Download A newly discovered founder population: the

Challenges
A newly discovered founder
population: the Roma/Gypsies
Luba Kalaydjieva,1* Bharti Morar,1 Raphaelle Chaix,2 and Hua Tang3
Summary
The Gypsies (a misnomer, derived from an early legend
about Egyptian origins) defy the conventional definition
of a population: they have no nation-state, speak different
languages, belong to many religions and comprise a
mosaic of socially and culturally divergent groups separated by strict rules of endogamy. Referred to as ‘‘the
invisible minority’’, the Gypsies have for centuries been
ignored by Western medicine, and their genetic heritage
has only recently attracted attention. Common origins
from a small group of ancestors characterise the 8–
10 million European Gypsies as an unusual trans-national
founder population, whose exodus from India played the
role of a profound demographic bottleneck. Social and
economic pressures within Europe led to gradual fragmentation, generating multiple genetically differentiated
subisolates. The string of population bottlenecks and
founder effects have shaped a unique genetic profile,
whose potential for genetic research can be met only by
study designs that acknowledge cultural tradition and
self-identity. BioEssays 27:1084–1094, 2005.
! 2005 Wiley Periodicals, Inc.
Introduction
Isolated founder populations have been a precious resource
for Mendelian genetics, contributing knowledge on novel
disorders, genes and mutations, as well as new experimental
and statistical approaches designed to exploit the special
characteristics of such populations.(1–4) As the term implies,
founder populations derive from a small number of ancestors,
with subsequent isolation (geographic, cultural or religious
etc.) leading to limited immigration and demographic growth
mainly from within. Reduced genetic diversity and founder
1
Western Australian Institute for Medical Research and Centre for
Medical Research, The University of Western Australia, Perth,
Australia.
2
Equipe de Génétique des Populations, Unité d’Eco-Athropologie,
Musée de l’Homme, Paris, France.
3
Public Health Sciences, Fred Hutchinson Cancer Research Center,
Seattle, Washington, USA
Funding agencies: The Wellcome Trust, the Australian Research
Council and the National Health and Medical Research Council.
*Correspondence to: Luba Kalaydjieva, Laboratory of Molecular
Genetics, WAIMR, B Block, QEII Medical Centre, Nedlands,
WA6009, Perth, Australia. E-mail: [email protected]
DOI 10.1002/bies.20287
Published online in Wiley InterScience (www.interscience.wiley.com).
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effect, resulting in a more homogeneous basis of inherited
disorders and predispositions, make it possible for genetic
studies to treat the whole population as one large family, where
individuals affected by a specific condition are likely to share
the same ancestral disease-causing DNA variant(s).
Unlike other founder populations, whose history, genealogy
and genetic epidemiology have been extensively documented,(5–8) the geographically dispersed and socially marginalised Gypsies have been ignored by European medicine for
hundreds of years, and their unique genetic heritage is only
now becoming a focus of interest for geneticists and medical
practitioners. Private (meaning confined to this population)
disease-causing mutations and evidence of founder effect
were published for the first time in 1996 in two independent
studies—of the novel Hereditary Motor and Sensory Neuropathy type Lom (HMSNL)(9) and of Limb-Girdle Muscular
Dystrophy 2C.(10) Further medical genetic research, adding to
the list of private mutations and aiming to understand their
molecular epidemiology, has revealed a peculiar combination
of genetic homogeneity and mutation sharing by affected
subjects across Europe(10 –12) and, at the same time, an
internal mosaic of striking differences in the prevalence of
genetic disorders and mutations between neighbouring Gypsy
communities in the same country. This epidemiological pattern
suggests a complex population structure, whose understanding is essential for further genetic research, as well as for
patient care and public health interventions. The issue has not
been addressed in earlier population genetic investigations
(summarised in ref. 13), relying on the random sampling of
‘‘pure-blood Gypsies’’, classified by country of residence, with
disregard for social structure and self-identity. Recent population studies, initiated and designed to answer the questions
raised by medical genetics, have made a big step forward and
characterised the Gypsies as one of the most interesting
founder populations and a valuable part of the European
genetic landscape.
The gypsies through the eyes of
social scientists
The potential of founder populations to contribute to understanding the genetic basis of human disease is largely
determined by historical demography: size and diversity of
the founding population, subsequent demographic growth,
extent of genetic isolation, and internal genetic differentiation
BioEssays 27:1084–1094, ! 2005 Wiley Periodicals, Inc.
