling pairs (ASP) may provide a useful screen for putative epigenetic marks.

No effect of birth weight on the risk of multiple sclerosis. A population-based study.

BACKGROUND: Genetic and environmental factors have important roles in multiple sclerosis (MS) susceptibility. A clear maternal effect has been shown in several population-based studies. This parent-of-origin effect could result from factors operating during gestation. It has been shown that a low birth weight increases the risk of several adult-onset diseases. In a population-based Canadian cohort, we investigated whether there is any difference in birth weight for MS index cases compared to spousal controls. METHODS: Using the longitudinal Canadian database, we identified 6,188 MS index cases and 1,640 spousal controls with birth weight information. Additionally, data were available on 164 discordant MS twins. The birth weight was compared between index cases and controls as well as for twin pairs. RESULTS: When stratifying by sex, no significant difference in birth weight was found (average female index case birth weight = 7.23 pounds, average female control birth weight = 7.19 pounds, p = 0.48; average male index case birth weight = 7.56 pounds, average male control birth weight = 7.55 pounds, p = 0.92). Furthermore, there was no difference in birth weight between affected and unaffected twins (average affected twin weight = 5.46 pounds, average unaffected twin weight = 5.44 pounds, p =0.85). CONCLUSIONS: The maternal effect in MS aetiology does not appear to act through a route that has an influence on birth weight. As birth weight is a relatively poor marker of fetal development, other factors involved in fetal and early development need to be explored to elucidate the mechanism of the increased MS risk conferred maternally.

HLA class I alleles tag HLA-DRB1*1501 haplotypes for differential risk in multiple sclerosis susceptibility.

The major locus for multiple sclerosis (MS) susceptibility is located within the class II region of the Major Histocompatibility Complex (MHC). HLA-DRB1 alleles, constituting the strongest MS susceptibility factors, have been widely exploited in research including construction of transgenic animal models of MS. Many studies have concluded that HLA-DRB1*15 allele itself determines MS-associated susceptibility. If this were true, haplotypes bearing this allele would confer equal risk. If HLA-DRB1*15 bearing haplotypes differed for risk, roles for other loci in this region would be implied and further study of the fine structure of this locus would be compelling. We have tested the hypothesis comparing haplotypes stratified by HLA class I tagging. We show here that HLA-DRB1*15-bearing-haplotypes in 1970 individuals from 494 MS families are indeed heterogeneous. Some HLA-DRB1*15 haplotypes determine susceptibility while others do not. Three groups of class I tagged HLA-DRB1*15 haplotypes were not over-transmitted: (i) HLA-DRB1*15-HLA-B*08 (TR = 25, NT = 23, Odds Ratio = 1.09), (ii) -HLA-B*27 (TR = 18, NT = 17, Odds Ratio = 1.06), and (iii) rare HLA-DRB1*15 haplotypes (frequency <0.02). Rare haplotypes were significantly different from common haplotypes, and transmissions were remarkably similar to those for class-I-matched non-HLA-DRB1*15 haplotypes. These results unambiguously indicate that HLA-DRB1*15 is part of a susceptibility haplotype but cannot be the susceptibility allele itself, requiring either epistatic interactions, epigenetic modifications on some haplotypes, or nearby structural variation. These findings strongly imply that differences among HLA-DRB1*15 haplotypes will furnish the basis for MHC-associated susceptibility in MS and raise the possibility that the MHC haplotype is the fundamental unit of genetic control of immune response.

Evidence for genetic regulation of vitamin D status in twins with multiple sclerosis.

