Maternal transmission of multiple sclerosis in a dutch population.

Abstract

To investigate the parental relationship of patients with multiple sclerosis (MS) from an extended pedigree with extensive genealogical information up to the middle of the 18th century.
Multiple sclerosis is a complex disease resulting from genetic and environmental factors. Parent-of-origin effect, a phenomenon when the same allele may express differently depending on the sex of the transmitting parent, may influence the risk for MS. We investigated parental relationships between patients with MS using extensive genealogical information available from the Genetic Research in Isolated Populations program. We compared the average kinship of the parents of MS patients. We further explored the distribution of shortest genealogical links between parents of MS patients. Subjects Twenty-four MS patients from the isolated population who could be linked within a large complex pedigree, including 2471 people in total.
The results consistently indicate a higher prevalence of maternal transmission of MS. The kinship between mothers of patients was 3.8 times higher than that between fathers (bootstrap P = .01). Among the 814 shortest connections between parents, 333 were maternal (40.9%, vs 25.0% expected), 98 were paternal (12.0%, vs 25.0% expected), and 383 were maternal-paternal (47.1%, vs 50.0% expected) (P < .001).
Mothers of MS patients were more closely related than their fathers. This skewed relationship shows evidence for a maternal effect in MS. The most likely explanation is a gene-environment effect that takes place in utero.

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ORIGINAL CONTRIBUTION
Maternal Transmission of Multiple Sclerosis
in a Dutch Population
Ilse A. Hoppenbrouwers, MD; Fan Liu, MD; Yurii S. Aulchenko, PhD; George C. Ebers, MD;
Ben A. Oostra, PhD; Cornelia M. van Duijn, PhD; Rogier Q. Hintzen, MD, PhD
Objective: To investigate the parental relationship of
patients with multiple sclerosis (MS) from an extended
pedigree with extensive genealogical information up to
the middle of the 18th century.
Design: Multiple sclerosis is a complex disease result-
ing from genetic and environmental factors. Parent-of-
origin effect, a phenomenon when the same allele may
express differently depending on the sex of the trans-
mitting parent, may influence the risk for MS. We
investigated parental relationships between patients
with MS using extensive genealogical information avail-
able from the Genetic Research in Isolated Populations
program. We compared the average kinship of the par-
ents of MS patients. We further explored the distribu-
tion of shortest genealogical links between parents of
MS patients.
Subjects: Twenty-four MS patients from the isolated
population who could be linked within a large complex
pedigree, including 2471 people in total.
Results:Theresultsconsistentlyindicateahigherpreva-
lence of maternal transmission of MS. The kinship be-
tweenmothersofpatientswas3.8timeshigherthanthat
betweenfathers(bootstrapP=.01).Amongthe814short-
est connections between parents, 333 were maternal
(40.9%, vs 25.0% expected), 98 were paternal (12.0%,
vs 25.0% expected), and 383 were maternal-paternal
(47.1%, vs 50.0% expected) (P?.001).
Conclusions:MothersofMSpatientsweremoreclosely
relatedthantheirfathers.Thisskewedrelationshipshows
evidenceforamaternaleffectinMS.Themostlikelyex-
planation is a gene-environment effect that takes place
in utero.
Arch Neurol. 2008;65(3):345-348
M
to play a role in determining MS risk by
adoption studies,1studies with half-
siblings,2twinstudies,3andstudiesofcon-
jugal MS.4Migration studies5,6have espe-
ciallypointedtoenvironmentalfactorsas
playing a role in MS.
Other influences, such as parent-of-
origin effects, are also described in deter-
mining MS risk. Parent of origin is a phe-
nomenonwhenthesamealleleisexpressed
differentlydependingonthesexofthetrans-
mitting parent. A study2of half-siblings
showedthatmaternalhalf-siblingshavesig-
nificantlyhigherriskofdevelopingMScom-
paredwithpaternalones,suggestingama-
ternal parent-of-origin effect. In contrast,
observations in offspring of affected par-
entsdemonstratedexcessofpaternalvsma-
ternal transmission.7
ULTIPLE SCLEROSIS
(MS)isacomplexdis-
easeresultingfromthe
interplay between ge-
neticandenvironmen-
tal factors. Genetic factors are implicated
Both studies in which a parent-of-
origineffectinMSwassuggestedwereper-
formed in differentially selected patient
groups: with nonaffected parents in the
study by Ebers et al2and affected parents
in the study by Kantarci et al.7They had
in common that only recent generations
of patients with MS were studied.
