Inter and intra-ethnic differences in the distribution of the molecular variants of TPMT, UGT1A1 and MDR1 genes in the South Indian population

Molecular variants of polymorphic drug metabolizing enzymes and drug transporters are attributed to differences in individual's therapeutic response and drug toxicity in different populations. We sought to determine the genotype and allele frequencies of polymorphisms for major phase II drug-metabolizing enzymes (TPMT, UGT1A1) and drug transporter (MDR1) in South Indians. Allelic variants of TPMT (*2,*3A,*3B,*3C & *8), UGT1A1 (TA)6>7 and MDR1 (2677G>T/A & 3435C>T) were evaluated in 450-608 healthy South Indian subjects. Genomic DNA was extracted by phenol-chloroform method and genotype was determined by PCR-RFLP, qRT-PCR, allele specific PCR, direct sequencing and SNaPshot techniques. The frequency distributions of TPMT, UGT1A1 and MDR1 gene polymorphisms were compared between the individual 4 South Indian populations viz., Tamilian, Kannadiga, Andhrite and Keralite. The combined frequency distribution of the South Indian populations together, was also compared with that of other major populations. The allele frequencies of TPMT*3C, UGT1A1 (TA)7, MDR1 2677T, 2677A and 3435T were 1.2, 39.8, 60.3, 3.7, and 61.6% respectively. The other variant alleles such as TPMT*2, *3A, *3B and *8 were not identified in the South Indian population. Sub-population analysis showed that the distribution of UGT1A1 (TA)6>7 and MDR1 allelic variants differed between the four ethnic groups. However, the frequencies of TPMT*3C allele were similar in the four South Indian populations. The distribution of TPMT, UGT1A1 and MDR1 gene polymorphisms of the South Indian population was significantly different from other populations.     

Genotype Frequencies of Drug-Metabolizing Enzymes Responsible for Purine and Pyrimidine Antagonists in a Healthy Asian-Indian Population

Purine and pyrimidine antimetabolites are used to treat leukemias, autoimmune diseases, and solid tumors. Detection of slow metabolizers before administration of the drugs is necessary to prevent any subsequent drug toxicity. With this aim, we determined the frequencies of normal and slow alleles in our population. Polymorphisms in genes encoding cytidine deaminase (CDA), dihydropyrimidine dehydrogenase (DPYD), and thiopurine-S-methyltransferase (TPMT) were documented in 225 healthy volunteers. The polymorphisms typed included CDA*3, DPYD*2A, TPMT*2A, TPMT*3B, and TPMT*3C. Methods used for genotyping included standard PCR-RFLP and allele-specific PCR reactions. The frequencies were 0.44?% for DPYD*2A, 0.67?% for TPMT*3B, and 0.89?% for TPMT*3C. The CDA*3 and TPMT*2A alleles were not detected. Although these polymorphisms have been demonstrated to be associated with drug toxicity in other populations, they appear to be very rare in the adult Indian population.     

The frequency and distribution of thiopurine S-methyltransferase alleles in south Iranian population

Thiopurine methyltransferase (TPMT) catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathiopurine. Variability in TPMT activity is mainly due to genetic polymorphism. The frequency of the four allelic variants of the TPMT gene, TPMT*2 (G238C), TPMT*3A (G460A and A719G), TPMT*3B (G460A) and TPMT*3C (A719G) were determined in an Iranian population from south of Iran (n = 500), using polymerase chain reaction (PCR)-RFLP and allele-specific PCR-based assays. Four hundred seventy four persons (94.8%) were homozygous for the wild type allele (TPMT*1/*1) and twenty five people were TPMT*1/*3C (5%). One patient was found to be heterozygous in terms TPMT*1 and *2 alleles with genotype of TPMT*1/*2 (0.2%). None of the participants had both defective alleles. The TPMT*3C and *2 were the only variant alleles observed in this population. The total frequency of variant alleles was 2.6% and the wild type allele frequency was 97.4%. The TPMT*3B and *3A alleles were not detected. Distributions of TPMT genotype and allele frequency in Iranian populations are different from the genetic profile found among Caucasian or Asian populations. Our findings also revealed inter-ethnic differences in TPMT frequencies between different parts of Iran. This view may help clinicians to choose an appropriate strategy for thiopurine drugs and reduce adverse drug reactions such as bone marrow suppression.     

