Edinburgh Research Explorer Historic, Demographic, and Genetic Evidence for Increased Population Frequencies of CCR5 Delta 32 Mutation in Croatian Island Isolates after Lethal 15th Century Epidemics Citation for published version: Biloglav, Z, Zgaga, L, Smoljanovic, M, Hayward, C, Polasek, O, Kolcic, I, Vitart, V, Zemunik, T, Boraska, V, Torlak, V, Mulic, R, Ropac, D, Grkovic, I, Rudan, D, Ristic, S, Barbalic, M, Campbell, H, Wright, AF & Rudan, I 2009, 'Historic, Demographic, and Genetic Evidence for Increased Population Frequencies of CCR5 Delta 32 Mutation in Croatian Island Isolates after Lethal 15th Century Epidemics', Croatian Medical Journal, vol. 50, no. 1, pp. 34-42. https://doi.org/10.3325/cmj.2009.50.34 Digital Object Identifier (DOI): 10.3325/cmj.2009.50.34 Link: Link to publication record in Edinburgh Research Explorer Document Version: Publisher's PDF, also known as Version of record Published In: Croatian Medical Journal Publisher Rights Statement: Copyright © 2009 by the Croatian Medical Journal. 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Oct. 2021 34 GENOMICS doi: 10.3325/cmj.2009.50.34 Historic, Demographic, and Zrinka Biloglav1, Lina Zgaga1, Mladen Smoljanović2, Caroline Genetic Evidence for Increased Hayward3, Ozren Polašek1, Ivana Kolčić1, Veronique Population Frequencies of Vitart3, Tatijana Zemunik2, CCR5Δ32 Mutation in Croatian Vesna Boraska2, Vesela Torlak4, Rosanda Mulić2, Darko Ropac2, Island Isolates after Lethal 15th Ivica Grković2, Diana Rudan5, Smiljana Ristić6, Maja Barbalić7, Century Epidemics Harry Campbell7, Alan F. Wright3, Igor Rudan8,9,10 1Andrija Štampar School of Public Health, School of Medicine, University of Zagreb, Croatia 2School of Medicine, University of Split, Aim To assess the frequency of 32 base pair deletion in Croatia CCR5 (CCR5Δ32), which has been shown to confer resis- 3Human Genetics Unit, Western General tance to HIV infection in a homozygous form, in 10 isolated Hospital, Edinburgh, UK island communities of Dalmatia, Croatia, with different his- 4 University of Split Hospital Center, Split, tories of exposure to epidemics during and since the me- Croatia dieval period. 5 “Dubrava” University Hospital, Zagreb, Methods In 2002, DNA analysis of 100 randomly selected Croatia individuals from each of the 10 isolated communities of 5 6School of Medicine, University of Rijeka, Croatian islands (Susak, Rab, Vis, Lastovo, and Mljet) showed Croatia high levels of 3-generational endogamy, indicating limited 7Institute for Anthropological Research, gene flow. Five of the communities were decimated by ep- Zagreb, Croatia idemics of unknown cause between 1449-1456, while the 8Department of Public Health Sciences, other 5 villages remained unaffected. Genotyping of the The University of Edinburgh Medical CCR5 gene was performed using the polymerase chain re- School, Edinburgh, United Kingdom action method with primers flanking the region contain- 9Croatian Centre for Global Health, ing 32-bp deletion. School of Medicine, University of Split, Croatia Results The frequency of CCR5Δ32 in the 5 villages af- 10 “Sestre Milosrdnice” University Hospital, fected by the epidemic was 6.1-10.0%, and 1.0-3.8% in the Zagreb, Croatia 5 unaffected villages. The Δ32 mutation was found in 71 of 916 alleles among the individuals from the affected vil- lages (7.5%), and in 24 of 968 alleles in unaffected villages (2.5%, χ2 = 27.3, P < 10−6). A previous study in 303 random Croatian blood donors showed the frequency of the CCR5 Δ32 of 7.1% in the general population. The difference re- Received: December 7, 2008 mained significant after correcting for population struc- Accepted: January 27, 2009 ture using both STRAT and STRUCTURE software and the genomic control test, to ensure results do not arise from Correspondence to: the background genetic differences. Zrinka Biloglav Andrija Štampar School of Public Health Conclusion Our results and historical evidence, suggest School of Medicine, University of Zagreb that the mid-15th century epidemic could have acted as a Rockefellerova 4 selection pressure for the CCR5Δ32 mutation. 