Challenges
and substructure.(14– 18) The Gypsies have no written chronicles, church records and historical research of their own, and
the puzzle of their history has been assembled from the
accounts of outsiders and from inferences of linguistic and
cultural anthropology studies. This is what the social sciences
tell us.
The current Gypsy population of Europe, around 10 million
people,(19) is equivalent to that of a medium-sized European
country. Dispersed throughout the continent, the Gypsies are
known under different names—Roma, Sinti, Manouches,
Romanichals, and Kalo, etc. Strictly speaking, ‘‘Roma’’, which
is increasingly used as a generic term, refers to Eastern
European Gypsies and will be used in this text when
discussing the Gypsies of Bulgaria.
The 200-year-old linguistic theory of the Indian origins of the
Gypsies(20) is widely accepted by social scientists, with different opinions dating the exodus to 1000–1500 years ago,
and the arrival in the Byzantine Empire to the 9th –11th century
AD. Settling in the Balkans has taken place in the 13th –
14th century, and the early diaspora into the rest of Europe
completed by the end of the 15th century.(20,21) The Balkans
have traditionally hosted the largest proportion of European
Gypsies, referred to as Balkan and Vlax Roma, depending on
their history of migrations and related dialects of Romanes
(classified according to the borrowings from other languages).
The Balkan Roma, speakers of ‘‘Balkan’’ or stratum I dialects
of Romanes, descend from the early Gypsy settlers in the
lands south of the Danube River, within the limits of the
Ottoman Empire.(20,21) The ancestors of the Vlax Roma
continued the journey north of the Danube, into the Wallachian
Principalities (present-day Romania), where Gypsy slavery
was instituted in the early 14th century.(22) Slavery has not only
played an important role in the social and biological history of
the Vlax Roma, but is also related to important later
migrations. During the Austrian–Turkish wars in the late
17th –early 18th century, temporary occupation of Wallachia
allowed large numbers to escape into the ethnically tolerant
Ottoman Empire:(21) these are speakers of ‘‘old Vlax’’ (stratum
II) dialects of Romanes. By the end of the 19th –beginning of
the 20th century, abolition of slavery led to mass migrations of
Vlax Roma, speaking ‘‘new Vlax’’ (stratum III) dialects, to all
parts of Europe. The latest migration wave, making the Roma a
visible presence in the big cities of Western Europe, was
triggered by the social and economic changes in Eastern
Europe of the 1990s and the wars in former Yugoslavia.
Adding to the complexity of historical migrations is the
traditional organisation of Gypsy society, which has long
fascinated cultural anthropologists and has been meticulously
described in many studies. The primary unit of this social
organisation is the Gypsy group, whose close resemblance to
the professional jatis of India has been interpreted as further
support for the Indian origins of the Gypsies.(20,21) Identity is
defined by the group ethnonym (usually reflecting a traditional
trade), customs and traditions, organs of self-rule, language,
history of migrations and religion. Persisting in the midst of the
nation states of Europe, Gypsy groups are separated from
each other by strict rules of endogamy, yet recognise no
political boundaries and may spread across many countries:
members of the same group in different countries are eligible
marriage partners, while intermarriage between neighbouring
communities in the same small town is often proscribed. Group
structure and diversity are particularly well preserved in the
Balkans. In the early 20th century, a British ethnologist serving
as the British consul in the Black Sea port city of Varna,
described 19 different Gypsy ‘‘tribes’’ in the North-East of
Bulgaria alone.(23)
Drawing a convoluted picture of historical migrations and a
mosaic social structure, linguists and cultural anthropologists
also favour an ethnically and linguistically diverse founding
population. Hypotheses on the origins of the proto-Gypsies
range from the lowest strata of the Indian caste system, to a
mixed society of warriors and camp followers fighting off the
early Islamic incursions in the north of India.(20,21,24) Some
scenarios assume a single founding event—the exodus from
India, while others allow for a slow continuous trickle of small
nomadic bands.(20,21) A geneticist’s summary of these data
would describe the Gypsies as a conglomerate of Asian
populations of largely unknown history and current size, that
may fit the observed pattern of Mendelian disorders but does
not satisfy the criteria for a large founder population of serious
potential for research into complex disorders.
