HLA class II DNA polymorphism in a Moroccan population from the Souss, Agadir area

Article

Reference

HLA class II DNA polymorphism in a Moroccan population from the Souss, Agadir area

IZAABEL, H, et al.

Abstract

HLA DRB1, DQA1 and DQB1 polymorphisms were analyzed by PCR-SSO typing in a sample of the Moroccan population from Souss. Uneven allelic frequency distributions are observed at each locus, with particularly high frequencies for DRB1*0701, DRB1*0301, DQA1*0501, DQA1*0201, and DQB1*0201. Only three haplotypes (DRB1*0701-DQA1*0201-DQB1*0201, DRB1*0301-DQA1*0501-DQB1*0201 and DRB1*11-DQA1*0501-DQB1*0301) account for nearly 50% of the total gene frequencies. A genetic distance analysis reveals that the Moroccan population is close to the Spanish and the Algerians, who live in geographically neighboring areas. However, the Souss population is also characterized by a lower level of genetic diversity compared to other African and European populations from the Mediterranean area. This may be the result of a rapid genetic drift due to their likely geographical and/or cultural isolation.

IZAABEL, H, et al . HLA class II DNA polymorphism in a Moroccan population from the Souss, Agadir area. Tissue Antigens , 1998, vol. 51, no. 1, p. 106-10

DOI : 10.1111/j.1399-0039.1998.tb02954.x PMID : 9459511

Available at:

http://archive-ouverte.unige.ch/unige:17063

Disclaimer: layout of this document may differ from the published version.

1 / 1

Brief communication

H. lzaabel H.-J. Garchon S. Caillat-Zucman G. Beaurain 0. Akhayat J.-F. Bach

A. Sanchez-Mazas

Key words:

anthropology: HLA class II; Morocco: North Africa; PCR-SSO: population genetics Acknowledgments

This work has been supported by aAction integree inter-universitaire Franco-Marocaine“

(no. 95/926), and by the Swiss F.N.R.S. grant 3100.049771.96 to A.S.M. We thank ^M.

Ouchrif and A. N’Bou for their help in obtaining donor blood samples and P. Przednowed P., E. Audran and I. Texier for their technical assistance. We sincerely acknowledge Jacques Hors and Sami Djoulah for providing us the updated data on HLA class II in Algerians from Oran.

Received 8 July 1997, resubmitted 1 September,

accepted for publication 1 5 September 1997 Copyflat 0 Munkagaafd 1998

Tissue Antigens. ISSN 0001-2815 i7ssue Antigens 1998: 51: 106110 Printed in Denmark . All rights reserved

HLA class II DNA polymorphism in a Moroccan population from the Souss, Agadir area

Abstract: HLA DRB1, DQAl and DQBl polymorphism were analyzed by FCR-SSO typing in a sample of the Moroccan population from Souss. Uneven allelic frequency distributions are observed at each locus, with particularly high frequencies for DRB1*0701, DRB1*0301, DQA1*0501, DQA1*0201, and DQB1*0201. Only three haplotypes (DRB1*0701-DQA1*0201-DQB1*0201, DRB1*0301-DQA1*0501-DQB1*0201 and DRB1*ll-DQA1*0501-DQB1*0301) account for nearly 50% of the total gene frequencies. A genetic distance analysis reveals that the Moroccan population is close to the Spanish and the Algerians, who live in geographically neighboring areas. However, the Souss population is also characterized by a lower level of genetic diversity compared to other African and European populations from the Mediterran- ean area. This may be the result of a rapid genetic drift due to their likely geographical andor cultural isolation.

The class

II

loci belonging to the major histocompatibility complex HLA are among the most polymorphic genetic systems in humans, containing at least 194 DRB1, 18 DQA1, and 31 DQBl alleles de- fined at the molecular level (1). This extensive HLA polymorphism is very useful in anthropology for investigating the genetic relation- ships between populations from different origins. Allele and haplo- type frequencies as well a s linkage disequilibrium differences are observed among populations from different geographic areas (2) and may help to retrace human migrations over the past.

Until recently, HLA class

II

allelic variations in North Africa were only known for Tunisia (3-5) and Algeria (6, 7), while no data were available for Morocco. The present Moroccan population is constituted both by Berber- (“Tamazight”) and Arabic-speaking groups whose languages belong to the Afro-Asiatic family (8).

