TY - JOUR
AU - Hsiao, P-J
AB - Abstract Background Adenosine triphosphate-binding cassette (ABC) transporters ABCG5 and ABCG8 are sterol export pumps regulating biliary cholesterol excretion. The formation of gallstones, supersaturated with cholesterol in bile, is determined by genetic and environmental factors. The interaction of susceptible gene polymorphisms with age, sex and body mass index in gallstone disease is unclear. Methods In a cross-sectional study, 979 subjects (880 men and 99 women, mean(s.d.) age 47·7(10·4) years) were recruited from a hospital-based population. Of these, 74 were diagnosed with gallstone disease by abdominal ultrasonography. Five non-synonymous polymorphisms, E604Q (ABCG5), D19H, C54Y, T400K and A632V (ABCG8), were analysed using the TaqMan® genotyping assay. Results The serum total cholesterol and both low- and high-density lipoprotein cholesterol levels were significantly lower in subjects with gallstones than in those without. 604Q (CC) and D19H (GC) genotypes were significantly associated with gallstone disease, even when adjusted for age, sex and body mass index. The genetic risk of developing gallstone disease was further stratified by age. The risk was greatly increased in subjects younger than 50 years with the D19H genotype and those of 50 years or more with the 604Q genotype. Conclusion Carriers of ABCG5 604Q or ABCG8 D19H polymorphisms have an increased risk of gallstone disease independent of age, sex and body mass index. Introduction Cholesterol gallstone disorder is one of the most common digestive diseases in industrialized countries, with a prevalence of 10–20 per cent. Bile supersaturated with cholesterol can lead to cholesterol crystal initiation, which is a critical step for cholesterol gallstone formation. Saturation of the bile with cholesterol is essentially dependent on the secretion of biliary cholesterol1,2. Genetic factors are important in gallstone diseases, which demonstrate family clustering3. The genetic contribution to gallstone disease is also supported by a higher prevalence in identical twins and first-degree relatives of subjects with gallstones4,5. As a result, genes involved in biliary cholesterol secretion may be related to gallstone formation. Adenosine triphosphate-binding cassette (ABC) transporters ABCG5 and ABCG8 represent apical sterol export pumps that promote active efflux of cholesterol from hepatocytes and excretion into bile. ABCG5 and ABCG8 proteins form a functional heterodimer, localized in the apical membrane of enterocytes and canalicular membrane of hepatocytes, and act as an efficient exporter to pump cholesterols into the bile6–8. Yu and colleagues9 have shown that biliary cholesterol concentration is extremely low in Abcg 5/8−/− mice. Overexpression of Abcg5/8, however, causes a fivefold increase in biliary cholesterol concentration. The ABCG5/ABCG8 heterodimer acts as a floppase to translocate cholesterol from the inner leaflet to the outer leaflet of the canalicular membrane9–11. Therefore ABCG5 and ABCG8 have been implicated as important regulators for the biliary excretion of cholesterol. Several family and twin studies have indicated the genes involved in biliary lipid secretion, such as ABCG5, ABCG8, FXR, CYP7A1 and ABCB4, which are all candidate genes involved in gallstone disease in humans1,2,4,5. It has been shown that cholesterol absorption efficiency is genetically determined12–14. In previous studies, five non-synonymous