The picture emerging from recent population
genetic studies
Population genetic studies of the Gypsies in the last few
years(25 – 29) have been facilitated by new technologies,
growing knowledge of variation in the human genome and
rapidly accumulating data on global genetic diversity (please
see box for a brief description of methodology). The design of
these studies, based on the social tradition of the Gypsy
people and made possible by a close interaction with cultural
anthropologists, has aimed at understanding the common
biological history of the Gypsy population of Europe, as well as
the relationship between cultural and genetic identity of a
diversity of Roma groups (Fig. 1).
A young founder population of common
Indian descent
Unambiguous proof of the Indian ancestry of the Gypsies
comes from three genetic marker systems: Y chromosome
haplogroup H-M82, mtDNA haplogroup M(25) (Fig. 2), and
the pathogenic 1267delG mutation in CHRNE(12) (causing
autosomal recessive congenital myasthenia), found on the
same ancestral chromosomal background in Gypsy, Indian
and Pakistani subjects.(29) While confirming the centuries-old
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Box: Brief description of methodology
Genetic variation in the Gypsy population has been
studied in nearly 2000 subjects, representing different
parts of Europe and divergent Gypsy groups. The
analyses included polymorphisms on the paternally
inherited Y chromosome, the maternally transmitted
mitochondrial (mt) DNA and biparentally inherited
autosomal markers (neutral variants and diseasecausing mutations). Slowly evolving or unique event
polymorphisms, which define Y chromosome and
mtDNA haplogroups and reflect ancient human history,
were used in comparison to global diversity data(51– 75)
to trace the continental origins of Gypsy lineages.
Markers of higher mutability, such as Y chromosomal
and autosomal microsatellites (with haplotypes defined
as the combination of marker alleles carried on the
same chromosome), the Y chromosomal minisatellite
MSY1,(76) and sequence variation in the mitochondrial
control region were used to assess current diversity and
infer recent population history. The population genetics
analysis tool Arlequin(77) was used to examine genetic
diversity (using parameters such as the observed
number of haplotypes, number of polymorphic sites,
and gene diversity), test demographic models based
on mtDNA sequence variation, and assess genetic
distances between populations using the number of
pairwise differences as the molecular distance. The
dating of historical events was based on coalescence time analysis of Y chromosome and autosomal
haplotypes.(27,29,78– 80) Historical demography parameters were inferred from genetic data using the
coalescence-based approach incorporated in the
Batwing software.(79)
Population structure was examined as described.(81)
linguistic theory of the Indian origins is no great triumph for
modern genetic research, the major, unexpected and mostsignificant result of these studies is the strong evidence of the
common descent of all Gypsies regardless of declared group
identity, country of residence and rules of endogamy. A staggering 47.3% of men carry H-M82 Y chromosomes, mtDNA
haplogroup M accounts for almost 30% of Gypsy subjects, and
congenital myasthenia is one of the most common Mendelian
disorders of this population with !4% average carrier rates of
the 1267delG mutation.
The Y chromosome H-M82 and the mtDNA M haplogroups
are characterised by limited internal haplotype and sequence
diversity, which can easily be explained with the accumulation
of mutations within the Gypsy population subsequent to its
founding, rather than variation among the founders.(25) Within
the H-M82 haplogroup, an identical 8-microsatellite Y chromo-
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some haplotype is shared by nearly 30% of Gypsy men, an
astonishing degree of preservation of a highly differentiated
lineage, previously described only in Jewish priests.(30)
Analysis of the highly mutable minisatellite MSY1 in these Y
chromosomes provides further evidence of limited variation,
with diversity values lower than in Finns, Basques and Cook
Islanders.(26) Similarly, nearly all mtDNA haplogroup M sequences fall into a single sub-haplogroup, M5.(25) These
closely related lineages, which form minute tight clusters
within the overall diversity of Asia, signal genetic homogeneity
among the founders—possibly a small group of related individuals separating from a single, ethnically defined population.
Based on the accumulated diversity, the most-recent
common ancestor of Gypsy men carrying H-M82 Y chromosomes is estimated to have lived around 39 generation ago.
Estimates in the same range, 32–36 generations ago,(29) are
obtained for the mean coalescence times of the microsatellite
haplotypes surrounding the two most-common and widespread founder mutations, 1267delG (congenital myasthenia)
and R148X (Hereditary Motor and Sensory Neuropathy
Lom(31)), used as an indicator of the time when these two
mutations were introduced into the overall Gypsy population.
