Genetics and gastrointestinal symptoms.

Gastrointestinal (GI) symptoms including nausea, vomiting, diarrhea, constipation, abdominal discomfort/pain, and heartburn are ubiquitous and as such are often the focus of nursing interventions. The etiologies of these symptoms include GI pathology (e.g., cancer, inflammation), dietary factors (e.g., lactose intolerance), infection, stress, autonomic nervous system dysregulation, medications, as well as a host of diseases outside the GI tract. This review focuses on a common condition (irritable bowel syndrome [IBS]) that is linked with both bowel pattern and abdominal discomfort/pain symptoms. Family and twin studies give evidence for a role of genetic factors in IBS. Whether genes are directly associated with IBS or influence disease risk indirectly by modulating the response to environmental factors remains unknown at this time. Given the multifactorial nature of IBS, it is unlikely that a single genetic factor is responsible for IBS. In addition, gene-gene (epistatic) interactions are also likely to play a role. Four genes coding for proteins involved in neurotransmission (i.e., the serotonin reuptake transporter [SERT], tryptophan hydroxylase [TPH], alpha2-adrenergic receptor [alpha2-ADR], catechol-o-methyl transferase [COMT]) and their potential relevance to GI symptoms and IBS will be reviewed. Further research using genome-wide association approaches with samples well characterized by ethnicity and standardized symptom subgrouping is needed.