polymorphisms in ABCG5 (E604Q) and ABCG8 (C54Y, D19H, T400K, A632V) have been linked to cholesterol homeostasis, especially in cholesterol absorption efficiency and cholesterol saturation of bile. The processes of bile excretion and intestinal absorption of cholesterol are interrelated and relatively determined by heritability15–17. Thus, single nucleotide polymorphisms (SNPs) of ABCG5 and ABCG8 were plausibly believed to play an important role in regulating biliary cholesterol excretion and gallstone formation. In human studies, ABCG8 has been identified as an important gene correlated with gallstone disease18. The His19 genotype of ABCG8, strongly associated with gallstone formation, was identified as a susceptible marker in a genome-wide scan of over 382 492 SNPs in German samples19. In a case–control study, heterozygosity for the lithogenic ABCG8 allele was associated with gallstone formation. The 19H allele of ABCG8 is regarded as a gallstone-susceptible candidate gene20. There are geographic and ethnic differences in the prevalence of gallstone disease. The aim of this study was to screen a population in Taiwan with the above five non-synonymous polymorphisms and to test the risk stratification and their interaction with age, sex and body mass index (BMI) status in gallstone disease. Methods A total of 1370 adult manual workers were included in this study, recruited through a health check-up centre in Kaohsiung Medical University Hospital in 2005. Any participants with secondary dyslipidaemia, including diabetes, nephrotic syndrome, Cushing syndrome or hypothyroidism, or users of lipid-lowering agents were identified by a detailed medical history review and biochemical analysis, and excluded. The remaining 979 adults (880 men and 99 women), with a mean(s.d.) age of 47·7(10·4) years, were enrolled in the SNP study. Under the supervision of the Institutional Review Board of Kaohsiung Medical University, a blood sample was taken from each subject after an overnight fast. All of these EDTA-treated blood samples then underwent DNA isolation by a standard method. Abdominal ultrasonography (3·5-MHz convex transducer, Toshiba SSA-250; Toshiba, Tokyo, Japan) was performed for every participant by qualified hepatologists trained at Kaohsiung Medical University to ensure interobserver consistency. Gallstones were identified as a characteristic echogenic focus with acoustic shadow in the fasting state using real-time ultrasonography. The gallstone group included 74 patients (70 men and four women); of these, nine had had a cholecystectomy for gallstone disease. All the other subjects were categorized as the ‘no stone’ group. Relevant non-synonymous polymorphisms of ABCG5 (E604Q) and ABCG8 (C54Y, D19H, T400K, A632V) associated with biliary cholesterol secretion were chosen for this study. Analysis was performed with the TaqMan® SNP genotyping assay (Applied Biosystems, Foster City, CA, USA). The specific primers were designed using Primer 3 software according to SNP reference of GenBank mapping in the National Center for Biotechnology Information database (rs6720173 for E604Q, rs11887534 for D19H, rs4148211 for C54Y, rs4148217 for T400K, rs6544718 for A632V). Detection of the above gene variants was performed according to the SNP genotyping reaction protocol using specific primers mixed with TaqMan® Master mix, allelic discrimination assay mix, distilled water and genomic DNA under the following conditions: 95 °C for 10 min, then 40 cycles