WORLD KIDNEY FORUM Balkan Nephropathy: Evolution of Our Knowledge

Giorgos Bamias, MD,1 and John Boletis, MD2

Balkan endemic nephropathy (BEN), originally described in the late 1950s as a chronic tubulointerstitial kidney disease, is identified by its unique epidemio- logical features. The most remarkable characteristic of BEN is the focal topo- World Kidney Forum graphical nature that characterizes its occurrence at the global, national, and Advisory Board even household level. BEN affects only certain endemic rural foci along tributaries of the Danube River in the Balkan countries of Bosnia, Bulgaria, Croatia, Romania, and Serbia. The spatial distribution has remained astonish- Rashad S. Barsoum ingly unchanged with time because the disease affects the same endemic Cairo, Egypt clusters as 50 years ago. The natural course of the disease is characterized by universal development of end-stage renal disease and the frequent develop- Christopher R. Blagg ment of upper urinary tract tumors, posing a substantial disease burden to the Mercer Island, Washington afflicted areas. The greatest challenge in the study of BEN has been the John Boletis elucidation of its cause. The unique features of the disease, in particular its Athens, Greece endemic nature and the long incubation period required for the disease to develop, have led to the proposal that BEN represents a unique environmental Garabed Eknoyan disease. The quest for the responsible environmental factor has been long and Houston, Texas diverse, and although no definitive answer has been provided to date, converg- ing lines of evidence support the theory that long-term consumption of food John T. Harrington contaminated with aristolochic acid underlies the pathogenesis of BEN. The Boston, Massachusetts present review describes the evolution of our knowledge of BEN in relation to the development of the main theories for its pathogenesis. Am J Kidney Dis 52:606-616. © 2008 by the National Kidney Foundation, Inc. n 1956, the first description I of a novel form of intersti- disease at the regional hospital of Yugoslavia.2 This series of tial kidney disease appeared in from 1950 to 1954. He was the original publications was com- the non-English literature. The first to observe the remarkable pleted in 1961, as it became story had started a decade ear- clustering of the patients in vil- evident that a similar nephrop- lier, when local physicians noted lages, families, and even house- athy was also prevalent in dis- a high prevalence of kidney dis- holds. After presenting the condi- crete regions of Romania.3 ease in certain settlements in north- tion at local meetings in 1953 and As a consequence of these west Bulgaria in the district of proposing the term “endemic early reports, 2 scientific con- Vratza nephritis” in 1955, Tanchev Vratza. This prompted a thorough 1 ferences were organized to ad- investigation by Tanchev, who et al published the first de- dress the facts for the new dis- tailed clinical description of studied 664 patients with renal ease. The first was held by the the new entity in 1956. A year World Health Organization in later, a “family outbreak” of 1965, and the second, 2 years 1 renal disease was noticed in From the First Department of Pro- later, by the CIBA Founda- paedeutic Medicine, Laikon Hospital; the neighboring country of 4,5 and 2Department of Nephrology and (what was at the time) Yugosla- tion. As a result of these Transplant Center, Laiko Hospital, Ath- via; a mother and 2 daughters meetings, a novel nosological ens, Greece. had died of renal failure, and entity was recognized that was Received February 26, 2008. Ac- designated Balkan endemic ne- cepted in revised form May 8, 2008. the father and son also had Address correspondence to John Bo- severe renal damage. It was phropathy (BEN). The term letis, MD, 17 Agiou Thoma St, Athens, soon recognized that a disease epitomized the 2 predominant Greece. E-mail: [email protected] with almost identical clinical features of the new disease; © 2008 by the National Kidney Foun- first, it existed in the Balkans dation, Inc. and epidemiological pheno- 0272-6386/08/5203-0025$34.00/0 type to the Vratza nephritis exclusively, and, second, it oc- doi:10.1053/j.ajkd.2008.05.024 existed in confined rural areas curred in endemic clusters.