We studied parent-of-origin effects of
MS transmission in a genetically isolated
population,withextensivegenealogicalin-
formationovercenturies.Mostcaseswere
notcloselyrelatedbutwereinitiallydiag-
nosed as sporadic MS cases. The clinical
MS phenotype was similar to MS in the
general Dutch population.8
METHODS
STUDY POPULATION AND
PATIENT ASCERTAINMENT
This study was performed within the frame-
work of the previously described Genetic Re-
search in Isolated Populations (GRIP) pro-
Author Affiliations:
Department of Neurology,
MS Centre Erasms
(Drs Hoppenbrouwers and
Hintzen), Genetic
Epidemiology Unit, Department
of Epidemiology and
Biostatistics (Drs Liu,
Aulchenko, and van Duijn), and
Department of Clinical Genetics
(Dr Oostra), Erasmus MC,
Rotterdam, the Netherlands;
and Wellcome Trust Centre for
Human Genetics and
Department of Clinical
Neurology, University of
Oxford, Oxford, England
(Dr Ebers).
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gram.9,10The Medical Ethics Committee of the Erasmus MC
approved GRIP protocols. The GRIP population is a geneti-
cally isolated community in the southwest of the Netherlands.
Fewerthan400individualsfoundedthepopulationinthemiddle
of the 18th century. Considerable population growth subse-
quently occurred. Until recently, there was minimal immigra-
tion. An estimated 20000 descendants of this population are
scattered over 8 adjacent communities. The genealogical da-
tabasecontainsinformationonmorethan90000people,span-
ning 23 generations. Residents in the GRIP area are generally
related via multiple lines of descent.
AscertainmentandclinicalcharacteristicsofMSpatientsin
the GRIP population have been described in detail previ-
ously.8In brief, 24 MS patients (5 men and 19 women) could
be linked to the most recent common ancestor in 14 genera-
tions. These 24 MS patients had given written informed con-
sent. Numerous connections exist between these patients via
multiple common ancestors.
PARENT-OF-ORIGIN EFFECT
We compared average kinship of parents of the 24 MS pa-
tients,testingwhetherpatientsweremoreoftenrelatedthrough
paternal or maternal lineage. Kinship coefficients were com-
puted using a computer software package (PEDIG).11Under
the null hypothesis of no parent-of-origin effect, the average
degree of relationship of fathers should not be different from
the one of mothers, assuming random mating.
When there is deviation from random mating (in particu-
lar,preferentialoutbreedingforoneofthesexes),thetestbased
on comparison of average kinships between mothers and fa-
thers is not correct. For example, if there is systematic out-
breeding of males, one would expect to observe higher kin-
shipbetweenmothersofanyrandomlyselectedgroupofpeople
from the population.
Toassesstheempiricalnulldistributionofdifferencesinpa-
rental relationship specific for our population, we performed
analysisusing10000replicas.Foreachtime,24individuals,ad-
justedforsexandagewiththepatients,wererandomlysampled
fromtheGRIPgenealogydatabase.Thisprocedureisalsoknown
asbootstrap.Averagekinshipwascomputedforfathersandmoth-
ers of these randomly sampled individuals, and the ratio be-
tween maternal and paternal kinships was computed. The pro-
portionofrealizationsinwhichtheratiowastheobservedratio
or more gives the empirical P value.
We further explored genealogical links between MS pa-
tients via all of their common ancestors using a software pack-
age (FCN; available at http://mga.bionet.nsc.ru/soft/index
.html). We next focused on the shortest connection between
patients.Underthehypothesisthatageneticfactorplaysarole
in MS, one assumes that patients are more closely related to
eachotherthancontrolsubjects.Intermsofgenealogicallinks,
this implies that, on average, links between MS patients are
shorter than those between controls. For the shortest genea-
logical link between 2 MS patients, there are 3 possible pat-
terns:2patientsarerelatedthroughtheirmothers,throughthe
father of one patient and the mother of the other patient, or
through their fathers. Under the null hypothesis of no parent-
of-origin effect, and assumption of random mating, the ex-
pecteddistributionofthese3patternsis25%throughtheirmoth-
ers,25%throughtheirfathers,and50%throughafatheranda
mother. A ?2test with 2 df was used as the test statistic.
In all analyses, when siblings were present as patients, the
parents were included in paternal/maternal samples only once
to avoid possible bias.
Wehadtheuniqueopportunitytotestparent-of-origineffect
in the same way for several other diseases in the GRIP area, in-
cluding Parkinson disease, late-onset Alzheimer disease, and
type 1 diabetes mellitus.
