Ramagopalan SV1, Lee JD, Yee IM, Guimond C, Traboulsee AL, Ebers GC, Sadovnick AD.

Abstract
Genetic and environmental factors have important roles in multiple sclerosis (MS) susceptibility. Several studies have shown an association between smoking and MS risk. Here, in a population-based Canadian cohort, we investigate the relationship between personal and maternal smoking exposure and the risk of MS. Using the longitudinal Canadian database, 3,157 MS cases and 756 spouse controls were administered questionnaires on active and passive smoking history. Mothers of cases and controls were also asked about their smoking exposure during pregnancy. The MS cases were more likely to have smoked than spouse controls (odds ratio 1.32, 95 % confidence interval 1.10-1.60, p = 0.003). This association was driven by an excess of ever-smokers in male MS cases. No association was seen with maternal active or passive smoking exposure during pregnancy. Ever-smoking is associated with increased MS risk in males. Further work is needed to understand the mechanism underlying this association.

Orton SM, Ramagopalan SV, Brocklebank D, Herrera BM, Dyment DA, Yee IM, Sadovnick AD, Ebers GC.

Abstract
BACKGROUND:
The ratio of female to male (F:M) multiple sclerosis (MS) cases varies geographically, generally being greater in areas of high prevalence. In many regions, including Canada, rising MS incidence in women has been implied by the marked increase in F:M ratio.

METHODS:
We examined the F:M ratio over time in MS patients in the Canadian Collaborative Study born outside Canada, with onset postmigration (n = 2531). We compared the trends to native-born Canadians, by region of origin and age at migration.

RESULTS:
Regression analysis showed that year of birth (YOB) was a significant predictor of sex ratio in immigrants (chi(2) = 21.4, p<0.001 correlation r = 0.61). The rate of change in sex ratio was increasing in all migrant subgroups (by a factor of 1.16 per 10-year period, p<0.001), with the steepest increase observed in those from Southern Europe (1.27/10 years, p<0.001). The overall immigrant F:M ratio was 2.17, but varied by country of origin. It was significantly lower in migrants from Southern Europe compared with Northern Europe or USA (1.89 vs 2.14 and 2.86, p = 0.023 and p = 0.0003, respectively). Increasing age at immigration was associated with decreasing sex ratio (p = 0.041). The sex ratio of individuals migrating <21 was significantly higher than those migrating > or =21 (2.79 vs 1.96, p = 0.004).

CONCLUSIONS:
MS sex ratio in immigrants to Canada is increasing but variable by region of origin and influenced by age at migration. The findings highlight the importance of environmental effect(s) in MS risk, which are likely gender-specific.

Ramagopalan SV, Yee IM, Dyment DA, Orton SM, Marrie RA, Sadovnick AD, Ebers GC; Canadian Collaborative Study Group.

Abstract
BACKGROUND:
Multiple sclerosis (MS) is a complex neurologic disease with a striking geographical distribution. In Canada, prevalence is high in Caucasians of Northern European ancestry and uncommon in North American Aboriginals, many of whom now have Caucasian admixture.

METHODS:
The population-based Canadian Collaborative Project on the Genetic Susceptibility to MS provided the characteristics of 58 individuals with 1 Caucasian and 1 North American Aboriginal parent from a database of 30,000 MS index cases.

RESULTS:
We found that MS index cases with a Caucasian mother and a North American Aboriginal father had a higher sib recurrence risk and greater F:M sex ratio (p = 0.043) than patients with a North American Aboriginal mother and Caucasian father.

CONCLUSIONS:
Maternal parent-of-origin effects in multiple sclerosis disease etiology previously seen in studies of half-siblings and avuncular pairs are also seen in Caucasian-North American Aboriginal admixture matings and warrant further investigation. A differential influence of maternal risk transmission on the sex ratio of affected offspring is implied. The method of analysis used may have broader implications for detection of parent-of-origin effects in admixture cohorts.

Ramagopalan SV1, Valdar W, Dyment DA, DeLuca GC, Yee IM, Giovannoni G, Ebers GC, Sadovnick AD; Canadian Collaborative Study Group.

Abstract

BACKGROUND:
Genetic and environmental factors have important roles in multiple sclerosis (MS) susceptibility. Several studies have attempted to correlate exposure to viral illness with the subsequent development of MS. Here in a population-based Canadian cohort, we investigate the relationship between prior clinical infection or vaccination and the risk of MS.

METHODS:
Using the longitudinal Canadian database, 14,362 MS index cases and 7,671 spouse controls were asked about history of measles, mumps, rubella, varicella and infectious mononucleosis as well as details about vaccination with measles, mumps, rubella, hepatitis B and influenza vaccines. Comparisons were made between cases and spouse controls.

