Common risk factors for gallbladder stones include physical inactivity and overnutrition, i.e. high calorie intake, in particular high carbohydrate intake, high glycaemic load, and low fibre intake [9]. These contribute to obesity (particularly central adiposity) as well as insulin resistance and diabetes, hence gallstones have been considered a “fellow traveler” of the metabolic syndrome [10]. Hyperinsulinaemia is associated with increased hepatic cholesterol uptake and secretion as well as hyposecretion of bile acids [11]. Low-fibre diet prolongs intestinal transit and thereby increases the synthesis of the lithogenic hydrophobic bile acid deoxycholic acid by intestinal bacteria that belong to the genus Clostridium [9]. Large prospective studies have estimated the risks associated with exogenous risk factors (Table 11.1). Since effects of these risk factors accumulate over time, it follows – together with age-dependent alterations of cholesterol homeostasis, bile secretion and gallbladder motility – that the prevalence of stones increases with age. For example, in Germany, the maximum prevalence rate of symptomatic gallstones of 57% was observed in women aged 70–79 years, estimated based on previous cholecystectomy and abdominal ultrasound [12].

Associations between multiple lithogenic (that is, promoting the formation of stones in an organic body) gene variants and gallstone formation have been observed, indicating that gallstone disease is a polygenic complex disorder. Quantitative trait locus analysis in inbred strains of mice fed a lithogenic diet containing a supraphysiological concentration of cholesterol has identified at least 25 lithogenic genes to date, including the hepatobiliary cholesterol transporter Abcg5/g8 [2]. The disease susceptibility loci have been mapped by identifying the genomic regions where the distribution of marker genotypes correlates with differences in stone phenotypes in experimental crosses of inbred mouse strains.

A well-known genetic risk factor in humans is sex, with women developing significantly more gallstones than men. This difference is, at least in part, due to the increased incidence of gallstones in pregnancy (5%). Estrogens induce hepatic cholesterol synthesis and secretion, and progesterone causes gallbladder hypomotility [2]. Genome-wide association studies (GWAS) in humans identified a single variant of the hepatobiliary cholesterol transporter ABCG8 (p.D19H) as the most frequent genetic risk factor for gallstone disease in humans [18]. About 5% of the European populations carry the p.D19H mutation of the ABCG8 gene. Subsequent studies showed that, for example, obese women over the age of 60 years who are homozygous carriers of the p.D19H risk allele have a 13% absolute 10-year risk of symptomatic gallstone disease compared to 2–4% in non-carriers in the same risk stratum [19]. The genetic association was replicated in multiple international cohorts (Table 11.2); hence this genetic factor represents a common gallstone risk factor worldwide [20]. Functional in vitro studies [21] and measurements of phytosterol and cholesterol precursor concentrations demonstrate that individuals predisposed to gallstone disease display increased biliary output of cholesterol in the setting of relatively low intestinal cholesterol absorption, indicating enhanced whole-body sterol clearance (Fig. 11.2). The comparison of serum sterols showed lower levels of phytosterols, which represent surrogate markers for intestinal cholesterol absorption and higher levels of cholesterol precursors reflecting cholesterol synthesis in gallstone disease patients than in controls [22]. An ethnic gradient in the ratios of phytosterols to cholesterol precursors is also apparent (Germans > Hispanics > Amerindians). Together with the common Gilbert promoter variant of the UDP glucuronosyl transferase gene (UGT1A1), which appears to be an additional risk factor predominantly in men, both genes confer about 15% of the population attributable gallstone risk [23]. The UGT1A1 variant might promote the formation of the bilirubin nidus of cholesterol gallstones.

A large meta-analysis of GWAS [24] identified additional susceptibility loci for gallstone disease, all of which confer low additional risk (Table 11.3). They might affect the rate-limiting enzyme of bile salt synthesis (cholesterol 7α-hydroxylase) and a sulfo-conjugation enzyme for bile salts as well as a glucokinase regulator known to be associated with diabetes and glycaemic traits. Of note, the recent GWAS in a Latin Chilean population comprising 529 cases (489 women) and 566 controls confirmed the previously known ABCG5/G8 association but also revealed a highly significant signal inside the GPR30 gene, which encodes the a G protein-coupled transmembrane estrogen receptor expressed in liver and gallbladder, in women [25]. The roles of ELMO1, TM6SF4 and TRAF3 in gallstone pathobiology have yet to be explored further.

In addition, rare mutations in ABCB4, ABCB11, CFTR (cystic fibrosis transmembrane conductance regulator, also known as ABCC7) or the CYP7A1 gene cause gallstone formation by leading to altered bile composition. A specific subgroup of patients with gallstones have low phospholipid associated-cholelithiasis (LPAC) syndrome. LPAC syndrome is defined by early-onset cholelithiasis (< 40 years), concurrent gallbladder, bile duct and/or intrahepatic cholesterol gallstones and recurrence of biliary symptoms after cholecystectomy [26]. LPAC syndrome is caused by mutations of the ABCB4 gene and is part of the phenotypic spectrum of ABCB4 deficiency, which also comprises severe cholestatic diseases in children [5]. Interestingly a recent GWAS for gallstone disease in 8,258 Icelandic patients, for whom discharge diagnoses were available from the Landspítali University Hospital in Reykjavík, revealed a significant association with ABCB4. The two ABCB4 mutations that were significantly associated with gallstones at the genome-wide level are the missense single nucleotide polymorphism p.G622E and the frameshift insertion p.L445GfsX22, which conferred odds ratios for gallstones of 2.74 and 3.10, respectively [27]. Interestingly in the Iceland population, ABCB4 variants were not only associated with intrahepatic cholestasis of pregnancy but with liver cirrhosis and cancer [27].