of 92 °C for 15 s alternating with 60 °C for 60 s. The ABI Prism 7500 sequence detection system (Applied Biosystems, Taipei, Taiwan) was used to detect gene variants using VIC® and FAM™ dyes (Applied Biosystems). Statistical analysis All statistical analyses were performed using SPSS® 13.0 for Windows® (SPSS, Chicago, Illinois, USA). Continuous variables are expressed as mean(s.d.). The comparison among groups for categorical variables was performed with Pearson χ2 tests. Continuous variables were compared by two-sample Student's t tests. Allele frequencies were estimated by direct gene counting. A χ2 test was used for testing Hardy–Weinberg equilibrium and power calculations for the sample size of each genotype. Haploview was used for estimating haploblocks, and haplotype analysis used a Hap-clustering program21. Binary logistic regression gave odds ratios of having gallstones under the influence of genotypes E604Q (CC versus GG + GC), D19H (GC versus GG) and C54Y (AA versus GG + GA). For the crude odds ratio, the presence or absence of gallstones was the dependent variable, and the E604Q, D19H or C54Y genotype was the independent variable. For the adjusted odds ratio, age, sex and BMI were also added into the previous logistic regression. P < 0·050 was considered significant with a two-tailed test. Results Table 1 shows the baseline data for the two groups. The prevalence of gallstone disease was 7·6 per cent in this population. Men were predominant, but there was no difference in sex distribution between the two groups. Ages ranged from 16 to 88 years, with 95 per cent between 25 and 65 years. Subjects with gallstones or those who had had an operation for gallstone disease were significantly older than the group without gallstone disease. There was no difference in BMI between the groups. Serum levels of total cholesterol, low-density lipoprotein cholesterol (LDLC) and high-density lipoprotein cholesterol (HDLC) were significantly lower in the gallstone group. Table 1 Baseline data for 979 recruited subjects . No stones (n = 905) . Gallstones (n = 74) . P* . Sex ratio (M : F) 810 : 95 70 : 4 0·226† Age (years) 45·8(8·7) 51·9(6·6) < 0·001 BMI (kg/m2) 24·4(3·3) 24·4(2·7) 0·954 AST (units/l) 29·3(20·0) 30·5(16·8) 0·635 ALT (units/l) 31·5(35·2) 32·2(27·4) 0·869 ALP (units/l) 131·6(34·6) 129·4(30·1) 0·600 Cholesterol (mg/dl) 182·8(34·0) 167·3(32·0) < 0·001 Triglyceride (mg/dl) 138·0(116·5) 124·2(37·7) 0·317 LDLC (mg/dl) 123·8(33·5) 110·4(28·5) 0·007 HDLC (mg/dl) 53·0(13·7) 48·8(10·2) 0·009 . No stones (n = 905) . Gallstones (n = 74) . P* . Sex ratio (M : F) 810 : 95 70 : 4 0·226† Age (years) 45·8(8·7) 51·9(6·6) < 0·001 BMI (kg/m2) 24·4(3·3) 24·4(2·7) 0·954 AST (units/l) 29·3(20·0) 30·5(16·8) 0·635 ALT (units/l) 31·5(35·2) 32·2(27·4) 0·869 ALP (units/l) 131·6(34·6) 129·4(30·1) 0·600 Cholesterol (mg/dl) 182·8(34·0) 167·3(32·0) < 0·001 Triglyceride (mg/dl) 138·0(116·5) 124·2(37·7) 0·317 LDLC (mg/dl) 123·8(33·5) 110·4(28·5) 0·007 HDLC (mg/dl) 53·0(13·7) 48·8(10·2) 0·009 Values are mean(s.d.). BMI, body mass index; AST, aspartate aminotransferase; ALT, alanine aminotransferase; ALP, alkaline phosphatase; LDLC, low-density lipoprotein cholesterol; HDLC, high-density lipoprotein cholesterol. * Two-sample Student's t test, except † Pearson χ2 test. Open in new tab Table 1 Baseline data for 979 recruited subjects . No stones (n = 905) . Gallstones (n = 74) . P* . Sex ratio (M : F) 810 : 95 70 : 4 0·226† Age (years) 45·8(8·7) 51·9(6·6) < 