Berbers are believed to be the descendants of a very ancient autoch- thonous Moroccan population, as they were probably present in the area since the Neolithic. The Afro-Asiatic languages may have been introduced by Neolithic farmers coming from the Near East (9).

Authon’ afflllatlonr:

H. Iraabel’~’.

H.-J. ^Garchon’,

S. Cailiat-Zucman2.

G. Beaurain’.

0. Akhayat’.

J:E Each’.

A. Sanchez-Ma~as~

‘Laboratory of Cellular and Molecular Biology, University Ibnou-Zohr. Agadir. Morocco.

’Laboratory INSERM U25.

H6pital Necker. Paris, France.

%aboratory 01 Genetics and Biometry, Departments of Anthropology and Ecology, University of Geneva, Switzerland Correspondence to:

Alicla SancherMazas Laboratory of Genetics

and Biometry Departments of

Anthropology and Ecology University of Geneva 12 rue Gustave-Revilliod CH-1227 Carouge Geneva Switzerland Fax +41 22-30003-51 E-mail:

AliciaSanchez-Maras@

anthro.unige.ch

lzaabel et al : HLA class II in a Moroccan population

Since then, the first important invasion was that of the Phoenicians coming from the East Mediterranean seacoast around 1000 B.C., who represented almost one tenth of the North African population at the time of the Roman conquest, in 146 B.C. (10, 11). Jewish com- munities also settled in many North Afncan localities during the 1st century. Arabs coming from the Middle East invaded the area during the 7th century, with a massive Bedouin immigration begin- ning in the 11th century. Other immigrants came from the North (Andalusians, Romanians) and from the South (black slaves from Sudan). All these populations probably contributed to the present Moroccan gene pool.

Berbers from Morocco presently belong to three main communi- ties: northern Berbers living in the Rif mountains, central Berbers living in the Atlas and southern Berbers living in the Anti-Atlas and the Sows valley. According to Murdock (12), Berber languages fall into 29 groups, among which the Shluh (Chleuch) include many tribes of the Grand Atlas, the Anti-Atlas, the intervening valley of the Souss River and the adjacent coast of Morocco. The purpose of this study was to determine the frequencies of HLA class I1 DNA DRB1, DQAl and DQBl alleles and haplotypes in a Moroccan population from the Souss area, and to compare them to other North African and European populations from several Mediterranean countries.

The sample studied is composed of 98 unrelated Moroccans liv- ing in the Souss region surrounding the city of Agadir (30"26'N, 9'36'W). Part of this sample was previously used as control to ana- lyze HLA-IDDM associations in North Africa on the basis of a par- tial characterization of HLA class I1 alleles (13). Genomic DNA was extracted from peripheral blood mixed with EDTA using short pro- teinase K digestion of detergent treated cells (14). The typing of genomic DNA for HLA-DRB1, -DQA1 and -DQBl loci was per- formed as previously described (15). The second exon of the DRBl, DQAl and DQBl genes was amplified by the polymerase chain reaction (PCR) using Taq polymerase and specific flanking primers (16). Amplified DNA was blotted onto nylon membranes, and alleles were identified following hybridization with digoxigenin-11-dUTP- labeled sequence-specific oligonucleotides (SSO) and detection with a chemoluminescence substrate (AMPPD, beringher Mannheim Biochemicals). The oligonucleotide probes used in each locus corre- spond to the polymorphic region of the second exon: 20 probes were used for DRBl typing, 8 for DR4 subtyping, 10 for DQAl and 12 for DQBl.

HLA-DRB1, DQAl and DQBl allele and haplotype frequencies were estimated by an expectation-maximization (EM) algorithm leading to mayimum likelihood (ML) estimates of gene frequencies (17, and taking into account a possible blank recessive allele at each locus. The standard deviations of allelic and haplotype fre-

quencies were obtained by a bootstrap procedure (18). The depar- ture from Hardy-Weinberg equilibrium was tested at each locus by an exact test using a Markov chain approach modified from Guo &

Thompson (19). These analyses were carried out by using the com- puter package ARLEQUIN (Excoffier L, Schneider S, Kuffer J-M, Roessli D, personal communication). Genetic distances between the Moroccans and other populations from the Mediterranean area (references in Legend for Fig. 1) were estimated by

Dxy ⁼

k

^{( x i - yj}

1

^{where and yi} are the frequencies of allele

i in populations x and y, respectively, and k the size of the frequency vector. Mean genetic distances over the loci DRB1, DQAl and DQBl were used to plot a principal coordinate analysis (21, 22) using the statistical package NTSYS (23).