Assuming a generation time of 30 years, these dates translate
to 960–1170 years ago, supporting the exodus from India as
the single recent founding event.
The Gypsy group was born in Europe
During the long journey from India to Europe, the Gypsies
added new words to their language and newcomers to their
society (Fig. 2). There is no documented history of their early
social organisation; however, old European chronicles already
mention small groups of 100–300 people with horses and
dogs, headed by ‘‘barons, kings or princes’’ and provide some
indirect evidence of tribal endogamy and hostilities between
groups.(19 –21) The splits leading to group formation could have
occurred at any time since the founding, while the description
of group organisation as a ‘‘fluid mosaic’’(19) implies multiple
divisions and mergers and changing rules of endogamy.
Genetic dating of the population fissions is again based on
microsatellite variation in Y chromosomes and in the autosomal regions surrounding four private disease-causing
mutations.(26,27,29) All marker systems suggest that the
earliest splits occurred 20–24 generations ago, i.e. from the
late 13th century onwards, when Gypsy settlement in Europe
has been documented beyond doubt.(20,21) The genetic data
point to a gradual process of consecutive separations, which
has continued until as recently as 6–8 generations ago.
The size of the founding population of individual groups is
estimated at several hundreds, with less than 100 for the
effective male population size of some groups.(27) These
figures may be inflated, as they are based on the overall
current diversity, including lineages that are likely to have been
Challenges
Figure 1. Roma groups from Bulgaria. The different groups have been selected to represent various criteria of group identity: group
ethnonym, history of migrations respectively dialects of Romanes; tradition of nomadism; religion. Ethnonym abbreviations: Kalaidjii—two
different groups residing in the north (kan) and south (kas) of the country, Lom (lom), Kalderash (kal), Darakchii (dar), Rudari (rud), Burgudjii
(bur), Feredjelii (fer), Turgovtzi (tur), Muzikanti (mus), Koshnitchari or Basketmakers (bas)—two different groups using different basketmaking technologies; Kovachi (bla). Pairs of groups living in close proximity in the same small town include kan/lom; fer/tur, kas/bas. The
Rudari (rud) and Kalderas (kal) represent groups which are geographically spread out, with members sampled from different geographic
locations. The Kalaidjii South (kas) belong linguistically to the Vlax category, however their genetic features are much closer to Balkan
groups.(29) In addition, genetic studies include Gypsy subjects from Romania, Serbia, Hungary, Lithuania and Spain.(25,29)
introduced by admixture subsequent to the founding. Such
small sizes are compatible with the early historical descriptions
of Gypsy groups, as well as with the data provided by
the Ottoman tax registries, for example listing a total of
!5,700 Gypsies in the territory of present-day Bulgaria in the
early 16th century.(21) The demographic growth of Gypsy
groups has been slow, with growth rate estimates based on Y
chromosome variation in the range of 1.0017–1.0084, substantially lower than the 1.016–1.027 proposed for other
European populations.(32)
Given the common origins and lack of pre-existing
differentiation of the early Gypsies, the formation of small
strictly demarcated jati-like groups is surprising in itself. Even
more surprising is the fact that the restitution of the ancient
Indian tradition has taken place several centuries after the
exodus, in the midst of European culture and social organisation. Social anthropologists attribute a major role in this
process to the economy of ‘‘symbiotic’’ nomadism.(21) The
Gypsies have always made a living by providing services to the
surrounding population. Such dependence on the macrosociety would have favoured disintegration as a result of the
economic pressure resulting from limited needs for specific
services. The low capacity of small regions and communities to
sustain blacksmiths, basket makers, and musicians etc. could
lead to a continual budding off of branches initially maintaining
contact with the old clan and eventually evolving into new,
geographically dispersed endogamous groups. The hostility of
the surrounding society has also exerted a profound influence
on this process. (1) Slavery in Romania involved the separation of groups of people based on their owner and trade,(22)
(2) murderous persecution of the Gypsies in Western Europe
in the early centuries after their arrival has made the small
mobile group a means of survival,(19) and (3) even the ethnically diverse and tolerant Ottoman Empire has encouraged the
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Figure 2. The origins of Gypsy Y chromosome and mtDNA haplogroups. Linguistic analysis has charted the Gypsy migration from India to
Europe through the Hindu Kush, along Persia and the southern shoreline of the Caspian Sea, through the southern Caucasus (Armenia)
and westwards to Anatolia and Byzantium. Genetic evidence of the geographical origins of paternal and maternal lineages in the Gypsies is
based on the study of unique event polymorphisms of the Y chromosome (left panel) and mtDNA (right panel), compared to published data
on other populations.(51–62) Y chromosome haplogroup H-M82 and mtDNA haplogroup M can be unambiguously assigned to Asia and the
Indian subcontinent. The wide geographical distribution of the remaining lineages precludes the tracing of their origins in the Gypsy
population. The internal diversity of the latter lineages points to multiple admixture events during the journey or after the arrival of the
Gypsies in Europe.