RESULTS
The general characteristics of the 24 MS patients are as
follows. Their mean (SD) age at onset of symptoms was
29 (9) years; at diagnosis, 36 (11) years. There was no
significant (P =.57) difference in age of symptom onset
between the 24 MS patients and 73 sporadic Dutch MS
patientsfromoutsidetheisolate.8,12Therewere19women
(79%) in the sample. The distribution of relapse-onset
MS (20 patients [83%]) and primary progressive onset
MS (4 patients [17%]) was not different from that in the
general MS population. Of the 24 patients, 15 were ini-
tiallydiagnosedasisolatedMScasesand9werefromfami-
lies in which patients were themselves aware of having
2 or more MS cases in their families. Of these 9 patients,
4 were affected sisters from one family, all participating
in this study. The other 5 patients were from families in
which 2 people were diagnosed as having MS: 2 partici-
pating patients were third-degree relatives, 2 participat-
ing patients were second-degree relatives, and 1 patient
had a first-degree relative with MS who did not want to
participate in this study. None of the parents or grand-
parents of the 24 patients was diagnosed as having MS.
The characteristics of the genealogy of the MS pa-
tients are as follows. The mean (SD) number of consan-
guineousloopsperpatientwas139.9(278.9),witharange
from 0 to 1205; the mean (SD) number of meioses per
loop was 12.4 (1.3), with a range from 0 to 29; and the
mean (SD) inbreeding was 1.4?10−3(1.9?10−3), with
a range from 0 to 7.7?10−3. Patients with MS could be
linked to multiple common ancestors in different gen-
erations. Each pair of patients shares, on average, 264.2
(SD,449.4)commonancestors(range,2-2936common
ancestors).Themeannumberofmeiosesseparatingapair
ofpatientswas22.2(SD,2.1),witharangefrom2to36,
which means that their common ancestry is, on aver-
age, 11 generations ago. The most recent common an-
cestor for all 24 patients could be identified 14 genera-
tionsago.Finally,themean(SD)kinshipforthepatients
was6.7?10−3(3.7?10−2),witharangefrom2?10−7to
0.3.
Toassesstheparent-of-origineffect,wecomparedthe
meankinshipofmothersandtheoneoffathers.Themean
kinship of mothers (0.0031) was 3.9 times higher than
the one of fathers (0.0008). A 2-independent-samples t
test comparing these kinships gives a significant P value
(?.001).Theempiricalnulldistributionoftheratiobe-
tween maternal and paternal kinships using 10000
samples of 24 age- and sex-matched controls randomly
selectedfromourgenealogicaldatabasewasderived.The
probabilityofobservingthesameoramoreextremekin-
ship ratio in this population was P=.01, indicating that
closer kinship between mothers of MS patients is not a
statisticalartifactoraconsequenceofviolationfromthe
random mating assumption.
We further explored genealogical links between MS
patients. In total, 36466 pairwise connections between
each possible pair of 24 MS patients were identified via
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796 ancestors. Among these connections, we counted
shortest connections between each pair of MS patients
in respect to the 3 possible patterns described in the
“Methods”section.Among814shortestconnections,333
werebetweenmothers(40.9%;25.0%expected),98were
betweenfathers(12.0%;25.0%expected),and383were
between a father and a mother (47.1%; 50.0% expected)
(P?.001) (Figure).
We also investigated parent-of-origin effect for sev-
eral other diseases in the GRIP area, using the same da-
tabase and the same method. For 67 patients with Par-
kinson disease, 103 with late-onset Alzheimer disease
(P =.52), and 39 with type 1 diabetes mellitus (P =.38)
who could be linked to a common ancestor, no signifi-
cant parent-of-origin effect could be found.
COMMENT
A pedigree of 24 patients with common clinical pheno-
types of MS was recently reconstructed.8
Herein,weshowthattheshortestconnectiontoacom-
mon ancestor between 2 individuals with MS was sig-
nificantly more often through their nonaffected mother
than through their nonaffected father, suggesting a ma-
ternal parent-of-origin effect. No significant parent-of-
origineffectwasobservedinseveralotherdiseasesinthe
same area. Thus, the effect seems to be specific for MS.
Mothersofthe24MSpatientswerealsomoreclosely
related to each other than their fathers.
Multiple sclerosis has a female-male ratio of 3:1. Po-
tentially, this carries the risk of bias when studying dis-
easetransmissionover2generationswhenparentsareaf-
fectedandwomenareatincreasedriskofMS.Ourapproach
hadnobiasintothisskewbecausenoneoftheparentsand
grandparentsofthe24MSpatientswereaffectedwithMS.8
A few other studies2,7,13analyzed parent-of-origin effects,
all using the information of 2 generations. The signifi-
cant difference with our study is that by using extensive
genealogicalinformationwewereabletostudytheshort-
est links by a multigenerational approach.
