Irritable Bowel Syndrome Lisa M Davis, PhD,1
Diagnostic Testing for Irritable Bowel Syndrome John Alsobrook II, PhD,2
Cole Harris, MS3
and Mark Pimentel, MD4
1. Vice President Product Development; 2. Vice President Clinical Laboratory Operations; 3. Vice President Discovery, Exagen Diagnostics, Albuquerque; 4. Director, Gastroenterology Motility Program, and Associate Professor of Medicine, Cedars-Sinai Medical Center
Abstract
Irritable bowel syndrome (IBS) is characterized by abdominal discomfort and disordered bowel function, and is considered a ‘functional’ disease with no physical or biochemical abnormalities observed on examination. The symptoms and etiology of IBS are heterogeneous, and the absence of a consistent disease biomarker has historically made IBS a diagnosis of exclusion. The Rome III criteria have emerged as a symptom-based diagnosis paradigm, although they have not been widely accepted in clinical practice. A positive diagnosis of IBS is critical to effective disease management. This report describes a simple blood-based IBS diagnostic assay based on gene expression measurements of a small set of genes, and includes a brief description of the gene discovery from a data set developed from inflammatory bowel disease (IBD) patients.
Keywords
Irritable bowel syndrome (IBS), gene expression microarrays, bioinformatic analysis of genomic data, IBS diagnosis, reverse transcription polymerase chain reaction (RT-PCR)
Disclosure: Lisa M Davis, PhD, John Alsobrook II, PhD, and Cole Harris, MS, are employees of Exagen Diagnostics. They each have less than a 5% interest in the company. Mark Pimentel, MD, is a Consultant for Salix Pharmaceuticals. He has received grants from Salix and Seaver Foundation. Cedars-Sinai has a licensing agreement with Salix. Received: March 16, 2011 Accepted: May 24, 2011 Citation: US Gastroenterology & Hepatology Review, 2011;7(1):27–30 Correspondence: Lisa M Davis, PhD, Exagen Diagnostics, Inc., 801 University Blvd SE, Albuquerque, NM 87106. E:
ldavis@exagen.com
Support: The publication of this article was funded by Exagen Diagnostics, Inc.
Irritable bowel syndrome (IBS) is a gastrointestinal disorder characterized by abdominal pain or discomfort, bloating, distension, and alterations in bowel habits with disordered defecation. It has been estimated that as much as 5–10% of the US population has IBS, with the prevalence higher among women than men.1
The syndrome is classified as a ‘functional’
disease because there is no obvious physical or biochemical defect identified on physical examination. The disease is subtyped into a diarrhea-predominant form (IBS-D), a constipation-predominant form (IBS-C), or a mixed form (IBS-M).2
IBS does not cause long-term damage
to the gastrointestinal tract, but the symptoms, which are chronic, intermittent, and typically begin in adolescence or young adulthood, can significantly degrade quality of life and activity level3 significant economic burden on the healthcare system.4–6
and create a There is no cure
for IBS although treatments involving pharmacotherapy, psychologic therapy, and dietary and behavior modifications are successful at alleviating symptoms.
IBS pathogenesis is not completely understood, but factors thought to contribute to the disorder include alterations in visceral sensations,7,8 gut motility,9,10
brain–gut interactions,11,12 psychologic factors.10,16 immune activation,13–15 and Evidence suggests that 5–30% of IBS cases are
the long-term consequence of an initiating bout of infectious gastroenteritis, although only 20–25% of gastroenteritis cases lead to IBS.17–19
Small intestinal bacterial overgrowth (SIBO) has also been © TOUCH BRIEFINGS 2011
Irritable Bowel Syndrome Treatments Treatments for IBS usually include diet modification, laxatives, antispasmodics, antidepressants, and tranquilizers. Surgery is almost never used to treat symptoms of IBS. Therapies aimed at relieving symptoms include bulking agents and osmotic and stimulant laxatives for IBS-C, and antidiarrheals, antispasmodics, and antidepressants for symptom and pain relief in IBS-D. Serotonin receptor antagonists and agonists are used to reduce visceral sensitivity and alter gastrointestinal transit times.21,22
without constipation.23
Antibiotic therapy has proven effective for IBS patients Other effective treatments include behavioral
therapies such as biofeedback, relaxation, and cognitive therapy.21
Irritable Bowel Syndrome Diagnosis As physical or organic abnormalities associated with IBS have not been observed, biochemical markers for a positive IBS diagnosis are not available. As such, IBS has been a diagnosis of exclusion, after eliminating other gastrointestinal disorders such as lactose intolerance, celiac disease, pathogenic gastroenteritis, and more serious conditions such as inflammatory bowel disease (IBD) and colon cancer. By contrast, the
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described in a significant number of patients with IBS, suggesting a role for bacteria in the etiology of IBS and an explanation for the common symptom of bloating.20
The post-infectious IBS and SIBO forms of IBS may have unique etiologies.
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