BACKGROUND: Multiple sclerosis (MS) risk is determined by both genes and environment. One of the most striking features of MS is its geographic distribution, particularly the pattern of high MS frequency in areas with low sunlight exposure, the main inducer of vitamin D synthesis. Recent epidemiologic, experimental, and clinical evidence support an effect for low environmental supplies of vitamin D in mediating an increased susceptibility to MS. OBJECTIVES: We 1) examined the association of serum 25-hydroxy-vitaminD [25(OH)D] concentrations and MS status and 2) assessed the genetic contribution to serum 25(OH)D concentrations and tested for its association with genetic variants in 2 candidate genes [vitamin D receptor and 1-alpha-hydroxylase (CYP27B1)]. DESIGN: We used a twin study approach, comprising adult pairs identified from the longitudinal population-based Canadian Collaborative Project on Genetic Susceptibility to MS. Monozygotic (MZ; n = 40) and dizygotic (DZ; n = 59) pairs, both concordant and discordant for MS, were studied. End-of-winter serum 25(OH)D concentrations were measured by radioimmunoassay, and genotypes were assessed by single nucleotide polymorphism (SNP) assay. RESULTS: Serum concentrations of 25(OH)D were highly correlated in MS-concordant pairs (r = 0.83, P < 0.001), but they were not significantly associated with having the disease (P = 0.4) when analyzed by logistic regression. Intraclass correlation for 25(OH)D concentration was significantly greater in MZ pairs (MZ, r: 0.71 > DZ r: 0.32, P = 0.006). Significant associations of 2 CYP27B1 SNP variants and 25(OH)D concentrations were observed. CONCLUSION: The findings indicate important genetic influences on regulation of seasonal circulating 25(OH)D concentrations in MS twins.

Methylation of class II transactivator gene promoter IV is not associated with susceptibility to multiple sclerosis.

BACKGROUND: Multiple sclerosis (MS) is a complex trait in which alleles at or near the class II loci HLA-DRB1 and HLA-DQB1 contribute significantly to genetic risk. The MHC class II transactivator (MHC2TA) is the master controller of expression of class II genes, and methylation of the promoter of this gene has been previously been shown to alter its function. In this study we sought to assess whether or not methylation of the MHC2TA promoter pIV could contribute to MS disease aetiology. METHODS: In DNA from peripheral blood mononuclear cells from a sample of 50 monozygotic disease discordant MS twins the MHC2TA promoter IV was sequenced and analysed by methylation specific PCR. RESULTS: No methylation or sequence variation of the MHC2TA promoter pIV was found. CONCLUSION: The results of this study cannot support the notion that methylation of the pIV promoter of MHC2TA contributes to MS disease risk, although tissue and timing specific epigenetic modifications cannot be ruled out.

Analysis of 45 candidate genes for disease modifying activity in multiple sclerosis.

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system unsurpassed for its variability in disease outcome. As little is conclusively known about MS disease mechanisms, we have selected a variety of candidate genes that may influence the prognosis of the disease based on their function. A cohort of sporadic MS cases, taken from opposite extremes of the putative distribution of long-term outcome using the most stringent clinical criteria to date, was used to determine the role of on MS disease severity. The MS cases selected represent the prognostic best 5 % (benign MS) and worst 5 % (malignant MS) of cases in terms of clinical outcome assessed by the EDSS. Genotyping the two sets of MS patients (112 benign and 51 malignant) and a replication cohort from Sardinia provided no evidence to suggest that the genes selected have any outcome modifying activity, although small effects of these genes cannot be ruled out.

Parental non-inherited HLA resistance alleles do not confer protection against multiple sclerosis.

Multiple sclerosis (MS) is a complex trait in which alleles at or near the class II loci HLA-DRB1 and HLA-DQB1 contribute significantly to genetic risk. HLA-DRB1*14 and DRB1*11 bearing haplotypes protect against MS and DRB1*01 and DRB1*10 interact with DRB1*15 to reduce risk of the disease. Recent work in other autoimmune diseases such as rheumatoid arthritis has suggested that maternal non-transmitted protective alleles can also confer disease resistance. In this investigation of 7093 individuals from 1432 MS families, we have analysed the transmission of HLA-DRB1*14,*11,*10 and *01 haplotypes, stratified by sex of parent. No significant transmission differences between mothers and fathers were found, suggesting that non-inherited resistance alleles do not appear to play a role in MS.

A first stage genome-wide screen for regions shared identical-by-descent in Hutterite families with multiple sclerosis.