0·001 BMI (kg/m2) 24·4(3·3) 24·4(2·7) 0·954 AST (units/l) 29·3(20·0) 30·5(16·8) 0·635 ALT (units/l) 31·5(35·2) 32·2(27·4) 0·869 ALP (units/l) 131·6(34·6) 129·4(30·1) 0·600 Cholesterol (mg/dl) 182·8(34·0) 167·3(32·0) < 0·001 Triglyceride (mg/dl) 138·0(116·5) 124·2(37·7) 0·317 LDLC (mg/dl) 123·8(33·5) 110·4(28·5) 0·007 HDLC (mg/dl) 53·0(13·7) 48·8(10·2) 0·009 . No stones (n = 905) . Gallstones (n = 74) . P* . Sex ratio (M : F) 810 : 95 70 : 4 0·226† Age (years) 45·8(8·7) 51·9(6·6) < 0·001 BMI (kg/m2) 24·4(3·3) 24·4(2·7) 0·954 AST (units/l) 29·3(20·0) 30·5(16·8) 0·635 ALT (units/l) 31·5(35·2) 32·2(27·4) 0·869 ALP (units/l) 131·6(34·6) 129·4(30·1) 0·600 Cholesterol (mg/dl) 182·8(34·0) 167·3(32·0) < 0·001 Triglyceride (mg/dl) 138·0(116·5) 124·2(37·7) 0·317 LDLC (mg/dl) 123·8(33·5) 110·4(28·5) 0·007 HDLC (mg/dl) 53·0(13·7) 48·8(10·2) 0·009 Values are mean(s.d.). BMI, body mass index; AST, aspartate aminotransferase; ALT, alanine aminotransferase; ALP, alkaline phosphatase; LDLC, low-density lipoprotein cholesterol; HDLC, high-density lipoprotein cholesterol. * Two-sample Student's t test, except † Pearson χ2 test. Open in new tab Table 2 shows allele frequencies of the five non-synonymous polymorphisms (ABCG5: E604Q; ABCG8: D19H, C54Y, T400K, A632V). The distributions of genotypes in the whole study group were in Hardy–Weinberg equilibrium. The allele frequencies were different to those reported previously in the European–American population. The C allele of D19H was quite rare (1·4 per cent) and the CC (His19) genotype was absent in the study population. ABCG8 A632V was not found. Compared with Caucasians, the dominant allele distribution (G : A) of C54Y was reversed. Of the five polymorphisms, one variant (ABCG8: A632V) was excluded from further analysis because of its monomorphic distribution. Table 2 Allele frequencies of the polymorphisms in ABCG5 and ABCG8 genes in 979 subjects Gene . Allele . NCBI SNP reference . Ratio . Frequency (%) . ABCG5: E604Q G1810C rs 6720173 G : C 89·5 : 10·5 ABCG8: D19H G55C rs 11887534 G : C 98·6 : 1·4 ABCG8: C54Y G161A rs 4148211 G : A 90·3 : 9·7 ABCG8: T400K C1199A rs 4148217 C : A 92·0 : 8·0 ABCG8: A632V T1895C rs 6544718 T : C 0 : 100 Gene . Allele . NCBI SNP reference . Ratio . Frequency (%) . ABCG5: E604Q G1810C rs 6720173 G : C 89·5 : 10·5 ABCG8: D19H G55C rs 11887534 G : C 98·6 : 1·4 ABCG8: C54Y G161A rs 4148211 G : A 90·3 : 9·7 ABCG8: T400K C1199A rs 4148217 C : A 92·0 : 8·0 ABCG8: A632V T1895C rs 6544718 T : C 0 : 100 NCBI, National Center for Biotechnology Information; SNP, single nucleotide polymorphism. Open in new tab Table 2 Allele frequencies of the polymorphisms in ABCG5 and ABCG8 genes in 979 subjects Gene . Allele . NCBI SNP reference . Ratio . Frequency (%) . ABCG5: E604Q G1810C rs 6720173 G : C 89·5 : 10·5 ABCG8: D19H G55C rs 11887534 G : C 98·6 : 1·4 ABCG8: C54Y G161A rs 4148211 G : A 90·3 : 9·7 ABCG8: T400K C1199A rs 4148217 C : A 92·0 : 8·0 ABCG8: A632V T1895C rs 6544718 T : C 0 : 100 Gene . Allele . NCBI SNP reference . Ratio . Frequency (%) . ABCG5: E604Q G1810C rs 6720173 G : C 89·5 : 10·5 ABCG8: D19H G55C rs 11887534 G : C 98·6 : 1·4 ABCG8: C54Y G161A rs 4148211 G : A 90·3 : 9·7 ABCG8: T400K C1199A rs 4148217 C : A 92·0 : 8·0 ABCG8: A632V T1895C rs 6544718 T : C 0 : 100 NCBI, National Center for Biotechnology Information; SNP, single nucleotide polymorphism. Open in new tab Table 3 shows the association between the genotypes of ABCG5 and ABCG8, and the presence of