DRB1, DQAl and DQBl allelic frequencies are presented in Table 1. The hypothesis of Hardy-Weinberg equilibrium is accepted at the 1% level for DQAl and DQBl @=0.086 and 0.036, respec- tively), but rejected for DRBl @=0.002). However, the significance found for DRBl may be due to incomplete subtyping of some DRBl alleles, as the test gives a nonsignificant result when DRBl frequen- cies are estimated after reassigning proportionally DRBl subtypes to these ambiguous alleles.

A total of 20 alleles are observed at the DRBl locus. The most relevant result is a very high frequency for DRB1*0701 (20.5%), one of the highest observed among all populations so far tested. The closest frequencies for this allele are found in Spanish (18.9% to 20.79'0) and Basques (19.4%). Among the DRB1*0701 haplotypes, 62% were DF34*01011, 5% were DRB4*01012, and 14% were DRB4*0103 (the remaining 19% could not be determined for the second DRB gene). The second frequent allele found in the Moroc- cans is DRB1*0301 (17.3%), which also exhibits a high frequency in Tunisians, Algerians from Oran, and some peculiar European populations (Sardinians and Basques). Overall, the DR3, DR7 and DR4 groups have high combined frequencies (18.8%, 20.5%, and 14.1%, respectively), while DR12 (1%) and DR14 (1.2%) are very rare and DR9 is not observed.

Eight alleles are found at the DQAl locus, among which DQA1*0501 is the most frequent (Z8.6'X0), followed by 0201 (20.2%).

Both alleles are usually frequent in Europeans and North Africans compared to other world populations. Among the 13 alleles ob- served at the DQBl locus, DQB1*0201 reaches a very high fre- quency (37.8%). The closest values are found in Tunisians (32.7%), Algerians from Oran (31%), Spanish (29.7% to 31.8%), and Basques (36.89'0).

Three-locus haplotypes are listed in Table 2. DRB1*0701 is al- most completely associated to DQA1*0201-DQB1*0201 (20.1 %), the other association being with DQA1*0201-DQBl*0303 (0.5%). The

2 i = 1

Tissue Antigens 1998: 51: 106-110 107

lzaabel et a1 : HLA class It in a Moroccan population

DRBl, D Q A l and D Q B l allele frequencles, and pvalues for Hardy-Welnberg equillbrlum, in the Moroccan populatlon from Souss (n=98 indlvlduals)

Allele

D R B l Frequency1 SDZ 0101

0102

0 1 3

0301 0302 0308 0402 0403 0405 0406 043 0701 08 1001 11

1201 1301 1302 1303 13'

1401 1501 1601 X

__

-

pvaiue4:

0.005 0.051 0.015 0.173 0.010 0.005

0.027 0.026 0.037 0.031 0.020 0.205 0.031 0.031 0.090

0.010 0.010

0.056 0.020 0.010

0.012 0.069 0.020 0.036

0.002

0.005 0.014 0.009 0.025 0.008 0.005 0.013 0.010

0.016 0.012 0.011 0.031 0.013 0.011 0.020 0.007 0.007 0.016 0.010

0.007 0.008 0.016 0.010 0.019

Allele

DQAl Frequency SD 0101

0102 0103 0201 0301 0401 0501 0601 X

-

-

pvalue4:

D Q B l

0201

0301 0302 0303 0401 0402 0501 0502 0503 0602 0603 0604 0605 X pvalue4:

0.110

0.148 0.015 0.202 0.142 0.041 0.286 0.005 0.051

-

0.086

0.378

0.144 0.105 0.005 0.005 0.031 0.112 0.020 0.017 0.066 0.011 0.025 0.031 0.050 0.036

0.022 0.026 0.008

0.027 0.022 0.014 0.030 0.004 0.023

0.034 0.021 0.021 0.005 0.005 0.011 0.021 0.009 0.008 0.017 0.006 0.014 0.013 0.020

' Number of initial conditions from which the EM is started=50.