separations by banning communication between Muslim and
Christian Gypsies and imposing higher taxes on Christians.(21)
The evolution of Gypsy groups into
genetic subisolates
Intermarriage between groups is generally proscribed or
subject to strict rules, which can be complicated, hierarchical
and asymmetrical for the two sexes. Failure to comply leads to
the expulsion of the couple or the assimilation of the member of
the higher-ranking into the lower-ranking group.(21) Interestingly, the ‘‘blood purity’’ laws are applied much more rigorously
between Roma groups than to the surrounding population,
and gadje outsiders, especially women, are often readily
assimilated. In some cases, mixed marriages can result in the
formation of a new Gypsy group, for example the Zhutane
Roma in Bulgaria (literally Jewish Roma) born in the common
deportation camps during World War II.(21)
The strongest genetic indication of severely limited intergroup migrations is provided by a study of the chromosomal
haplotypes surrounding the R148X founder mutation in
three Vlax Roma groups, where R148X occurs at very high
frequencies, with carrier rates ranging between 10 and
16%.(29) While the common origin of the mutation is clearly
documented by a shared small conserved region around the
mutated site, extended haplotypes spanning larger genetic
distances have evolved independently, generating unique,
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group-specific haplotype profiles.(29) The striking lack of
haplotype sharing is evidence of strict inter-group endogamy
throughout the history of Roma groups.
At the same time, genetic data support the declared
tolerance towards outsiders, which appears to have always
been part of Gypsy culture. Non-Indian Y chromosome and
mtDNA lineages contribute to the genetic profile of the Gypsies
(Fig. 2), with high internal diversity suggesting multiple
admixture events.(25) A higher proportion of admixed lineages
and a stronger signal of demographic growth are observed in
the Balkan than in the Vlax Roma (Fig. 3). The majority of
Balkan groups included in the genetic studies have settled
centuries ago, in contrast to a long history of nomadism
persisting among the Vlax Roma until their forced sedentarisation in the 1950s. Nomadic groups are known to be more
conservative and to adhere strictly to social and cultural
traditions.(20,21) The social reasons behind the different
demographic regimes and proportion of admixed lineages
may be related to internal differences in the tolerance to
intermarriage and/or to the historically closer relationships
with the surrounding populations. The harsh conditions of
nomadic life may also have played a role, affecting life
expectancy, population growth and genetic diversity.
Small population size, strong drift effects, limited intergroup gene flow and differential admixture have led to rapid
genetic differentiation between Gypsy groups. The extent of
Challenges
Figure 3. Paternal and maternal lineages in Roma groups from Bulgaria. Proportions of Indian Y chromosome H-M82, mtDNA
haplogroup M5 and of other, admixed lineages in the Vlax Roma with a recent history of nomadism (left panel) and in the sedentary Balkan
groups from Bulgaria. Ethnonym abbreviations are as shown in Figure 1. Preservation of the ancestral Y chromosome lineage is particularly
strong in the Vlax compared to the Balkan Roma (two-tailed permutation test P ¼ 0.017). mtDNA lineages show greater overall diversity in
the entire Gypsy population,(25) with the difference in the proportions of ancestral versus admixed lineages between Vlax and Balkan Roma
not reaching statistical significance (P ¼ 0.071). A rank-test comparison of the mean growth rate values, estimated using Batwing, shows a
marginally higher demographic growth in Balkan than in Vlax groups (two-tailed test P ¼ 0.043).
divergence becomes evident in comparison to global populations (Fig. 4). The most striking feature of the multidimensional
scaling (MDS) plot, based on mtDNA sequences, is the dispersal and large genetic distances separating Gypsy groups.