606 American Journal of Kidney Diseases, Vol 52, No 3 (September), 2008: pp 606-616 World Kidney Forum 607

In the following years, the clini- tal unless renal dialysis therapy in 142 settlements in the former cal and epidemiological character- is introduced. It therefore is Yugoslavia, 40 in Bulgaria, and istics of BEN were clarified.6-8 It evident that from the clinical 40 in southwest Romania, the represents a discrete form of stand point, the new entity only total area not exceeding 500 tubulointerstitial nephropathy added one more subcategory miles in length or 20,000 km2 with insidious presentation and to the long list of interstitial in surface (Fig 2). This geo- slow progression. Nonspecific renal diseases. BEN would graphic distribution is so stable symptoms and anemia typically have never achieved such sci- that 50 years after the original develop before significant renal entific attention and such nomi- description, no new endemic dysfunction.9,10 The latter ensues nated adjectives as “mysteri- areas have been reported and eventually and manifests as re- ous” and “enigmatic” if not for no endemic areas became free duced tubular transport, low-mo- its unique epidemiological from BEN. All affected re- lecular-weight proteinuria, and an characteristics. gions consist of villages or increase in serum urea nitrogen From the very beginning, it small towns built on the allu- level, but no high blood pressure was recognized that the most vial planes of tributaries of the or edema, findings usually en- remarkable feature of BEN is Danube River. In accord with countered in every form of ad- its focal nature.8,16-20 At the that observation, the disease af- vanced nephropathy.11,12 Histo- global level, the disease has fects only rural farming popu- logically, interstitial fibrosis and been described in Balkan coun- lations, but never inhabitants tubular atrophy are prominent fea- tries only: the aforementioned of big cities. The focal nature tures, as opposed to the absence Bulgaria and Romania, as well of BEN is so remarkably firm of significant inflammatory as Bosnia, Serbia, and Croatia, that afflicted villages are in changes (Fig 1).13-15 In the fi- countries formed after the divi- close proximity to unaffected nal stages, the kidneys are re- sion of the former Yugoslavia. ones, only 2 to 3 km apart. duced in size, sometimes On a national scale, BEN cases Finally, the focal nature is even weighing as little as 50 g and are not distributed evenly preserved at the local level. measuring just 2 to 3 cm.12,13 throughout each affected coun- That means that within an af- The outcome is universally fa- try. They are strictly confined fected village, one can find dis- eased households that exist next to disease-free ones. In a single household, only indi- viduals “living under the same roof and eating the same food” may be affected. However, BEN does not show a prefer- ence for specific ethnic or reli- gious groups. This was shown when Croatian aboriginals were compared with Ukrainian im- migrants in the area of Slavon- ski Brod in regard to several parameters of renal function. It was clearly shown that the sole factor determining the pres- ence or absence of pathologi- cal values was residency in an endemic versus a nonendemic area.21 Apart from its focal nature, Figure 1. Histological features of Balkan endemic nephropathy. The dense interstitial fibrosis is in contrast to the preservation of glomeruli. (Adapted from BEN is also characterized by a Nadasdy and Sedmak,15 with permission.) long incubation period. For an 608 Bamias and Boletis

of the endemic villages were concerned, the reason was simple. The sudden misfortune that was laid upon their lives after the end of World War II could not have any other expla- nation but the interference of supernatural forces, divine or otherwise. It therefore was not unexpected that they tried to calm these forces with rituals and ceremonies and protect themselves by wearing amu- lets. However, for the health sci- entists, the unique characteris- tics of BEN offered different opportunities. This was a dis- Figure 2. Map shows the distribution of endemic foci of Balkan nephropa- ease with a distinct, homoge- thy. (Adapted with permission from Stefanovic and Cosyns.8) neous phenotype, affecting a small part of the world, con- individual to have the disease, increased risk of developing fined to certain recognized ar- he or she must live in the en- upper urinary tract tumors.23-26 eas, and with all the afflicted demic area for at least 15 to 20 This association was already people easily identifiable and years. This probably explains known in the 1960s, but be- therefore amenable to thor- why the disease has never been came more pronounced in later