Polymorphisms of the TPMT gene in the Czech healthy population and patients with inflammatory bowel disease

Genetic variation in thiopurine S-methyltransferase (TPMT) is a major factors for wide variation in the metabolism and safety of thiopurine drugs. We investigated the frequency of functional gene polymorphisms in 396 patients with inflammatory bowel disease and 300 healthy subjects. Frequencies of functionally deficient alleles TPMT*2, TPMT*3A, TPMT*3B, and TPMT*3B in the patient group were 0.1%, 4.3%, 0.1%, and 0.4%, respectively, and were similar to those of healthy subjects in the Czech population. Our results provide necessary information for pharmacoeconomic studies in the Czech Republic.     

Genetic analysis of thiopurine methyltransferase polymorphism in a Japanese population

Thiopurine methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathiopurine. Several mutations in the TPMT gene have been identified which correlate with a low activity phenotype. The molecular basis for the genetic polymorphism of TPMT has been established for European Caucasians, African-Americans, Southwest Asians and Chinese, but it remains to be elucidated in Japanese populations. The frequency of the four allelic variants of the TPMT gene, TPMT*2 (G238C), TPMT*3A (G460A and A719G), TPMT*3B (G460A) and TPMT*3C (A719G) were determined in Japanese samples (n=192) using polymerase chain reaction (PCR)-RFLP and allele-specific PCR-based assays. TPMT*3C was found in 0.8% of the samples (three heterozygotes). The TPMT*2, TPMT*3A and TPMT*3B alleles were not detected in any of the samples analyzed. This study provides the first analysis of TPMT mutant allele frequency in a sample of Japanese population and indicates that TPMT*3C is the most common allele in Japanese subjects.     

In vitro characterization of four novel non-functional variants of the thiopurine S-methyltransferase

Human thiopurine S-methyltransferase (TPMT) is an enzyme responsible for the detoxification of widely used thiopurine drugs such as azathioprine (Aza). Its activity is inversely related to the risk of developing severe hematopoietic toxicity in certain patients treated with standard doses of thiopurines. DNA samples from four leucopenic patients treated with Aza were screened by PCR-SSCP analysis for mutations in the 10 exons of the TPMT gene. Four missense mutations comprising two novel mutations, A83T (TPMT*13, Glu(28)Val) and C374T (TPMT*12, Ser(125)Leu), and two previously described mutations, G430C (TPMT*10, Gly(144)Arg) and T681G (TPMT*7, His(227)Gln) were identified. Using a recombinant yeast expression system, kinetic parameters (K(m) and V(max)) of 6-thioguanine S-methylation of the four TPMT variants were determined and compared to those obtained with wild-type TPMT. This functional analysis suggests that these rare allelic variants are defective TPMT alleles. The His(227)Gln variant retained only 10% of the intrinsic clearance value (V(max)/K(m) ratio) of the wild-type enzyme. The Ser(125)Leu and Gly(144)Arg variants were associated with a significant decrease in intrinsic clearance values, retaining about 30% of the wild-type enzyme, whereas the Glu(28)Val variant produced a more modest decrease (57% of the wild-type enzyme). The data suggest that the sporadic contribution of the rare Glu(28)Val, Ser(125)Leu, Gly(144)Arg, and His(227)Gln variants may account for the occurrence of altered metabolism of TPMT substrates. These findings improve our knowledge of the genetic basis of interindividual variability in TPMT activity and would enhance the efficiency of genotyping methods to predict patients at risk of inadequate responses to thiopurine therapy.     

Four human thiopurine s-methyltransferase alleles severely affect protein structure and dynamics

Thiopurine S-methyltransferase (TPMT) metabolizes cytotoxic thiopurine drugs used in the treatment of leukemia and inflammatory bowel disease. TPMT is a major pharmacogenomic target with 23 alleles identified to date. Several of these alleles cause rapid protein degradation and/or aggregation, making it extremely difficult to study the structural impact of the TPMT polymorphisms experimentally. We, therefore, have performed multiple molecular dynamics simulations of the four most common alleles [TPMT*2 (A80P), *3A (A154T/Y240C), *3B (A154T) and *3C (Y240C)] to investigate the molecular mechanism of TPMT inactivation at an atomic level. The A80P polymorphism in TPMT*2 disrupts helix α3 bordering the active site, which breaks several salt-bridge interactions and opens up a large cleft in the protein. The A154T polymorphism is located within the co-substrate binding site. The larger threonine alters the packing of substrate-binding residues (P68, L69, Y166), increasing the solvent exposure of the polymorphic site. This packing rearrangement may account for the complete lack of activity in the A154T mutant. The Y240C polymorphism is located in β-strand 9, distant from the active site. Side-chain contacts between residue 240 and helix α8 are lost in TPMT*3C. Residues 154 and 240 in TPMT*3A are connected through a hydrogen-bonding network. The dual polymorphisms result in a flattened, slightly distorted protein structure and an increase in the thiopurine-binding site solvent accessibility. The two variants that undergo the most rapid degradation in vivo, TPMT*2 and *3A, are also the most deformed in the simulations.     