SD: standard deviation, generated by 500 bootstrap replicates.

Three DRB1*01. four DRB1'04 and two DRB1'13 alleles could not be unambiguously sub Number of steps carried out for Markov chain=100.000.

typed.

Table 1. Most frequent alleles are underlined

frequency observed for DRB1*0701-DQA1*0201-DQB1*0201 is about twice that observed in other North African and European populations. DRB1*0301-DQA1*0501-DQB1*0201 is also more fre- quent in Moroccans (17.3%) than in neighboring populations (about 12% in Maghreb, and generally less in Europe) except Sardinians (24.1%). DRB1*11-DQA1*0501-DQB1*0301 (7.4% in Moroccans) is observed in many world populations but more particularly in Alger- ians from Oran (13.8%). Altogether, these three haplotypes reach a

Three-locus haplotype frequencles In the Moroccan populatlon from Souss (n=

98 indlvlduals)

DRB1-DOA1-DOB1 haDlOtVDeS 0701

0301 11 1501 0102 0405 blank 0402 1302 1302 1001 1601 1303 0 1 0403 04 0406 1401 0302 11 0406 08 1301 1201 1501 04 08 0406 1302 1501 08 1001 13 0101 08 08 13 0701 1501 0308 11 0403 0403 0403 0403

0201 0501 0501 0102 0101 0301 blank 0301 0102 0102 0101 0102 0501 0101 0301 0301 0301 0101 0401 0401 0301 0401 0103 0501 blank 0301 0601 0301 0102 0401 0401 0301 0102 0101 0501 0102 0103 0201 0102 0501 0102 0301 0102 blank blank

0201 0201 0301 0602 0501 0302 blank 0302 0604 0605 0501 0502 0301 0501 0302 0302 blank 0503 0402 0301 0402 0402 0603 0301 0602 0301 0501 0401 0501 0501 0302 0301 0605 0501 0301 0602 0201 0303 0503 0201 0301 0301 0302 0302 0301

Frequencp 0.201 0.173 0.074 0.054 0.051 0.038 0.032 0.027 0.026 0.026 0.026 0.020 0.020 0.015 0.015 0.015 0.015 0.012 0.010 0.010 0.010 0.010 0.010 0.010 0.007 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.004 0.001 0.001

SDb 0.026 0.026 0.018 0.015 0.016 0.013 0.019 0.012 0.011 0.011 0.010 0.013 0.010 0.011 0.009 0.008 0.008 0.007 0.008 0.007 0.007 0.007 0.007 0.006 0.007 0.006 0.006 0.006 0.006 0.006 0.006 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.004 0.006 0.005 0.001 0.001

a Number of initial conditions from which the EM is started=50.

' SD: standard deviation, generated by 500 bootstrap replicates

Table 2

lzaabel et al : HLA class I1 in a Moroccan population

combined frequency of almost 50% (44.8%) in the studied popula- tion.

The results of the principal coordinate analysis is shown in Fig.

0 25

l0rCXCP"l

Algenanr I

0.

Arhkcnnu Spmrh Gypsics

Moroccan Jcvr

.

.o 25

A i l s I - ^35%

1

^Barqwr

. 1 _I

E l

1

Moroccan Jcw,

1

^Ashkcnari

A i i s 1. 35%

.O 25

Fis 1. Principal coordinate analysis for 13 M e d i t e r r a n e a n popu- lation samples tested for DRBl, DQA1, a n d D m l polymorphisrns.

a. Axis I (horizontal) and Axis II (vertical). b. Axes I (horizontal) and Axis I11 (vertical).

Population samples: Algerians 1: 99 Algerians from Oran; Algerians 2: 99 Al- gerians from Algiers; Ashkenazi: 132 Ashkenazi Jews from central and eastern Europe; Basques: 80 Spanish Basques; French: 171-180 French; Spanish Gypsies: 77 Spanish Gypsies; Italians: 284-492 Italians and 99-100 Italians;

Moroccans: 98 Moroccans (present study); Moroccan Jews: 94 Moroccan Jews;

Sardinians: 91 Sardinians; Spanish 154-166 Spanish and 176 Spanish.