ough investigation and re- diagnosed in children. Accord- years when the life expectancy search. It therefore is not unex- ingly, a native who leaves the of patients with BEN increased pected that one of the first area before reaching the age of significantly as a result of the reports of BEN also announced 20 years is spared from devel- broad use of dialysis therapy. a definitive answer to its patho- oping BEN. Conversely, immi- The estimated incidence of tu- genesis, because Serbian inves- grants into an afflicted focus mors of urothelial origin has tigators considered it to be the become susceptible after liv- been 57 times greater in BEN result of lead poisoning of the ing there for 15 to 20 years. After endemic regions between 1969 flour in endemic regions.28 being exposed to the risk of devel- and 1977 compared with non- Ironically, 50 years later, the oping BEN, it takes an equally endemic areas; similarly, blad- precise cause of BEN has not long time before clinical manifes- der cancer was 12 times more been definitely established. tation occurs. Therefore, the frequent.27 These epidemio- Meanwhile, perhaps no other typical peak of the disease takes logical studies provided a human disease has produced place between the third and strong link between BEN and so many hypotheses in an ef- fifth decades. This may ex- upper urinary tract tumors. fort to elucidate its causal fac- plain why BEN was not recog- THE SEARCH FOR A CAUSE tors. The quest for the cause of nized before World War II; the BEN proved not to be an easy average life expectancy at the It was not long after the task because of many factors. time (40 to 50 years) may sim- original description of BEN First, the epidemiological data ply have been too short to al- that the search for its cause from the countries where the low the disease to reach the started. For a disease with such disease was prevalent were not clinical stage.22 an intriguing epidemiological of perfect quality. Second, col- Finally, even in the first re- profile, it was inevitable that laboration between investiga- ports of BEN, it was recog- there was room for wide specu- tors from these different coun- nized that such patients were at lation. As far as the inhabitants tries did not take place. As a World Kidney Forum 609 consequence, results from stud- prevalent to the inflicted foci? eas by ochratoxin A (OTA),29 a ies in one country were never Another pivotal question re- toxic product of molds that be- confirmed in the others. Third, lated to the long incubation pe- long to the Aspergillus or Peni- no matter how fascinating its riod of the disease, which cillium fungal genera. This nature may be, BEN is a rare pointed to a long exposure to a “mycotoxin” theory was built disorder affecting only some low-dose harming agent that around the remarkable similar- 10,000s of people in confined existed in the environment for ity between BEN and porcine Balkan villages, with a practi- many years. If that is the case, nephropathy.30 The latter has a cal consequence being a lack why then did BEN appear only similar confined geographic of funding resources for its during the second half of the distribution because it mainly study. Finally, political and so- century in the endemic areas occurs in Northern Europe and cial events that took place in and not before? Such a tempo- shares many pathological char- the troubled region of the Bal- ral association requires a ma- acteristics with BEN. Porcine kan Peninsula had their own jor local environmental change nephropathy is caused by OTA, negative effect on the efforts to before the first appearance of raising the possibility for a find a solution to the mystery the disease, and such an alter- similar connection between of BEN. One has to keep in ation is not easy to identify in BEN and mycotoxins. There- mind that the political tensions the history of the region. In fore, an effort to provide evi- that followed the end of World addition, any etiologic hypoth- dence for such an association War II created a situation in the esis should take into consider- was started. Balkan area that made a rare ation not only the nephropathy From a general point of nephropathy much more a lo- itself, but also the increased view, the establishment of a cal disturbance than a national incidence of upper urothelial cause-and-effect link between priority. neoplasms in the patients. Fi- an environmental factor and a No matter what the obstacles nally, if somebody were to disease, the so-called exposure were, research about the caus- solve the mystery of BEN, he analysis, consists of a stepwise ative factor(s) of BEN started or she should use information approach.31,32 Briefly, the agent almost immediately after its from both animal models