ABCMdb

PMID: 17626266

Grunhage F, Acalovschi M, Tirziu S, Walier M, Wienker TF, Ciocan A, Mosteanu O, Sauerbruch T, Lammert F
Increased gallstone risk in humans conferred by common variant of hepatic ATP-binding cassette transporter for cholesterol.
Hepatology. 2007 Sep;46(3):793-801., [PubMed]

Sentences

No. Mutations Sentence Comment

5 ABCG8 p.Asp19His In ASPs, gallstones were strongly linked to the D19H variant of the ABCG8 gene (NPL score ‫؍‬ 7.1; P ‫؍‬ 4.6 ؋ 10-13). Login to comment 7 ABCG8 p.Asp19His Consistent with the mouse model, heterozygosity for the lithogenic ABCG8 allele was associated with gallstones in humans; 21.4% of gallstone patients carried the heterozygous D19H genotype, compared with 8.6% of controls (OR ‫؍‬ 2.954; P ‫؍‬ 0.026). Login to comment 52 ABCG8 p.Asp19His ABCG8 p.Thr400Lys ABCG8 p.Tyr54Cys Forgenotyping,weselectedfunctionallyrelevantnonsyn- onymous coding single-nucleotide polymorphisms (SNPs) of the ABCG5/G8 genes (Fig. 1): ABCG5 rs6720173 ϭ c.1810GϾC(p.E604Q);ABCG8rs11887534ϭc.55GϾC (p.D19H), rs4148211 ϭ c.161AϾG (p.Y54C), rs4148217 ϭ c.1199CϾA (p.T400K), and rs6544718 ϭ c.1895CϾT (p.A632V).22,23,25,28,29 All SNPs were genotyped using solution-phase hybridization reactions with 5Ј-nuclease and fluorescence detection (TaqMan assays) in a 7300 Real-Time polymerase chain reaction (PCR) system (Applera, Norwalk, CT). Login to comment 86 ABCG8 p.Asp19His The genetic linkage analysis of the ASPs revealed highly significant linkage between the presence of gallstones and carrying the D19H variant of the ABCG8 gene (NPL score ϭ 7.1). Login to comment 89 ABCG8 p.Asp19His Therefore, we performed a sensitivity analysis for the D19H variant (Fig. 2, Tables 4 and 5). Login to comment 93 ABCG8 p.Asp19His Finally, with 23% of cases phenotyped by ultrasound (Table 2), we determined linkage with ABCG8 D19H exclusively in cases confirmed by cholecystectomy (symptomatic patients), obtaining a single-point NPL score of 4.3 (P ϭ 1.78 ϫ 10-8). Login to comment 94 ABCG8 p.Asp19His ABCG8 p.Thr400Lys ABCG8 p.Tyr54Cys In contrast to ABCG8 D19H, no significant single-point linkage was detected for the other ABCG5/G8 SNPs (p.E604Q, p.Y54C, p.T400K, p.A632V). Login to comment 95 ABCG8 p.Asp19His Genetic Association Study Confirmed Lithogenic Effects of ABCG8 Variant D19H. Login to comment 96 ABCG8 p.Asp19His To obtain additional evidence that ABCG8 D19H represents a lithogenic risk factor, we performed an association (case-control) study. Login to comment 100 ABCG8 p.Asp19His Sensitivity analysis of the ABCG8 D19H variant. Login to comment 105 ABCG8 p.Asp19His Table 6 demonstrates that the ABCG8 D19H variant was significantly associated with the presence of gallstones in cases: the 19H (c.55C) allele was significantly more common in cases than in controls (OR ϭ 3.018; P ϭ 0.017; Table 6). Login to comment 107 ABCG8 p.Asp19His Consistent with the mouse model,16 heterozygosity for the lithogenic ABCG8 allele is associated with gallstones in humans: 21.4% (18 of 84) of all gallstone patients carried the heterozygous D19H genotype, as compared with 8.6% (6 of 70) of the controls (OR ϭ 2.954; P ϭ 0.026). Login to comment 109 ABCG8 p.Asp19His Because controls were significantly younger (P ϭ 0.024) and leaner (P Ͻ 0.001) than the affected patients, we analyzed the effects of the known lithogenic risk factors age, sex, and BMI as well as the D19H variant separately by logistic regression analysis in cases and controls. Login to comment 110 ABCG8 p.Asp19His In univariate analysis, only age (OR ϭ 1.033; P ϭ 0.026; 95% CI 1.004-1.063), BMI (OR ϭ 1.244; P Ͻ 0.001; 95% CI 1.113-1.366), and D19H (OR ϭ 3.167; P ϭ 0.021; 95% CI 1.188-8.438) are significant risk factors for gallstones. Login to comment 111 ABCG8 p.Asp19His We included these 3 risk factors as covariates in multiple logistic regression analysis and observed a significant effect for BMI (Exp[B] ϭ 1.244; P Ͻ 0.001; 95% CI 1.133-1.366), a trend for D19H (Exp[B] ϭ 2.651; P ϭ 0.063), and no effect for age. Login to comment 114 ABCG8 p.Asp19His ABCG8 p.Asp19His The PAF of ABCG8 D19H is 0.08, that is, the D19H variant contributed 8% to the total gallstone risk. Login to comment 115 ABCG8 p.Asp19His This PAF is exactly in the range expected for polygenic traits such as gallstones, which are the result of the interaction between multiple genes and environmental factors.8 Discussion This combined linkage and association study provides strong evidence that the D19H variant in the first exon of Table 4. Login to comment 116 ABCG8 p.Asp19His Sensitivity Analysis with GENEHUNTER-MODSCORE (GHM)- NPL Score for ABCG8 Variant D19H (Single-Point Analysis) Frequency of 19H (c.55C) allele Origin of data NPL score P 0.001 9.46451 1.10 ϫ 10-22 0.01 9.22681 1.35 ϫ 10-21 0.05 8.25925 1.86 ϫ 10-17 0.08 Entrez