A similar and even more pronounced pattern is presented by
the tribal groups of India, in sharp contrast to other (especially
European) populations, which cluster closely together. Significant internal substructure in the Gypsy population is also
supported by other genetic systems, namely Y chromosomes,
neutral autosomal polymorphisms, and disease mutations and
their linked haplotypes (refs(25,29) and Table 1). On a condensed time scale, the history of the Gypsies (and, to a large
extent, the social phenomena behind it) reproduces the more
widely known history of the Jews, with the exodus, diaspora
and fragmentation into small geographically dispersed communities. Possibly smaller historical population size, stronger
drift effects and persisting group separation, maintained by
social tradition and marriage customs, account for the marked
internal differentiation of the Roma, making the group the
basic unit of genetic research, as it is of social organisation.
Genetic correlates of group identity
Analysis of the correspondence between genetic affinities and
the cultural anthropology classification of Roma groups shows
that most criteria defining group identity do not reflect genetic
similarities. Neither ethnonyms nor religion shared between
Roma groups predict common genetic profiles and, contrary to
other Europeans,(34) genetic and geographical distances
show no correlation.(25) Higher order classification into metagroups, divided by particularly rigid rules of endogamy, separates groups which are genetically very close.(26) The only
cultural anthropological criterion reflecting genetic relatedness is the history of migrations, hence dialects of Romanes.(25,29) The Balkan and Vlax Roma, and the Gypsies of
Western Europe have been separated since the early migrations of the 14th century. Within each migrational category, the
earliest internal splits have taken place simultaneously with the
migrational separations, but the gradual and prolonged
process of group formation has maintained intermarriage
within each category for generations, with differential admixture from surrounding European populations contributing to
the distinctive genetic profiles of migrational categories.(25,29)
The impact on genetic disease
A list of the private Gypsy mutations, known to be associated
with single-gene disorders, is presented in Table 2. The list
is not exhaustive and reflects the interests of individual
researchers rather than comprehensive studies of the genetic
disease heritage of the population. The major lesson learned
from Mendelian genetics so far is that the identification of a
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Figure 4. Genetic distances between Gypsy groups and other Eurasian populations. Fst between Gypsy groups and other Eurasian
populations(63–75) were computed for the mtDNA hypervariable segment 1, using the number of differences between sequences as the
molecular distance. Multidimensional scaling analysis was performed to represent the distance matrix in 2 dimensions. Stress ¼ 14.9%.
Colour codes: Gypsy black, European red, Middle Eastern green, Central Asian light blue, Pakistani blue, and Indian orange. Abbreviations:
Gypsy populations include the Roma groups from Bulgaria (shown in Fig. 1), as well as Gypsies from Spain (spR); Lithuania (liR), Serbia
(seR), Romania (roR) and Hungary (huR). Indian tribal populations:(67) Koragas (kor), Bettakurumba (bet), Mullukurunan (muln),
Mullukurumba (mulm), Paniya (pan),Apatani (apa), Adi (adi), Nishi (nis), Soligas (sol), Andh (anh), Naga (nog), Kuruchian (kru),
Jenukurumba (jen), Thoti (tho), Pardhi (pad), Yerava (yer), Kattunaiken (kat).
small number of affected Gypsy families sharing the same
private mutation usually signals a widespread problem, involving large numbers of patients in many countries. Currently
available frequency data(29,37) show that an average of 1 in
8 subjects in the general Gypsy population is a carrier of one of
the five mutations tested. Within individual Gypsy groups,
carrier rates for specific mutations often exceed 5% and can be
as high as 16%. Mendelian disorders are thus a considerable
health burden, making community-based carrier testing programs a highly beneficial public health initiative. Such
programs would be facilitated by the allelic homogeneity,
which allows simple testing procedures and high detection
rates.