Analysis of common CFTR polymorphisms 5T, M470V and R75Q in healthy Serbian population

Three common CFTR polymorphisms, 5T, M470V and R75Q, have been shown to be relatively frequent in Serbian patients with monosymptomatic CF disorders. Since there is a variation in distribution of common polymorphisms among different populations, it was important to compare their frequencies in patients with the frequencies in healthy population in order to assess the possible role of these polymorphisms in the monosymptomatic CF disorders. Samples obtained from 100 healthy Serbian individuals were analyzed for the presence of CFTR 5T, M470V and R75Q variants by PSM, RFLP and DGGE methods, respectively. Allele 5T was present in two individuals, giving the allelic frequency of 1% (2/200 alleles). The frequency obtained for allele M470 was 45% (90/200 alleles), while V470 allele was present with the frequency of 55% (110/200 alleles). Polymorphism R75Q was present in two individuals, with allelic frequency of 1% (2/200 alleles). Our study has shown that the frequencies of two common polymorphisms, 5T and M470V, differ significantly in Serbian population in comparison with other South European populations. Since it appears that Serbian population has a specific distribution of studied CFTR gene variants, it would also be interesting to analyze other common variants of this gene in our population. Such data can also be potentially useful as anthropogenetic markers in population studies.     

Associations of HLA DR and DQ molecules with Lyme borreliosis in Latvian patients

ABSTRACT: BACKGROUND: Many autoimmune diseases are associated with variants of HLA genes such as those encoding the MHC complex. This correlation is not absolute, but may help in understanding of the molecular mechanism of disease. The purpose of this study was to determine HLA-DR,-DQ alleles in Latvian patients with Lyme borreliosis and control (healthy) persons. Case patients and control subjects were similar in age, gender and ethnic heritage and differed only as regards the presence of Borrelia burgdorferi infection. The study included 20 patients with clinical stage - erythema migrans and 25 control (healthy) persons. HLA genotyping was performed by PCR with sequence-specific primers. RESULTS: The results show difference in HLA-DRB1 alleles distribution between patients and control subjects. The frequencies of HLA-DRB1 *04 (OR 8.65; p<0.022) and HLA-DRB1 *17 (03) (OR 7.00; p<0.048) were increased in the Lyme disease patients. And the frequency of allele DRB1*13 (OR 0.13; p<0.033) was lower in Borreliosis patients and higher in control group. But, significant differences in frequencies of HLA-DQ alleles we did not detect. CONCLUSIONS: HLA predisposition to Lyme borreliosis appears not to be limited to HLA molecules, but some HLA-DR alleles also have a significant influence, and, may have implications in our understanding of pathogenesis of this disease. In particular, HLA-DRB1*04 and DRB1 *17 (03) may contribute to the Lyme borreliosis development in Latvian population KEYWORDS: Lyme borreliosis, HLA alleles, PCR.     

Does HLA Class II Haplotype play a role in Adult Acute Disseminated Encephalomyelitis? Preliminary Findings from a Southern Italy hospital-based study

Acute Disseminated Encephalomyelitis (ADEM) is an acute, multifocal, monophasic, inflammatory demyelinating disease of the central nervous system that affects predominantly children. Aim of the study was to evaluate the distribution of Human Leukocyte Antigen (HLA) class II haplotype in adult ADEM patients, in order to better characterize this rare clinical entity. Six patients (3 males and 3 females; median age 50 years) with ADEM were retrospectively studied in our Neurology Unit; 29 healthy subjects (8 males and 21 females, mean age 43.4±14.3) were the control group. All the study subjects were molecularly typed for HLA class II haplotype. The frequencies of HLA-DRB1*16 (17% vs 3% in control group; Py=0.02) and HLA-DQB1*05 (42% against 24% in the control group; Py=0.010), as well as the association HLA-DRB1*16/HLA-DQB1*05 were significantly increased in ADEM population compared to the control group. The frequencies of allelic association between 13-04 (P < 0.01) and homozygosis 14 (P < 0.05) alleles at HLA-DRB1* locus and 05-02 (P < 0.05) alleles at HLA-DQB* locus also were increased in ADEM patients. Our preliminary data provide further evidence that the HLA-DR/DQ haplotypes may be involved in susceptibility to immunomediate demyelinating diseases of central nervous system in the Caucasian population.     