10000 Zagreb, Croatia [email protected] www.cmj.hr Biloglav et al: Influence of 15th Century Epidemics on Frequencies of CCR5Δ32 Mutation in Croatian Island Isolates 35 C-C chemokine receptor 5 (CCR5) has been shown to be is supported by historical evidence of severe plague epi- a co-receptor for the macrophage-tropic strains of HIV-1 demics that affectted Europe during medieval times and (1,2). In the mid-1990, it was discovered that a mutant vari- beyond, especially in the period between 1347 and 1670 ant of this gene with a 32 bp deletion in homozygous form (3,11,12). Recently, several research groups have investigat- provides almost complete resistance to HIV (1,2), where- ed this proposal, with contradictory results. The study of as the heterozygous form provides partial resistance and 2900-year-old skeletons from the Bronze Age burials in cen- slower progression of AIDS. This mutation is highly preva- tral Germany revealed that the frequency of the CCR5Δ32 lent in European populations with an average frequency mutation was similar to that in victims from the 14th cen- of 10% but it is almost absent in African, American Indi- tury pandemic in Lubeck in northern Germany (13,14). Ani- an, and East Asian populations. Within Europe, it shows a mal studies compared susceptibility to infection and lethal strong geographical north-to-south cline, which ranges outcome in CCR5-deficient and normal mice after infection from a frequency of 0.16 in Mordvinia to 0.04 in Sardin- with Y. pestis and showed no difference between these two ia (3). Slavic populations in the Central Europe are placed groups (15). However, caution is needed when interpreting in the middle of the European gradient and the estimat- the results of animal studies, since differences in the patho- ed frequencies – 10.9% for Poles (4), 10.7% for Czechs (5), genesis of Y. pestis between mice and men cannot be ex- 8.7% for Slovenes (6), and 7.1% for Croatians (7) – are simi- cluded. Furthermore, in vitro experiments of macrophage lar as those expected based on their geographic location. uptake of Y. pestis showed a 30-fold reduction in homo- The analysis of flanking microsatellites in multiple popula- zygous mutant mice (16). Some epidemiological models tions showed long-range linkage disequilibrium between based on highly complex sets of assumptions supported selected microsatellite alleles and the 32-bp deletion, the role of plague (9), while others supported the role of which indicates that it traces its origin from a single mu- smallpox (17), and yet others found no evidence of positive tation event, probably having taken place in North-East- selection at all (18). All these studies indicate that the role ern Europe (8). The high frequency, relatively recent origin, of the 32-bp deletion in relationship to Y. pestis infection is and geographic distribution of the CCR5-32 deletion allele still inconclusive. (CCR5Δ32) together indicate that the deletion has been intensely selected in Europe. Although the allele confers Some scientists proposed that highly pathogen filovi- resistance against HIV-1, HIV has not been present in the ruses, closest to those of Ebola and Marburg, could have human population long enough to account for this selec- caused such a high case-fatality and rapid outbreaks due tive pressure associated with either the heterozygous or to person-to-person transmition. In this case, the loss of homozygous form (8,9). CCR5 protein on the surface of the cell would represent an advantage because it prevents the entry of the virus Controversies regarding the etiology of selection pressure into the cell (9). in Europe still remain and there is a prevailing hypothesis that selective rise of this mutation to its current frequen- In this study, we aimed to present further genetic and ep- cy can be attributed to bubonic plague. An alternative hy- idemiological evidence to this ongoing debate. So far, to pothesis suggests that viral diseases, such as smallpox or investigate the hypotheses related to the possible selec- viral heamorraghic fever, were the cause of such a rise. tion pressure on CCR5Δ32 frequencies in Europe, different epidemiological study designs have been deployed but Lucotte et al (10) compared the frequencies among 40 with inconclusive answers. An ideal case-control study populations from Europe, the Middle East, and North Af- should compare the frequencies of this mutation among rica and confirmed the north-to-south cline. Their research European sub-populations. Those affected and decimat- suggested that the CCR5 32 bp deletion occurred 1000- ed by epidemics throughout medieval period would be 1200 years ago and that the Vikings probably disseminated cases and the spared ones would be controls. Carefully it from north to south. They proposed that it was possibly documented demographic histories should be essential protective against smallpox in the 8th-10th century. for classification of populations in terms of exposure. Ad- ditionally, both study populations should have the same In contrast, other researchers hypothesized a more recent genetic origin and very low immigration rates since the origin of the mutation and a much stronger selection pres- medieval period to preserve the possible differences in sure.