gallstones. There was a significant correlation of gallstone disease with the genotype distribution of E604Q, D19H and C54Y polymorphisms. The minor alleles of E604Q, D19H and C54Y polymorphisms were overexpressed in patients with gallstones compared with controls. For example, in the E604Q polymorphism, the frequency of the CC genotype was 4 per cent in the gallstone group compared with 0·7 per cent in the stone-free group, and the frequency of the D19H (GC) variant was 8 per cent in the gallstone group compared with 2·1 per cent in the group without gallstones. Table 3 Association of genotype frequency of ABCG5 and ABCG8 with gallstone development . No stones (n = 905) . Gallstones (n = 74) . P* . Power (%) . ABCG5: E604Q (G1810C)  Genotype   GG 691 (79·2) 52 (74) 0·011 18   GC 175 (20·1) 15 (21)   CC 6 (0·7) 3 (4) ABCG8: D19H (G55C)  Genotype   GG 851 (97·9) 66 (92) 0·001 79   GC 18 (2·1) 6 (8) ABCG8: C54Y (G161A)  Genotype   GG 747 (82·5) 54 (73) 0·041 53   GA 152 (16·8) 18 (24)   AA 6 (0·7) 2 (3) ABCG8: T400K (C1199A)  Genotype   CC 739 (84·5) 58 (79) 0·463 22   CA 134 (15·3) 15 (21)   AA 2 (0·2) 0 (0) . No stones (n = 905) . Gallstones (n = 74) . P* . Power (%) . ABCG5: E604Q (G1810C)  Genotype   GG 691 (79·2) 52 (74) 0·011 18   GC 175 (20·1) 15 (21)   CC 6 (0·7) 3 (4) ABCG8: D19H (G55C)  Genotype   GG 851 (97·9) 66 (92) 0·001 79   GC 18 (2·1) 6 (8) ABCG8: C54Y (G161A)  Genotype   GG 747 (82·5) 54 (73) 0·041 53   GA 152 (16·8) 18 (24)   AA 6 (0·7) 2 (3) ABCG8: T400K (C1199A)  Genotype   CC 739 (84·5) 58 (79) 0·463 22   CA 134 (15·3) 15 (21)   AA 2 (0·2) 0 (0) Values in parentheses are percentages. * Pearson χ2 test. Open in new tab Table 3 Association of genotype frequency of ABCG5 and ABCG8 with gallstone development . No stones (n = 905) . Gallstones (n = 74) . P* . Power (%) . ABCG5: E604Q (G1810C)  Genotype   GG 691 (79·2) 52 (74) 0·011 18   GC 175 (20·1) 15 (21)   CC 6 (0·7) 3 (4) ABCG8: D19H (G55C)  Genotype   GG 851 (97·9) 66 (92) 0·001 79   GC 18 (2·1) 6 (8) ABCG8: C54Y (G161A)  Genotype   GG 747 (82·5) 54 (73) 0·041 53   GA 152 (16·8) 18 (24)   AA 6 (0·7) 2 (3) ABCG8: T400K (C1199A)  Genotype   CC 739 (84·5) 58 (79) 0·463 22   CA 134 (15·3) 15 (21)   AA 2 (0·2) 0 (0) . No stones (n = 905) . Gallstones (n = 74) . P* . Power (%) . ABCG5: E604Q (G1810C)  Genotype   GG 691 (79·2) 52 (74) 0·011 18   GC 175 (20·1) 15 (21)   CC 6 (0·7) 3 (4) ABCG8: D19H (G55C)  Genotype   GG 851 (97·9) 66 (92) 0·001 79   GC 18 (2·1) 6 (8) ABCG8: C54Y (G161A)  Genotype   GG 747 (82·5) 54 (73) 0·041 53   GA 152 (16·8) 18 (24)   AA 6 (0·7) 2 (3) ABCG8: T400K (C1199A)  Genotype   CC 739 (84·5) 58 (79) 0·463 22   CA 134 (15·3) 15 (21)   AA 2 (0·2) 0 (0) Values in parentheses are percentages. * Pearson χ2 test. Open in new tab For further analysis of the odds ratios of minor genotypes with gallstone disease, carriers of GG and GC genotypes of E604Q and those of GG and GA genotypes of C54Y were combined. The risk stratification of these minor genotypes for gallstone disease was determined and adjusted by age, sex and BMI, which are well established as independent risk factors for gallstone disease (Table 4). The 604Q (CC) and D19H (GC) variant contributed a significant and independent risk of gallstone formation, even after adjusting for age, sex and BMI. On the basis of these four SNPs in ABCG8, a haplotype analysis study was conducted. There was no significant difference in the distribution of each haplotype between the gallstone disease and stone-free