Fatal myelotoxicity after azathioprine treatment

Azathioprine and 6-mercaptopurine have been used for many years in the treatment of inflammatory bowel disease. Approximately 0.3% of the population are homozygous for variant alleles associated with extremely low thiopurine S-methyltransferase enzyme activity. We describe the case of a young patient with ulcerative colitis, homozygous for TPMT*3A alleles, who suffered fatal azathioprine-induced myelotoxicity after standard dosing with azathioprine. Screening for decreased activity of TPMT in patients prior to azathioprine treatment is advised to minimize the risk of drug-induced toxicity.     

Mutational spectrum of dihydropyrimidine dehydrogenase gene (DPYD) in the Tunisian population

Dihydropyrimidine dehydrogenase enzyme (DPD) deficiency is a pharmacogenetic syndrome leading to severe side-effects in patients receiving therapies containing the anticancer drug 5-fluorouracil (5-FU). The aim of this population study is to evaluate gene variations in the coding region of the dihydropyrimidine dehydrogenase gene (DPYD) in the Tunisian population. One hundred and six unrelated healthy Tunisian volunteers were genotyped by denaturing HPLC (DHPLC). Twelve variants in the coding region of the DPYD were detected. Allele frequencies of DPYD*5 (A1627G), DPYD*6 (G2194A), DPYD*9A (T85C), A496G, and G1218A were 12.7%, 7.1%, 13.7%, 5.7%, and 0.5%, respectively. The DPYD alleles DPYD*2A (IVS 14+1g>1), DPYD*3 (1897 del C) and DPYD*4 (G1601A) associated with DPD deficiency were absent from the examined subjects. We describe for the first time a new intronic polymorphism IVS 6-29 g>t, found in an allelic frequency of 4.7% in the Tunisian population. Comparing our data with that obtained in Caucasian, Egyptian, Japanese and African-American populations, we found that the Tunisian population resembles Egyptian and Caucasian populations with regard to their allelic frequencies of DPYD polymorphisms. This study describes for the first time the spectrum of DPYD sequence variations in the Tunisian population.     

Apolipoprotein E and H polymorphisms in Mongolian Buryat: allele frequencies and relationship with plasma lipid levels

A Buryat population consisting of seven tribal groups in eastern Mongolia has been screened to determine the frequency distribution of different apolipoprotein E and H alleles (APOE and APOH, genes) coding for common isoforms and their association with quantitative plasma lipid levels. Allele frequencies at the APOE locus in 125 healthy Buryat aged 17 to 73 years were highest for APOE*3 (0.804), followed by APOE*4 (0.164) and APOE*2 (0.032). The APOH locus had high frequencies of APOH*2 (0.912) and APOH*3 (0.088). APOH*1 was not detected. No significant differences were observed in the overall APOE allele frequencies between the Buryat and the Siberian Evenki, Inuits, and Indians in Asia, or with some European whites. The frequency distribution of the overall APOH alleles of the Buryat was similar to that of the Japanese in Asia. Overall plasma lipid levels of the Buryat (males aged 20 to 73 years, females aged 21 to 64 years) were considerably lower, comparable to those of the Evenki. The APOE*4/E*3 males had significantly high total- and LDL-cholesterol levels compared with the APOE*3/E*3 males (p < 0.025 and p < 0.01, respectively). No significant effects of the APOH genotypes on any of the plasma lipid levels were observed. In particular, our data regarding APOE suggest that the Buryat are genetically close in allele frequencies to the Evenki and Inuits, but differ from them in the association of genotype APOE*4/E*3 with cholesterol levels.     