The complexity of multiple sclerosis (MS) genetics has made the search for novel genes using traditional sharing methods problematic. In order to minimize the genetic heterogeneity present in the MS population we have screened the Canadian MS population for individuals belonging to the Hutterite Brethren. Seven Hutterites with clinically definite MS were ascertained and are related to a common founder by eight generations. Six of the 7 affected individuals and 21 of their unaffected family members (total = 27) were genotyped for 807 markers. Haplotypes were then inspected for sharing among the six MS patients. There were three haplotypes shared among all six MS patients. The haplotypes were located at 2q34-35, 4q31-32, and 17p13. An additional 15 haplotypes were shared among five of the six Hutterites MS patients. The HLA Class II region was one of the highlighted regions; however, the shared MHC haplotype bore the DRB1*04 allele and not the MS-associated DRB1*15 allele providing further evidence of the complexity of the MHC. Additional genotyping to refine the haplotypes followed by screening for potential variants may lead to the identification of a novel MS susceptibility gene(s) in this unique population.

Parental transmission of HLA-DRB1*15 in multiple sclerosis.

Multiple sclerosis (MS) is a complex trait in which HLA-DRB1*15 bearing MHC haplotypes increase risk of MS in people of Northern European descent. In this investigation of 7,334 individuals from 1,515 MS families, the largest cohort used to study the HLA-DRB1 locus to date, we analysed the transmission of HLA-DRB1*15 haplotypes stratified by sex of transmitting parent. A significant over transmission of HLA-DRB1*15 from mothers was observed (chi (2) = 7.73, P = 0.0054), suggesting that parent of origin effects at the MHC determine susceptibility to MS.

A genome-wide scan in forty large pedigrees with multiple sclerosis.

The epidemiology of multiple sclerosis suggests that a complex interaction of genes and environment contribute to susceptibility. To enrich for families with large genetic effects and to potentially reduce genetic heterogeneity, we screened a sample of 18,794 probands and identified forty families with four or more affected individuals. Within these 40 families, HLA DRB1*15 was present in 70% of affected individuals; the transmission disequilibrium test showed a significant excess in transmission of DRB1*15 alleles to affected individuals (47 transmitted, 19 untransmitted, chi (2) = 11.9, p = 0.00057). A 10 cM genome scan was performed and analyzed for linkage under a parametric model with heterogeneity. No excess of significant sharing was observed (HLOD > 3.3) in the parametric multipoint analysis. No region exceeded that for marker GATA8A05 with an HLOD = 1.11. Follow-up genotyping with 17 microsatellites revealed a significant two-point parametric HLOD = 3.99 at marker D4S1597. Transmission disequilibrium tests for markers in this candidate region showed no transmission distortion. A scan for variants in a gene adjacent to D4S1597, PALLD, was negative for synonymous or nonsynonymous changes. A final multipoint scan incorporating all microsatellites in the region provided an HLOD = 1.30. The inability to find significant linkage in these highly penetrant families suggests that linkage is not the optimal tool for dissecting the inheritance of MS.

The inheritance of resistance alleles in multiple sclerosis.

Multiple sclerosis (MS) is a complex trait in which alleles at or near the class II loci HLA-DRB1 and HLA-DQB1 contribute significantly to genetic risk. HLA-DRB1*15 and HLA-DRB1*17-bearing haplotypes and interactions at the HLA-DRB1 locus increase risk of MS but it has taken large samples to identify resistance HLA-DRB1 alleles. In this investigation of 7,093 individuals from 1,432 MS families, we have assessed the validity, mode of inheritance, associated genotypes, and the interactions of HLA-DRB1 resistance alleles. HLA-DRB1*14-, HLA-DRB1*11-, HLA-DRB1*01-, and HLA-DRB1*10-bearing haplotypes are protective overall but they appear to operate by different mechanisms. The first type of resistance allele is characterised by HLA-DRB1*14 and HLA-DRB1*11. Each shows a multiplicative mode of inheritance indicating a broadly acting suppression of risk, but a different degree of protection. In contrast, a second type is exemplified by HLA-DRB1*10 and HLA-DRB1*01. These alleles are significantly protective when they interact specifically in trans with HLA-DRB1*15-bearing haplotypes. HLA-DRB1*01 and HLA-DRB1*10 do not interact with HLA-DRB1*17, implying that several mechanisms may be operative in major histocompatibility complex-associated MS susceptibility, perhaps analogous to the resistance alleles. There are major practical implications for risk and for the exploration of mechanisms in animal models. Restriction of antigen presentation by HLA-DRB1*15 seems an improbably simple mechanism of major histocompatibility complex-associated susceptibility.