Genetic distances: The genetic distances were computed on the basis of 43 DRBl (0101,0102,0103, 1501, 1502, 1601,1602, 0301, 0302,0401, 0402,0403, 0404, 0405,0406, 0407,0408, 0409,0410,0411, 1101, 1102, 1103, 1104, 1201, 1202, 1301,1302, 1303, 1304, 1305, 1401, 1402, 1403, 1404, 1405, 07,0801, 0802,0803,0804,0901,1001), 8 DQAl (0101, 0102,0103,0201,0301,0302, 0303, 0401,0402) and 15 DQBl (0501, 0502,0503, 0504, 0601, 0602, 0603, 0604, 0605, 0201, 0301, 0302, 0303, 0401, 0402) alleles. A few additional alleles detected in some of the samples where they were tested ORB1 0303, 0806, 1109, 1306, 1310 and 1504) were grouped within a category "other", including also the "blank" frequency.

1. The first three principal axes explain 68% of the total variance.

The Moroccans from Souss are rather isolated from the other North Africans (Algerians) whose frequencies are very close to the Euro- peans (Fig. la). However, they are also genetically related to the southwestern Europeans (Spanish, French, and Basques) and the Algerians from Oran, while the eastern Mediterranean populations (Italians, Sardinians) are more distant. This result agrees with a geographic differentiation of these populations (Fig. 1). The Moroc- can Jews cluster with the Ashkenazi Jews rather than with the Mor- occans from Souss, in accordance with a common ancestry of the Jewish community. The Sardinians present very peculiar frequen- cies (very high for DRB1*1601, DRB1*0301, DQA1*0102, DQA1*0501, and DQB1*0502) but are genetically related to the Ital- ians. The Spanish Gypsies are highly differentiated from the other Spanish populations (high DRB1*1601, DRB1*1401, DQA1*0101, DQA1*0102, and DQB1*0503 frequencies), as also observed for other genetic systems.

The present HLA class I1 study is the first concerning a well defined population sample from a remote locality in south-western Morocco. As described above, this geographic area is inhabited by a group of Berber people, defined a s southern Berbers, though several population groups from other origins may have contributed to the total Moroccan gene pool. The PCR-SSO typings of HLA DRB1, DQAl and DQBl polymorphisms reported in this study reveal that the Moroccans from Souss are genetically related to the southwest- ern Europeans (specially Spanish) and Algerians, who are geo- graphically close. A substantial amount of gene flow has thus prob- ably been present among the populations of these neighboring areas in spite of their likely wide cultural (for example, linguistic) differ- ences, On the other hand, the Moroccan population from Souss ex- hibits some high frequency alleles (like DRB1*0701 and DQB1*0201) responsible for uneven allelic distributions. The esti- mated heterozygosities are among the lowest observed compared to the other studied populations. For DRBl (heterozygosity of 90% in Moroccans), only Basques and Sardinians exhibit lower values (87.1% and 87.4%, respectively, compared to 91-94% in the other North African and European populations). A similar result is found for DQBl (80.3% in Moroccans, 79.9% in both Basques and Sardini- ans, compared to 82.87% in the other North African and European populations). For DQAl (81.9% in the Moroccans), lower hetero- zygosities are found in Sardinians (73.6%), Gypsies (77.5%), Italians (78% to 79.3%) and Algerians from Oran (77.9%). The DRB1- DQA1-DQB1 haplotypic distribution is also very homogeneous, since only 3 haplotypes account for almost 50% of the total gene frequencies. Thus, the Souss population is characterized by a lower level of HLA class I1 genetic diversity than in most surrounding populations. This may be the result of a rapid genetic drift occur-

Tissue Antigens 1998: 51: 106-110 109

lzaabel et al : HLA class II in a Moroccan population

ring in the history of this population, which would be explained by rare genetic exchanges with neighboring people due to their remote geographic location, at the fringe of the Sahara desert, and to their cultural isolation as Berber people. In addition, the close genetic distance found between the Moroccans from Souss and the Oranese,

probably also of Berber descent (T. Hors & S. Djoulah, personal communication), would confirm the common origin of different Berber communities disseminated throughout remote areas of North Africa.

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