Frequency of single nucleotide polymorphisms of CYP2D6 in the Czech population

CYP2D6 is a member of cytochrome P450 enzymes that metabolise over 25% of commonly used drugs. Genetic polymorphisms can cause insufficient drug efficacy at usually administered doses or can be the cause of adverse drug reaction. CYP2D6 genotyping can be used to predict CYP2D6 phenotype and thereby explain some abnormalities in drug response and thus optimize pharmacotherapy. The aim of this study was to investigate the frequency of functionally important variant alleles of the CYP2D6 gene throughout the Czech population to predict the prevalence of ultra-rapid and poor metabolizer phenotypes. The DNA of 223 unrelated, healthy volunteers was analysed to detect the presence of CYP2D6*6, *5, *4, *3 and gene duplication. The variant allele frequencies in our population were 0.22%, 3.14%, 22.87%, 1.12% and 3.14% for CYP2D6*6, CYP2D6*5, CYP2D6*4, CYP2D6*3 and CYP2D6*MxN, respectively. Fifteen subjects carried two variant alleles leading to predicted poor type of metabolism, 84 subjects were heterozygous extensive metabolizers (het-EM). The full-text contains detailed comparison with European white populations. The distribution of variant alleles complies with the Hardy-Weinberg equilibrium. The frequencies of functional variant alleles of CYP2D6 in Czech population are in concordance with other Caucasian populations.     

Functional evaluation of GJB2 variants in nonsyndromic hearing loss

Mutations in the gap junction β2 (GJB2) gene, encoding the connexin26 (CX26) protein, are the most common cause of non-syndromic hearing loss (HL) in many populations. In the East Asian population, two variants, p.V27I (c.79G>A) and p.E114G (c.341G>A), are considered benign polymorphisms since these variants have been identified in both HL patients and normal hearing controls. However, some studies have postulated that homozygotes carrying both p.V27I and p.E114G variants could cause HL. To elucidate possible roles of these variants, we used in vitro approaches to directly assess the pathogenicity of four haplotypes generated by the two polymorphisms: VE (wild type), I*E (p.V27I variant only), VG* (p.E114G variant only), I*G* (both variants). In biochemical coupling assays, the gap junctions (GJs) composed of VG* and I*G* types displayed defective channel activities compared with those of VE wild types or I*E types, which showed normal channel activities. Interestingly, the defect in hemichannel activity was a bit less severe in I*G* type than VG* type, suggesting that I* variant (p.V27I) may compensate for the deleterious effect of G* variant (p.E114G) in hemichannel activities. Our population studies using 412 Korean individuals showed that I*G* type was detected at around 20% in both HL patients and normal controls, suggesting that I*G* type may not be a pathogenic polymorphism. In contrast, VG* type was very rare (3/824) and detected only in HL patients, suggesting that VG* homozygotes (VG*/VG*) or compound heterozygotes carrying VG* type with other mutations may cause HL.     

Analysis of common CFTR polymorphisms 5T, M470V, and R75Q in healthy Serbian population

Three common CFTR polymorphisms, 5T, M470V, and R75Q, have been shown to be relatively frequent in Serbian patients with monosymptomatic CF disorders. Since there is a variation in distribution of common polymorphisms among different populations, it was important to compare their frequencies in patients with the frequencies in healthy population in order to assess the possible role of these polymorphisms in the monosymptomatic CF disorders. Samples obtained from 100 healthy Serbian individuals were analyzed for the presence of CFTR 5T, M470V, and R75Q variants by PSM, RFLP, and DGGE methods, respectively. Allele 5T was present in two individuals, giving the allelic frequency of 1% (2/200 alleles). The frequency obtained for allele M470 was 45% (90/200 alleles), while V470 allele was present with the frequency of 55% (110/200 alleles). Polymorphism R75Q was present in two individuals, with allelic frequency of 1% (2/200 alleles). Our study has shown that the frequencies of two common polymorphisms, 5T and M470V, differ significantly in Serbian population in comparison with other Southern European populations. Since it appears that Serbian population has a specific distribution of studied CFTR gene variants, it would also be interesting to analyze other common variants of this gene in our population. Such data can also be potentially useful as anthropogenic markers in population studies. The text was submitted by the authors in English.     