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The Gypsies have already made a contribution to Mendelian genetics through four novel private conditions: Hereditary
Motor and Sensory Neuropathy types Lom and Russe—two
severe forms of autosomal recessive Charcot-Marie-Tooth
disease;(9,31,38) Congenital Cataracts Facial Dysmorphism
Neuropathy syndrome, a developmental disorder affecting the
basal transcription machinery;(35) and a new form of immune
deficiency, characterised by absence of CD8þ cells.(45)
Furthermore, private mutations in the Gypsies, causing known
disorders of wide ethnic distribution, facilitate genotype–
phenotype correlations in large genetically homogeneous
groups of affected individuals carrying the same molecular
defect.(11,12,50) Similar to other founder populations, gene
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Table 1. Genetic differentiation of Roma groups in Bulgaria
Genetic cluster
BLA N ¼ 54
DAR N ¼ 46
KAL N ¼ 33
KAN N ¼ 69
KAS N ¼ 39
LOM N ¼ 71
MUS N ¼ 51
RUD N ¼ 51
37
7
1
2
2
0
3
2
2
27
2
5
6
0
4
0
1
1
21
4
2
1
1
3
10
12
8
21
6
6
4
2
6
1
6
6
8
4
7
1
7
3
7
8
2
32
8
4
6
6
5
1
4
0
29
0
1
0
1
1
1
2
0
45
C.1
C.2
C.3
C.4
C.5
C.6
C.7
C.8
Analysis of 28 unlinked autosomal microsatellites selected from the World Diversity Panel(49) among the top 100 markers providing the best differentiation
between European and Asian populations (the set overlaps partly with the markers used in a similar analysis of Jewish populations(33)). Stratification was
assessed using the software tool Structure (vs 2.0)(81) under a non-admixture model, assuming 8 underlying sub-populations. The observed genetic clusters
follow the boundaries of self-declared Roma group identity, with most clusters formed mainly (in some cases exclusively) by individuals from a specific group.
Significant genetic differentiation is also revealed by analysis of the pairwise differences between mtDNA sequences and Y chromosome haplotypes in
different Roma groups(25), where Fst ¼ 0.05, P ¼ 0 is obtained for mtDNA sequences and Fst ¼ 0.14 P ¼ 0 for Y chromosome haplotypes.
mapping is based on the assumption of a single founder
mutation inherited from a common ancestor on a chromosomal segment identical by descent (IBD). The unique advantage of the Gypsies as a founder population is related to the
internal structure and the genetic differentiation between
Gypsy groups. Independent haplotype diversification makes
the informed sampling of affected individuals from different
Gypsy groups a particularly efficient approach, where the
critical gene interval is defined as the minimum region shared
IBD between groups.(29) Incorporating population history in
gene-cloning strategies has prompted the novel ‘‘Not-Quite
Identical By Descent’’ (NQIBD) approach,(35) which could be
applicable to other young isolates as well. In this approach, the
identification of the mutated gene was greatly facilitated by
tracing the origin of the mutation to a recent event occurring on
a common haplotype background, which allowed the detection
Table 2. . Private mutations associated with Mendelian disorders in the Gypsies
Disorder
With demonstrated
founder effect
Reported in a small
number of families,
no extensive mutation
frequency data yet
OMIM #
Inheritance
Locus
Gene
Mutation
Ref.
HMSN-Lom1
601455
AR
8q24
NDRG1
R148X
Congenital cataracts facial
dysmorphism neuropathy1
Limb-girdle muscular
dystrophy 2C1
Congenital myasthenia1
Galactokinase deficiency1
HMSN-Russe
Gitelman syndrome
Neuronal ceroid lipofuscinosis
604168
AR
18qter
CTDP1
IVS6 þ 389C > T
35
253700
AR
13q12
SGCG
C283Y
10
254210
230200
605285
263800
606725
AR
AR
AR
AR
AR
17p13
17q24
10q23
16q13
15q21
CHRNE
GK1
1267delG
P28T
SLC12A3
CLN6
Congenital glaucoma
231300
AR
2p21
CYP1B1
IVS9 þ 1G > T
Unidentified, shared
haplotype
E387K
Glanzmann thrombasthenia
Ataxia-teleangiectasia
Von Willebrand disease
CD8þ T-cell deficiency
Congenital nemaline myopathy
Polycystic kidney disease
Hyperparathyroidism-jaw
tumour syndrome
273800
208900
277480
186910
102610
173900
145000
AR
AR
AR
AR
AR
AD
AD
17q21
11q22
12p13
2p12
1q42
4q21
1q31.2
ITGA2B
ATM
VWF
CD8A
ACTA1
PKD2
HRPT2
9,31
13
36,37
38
39
40
IVS15-1G > A
9010_9037del28
Q1311X
G90S
R39X
R306X
Exon 8 del2
(TG or GT)
41
42
43
44
45
46
47
48
1
Used in the genetic analyses of Gypsy population history (ref. 29 and 37). AR autosomal recessive, AD autosomal dominant.