Our findings are in line with the results of the Cana-
dian study in which the difference in MS risk was inves-
tigatedforhalf-siblingsofMSpatientswithasharednon-
affected parent. A shared mother was associated with a
higher MS risk.2
In contrast, a recent study7in the United States ob-
served that fathers transmit the disease more fre-
quently.ThiswasexplainedbytheCartereffect.Accord-
ing to this theory, men are more resistant to MS because
theyrequireahighergeneticloadandthusaremorelikely
to transmit the genetic risk of the disease to their chil-
dren. This phenomenon was not observed by others.13
OurapproachdifferedfromthatofKantarcietal7inthat
wedidnotstudymultiplexfamiliesandparentswerenot
affected.
Taking together all available data on parental trans-
missionofMS,onecanconcludethattheMS-affectedsta-
tus of the parent may influence transmission of disease.
Maternal transmission could be a result of several fac-
tors: genetic, environmental, or both. There are at least 3
single genetic explanations. None of them are supported
heavilybycurrentdata.First,maternaleffectscouldbeex-
ertedbydirecttransmissionviamitochondrialgenesorin-
directlybyautosomalgenesinvolvedinmitochondrialpath-
ways,suchasUCP2(uncouplingprotein2gene)(GenBank
MIM 601693). This gene has a neuroprotective function
and may contribute to MS susceptibility.14,15Thus far, at-
tempts to link mitochondrial mutations with MS suscep-
tibility have been disappointing.16-18
Asecondpossiblegeneticexplanationisgenomicim-
printing.19This has been insufficiently explored.
A third explanation could be the interaction between
genesandfemale-specificenvironmentalfactors,suchas
hormonal, intrauterine, or perinatal factors.
Recent findings have demonstrated an increasing fe-
male to male sex ratio, strongly suggesting an environ-
mental origin. It seems that the relative role of environ-
mental factors in determining MS susceptibility has
changed during the past century, in possible interaction
with genetic interactions.20
Our data show that MS patients are more often re-
lated through their mother than through their father, at
least in the pedigree studied herein. Because MS in this
pedigreehasacommonclinicalphenotypeandmostcases
were initially diagnosed as sporadic MS cases, our find-
ings are likely to be representative of the total MS popu-
lation. These findings support a maternal parent-of-
origin effect in MS. There is reason to assume that this
effectiscausedbyaninteractionofgeneticandenviron-
mental factors.21Dense genotyping in this pedigree can
help to unravel the genetic contribution, thus aiding in
resolving the nature-nurture dilemma in MS.
Accepted for Publication: September 9, 2007.
Correspondence: Rogier Q. Hintzen, MD, PhD, Depart-
ment of Neurology, Erasmus MC, P. O. Box 2040, 3000
CA Rotterdam, the Netherlands (rhintzen@xs4all.nl).
Author Contributions: Study concept and design: Hop-
penbrouwers, Liu, Oostra, van Duijn, and Hintzen. Ac-
quisition of data: Hoppenbrouwers and Hintzen. Analy-
sis and interpretation of data: Hoppenbrouwers, Liu,
Aulchenko, Ebers, van Duijn, and Hintzen. Drafting of
the manuscript: Hoppenbrouwers, Liu, Aulchenko, van
Duijn,andHintzen.Criticalrevisionofthemanuscriptfor
important intellectual content: Hoppenbrouwers, Liu,
Aulchenko, Ebers, Oostra, van Duijn, and Hintzen. Sta-
333 (40.9%)
383 (47.1%)
98 (12.0%)
Figure. Observed distribution of connections between patients with multiple
sclerosis (MS). Solid circles indicate female patients with MS; open circles,
unaffected mothers of patients with MS; and open squares, unaffected
fathers of patients with MS.
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tisticalanalysis:Hoppenbrouwers.Obtainedfunding:van
Duijn and Hintzen. Administrative, technical, and mate-
rial support: Oostra, van Duijn, and Hintzen. Study su-
pervision: van Duijn and Hintzen.
Financial Disclosure: None reported.
Funding/Support: This study was supported by grants
fromMSResearchNetherlands(DrsvanDuijnandHint-
zen); the Netherlands Organisation for Scientific Re-
search (Dr Hintzen); and Erasmus MC. The GRIP study
is supported by the Centre for Medical Systems Biology.
Additional Contributions: All patients and their rela-
tives, general practitioners, and neurologists contrib-
uted to the study; P. Veraart helped in genealogy; and E.