of has to be present in an endemic recognition as a discrete noso- interstitial nephropathy and the area and in quantities large logical entity. For a disease recognized effects of the candi- enough to induce health dam- with such a narrow, defined, date environmental factors in age. In addition, there should and well-preserved geographic human health and disease. be evidence regarding how the distribution, it was a logical Given all these varied ques- offending agent moves from assumption that the causative tions, it is not surprising that the environmental source to the factor should be an environ- throughout the years, the effort human organism. Moreover, to- mental one endemic to the af- to solve the riddle of BEN in- pographical specificity should flicted regions. Nonetheless, volved not only nephrologists, exist, meaning that the agent along with this ecological influ- but also scientists from such must be more prevalent in en- ence, other factors had to be diverse fields as occupational demic compared with nonen- taken into consideration. For medicine, animal models of hu- demic regions. Finally, if the example, an obvious question man disease, environmental same agent occurs in other ar- was how could such an envi- sciences and epidemiology, on- eas of the world, a similar dis- ronmental trigger selectively cology, genetics, and geology. ease would be expected to be affect certain villages and One of the first comprehen- found there as well. If not, an households and leave the ones sive hypotheses regarding the explanation should be offered. just next to them undisturbed? pathogenesis of BEN appeared The application of these Could these differences be ex- in the literature in the early principles in the case of the plained by the existence of ge- 1970s. Akhmeteli and then ochratoxin/BEN association netic variability between dis- Krogh proposed that BEN was has produced ambivalent re- eased and healthy families? Or the result of contamination of sults. Contamination of food could it be an infectious agent the food chain in endemic ar- with OTA is very frequent, and 610 Bamias and Boletis widespread exposure is com- latter, as well. The evidence spersed among wheat grains mon in several places in the for the role of OTA as the caus- during the harvest. The local world, including Western na- ative factor for BEN was criti- villagers did not make an ef- tions.33,34 Some, but not all, cally reviewed in a recent inter- fort to remove the contami- studies have detected greater national symposium held in nants during flour preparation. levels of OTA in the foodstuff Zagreb.42 A series of argu- Because bread is the major con- consumed in endemic versus ments against such a role were stituent of the local diet, con- nonendemic areas, as well as presented; the strongest were tamination of the wheat with in affected versus nonaffected the uneven geographic distribu- even a few seeds of A clemati- households.30,35-37 Other stud- tion of food contamination with tis could result in low-dose ies reported that patients with OTA and BEN and the lack of long-term intoxication with the BEN have increased serum and definitive proof for OTA-DNA offending agent. Continuing his urine concentrations of OTA, adduct formation. sound scientific approach, Ivic´ indicating greater consump- A different pathogenetic hy- went on and fed rabbits with tion of the mycotoxin.38 It pothesis was proposed by Ka- flour prepared from A clemati- therefore could be the case that zantzis43 in 1967 during the tis seeds. The rabbits devel- (although the contamination of conference on BEN organized oped nephropathy, which, at the food chain is ubiquitous) by the CIBA Foundation. He the histological level, re- patients with BEN are exposed claimed that contamination of sembled the findings of BEN. to greater quantities of OTA as the baking flour in endemic Ivic´ even proved the carcinoge- a result of some still unidenti- areas by seeds of the birthwort netic potential of the plant be- fied practice in food process- Aristolochia clematitis was cause rats developed sarcomas ing and consumption. Nonethe- causing the disease (Fig 3). Ap- at the site of injection of aque- less, it was shown in the same parently, a toxic constituent ous extracts of A clematitis.47 studies that the variation in was contained in the seeds of It is surprising that Ivic´’s thor- OTA values within the affected the plant and induced the renal ough approach and well-docu- population was very high and damage. The initial explora- mented results failed to attract often overlapped greatly with tion of this theory is attributed more interest from the scien- values from nonendemic areas to Ivic´,44 who analyzed avail- tific community until many of the