BioEssays 27.10
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Challenges
Table 3. Probability of allele sharing between Roma groups
Allele frequency
in a given group
<0.02
0.02–0.065
0.065–0.13
0.13–0.25
Probability of allele occurring in n other groups
0
0.629
0.087
0.000
0.000
1
0.185
0.105
0.000
0.000
2
0.074
0.140
0.019
0.000
3
0.074
0.210
0.000
0.000
4
0.037
0.140
0.019
0.017
5
0.000
0.122
0.173
0.017
6
0.000
0.087
0.365
0.070
7
0.000
0.105
0.423
0.894
The estimates are based on the allele frequency distributions of 28 unlinked autosomal markers (marker set as used in the genetic differentiation analysis,
Table 1). For each allele, we recorded two characteristics: the number of Gypsy groups where the allele was observed, and the maximum frequency of the allele
(pmax). We then grouped all alleles into four categories based on pmax. For each category, we computed the proportion of alleles, which are observed in 0,1,2,
etc. other Gypsy groups. The thresholds for the four categories were chosen to have approximately equal numbers of alleles in each bin. The distribution of
these neutral, low-frequency microsatellite alleles resembled that observed for rare recessive mutations, causing Mendelian disorders in the Roma (Table 1 in
ref. 29).
of the mutation by comparing the sequence of a small part of
the critical gene region between the two chromosomes of a
single carrier parent.
The potential of the Gypsies to help research into common,
genetically complex disorders is still in need of solid proof.
The specific advantage in this case is again related to the
combination of a primary founder effect !40 generations
ago for the entire Gypsy population, with secondary founder
effects 6–24 generations ago giving rise to divergent subisolates. The strong primary founder effect raises expectations of
a relatively homogeneous genetic basis of complex disorders
across subisolates and, similar to the general approach used
in Mendelian disorders, their unique, group-specific, haplotype
profiles could provide a powerful tool for positional cloning,.
Based on the current data, the best approach to the
identification of susceptibility genes would involve initial crude
mapping in extended multiplex families from a single Gypsy
group, with replication, fine mapping and association studies
based on the informed cross-sampling of genetically related
groups. At the same time, presumed high frequencies of
diverse susceptibility alleles in all populations warrant caution
and, in combination with the contribution of differential admixture to the genetic divergence of Gypsy groups, question the
concept of the Gypsies as a single isolated founder population
suitable for the study of genetically complex disorders. The
internal stratification of the Gypsy population warrants caution
in association studies, with an informed selection of cases and
controls based on knowledge of the cultural anthropology and
genetic affinities of the individual Gypsy groups involved.
Table 3 shows the estimated probabilities of sharing the same
susceptibility allele between Gypsy groups, given a frequency
of that allele in an individual group. These estimates, based on
neutral autosomal polymorphisms, are in agreement with the
observed distributions of private mutations causing Mendelian
disorders, where the highest frequency attained by a given
mutation in a particular Gypsy group correlated with the overall
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BioEssays 27.10
number of groups where the mutation was detected.(29) The
real situation is likely to differ between complex disorders and a
true assessment can only be based on empirical studies, some
(e.g. an investigation of bipolar affective disorder) currently in
progress.
Conclusion
Many challenges have already been met by recent research
into the genetics of the Gypsies. Breaking the divide between
cultural and genetic anthropology has been crucial to unravelling biological history and inferring the parameters of historical
demography. Involvement in these studies has been beneficial
for all sides—researchers have come to appreciate this
unusual population and its multiple social and medical
problems, and affected families and communities have seen
improvements in health care. Yet the big challenge still lies
ahead. The story that we have told is the genetic image of
xenophobia, the fate of an Asian people fractured and
dispersed among Europeans and responding to hostility with
a labyrinth of walls of endogamy. It may well be applicable to
the numerous Asian, Middle Eastern and African immigrant
communities now forming in the midst of prosperous
united Europe. Without true integration and access to
education and health care, genetic studies of the Gypsies will
stall and what has already been achieved will come to be
regarded as a curious and brief episode outside of mainstream
genetics.
Acknowledgments
We wish to thank the numerous Gypsy families and communities for participation in these studies, Dr. Ivailo Tournev and
other colleagues from Bulgaria and other countries for sample
collection and for providing data on other populations, and
Elena Marushiakova and Vesselin Popov for expert advice on
the cultural anthropology of the Roma and guidance throughout these studies.
Challenges
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