Croes, MD, PhD, helped in data collection.
REFERENCES
1. Ebers GC, Sadovnick AD, Risch NJ; Canadian Collaborative Study Group. A ge-
neticbasisforfamilialaggregationinmultiplesclerosis.Nature.1995;377(6545):
150-151.
2. Ebers GC, Sadovnick AD, Dyment DA, Yee IM, Willer CJ, Risch N. Parent-of-
origin effect in multiple sclerosis: observations in half-siblings. Lancet. 2004;
363(9423):1773-1774.
3. Willer CJ, Dyment DA, Risch NJ, Sadovnick AD, Ebers GC. Twin concordance
andsiblingrecurrenceratesinmultiplesclerosis.ProcNatlAcadSciUSA.2003;
100(22):12877-12882.
4. Robertson NP, O’Riordan JI, Chataway J, et al. Offspring recurrence rates and
clinical characteristics of conjugal multiple sclerosis. Lancet. 1997;349(9065):
1587-1590.
5. AlterM,KahanaE,LoewensonR.Migrationandriskofmultiplesclerosis.Neurology.
1978;28(11):1089-1093.
6. HammondSR,EnglishDR,McLeodJG.Theage-rangeofriskofdevelopingmul-
tiple sclerosis: evidence from a migrant population in Australia. Brain. 2000;
123(pt 5):968-974.
7. Kantarci OH, Barcellos LF, Atkinson EJ, et al. Men transmit MS more often to
their children vs women: the Carter effect. Neurology. 2006;67(2):305-310.
8. Hoppenbrouwers IA, Cortes LM, Aulchenko YS, et al. Familial clustering of mul-
tiple sclerosis in a Dutch genetic isolate. Mult Scler. 2007;13(1):17-24.
9. Aulchenko YS, Heutink P, Mackay I, et al. Linkage disequilibrium in young ge-
netically isolated Dutch population. Eur J Hum Genet. 2004;12(7):527-534.
10. Pardo LM, MacKay I, Oostra B, van Duijn CM, Aulchenko YS. The effect of ge-
netic drift in a young genetically isolated population. Ann Hum Genet. 2005;
69(pt 3):288-295.
11. Boichard D. PEDIG: A FORTRAN package for pedigree analysis studied for large
populations.Paperpresentedat:Proceedingsofthe7thWorldCongressonGe-
neticsAppliedtoLivestockProduction;August19-23,2002;Montpellier,France.
12. Buljevac D, Flach HZ, Hop WC, et al. Prospective study on the relationship be-
tween infections and multiple sclerosis exacerbations. Brain. 2002;125(pt 5):
952-960.
13. Herrera BM, Ramagopalan SV, Orton S, et al. Parental transmission of MS in a
population-basedCanadiancohort[publishedonlineaheadofprintJune27,2007].
Neurology. 2007;69(12):1208-1212.
14. Vogler S, Goedde R, Miterski B, et al. Association of a common polymorphism
in the promoter of UCP2 with susceptibility to multiple sclerosis. J Mol Med.
2005;83(10):806-811.
15. Vogler S, Pahnke J, Rousset S, et al. Uncoupling protein 2 has protective func-
tion during experimental autoimmune encephalomyelitis. Am J Pathol. 2006;
168(5):1570-1575.
16. Chalmers RM, Robertson N, Compston DAS, Harding AE. Sequence of mito-
chondrial DNA in patients with multiple sclerosis. Ann Neurol. 1996;40(2):
239-243.
17. Kalman B, Alder H. Is the mitochondrial DNA involved in determining suscepti-
bility to multiple sclerosis? Acta Neurol Scand. 1998;98(4):232-237.
18. Harding AE, Sweeney MG, Miller DH, et al. Occurrence of a multiple sclerosis-
likeillnessinwomenwhohaveaLeber’shereditaryopticneuropathymitochon-
drial DNA mutation. Brain. 1992;115(pt 4):979-989.
19. Morison IM, Paton CJ, Cleverley SD. The imprinted gene and parent-of-origin
effect database. Nucleic Acids Res. 2001;29(1):275-277.
20. Orton SM, Herrera BM, Yee IM, et al; Canadian Collaborative Study Group.
Sex ratio of multiple sclerosis in Canada: a longitudinal study. Lancet Neurol.
2006;5(11):932-936.
21. Willer CJ, Dyment DA, Sadovnick AD, Rothwell PM, Murray TJ, Ebers GC; Ca-
nadian Collaborative Study Group. Timing of birth and risk of multiple sclerosis:
population based study. BMJ. 2005;330(7483):120-124.
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