groups. Table 4 Gallstone risk associated with ABCG5 and ABCG8 polymorphisms Genotype . Crude odds ratio . P† . Adjusted odds ratio* . P† . E604Q  GG + GC 1·0  CC 6·5 (1·6, 26·4) 0·009 4·7 (1·1, 21·1) 0·042 D19H  GG 1·0  GC 4·3 (1·7, 11·2) 0·003 3·5 (1·2, 9·6) 0·018 C54Y  GG + GA 1·0  AA 4·1 (0·8, 20·9) 0·085 3·2 (0·6, 17·3) 0·170 Genotype . Crude odds ratio . P† . Adjusted odds ratio* . P† . E604Q  GG + GC 1·0  CC 6·5 (1·6, 26·4) 0·009 4·7 (1·1, 21·1) 0·042 D19H  GG 1·0  GC 4·3 (1·7, 11·2) 0·003 3·5 (1·2, 9·6) 0·018 C54Y  GG + GA 1·0  AA 4·1 (0·8, 20·9) 0·085 3·2 (0·6, 17·3) 0·170 Values in parentheses are 95 per cent confidence intervals. * Adjusted for age, sex and body mass index. † Binary logistic regression. Open in new tab Table 4 Gallstone risk associated with ABCG5 and ABCG8 polymorphisms Genotype . Crude odds ratio . P† . Adjusted odds ratio* . P† . E604Q  GG + GC 1·0  CC 6·5 (1·6, 26·4) 0·009 4·7 (1·1, 21·1) 0·042 D19H  GG 1·0  GC 4·3 (1·7, 11·2) 0·003 3·5 (1·2, 9·6) 0·018 C54Y  GG + GA 1·0  AA 4·1 (0·8, 20·9) 0·085 3·2 (0·6, 17·3) 0·170 Genotype . Crude odds ratio . P† . Adjusted odds ratio* . P† . E604Q  GG + GC 1·0  CC 6·5 (1·6, 26·4) 0·009 4·7 (1·1, 21·1) 0·042 D19H  GG 1·0  GC 4·3 (1·7, 11·2) 0·003 3·5 (1·2, 9·6) 0·018 C54Y  GG + GA 1·0  AA 4·1 (0·8, 20·9) 0·085 3·2 (0·6, 17·3) 0·170 Values in parentheses are 95 per cent confidence intervals. * Adjusted for age, sex and body mass index. † Binary logistic regression. Open in new tab Epidemiological surveys demonstrate that the risk of cholesterol gallstone disease increases with age. The gallstone risk associated with 604Q and D19H polymorphisms was further stratified into different age groups (Table 5). In the gallstone group, 25 younger subjects had a mean(s.d.) age of 40·1(6·4) (range 16–49) years (only two of 548 subjects in the whole younger group had the 604Q (CC) variant, and these were excluded). The older 47 subjects had a mean(s.d.) age of 57·2(6·4) (range 50–88) years. The result clearly demonstrated a significant risk of gallstone disease associated with 604Q in subjects older than 50 years and a greater risk associated with the D19H polymorphism in those younger than 50 years. Table 5 Gallstone risk associated with ABCG5 and ABCG8 polymorphisms stratified by age Genotype . Age < 50 years . Age ≥ 50 years . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . E604Q  GG + GC 1·0  CC† 6·0 (1·3, 27·7) 0·022 6·4 (1·3, 30·7) 0·020 D19H  GG 1·0 1·0  GC 6·4 (1·3, 32·7) 0·025 12·4 (1·7, 90·0) 0·013 2·8 (0·9, 9·2) 0·088 2·5 (0·8, 8·6) 0·133 Genotype . Age < 50 years . Age ≥ 50 years . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . E604Q  GG + GC 1·0  CC† 6·0 (1·3, 27·7) 0·022 6·4 (1·3, 30·7) 0·020 D19H  GG 1·0 1·0  GC 6·4 (1·3, 32·7) 0·025 12·4 (1·7, 90·0) 0·013 2·8 (0·9, 9·2) 0·088 2·5 (0·8, 8·6) 0·133 Values in parentheses are 95 per cent confidence intervals. * Adjusted for age, sex and body mass index. † Analysis was not done for the younger group because only two subjects had the 604Q (CC) variant from a total of 548 subjects younger than 50 years. ‡ Binary logistic regression. Open in new tab Table 5 Gallstone risk associated with ABCG5 and ABCG8 polymorphisms stratified by age Genotype . Age < 50 years . Age ≥ 50 years . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . E604Q  GG + GC 1·0  CC† 6·0 (1·3, 27·7) 0·022 6·4 (1·3, 30·7) 0·020 D19H  GG 1·0 1·0  GC 6·4 (1·3, 32·7) 0·025 12·4 (1·7, 90·0) 0·013 2·8 (0·9, 9·2) 0·088 2·5 (0·8, 8·6) 0·133 Genotype . Age < 50 years . Age ≥ 50 years . