SI and irritable bowel syndrome: Despite demonstrated heritability, however, previous IBS candidate-gene studies lacked power and replication, except for serotonin, sucrase-isomaltase and ion channel genes.10, 11, 12, 13 Recently, well-powered genome-wide association studies (GWAS) of IBS and endophenotypes (eg, gut motility) have emerged, which made use of genotypic and health-related data from large cohorts and population-based biobanks.9