world. Moreover, there able data and performed field years later. was no constant association be- and laboratory studies to pro- However, this was to change tween consumption of OTAand vide a well-documented hypoth- in 1993, when many cases of its levels in serum or urine. esis on the pathogenesis of BEN. Chinese herb nephropathy A strong argument against Again, animal studies set the back- erupted.48 Several hundred the mycotoxin theory is that ground. Ivic´ was aware of publica- young Belgian women devel- OTA had never been linked to tions of such Croatian scientists as oped end-stage renal disease any type of nephropathy in hu- Dumic45 and Martincic46 report- after receiving slimming pills mans. However, this argument ing that horses consuming hay at a single medical clinic in may be subject to challenge that contained seeds of A Brussels. The regimen con- after the proposal in the 1990s clematitis experienced renal tained 2 Chinese herbs, and it that 2 other forms of interstitial disease with proteinuria. More eventually was proved that it was nephropathy may be associ- strikingly, when kidneys from contaminated with aristolochic ated with OTA: the first is en- these horses were examined acid, a main toxic product of demic in Tunisia,39,40 and the histologically, they showed tu- Aristolochia species. Its presence second is the karyomegalic in- bulointerstitial damage with in the slimming regimen was the terstitial nephropathy.41 Both minimal inflammation, a pic- result of accidental substitution types of renal disease share ture that was analogous to of the prescribed herb Stephania clinicopathologic similarities BEN.45,46 To prove his hypoth- tetrandra (‘Han Fang-ji’) by with BEN and support the hy- esis, Ivic´ performed field stud- Aristolochia fangchi (‘Guang pothesis that OTA toxicity may ies and observed that seeds Fang-ji’). Therefore, the name underlie the pathogenesis of the from A clematitis were inter- of the Belgian disorder changed World Kidney Forum 611

contain such adducts. Arlt et al53 were the first to prove that this hypothesis is correct by detecting aristolochic ac- id–specific adducts in all uri- nary tract tissues from patients with BEN that they examined. Conversely, OTA-specific ad- ducts were detected with much lower density and in only some of the examined tissues. Re- cently, work by Grollman et al42,54 expanded these results by showing that aristolochic acid– specific adducts were present in the renal cortex of 5 patients with BEN from an endemic region in Croatia, but not in 5 patients with other forms of chronic renal disease or 5 pa- tients with upper urinary tract transitional cell cancer living in a nonendemic area of Croatia. In addition, when a p53 mutational spectra analysis was performed in urothelial cancer specimens from patients living in endemic foci, a “signature” mutation Figure 3. Aristolochia clematitis (birthwort) as shown in an illustration from (A:T¡T:A) was detected. Inter- Otto Wilhelm Thomé’s Flora von Deutschland, Österreich und der Schweiz, estingly, this molecular mark is reproduced from www.biolib.de with permission from Kurt Stueber. also induced by aristolochic acid in animal models of carci- to Chinese herb nephropathy, or with Chinese herb nephropa- nogenesis and was observed in aristolochic acid nephropathy. It thy.51,52 one patient with aristolochic was soon realized that this dis- These intriguing reports re- acid nephropathy and ureteral ease had many similarities to newed scientific interest and tumor.42 Therefore, aristolo- BEN, especially in the morpho- stimulated new research that chic acid appears to be respon- logical characteristics, which resulted in strong evidence sup- sible not only for the develop- were almost identical in the 2 porting a dominant role for ment of renal injury, but also conditions. This similarity sug- aristolochic acid in the patho- for the high incidence of gested that the same factor, ie, genesis of BEN. After its meta- urothelial cancer in patients aristolochic acid, could be re- bolic activation, aristolochic with BEN. A recent publica- sponsible for both conditions.49 acid reacts with DNA to gen- tion by Lemy et al55 provides This association was supported erate covalent aristolactam- convincing evidence for the further by the development of DNA adducts. Some forms of carcinogenic potential of aris- renal failure in Japanese patients these adducts are stable and tolochic acid. This was a case receiving an aristolochic acid– can be detected in the af- series in Belgian patients under- containing remedy for atopic fected tissues. Therefore, if going renal transplantation for dermatitis.50 Interestingly, up- aristolochic acid were to end-stage renal failure caused per urothelial neoplasms also