Genotypes of vitamin-D-binding protein (DBP) in patients with chronic obstructive pulmonary disease and healthy population of Republic Bashkortostan

The distribution of alleles and genotypes of vitamin D-binding protein (DBP) gene has been studied in patients with Chronic Obstructive Pulmonary Disease (COPD, n = 298) and healthy individuals (n = 237) from two ethnic groups (Tatars and Russians) living in Republic Bashkortostan. Statistically significant differences in the distribution of DBP gene genotypes between Tatars and Russians (chi2 = 8.854, df = 5, P = 0.04) were revealed. The pattern of allele's distribution within DBP gene was similar in healthy control subjects of both ethnic groups, with gradient reduction in row GC*1S> GC*1F> GC*2. The most common genotypes were: GC*1F/1S in Tatars (36.79%) and GC*1S/2 in Russians (34.62%). It has been shown, that Tatars with genotype GC*1F/1S have a lower risk of COPD development: the frequency of GC*1F/1S genotype in COPD patients was significantly lower than in healthy individuals (19.85% versus 36.79%; chi2 = 7.622, P = 0.0067, Pcor = 0.0335; OR = 0.42 CI 95% 0.22-0.79). At the same time, COPD patients from the same group had higher frequency of GC* 1F/2 genotype than healthy individuals (19.08% versus 8.49%; chi2 = 4.52, P = 0.033, Pcor = 0.165; OR = 2.54 CI 95% 1.067-6.20). In Russian population the distribution of alleles and genotypes of DBP gene were similar in COPD patients and healthy individuals.     

Structural Characteristics Determine the Cause of the Low Enzyme Activity of Two Thiopurine S-Methyltransferase Allelic Variants: A Biophysical Characterization of TPMT*2 and TPMT*5

The enzyme thiopurine S-methyltransferase (TPMT) is involved in the metabolism of thiopurine drugs used to treat acute lymphoblastic leukemia and inflammatory bowel disease. Thus far, at least 29 variants of the TPMT gene have been described, many of which encode proteins that have low enzyme activity and in some cases become more prone to aggregation and degradation. Here, the two naturally occurring variants, TPMT*2 (Ala80 → Pro) and TPMT*5 (Leu49 → Ser), were cloned and expressed in Escherichia coli. Far-UV circular dichroism spectroscopy showed that TPMT*2 was substantially destabilized whereas TPMT*5 showed much greater stability comparable to that of wild-type TPMT (TPMTwt). The extrinsic fluorescent molecule anilinonaphthalene sulfonate (ANS) was used to probe the tertiary structure during thermal denaturation. In contrast to TPMTwt, neither of the variants bound ANS to a large extent. To explore the morphology of the TPMT aggregates, we performed luminescent conjugated oligothiophene staining and showed fibril formation for TPMT*2 and TPMT*5. The differences in the flexibility of TPMTwt, TPMT*2, and TPMT*5 were evaluated in a limited proteolysis experiment to pinpoint stable regions. Even though there is only one amino acid difference between the analyzed TPMT variants, a clear disparity in the cleavage patterns was observed. TPMT*2 displays a protected region in the C-terminus, which differs from TPMTwt, whereas the protected regions in TPMT*5 are located mainly in the N-terminus close to the active site. In conclusion, this in vitro study, conducted to probe structural changes during unfolding of TPMT*2 and TPMT*5, demonstrates that the various causes of the low enzyme activity in vivo could be explained on a molecular level.     

Five polymorphisms of the apolipoprotein B gene in healthy Bulgarians

Five APOB polymorphisms (I/D in the promoter region, XbaI [codon 24881, MspI [codon 3611], EcoRI [codon 41541, and 3' VNTRs) were studied in a population sample of 147 healthy normolipemic Bulgarians. For all biallelic loci, the observed genotype distributions do not deviate from Hardy-Weinberg equilibrium. In Bulgaria the insertion allele and the MspI+ allele of APOB presented the highest allelic frequencies (0.793 +/- 0.024 and 0.959 +/- 0.012, respectively) among the European population groups studied so far. The allele frequencies of the other two biallelic polymorphisms (XbaI and EcoRI) found in the Bulgarian population are similar to those previously described in other Caucasian populations. Analysis of the 3' VNTR polymorphism revealed 11 different alleles. Like studies in other Caucasian populations, this study found bimodal allele-size distribution and a high level of heterozygosity. The frequency of allele *31 (0.162 +/- 0.022) among Bulgarians is higher than that of any other European population group studied so far. Genetic distances between Bulgarians and each of six populations from southeastern Europe for which 3' VNTR allele frequencies are available showed an increase in the order: Albanians相似文献