RESULTS:
Spouse controls and stratification by sex appear to correct for ascertainment bias because with a single exception we found no significant differences between cases and controls for all viral exposures and vaccinations. However, 699 cases and 165 controls reported a history of infectious mononucleosis (p < 0.001, corrected odds ratio 2.06, 95% confidence interval 1.71-2.48). Females were more aware of disease history than males (p < 0.001). CONCLUSIONS: The data further confirms a reporting distortion between males and females. Historically reported measles, mumps, rubella, varicella and vaccination for hepatitis B, influenza, measles, mumps and rubella are not associated with increased risk of MS later in life. A clinical history of infectious mononucleosis is conspicuously associated with increased MS susceptibility. These findings support studies implicating Epstein-Barr virus in MS disease susceptibility, but a co-association between MS susceptibility and clinically apparent infectious mononucleosis cannot be excluded. [/accordion] [accordion title="Parent-of-origin effects in MS: observations from avuncular pairs. Neurology 2008;71:799–803." style="accordion-style3"]
Herrera BM1, Ramagopalan SV, Lincoln MR, Orton SM, Chao MJ, Sadovnick AD, Ebers GC.

Abstract

BACKGROUND:
Multiple sclerosis (MS) is a complex neurologic disease of unknown etiology and inheritance pattern, but with increasing incidence among females. The study of aunt/uncle-niece/nephew (AUNN) pairs has potential to shed light on the on complex trait inheritance as this group can be divided into eight different pair types by gender, MS status, and parent of origin.

METHODS:
Using a cohort of 807 avuncular MS families with 938 affected AUNN pairs ascertained from a longitudinal, population-based Canadian database, we examined differential MS transmission by separating affected pairs into likely maternal and paternal trait origin.

RESULTS:
We observed an increased number of avuncular pairs connected through unaffected mothers compared to unaffected fathers (p = 0.008). To restrict confounders introduced by families with multiple pairs the overall number of maternal and paternal families were compared, to reveal a significantly higher number of maternal families (p = 0.038). Female-to-male sex ratios were higher among affected nieces/nephews when compared to the sex ratio for aunts/uncles (0.00042).

CONCLUSIONS:
This observation independently confirms previous findings of a "maternal parent-of-origin" effect in multiple sclerosis (MS) susceptibility. These findings highlight the special contribution that can be derived from avuncular pairs. These underutilized pairings can compare transmission by the gender of affected aunt-uncle, the unaffected transmitting parent, and by that of the affected offspring. This strategy may be especially profitable in diseases where parent-of-origin effects are being sought. These findings also independently confirm the increasing rate of MS in females, demonstrating that familial cases are influenced by the same environmental factors as the general MS population.

Orton SM, Herrera BM, Yee IM, Valdar W, Ramagopalan SV, Sadovnick AD, Ebers GC; Canadian Collaborative Study Group.

Abstract

BACKGROUND:
Incidence of multiple sclerosis is thought to be increasing, but this notion has been difficult to substantiate. In a longitudinal population-based dataset of patients with multiple sclerosis obtained over more than three decades, we did not show a difference in time to diagnosis by sex. We reasoned that if a sex-specific change in incidence was occurring, the female to male sex ratio would serve as a surrogate of incidence change.

METHODS:
Since environmental risk factors seem to act early in life, we calculated sex ratios by birth year in 27 074 Canadian patients with multiple sclerosis identified as part of a longitudinal population-based dataset.

FINDINGS:
The female to male sex ratio by year of birth has been increasing for at least 50 years and now exceeds 3.2:1 in Canada. Year of birth was a significant predictor for sex ratio (p<0.0001, chi(2)=124.4; rank correlation r=0.84).

INTERPRETATION:
The substantial increase in the female to male sex ratio in Canada seems to result from a disproportional increase in incidence of multiple sclerosis in women. This rapid change must have environmental origins even if it is associated with a gene-environment interaction, and implies that a large proportion of multiple sclerosis cases may be preventable in situ. Although the reasons why incidence of the disease is increasing are unknown, there are major implications for health-care provision because lifetime costs of multiple sclerosis exceed pound1 million per case in the UK.

Ebers GC, Sadovnick AD, Dyment DA, Yee IM, Willer CJ, Risch N.

Abstract

Multiple sclerosis is a complex trait in which occurrence rates in offspring are 20-50-fold greater than in the general population. Parent-of-origin effects have been difficult to screen for, since most cases are sporadic. We have compared recurrence risks in half-siblings with respect to their parent in common. Of the 1567 index cases with half-siblings in multiple sclerosis clinics across Canada, we recorded 3436 half-siblings and 2706 full-siblings. Age-adjusted full-sibling risk was 3.11%. By contrast, half-sibling risk in the same families was significantly lower at 1.89% (chi2 test, p=0.006), but higher than expected if familial risk was simply polygenic. For maternal half-siblings, the risk was 2.35% (34 affected siblings of 1859), and 1.31% for paternal half-siblings (15 of 1577), (p=0.048). The difference in risk suggests a maternal parent-of-origin effect in multiple sclerosis susceptibility.

