Search

The etiology of gallstone disease in humans is complex, since multiple genes and gene-gene interactions might all contribute to the formation of gallstones. Due to the limitations of genetic analysis in humans, important information on gallstone genes derives from animal studies, in particular crossbreeding experiments in inbred mouse strains that differ in genetic susceptibility to gallstone formation. In the existing work, we analyzed genetic variations (polymorphisms) in gallstone candidate genes in an association study with 184 matched pairs of gallstone carriers (cases) and healthy controls. For the selection of suitable candidate genes, we employed the murine 'gallstone map' (Lammert et al. Gastroenterology 2001;120:221-238). Within the Lith1 locus, the orthologous genes of the LDL receptor related protein 2 (LRP2) and the bile salt export pump (ABCB11) were tested. Further candidate genes included hepatic lipase (LIPC) in the Lith5 locus and the hepatic HDL receptor (SRB1) known to be associated with serum levels of HDL cholesterol, the major source of biliary cholesterol. In addition, established human candidate genes like the apolipoprotein E (APOE) and the cholesteryl ester transfer protein (CETP) were included in the study.Suitable single nucleotide polymorphisms (SNPs) were identified by database searches (NCBI genbank, JSNP database, HGV base), based on genomic localizations, allele frequencies and functional relevance. For genotyping, different methods were employed, including restriction fragment length polymorphism analysis, direct DNA sequencing, SNaPshot mini-sequencing and TaqMan assays, which proved to be most reliable in our study. The genetic analysis revealed that none of the polymorphisms were directly associated with the presence of gallstones. However, several genetic associations with lithogenic risk factors could be demonstrated. Significant associations were identified for SNPs in the ABCB11, APOE, CETP, LIPC, LRP2 and SRB1 genes and body mass index, total serum cholesterol and HDL cholesterol concentrations as well as serum triglyceride levels. This study identifies for the first time an association between human genes and lithogenic risk factors. It remains to be investigated whether additional polymorphisms or haplotypes of human genes or gene-gene interactions determine gallstone formation. The identification of the whole ensemble of lithogenic genes will contribute to the design of new strategies for prevention and therapy of this exceptionally common digestive disease.