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . Crude odds ratio . P‡ . Adjusted odds ratio* . P‡ . E604Q  GG + GC 1·0  CC† 6·0 (1·3, 27·7) 0·022 6·4 (1·3, 30·7) 0·020 D19H  GG 1·0 1·0  GC 6·4 (1·3, 32·7) 0·025 12·4 (1·7, 90·0) 0·013 2·8 (0·9, 9·2) 0·088 2·5 (0·8, 8·6) 0·133 Values in parentheses are 95 per cent confidence intervals. * Adjusted for age, sex and body mass index. † Analysis was not done for the younger group because only two subjects had the 604Q (CC) variant from a total of 548 subjects younger than 50 years. ‡ Binary logistic regression. Open in new tab Discussion This study found a significant correlation between the distribution of E604Q and D19H (GC) polymorphisms and gallstone disease in the Taiwanese population. In addition, after adjusting for other confounding risk factors (age, sex and BMI), the 604Q (CC) and D19H (GC) polymorphisms were still significant independent risk factors for developing gallstone disease. The risk associated with 604Q was stronger in older people, whereas the risk associated with D19H was greater in those younger than 50 years. The study also found that serum levels of total cholesterol, LDLC and HDLC were significantly lower in subjects with gallstones than in those without. Gallstone formation results from a complex interaction between multiple predisposing genes and environmental factors. Genetic susceptibility for gallstone formation is influenced by well known risk factors including age, sex, obesity, parity and medication1,2,4,22,23. In this study population, polymorphism of 604Q or D19H and age were independently associated with gallstone disease in univariable analysis. The ageing process brings a more lithogenic bile resulting from increased intestinal cholesterol absorption, enhanced hepatic secretion of cholesterol and decreased bile acid synthesis. The ensuing supersaturated bile leads to an increased risk of cholesterol gallstone formation with ageing2,13,14,23. Cholesterol is absorbed from the intestine, packaged in chylomicron remnant and transported to the liver, contributing to biliary cholesterol secretion. Biliary excretion and intestinal absorption of cholesterol are related and regulated by the ABCG5 and ABCG8 polymorphisms12–14. In this large-scale ultrasonography study, carriers of 604Q and D19H variants retained their high risk of gallstone formation even after adjusting for age, sex and BMI status. The gallstone risk for D19H carriers was much greater in those younger than 50 years. Consistent with previous studies in Caucasians19,20, this finding supports the hypothesis that the D19H polymorphism may affect the transporter function resulting in gallstone formation in earlier life. The genetic risk of gallstone disease associated with 604Q may enhance the ageing effect. One implication of this study is that 604Q and D19H polymorphisms could be considered as susceptible gene markers for gallstone disease in the Taiwanese population. These two non-synonymous polymorphisms may alter the conformation of ABCG5 and ABCG8 transporters to modulate the intestinal absorption efficiency or the biliary secretion of cholesterol. Epidemiological studies have indicated an association between low plasma HDLC levels and gallstone prevalence5. Supersaturation of bile with excess cholesterol is an essential step in gallstone formation. Bile is the major route for the elimination of excess cholesterol from the liver. In