Objectives To determine if risk of multiple sclerosis (MS) is associated with month of birth in countries in the northern hemisphere and if factors related to month of birth interact with genetic risk. Design Population based study with population and family based controls and a retrospective cohort identified from death certificates. A post hoc pooled analysis was carried out for large northern datasets including Sweden and Denmark. Setting 19 MS clinics in major cities across Canada (Canadian collaborative project on the genetic susceptibility to multiple sclerosis); incident cases of MS from a population based study in the Lothian and Border regions of Scotland; and death records from the UK Registrar General. Populations 17 874 Canadian patients and 11 502 British patients with multiple sclerosis. Main outcome measure Diagnosis of multiple sclerosis. Results In Canada (n = 17 874) significantly fewer patients with MS were born in November compared with controls from the population census and unaffected siblings. These observations were confirmed in a dataset of British patients (n = 11 502), in which there was also an increase in the number of births in May. A pooled analysis of datasets from Canada, Great Britain, Denmark, and Sweden (n = 42 045) showed that significantly fewer (8.5%) people with MS were born in November and significantly more (9.1%) were born in May. For recent incident data, the effect of month of birth was most evident in Scotland, where MS prevalence is the highest. Conclusions Month of birth and risk of MS are associated, more so in familial cases, implying interactions between genes and environment that are related to climate. Such interactions may act during gestation or shortly after birth in individuals born in the northern countries studied.

Size and ascertainment constraints often limit twin studies to concordance comparisons between identical and fraternal twins. Here we report the final results of a longitudinal, population-based study of twins with multiple sclerosis (MS) in Canada. Bias was demonstrably minimized, and an estimated 75% of all Canadian MS twin pairs were ascertained, giving a sample sufficiently large (n ‫؍‬ 370) to permit additional informative comparisons. Twinning was not found to affect prevalence, and twins with MS did not differ from nontwins for DR15 allele frequency nor for MS risk to their siblings. Probandwise concordance rates of 25.3% (SE ؎ 4.4) for monozygotic (MZ), 5.4% (؎2.8) for dizygotic (DZ), and 2.9% (؎0.6) for their nontwin siblings were found. MZ twin concordance was in excess of DZ twin concordance. The excess concordance in MZ was derived primarily from like-sexed female pairs with a probandwise concordance rate of 34 of 100 (34 ؎ 5.7%) compared with 3 of 79 (3.8 ؎ 2.8%) for female DZ pairs. We did not demonstrate an MZ͞DZ difference in males, although the sample size was small. We observed a 2-fold increase in risk to DZ twins over nontwin siblings of twins, but the difference was not significant. Multiple sclerosis (MS) is one of the most common neurological diseases affecting young adults (1). In Canada, at least 1 in 1,000 individuals has the disease (2-4), and twice as many women are affected compared with men. It is widely believed that susceptibility to MS is determined by a complex interaction between susceptibility genes and environment. Twin studies have played an important role in current concepts of complex traits including MS and have consistently demonstrated an excess of monozygotic (MZ) over dizygotic (DZ) concordance (refs. 5-19 and Table 1).The magnitude of the MZ-to-DZ difference has implied non-Mendelian inheritance (20). However, in more recent data, it seems that the absolute level of concordance in MZ twins also reflects the background population prevalence. Whereas in Canada and northern Europe concordance rates are high, in southern Europe twin concordance rates mirror the lower prevalence (ref. 5 and L. Ristori, S. Cannoni, and M. Salvetti, unpublished data). Uncertainty has remained about final concordance rates, because twins in previously reported studies retained considerable residual risk based on corrections for age of onset. Corrections can be readily calculated for the general population, but applying it to twins may be inappropriate because the age onset correlations are so much larger for concordant MZ pairs than for siblings (sibs) (21).Twin studies in MS and other putative autoimmune diseases have generally been small. Data have been insufficient in any single study to adequately assess the impact of ascertainment bias, a common confounder of twin studies (22). Questions beyond the comparison of MZ with DZ concordance have been left unanswered, and even this comparison shows wide confidence intervals in published data. Furthermore, it has not been possible to study an...

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.

Multiple sclerosis (MS) is probably aetiologically heterogeneous. Systematic genetic epidemiological and molecular genetic studies have provided important insights. Both genetic and non-genetic (environment, stochastic) factors may be involved in susceptibility as well as outcome, but we have yet to understand their relative roles. Any environmental factor is likely to be ubiquitous and act on a population-basis rather than within the family microenvironment. Taken together, the results of genome screening studies provide strong evidence for exclusion of a major locus in MS. There are, however, many genes that seem to be associated with MS. These include, but are in no way limited to, HLA classes I and II, T-cell receptor beta, CTLA4, ICAM1, and SH2D2A. The future of MS genetics, as for most common complex disorders, will be dependent on the resources available, ranging from biological samples and comprehensive databases of clinical and epidemiological information to the development of new technologies and statistical methods.