blame for BEN, renal tissue by slimming pill–related aris- developed in some patients from these patients should tolochic acid nephropathy. In the 612 Bamias and Boletis pathological examination of the rendering the making of con- history of BEN. The increased resected specimens, upper-tract taminated flour highly improb- incidence of urothelial can- urothelial carcinoma was diag- able. If this hypothesis proves cers also can be explained by nosed in 45% of patients. More to be true, we can be optimistic this theory because these toxic interestingly, on long-term fol- that a decrease in the incidence organics are well-known car- low-up, there was a 40% inci- of BEN should be expected in cinogenic factors. Maybe the dence of bladder carcinoma. It the years ahead. most impressive application was concluded from this study No review of the evolution of the lignite hypothesis is that the pathogenic properties of our knowledge of BEN is that it may be used as a pre- of aristolochic acid exist for a complete if it does not address dictive model.22 An area in long time after cessation of ex- the so-called “lignite hypoth- Serbia that was not known to posure. esis.” This theory was devel- be endemic was proved to be To date, the aristolochic acid oped in the 1990s by scientists such after it was recognized hypothesis perhaps offers the of the US Geological Sur- to lay close to a low rank coal best-characterized model for vey.57,58 It originated from the field. Research on the role of the pathogenesis of BEN.42,56 primary observation that there the Pliocene lignites in the The pivotal work of Ivic´ com- was a spatial relationship be- pathogenesis of BEN required bined with modern state-of-the- tween the endemic villages with a lot of field studies and thus art biochemical and molecular BEN and the locations of Plio- it was abruptly interrupted techniques have promulgated a cene lignite deposits in the Bal- when the war broke out in pathogenetic concept that ex- kans. All endemic areas are Yugoslavia in 1993.63 plains most of the epidemio- in close vicinity to low rank Although the environmental logical and clinical parameters coals. The lignite theory factor(s)–centered theories domi- of BEN. However, a critical claims that toxic organic sub- nated the efforts to explain the question still is unanswered; stances from these coals leak etiopathogenesis of BEN, alterna- why do only 2% to 5% of the into groundwater and are tive explanations were sought, residents in an endemic area transported to the wells that as well. The infection theory develop the disease?22 This exist in the alluvial valleys, claims that BEN is caused by a cannot be attributed easily to below the lignite deposits.59 coronavirus. Uzelac-Keserovic´ preferential exposure of such a This was shown to be true be- et al64 developed epithelial cell small minority of the popula- cause studies reported greater monolayer cultures from kidney tion to aristolochic acid, but it concentrations of these organic biopsy specimens obtained from could result from genetic poly- compounds in the water from patients with BEN and control morphisms. Nevertheless, if the wells in the endemic areas patients. They were able to de- aristolochic acid hypothesis is compared with those in nonen- tect a novel virus, named the true, the most important clini- demic ones.60 The final link in EBN virus, that was present in cal conclusion is that BEN is the exposure chain is that people BEN-derived epithelial cell preventable with simple mea- in the villages use water from cultures, but from none of the sures. One can safely predict their wells for drinking and control cultures. It was pro- that contamination of the flour cooking purposes.22,61,62 In line posed that the microorganism with A clematitis seeds has al- with this, settlements where most was a novel coronavirus based ready been eliminated as a re- inhabitants use the same limited on its cross-reactivity with hu- sult of the changing ways of number of wells show hyperen- man coronaviruses OC43 and life and work in the endemic demicity for BEN. The presence 229E, as well as a pig corona- areas.56 The widespread use of of small concentrations of or- virus known as transmissible herbicides and use of new har- ganic toxic products in the gastroenteritis virus (TGEV).64 vesting techniques has led to water of the wells is compat- When seroreactivity to anti- decreased growth of A clemati- ible with a slow low-level, gens from the new coronavirus tis in the harvesting fields. but relentless, poisoning of was tested, it was shown to be Nowadays, fewer and fewer the villagers, a concept that very high in patients with BEN families bake their own bread, fits very well with the natural on dialysis therapy (87% by