human studies, most of the cholesterol secreted into bile comes from: circulating plasma lipoproteins, free cholesterol carried by HDL particles binding to the scavenger receptor class B type 1 (SRB1), uptake of cholesterol by LDL receptors or LDL receptor-related proteins, and dietary cholesterol in the chylomicron remnant. Newly synthesized cholesterol contributes very little (5–20 per cent) to biliary cholesterol secretion1,4,5,24. In cholesterol homeostasis, plasma HDLC plays a key role in reverse cholesterol transport to the liver. Biliary cholesterol hypersecretion in gallstone-susceptible mice is associated with decreased plasma HDLC25. The biliary secretion of free cholesterol markedly increases in SRB1 transgenic mice and transport of cholesterol into bile is mediated mainly by SRB126. The present study demonstrated that serum levels of total cholesterol, LDLC and HDLC were significantly lower in subjects with gallstones than in stone-free subjects. Acalovschi and co-workers17 found that polymorphisms at D19H and Q604E were significantly associated with a lithogenic plasma lipid profile in siblings with gallstone disease. Polymorphisms of ABCG5 and ABCG8 genes may alter the transporter function, modify the intrahepatic cholesterol content and regulate the reverse cholesterol transport in cholesterol homeostasis. It is possible that gallstone formation may be a byproduct of excess cholesterol excretion into bile to keep serum levels of cholesterol-containing lipoproteins lower. Gallstone disease is a common clinical entity, with a prevalence of 10–15 per cent detected by ultrasonography in Western populations. The overall prevalence is lower in Asia, ranging from 3 to 15 per cent1,2,5. This difference may relate to both dietary habits and genetic factors. The relationship between diet and gallstones is still controversial27. Cholesterol gallstones are responsible for 80–90 per cent of all gallstones in Western countries1,2,4. As a result of westernization of dietary habits, the composition of gallstones has altered: up to 77 per cent in Chinese populations are now cholesterol gallstones2,18. In the present hospital-based ultrasonography study, the prevalence of gallstones was 7·6 per cent, consistent with previous community studies in Taiwan where the prevalence ranged from 4·3 to 10·7 per cent28. Compared with the reports by Buch and colleagues19 and Grünhage and co-workers20, the lower prevalence of the minor allele of D19H (1·4 versus 8·5 per cent) in the present study may explain the lower prevalence of gallstone formation (8·3 versus 21·4 per cent) in Taiwanese compared with Caucasian populations. Even the lower prevalence of the minor allele in the present population supports the previous suggestion that the D19H variant contributes to the genetic risk of gallstone disease, especially in the young. Compared with the reports on Caucasians, the gallstone risk of older 604Q carriers is a novel finding in the present study; however, owing to limited power in the sample size, this needs further study for validation. 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TI - Significant association of ABCG5 604Q and ABCG8 D19H polymorphisms with gallstone disease
JF - British Journal of Surgery
DO - 10.1002/bjs.6178
DA - 2008-07-11
UR - https://www.deepdyve.com/lp/oxford-university-press/significant-association-of-abcg5-604q-and-abcg8-d19h-polymorphisms-vrUAsvgqnE
SP - 1005
EP - 1011
VL - 95
IS - 8
DP - DeepDyve
ER -