Willer CJ, Dyment DA, Risch NJ, Sadovnick AD, Ebers GC; Canadian Collaborative Study Group.

Abstract

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 MZ/DZ 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.

Sadovnick AD, Yee IM, Ebers GC; Canadian Collaborative Study Group.

Abstract

Using population-based data, the authors identified 24 MS index cases whose parents were related. Twenty-two had 67 sibs of whom 6 also had MS, yielding a recurrence risk of approximately 9%, significantly higher than for sibs of MS index cases from nonconsanguineous parents. These findings support the concept that multiple interacting genes increase the risk of MS.

Sadovnick AD, Yee IM, Ebers GC; Canadian Collaborative Study Group.

Abstract

Multiple sclerosis (MS) is now thought to be a complex trait determined by genetic and non-genetic (environmental) factors. The study group, identified from the Canadian Collaborative Project on Genetic Susceptibility to MS, consisted of 1,083 MS index cases, 2,166 of their parents and 3,112 of their sibs. The results, together with those of a previous study on an independent data set, suggest that gender, age of MS onset and having one parent with MS may individually and interactively alter sib risks for MS. These data are important for genetic counselling and for molecular genetic (genome screens, candidate gene analyses) studies.

Sadovnick AD, Ebers GC, Dyment DA, Risch NJ.

Abstract

BACKGROUND Increased familial risks in multiple sclerosis (MS) range from 300-fold for monozygotic twins to 20-40-fold for biological first-degree relatives, suggesting a genetic influence. Yet if one identical twin has MS the other usually will not. One way of sorting out the contributions of genes and environment is to study half-sibs. METHODS In a Canadian population-based sample of 16 000 MS cases seen at 14 regional MS clinics one half-sib (or more) was reported by 939 index cases. By interview we elicited information on family structure and an illness in half-sibs and any full brothers or sisters. FINDINGS The age-adjusted MS rate in the 1839 half-sibs of these index cases was 1.32 percent compared with 3.46 percent for the 1395 full sibs of the same cases (p<0.001; likelihood ratio test). There were no significant differences in risk for maternal versus paternal half-sibs (1.42 percent vs 1.19 percent) or for those raised together versus those raised apart from the index case (1.17 percent vs 1.47 percent). INTERPRETATION Besides demonstrating the power and the feasibility of using half-sib studies to throw light on the aetiology of complex disorders, our findings show that a shared environment does not account for familial risk in MS and that maternal effects (such as intrauterine and perinatal factors, breastfeeding, and genomic imprinting) have no demonstrable effect on familial risk. Halving the number of potentially contributory genes (by comparing full-sib and half-sib rates) lowers the risk of MS by a factor of 2.62, an observation consistent with a polygenic hypothesis.

Ebers GC, Sadovnick AD, Risch NJ.

Abstract

Genetic-environmental interactions probably underlie spontaneous human autoimmune disorders, a category of complex traits thought to include multiple sclerosis (MS). The geographical distribution and familial aggregation of this disease have often been ascribed to the role of infectious agents, but there is no consensus. Increased family risks range from 300-fold for monozygotic twins to 20-40-fold for biological first-degree relatives over the general population prevalence of 0.1% (ref. 6). We screened a population-based sample of 15,000 individuals with MS by using standardized, personally administered questionnaires to identify adopted index cases and/or those who had adopted relatives. The frequency of MS among first-degree non-biological relatives living with the index case was no greater than expected from Canadian population prevalence data and significantly less than for biological relatives. These findings indicate that familial aggregation of MS is genetically determined: no effect of shared environment was detectable.

Sadovnick AD, Baird PA, Ward RH.

Abstract

Two important characteristics of multiple sclerosis (MS) are familial clustering and a variable age of onset. There is increasing evidence for a genetically influenced susceptibility in MS. Because of this, patients and their relatives are increasingly asking about the risk for relatives of developing MS.

In the MS Clinic in Vancouver, genetic histories are taken routinely for all patients and are updated annually. Patients do not attend the clinic specifically to participate in genetic studies, which could result in over-representation of familial cases.

Data were available for 815 MS index cases and 11,345 of their relatives. Age-specific MS risks were calculated for first-, second-, and third-degree relatives of probands and are presented in an easy-reference format. In general, first-degree relatives of probands have a risk that is 30–50 times greater than the 0.1% risk for the general population.

Sadovnick AD, Baird PA.

Abstract

Increasingly, MS patients ask neurologists about the risk that their close relatives will also develop MS. We calculated age-adjusted empiric recurrence risks from data on 815 index cases and over 3,000 of their siblings and children. In general, the risk for these relatives to develop MS is 3 to 5%, which is 30 to 50 times the 0.1% rate for the general population.