World Kidney Forum 613 neutralization activity and 95% posed that a specific BEN-asso- differences in the study design by immunofluorescent assay, ciated locus exists in 3q25 com- or true epidemiological differ- respectively) and controls from bined with instability of the long entiation between endemic ar- endemic areas (74% and 80%), arm of chromosome 3.67,68 Inter- eas. but not in controls from nonen- estingly, this alteration in 3q25 Fifty years after its original demic regions (13.5% and may also determine the genetic description, BEN has shown 60.5%). Nonetheless, the coro- susceptibility for the develop- impressive stability in regard navirus theory was put in dis- ment of the disease in relatives to its epidemiological profile pute when Vero cells infected of patients with BEN.69 Addi- and clinical phenotype. Al- with EBN virus were tested tional data generated from the though this stability initially further with various methods, same group link the increased generated optimism for the including electron microscopy prevalence of urothelial neo- identification of the causative studies.65 No similarities be- plasms that occurs in patients agent(s), this proved to be a tween EBN virus and coronavi- with BEN to genetically deter- much more difficult task.74 The ruses were observed in that mined aberrations in oncogen- most widely accepted theories study. esis. Patients with BEN were have failed to date to answer The strict clustering of BEN tested for chromosomal aberra- the main critical question: what cases in selected families has tions induced by X-rays or fo- is the basis for the focal-topo- raised the possibility that ge- lic acid deprivation.70 There graphical nature of BEN? BEN netic factors may determine its was increased frequency of the is definitely not a genetic disor- clinical and epidemiological aforementioned abnormality in der in that it does not follow a profile. This theory was estab- 3q25, but also in 3 other areas that pattern of Mendelian inheri- lished by detailed family inves- all contain oncogenes, namely tance. Conversely, BEN clus- tigations in Bulgarian patients c-src (CSK,1q36), raf-1 (RAF1, ters in familial foci, indicating with BEN. After studying 4,077 3p25), and myb (MYB, 6q23). exposure to a common environ- patients from 417 BEN-af- It has been estimated that mental offense. Nevertheless, fected families, Toncheva et 100,000 people are at risk of it is difficult to appreciate al66 were led to the conclusion BEN, whereas 25,000 have the which environmental agent that all patients with BEN be- disease. It is not clear what the could be so selective as to af- long to certain families. Even current trend for BEN inci- fect only a small minority of residents of nonendemic foci dence is because results from closely residing individuals. In who were found to have BEN studies performed in different regard to that question, one were identified to be members endemic areas produced con- needs to consider the possibil- of BEN families and to have flicting information. Some epi- ity of BEN-like diseases exist- moved from their birthplaces. demiological reports reported ing in other parts of the world. In addition, BEN shows some an increase between 1967 and Supporters of the mycotoxins or epidemiological characteris- 1970, a plateau between 1970 the lignite hypothesis have al- tics typical of genetic disor- and 1984, and a final decrease ready proposed that BEN is part ders. For example, the propor- in disease prevalence in some of and may be the most obvious tion of sick offspring increases endemic areas.71 Similarly, a example of a panendemic ne- according to the number of par- decreasing incidence with time phropathy that takes place in lo- ents affected. Accordingly, the was found in another endemic cations characterized by the con- risk of developing the disease area during a surveillance pe- tamination of the food or water is much greater in first-degree riod between 1978 and 1997.72 supplies by OTAor coal-derived than second-degree relatives Nevertheless, for certain en- organic toxic substances, respec- and decreases substantially in re- demic regions, BEN continues tively.75,76 mote relatives.66 To further to pose a major health prob- As the case is for most hu- elaborate the genetic component lem, and it seems that the inci- man diseases, it is likely that of BEN, cytogenetic studies dence of new cases remains BEN is a multifactorial disor- were performed by the same stable over time.73 Probably, der. An environmental factor group of scientists. They pro- these differences are related to probably is superimposed on a 614 Bamias and Boletis certain genetic background to REFERENCES demic nephropathy. 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