An accurate diagnosis is an integral component of patient care for children with rare genetic disease. Recent advances in sequencing, in particular whole‐exome sequencing (WES), are identifying the genetic basis of disease for 25–40% of patients. The diagnostic rate is probably influenced by when in the diagnostic process WES is used. The Finding Of Rare Disease GEnes (FORGE) Canada project was a nation‐wide effort to identify mutations for childhood‐onset disorders using WES. Most children enrolled in the FORGE project were toward the end of the diagnostic odyssey. The two primary outcomes of FORGE were novel gene discovery and the identification of mutations in genes known to cause disease. In the latter instance, WES identified mutations in known disease genes for 105 of 362 families studied (29%), thereby informing the impact of WES in the setting of the diagnostic odyssey. Our analysis of this dataset showed that these known disease genes were not identified prior to WES enrollment for two key reasons: genetic heterogeneity associated with a clinical diagnosis and atypical presentation of known, clinically recognized diseases. What is becoming increasingly clear is that WES will be paradigm altering for patients and families with rare genetic diseases.

Mechanisms for observed associations within the major histocompatibility complex (MHC) and autoimmune diseases including multiple sclerosis (MS) remain uncertain. Genotyping of the HLA Class II DRB1 locus in 4347 individuals from 873 multiplex families with MS highlights the genetic complexity of this locus. Excess allele sharing in sibling pair families lacking DRB1*15 and DRB1*17 (58.5% sharing; P=0.012) was comparable to that seen where parents were DRB1*15 positive (62%, P=0.0006). DRB1*17 (P=0.00027) was clearly established as an MS susceptibility allele in addition to DRB1*15 (P<10(-14)). DRB1*14 showed striking under-transmission (P=0.000032) to affected offspring newly establishing this allele as a broadly acting resistance factor. Trans interactions were seen in both DRB1*15 and non-DRB1*15 bearing genotype combinations. DRB1*08 was transmitted preferentially with DRB1*15 (P=0.0114) and, in the presence of DRB1*08, the transmission of DRB1*15 was almost invariable (37 transmissions to one non-transmission). DRB1*01 was under-transmitted to offspring in the presence of DRB1*15 (P=0.019). Both DRB1*01 and DRB1*14 haplotypes carry DQA1*01-DQB1*05 alleles, suggesting a common DQ-related mechanism for the protection mediated by these haplotypes. These studies demonstrate that it is the Class II genotype that determines susceptibility and resistance to MS. By analogy with celiac disease and type I diabetes, the pattern of susceptibility strongly supports an autoimmune aetiology.

Deficiency in BRCA dependent DNA inter-strand crosslink (ICL) repair is intimately connected to breast cancer susceptibility and to the rare developmental syndrome, Fanconi Anemia (FA). Bona fide FA proteins, BRCA2 (FANCD1), PALB2 (FANCN), and BRIP1 (FANCJ) interact with BRCA1 during ICL repair. However, lack of detailed phenotypic and cellular characterization of a patient with biallelic BRCA1 mutations has precluded assignment of BRCA1 as a definitive FA susceptibility gene. Here we report the presence of biallelic BRCA1 mutations in a woman with multiple congenital anomalies consistent with a FA-like disorder and breast cancer at age 23. Patient cells exhibited deficiency in BRCA1 (FANCS) and Rad51 localization to DNA damage sites, combined with radial chromosome formation and hypersensitivity to ICL inducing agents. Restoration of these functions was achieved by ectopic introduction of a BRCA1 transgene. These observations provide evidence in support of BRCA1 as a new Fanconi anemia subtype (FA-S).

Genetic susceptibility to multiple sclerosis is associated with genes of the major histocompatibility complex (MHC), particularly HLA-DRB1 and HLA-DQB1 (ref. 1). Both locus and allelic heterogeneity have been reported in this genomic region. To clarify whether HLA-DRB1 itself, nearby genes in the region encoding the MHC or combinations of these loci underlie susceptibility to multiple sclerosis, we genotyped 1,185 Canadian and Finnish families with multiple sclerosis (n = 4,203 individuals) with a high-density SNP panel spanning the genes encoding the MHC and flanking genomic regions. Strong associations in Canadian and Finnish samples were observed with blocks in the HLA class II genomic region (P < 4.9 x 10(-13) and P < 2.0 x 10(-16), respectively), but the strongest association was with HLA-DRB1 (P < 4.4 x 10(-17)). Conditioning on either HLA-DRB1 or the most significant HLA class II haplotype block found no additional block or SNP association independent of the HLA class II genomic region. This study therefore indicates that MHC-associated susceptibility to multiple sclerosis is determined by HLA class II alleles, their interactions and closely neighboring variants.