The goal of this observational genetic case-control study is to learn whether two specific genetic variants in ABCG8 and UGT1A1 are associated with gallstone disease after bariatric surgery. The study includes adults who have previously undergone bariatric surgery.

The main questions it aims to answer are whether the ABCG8 D19H variant and the UGT1A1 rs6742078 variant are associated with an increased risk of gallstone disease requiring cholecystectomy after bariatric surgery.

Researchers will compare patients who underwent bariatric surgery and later had their gallbladder removed because of gallstone disease with patients who underwent bariatric surgery but did not develop gallstone disease or undergo cholecystectomy during follow-up.

Participants will provide one blood sample for targeted genetic analysis and complete questionnaires about health, previous surgery, medication use, family history, and gastrointestinal quality of life. Relevant clinical information will also be collected from medical records.

Inclusion Criteria:

• Bariatric surgery

Exclusion Criteria:

• Gallstone disease or cholecystectomy prior to bariatric surgery

Adults who previously underwent bariatric surgery in the Region of Southern Denmark will be included. The study population consists of two groups: cases and controls.

Cases are patients who underwent bariatric surgery and subsequently underwent cholecystectomy due to gallstone disease.

Controls are patients who underwent bariatric surgery and have had at least five years of follow-up without registered gallstone disease or cholecystectomy.

All participants will be identified through hospital records in the Region of Southern Denmark. Participants will provide a blood sample for targeted genetic analysis of selected variants in ABCG8 and UGT1A1 and complete questionnaires on health, medication use, family history, and gastrointestinal quality of life.

Small study. Individual participant data will not be shared due to the sensitive nature of genetic and clinical data and restrictions under Danish data protection regulations. Aggregated results can be shared in publications and upon reasonable request, where legally and ethically permissible.