SNP database 7.51923 1.25 ϫ 10-14 0.10 7.20748 1.55 ϫ 10-13 0.11 84 ASP families 7.06879 4.60 ϫ 10-13 0.15 6.28671 1.23 ϫ 10-10 0.20 5.46859 2.03 ϫ 10-8 0.25 4.73440 1.03 ϫ 10-6 0.30 4.07076 0.000023 0.40 2.91714 0.001767 0.50 1.95043 0.025658 0.75 0.13854 0.442483 0.90 -0.61822 0.729508 0.95 -0.81959 0.792454 0.99 -0.96153 0.830702 0.999 -0.99102 0.840238 Table 5. Login to comment 117 ABCG8 p.Asp19His Sensitivity Analysis with GENEHUNTER-MODSCORE (GHM)- NPL Score for ABCG8 Variant D19H (Multipoint Analysis) Frequency of 19H (c.55C) allele Origin of data NPL score P 0.001 8.66913 4.23 ϫ 10-19 0.01 6.76402 4.19 ϫ 10-12 0.05 4.85695 5.68 ϫ 10-7 0.08 Entrez SNP database 4.16629 0.000015 0.10 3.93152 0.000042 0.11 84 ASP families 3.83382 0.000063 0.15 .33767 0.000425 0.20 .88350 0.001975 0.25 2.50882 0.006153 0.30 2.18649 0.014481 0.40 1.64580 0.050166 0.50 1.19845 0.115047 0.75 0.33078 0.370026 0.90 -0.06949 0.527678 0.95 -0.18622 0.573232 0.99 -0.27374 0.605938 0.999 -0.29271 0.614403 Table 6. Login to comment 118 ABCG8 p.Asp19His ABCG8 p.Asp19His Distributions of Alleles and Genotypes for ABCG8 D19H in Cases with Gallstones and Stone-Free Controls and Tests for Association ABCG8 D19H (c.55G>C) allele/genotype Count (frequency) of alleles/genotypes Cases (2N ‫؍‬ 168) Controls (2N ‫؍‬ 140) G 148 (0.88) 134 (0.91) C 20 (0.12) 6 (0.09) GG 65 (0.77) 64 (0.91) GC 18 (0.21) 6 (0.09) CC 1 (0.01) 0 (0.00) Test for association ␹2 P Allele frequency difference test 5.735 0.017 Armitage`s trend test 5.783 0.016 OR statistics OR 95% CI [C] 7 [G] 3.018 1.177-7.740 [CC ϩ CG] 7 [GG] 3.118 1.170-8.313 [CG] 7 [GG] 2.954 1.102-7.920 ␹2 Statistics, P values, odds ratios (OR), and confidence intervals (CI) were determined using contingency table statistics. Login to comment 126 ABCG8 p.Asp19His In fact, the significant linkage results for the ABCG8 D19H variant in symptomatic cases only (as defined by history of cholecystectomy) suggest that the variant is linked to the presence of both gallstones and gallbladder disease. Login to comment 130 ABCG8 p.Asp19His ABCG8 p.Asp19His To assess whether the association results for the D19H variant were affected by confounding risk factors for gallstones, we performed multivariate analysis that included the D19H variant and lithogenic risk factors. Login to comment 135 ABCG8 p.Asp19His The association between serum plant sterol concentration and this nonconservative substitution suggests that the change from aspartic acid to the polar histidine at amino acid 19 alters ABCG5/G8 function.22 Because serum plant sterol levels are lower in 19H carriers, the predicted change would be expected to increase transporter expression or function, although effects on ABCG5/G8 function can only be determined after reconstitution in in vitro sterol transfer assays.44 Our previous study of siblings with gallstones25 and other reports23 have also observed significantly lower serum levels of total and LDL cholesterol in 19H carriers, indicating that D19H represents a gain-of-function variant that increases ABCG5/G8-mediated removal of plant sterols and cholesterol into bile and intestine. Login to comment 136 ABCG8 p.Asp19His Hypersecretion of cholesterol from liver with cholesterol supersaturation of bile represents the common defect in patients with cholesterol gallstones.4,18,45 Furthermore, the 19H allele has also been associated with higher serum levels of cholesterol precursors (cholestanol, lathosterol),23 indicating increased cholesterol biosynthesis, as has been observed in obese gallstone patients.46,47 These findings taken together suggest low intestinal cholesterol absorption and high compensatory cholesterol biosynthesis in carriers of the ABCG8 D19H variant, as hypothesized previously by Gylling et al.23 Of note, the up-regulated cholesterol biosynthesis in these subjects explains the greater efficacy of HMG-CoA reductase inhibitors such as atorvastatin therapy in 19H carriers.28 In fact, statins are reported to decrease the cholesterol saturation index of duodenal bile and to dissolve gallstones in some patients48 but not in gallstone patients in general.49 We have proposed50 that the identification of common gallstone genes (LITH or GBD) should be based on complementary evidence from (1) genetic studies in mice and/or humans, (2) phenotypic characterization of genetically defined animal models (for example, knockout or transgenic mice), and (3) epidemiological studies defining the overall clinical relevance. Login to comment 138 ABCG8 p.Asp19His Given the estimated PAF for the ABCG8 D19H variant of 8% and the estimation that genetic determinants account for 25% to 29% of the phenotypic variation in gallstone disease,10,11 approximately 30% of the genetic effects might be a result of this specific risk variant. Login to comment