Prevalence and Predictors of Irritable Bowel Syndrome

Introduction 

Irritable bowel syndrome (IBS) is a clinical diagnosis characterized by the presence of abdominal pain or discomfort associated with altered bowel habits. Irritable bowels syndrome remains a medical challenge in the 21^st century due to the absence of confirmative investigation or biomarker for the diagnosis, and therefore, clinical diagnosis remains the major option.  It has three main sub-types, constipation-predominant IBS (C-IBS), diarrhea-predominant IBS (D-IBS) and IBS with mixed features of both diarrheas as well as constipation (M-IBS). Its pathophysiology and underlying mechanisms remain elusive. It is traditionally believed that IBS is a result of multiple factors including hypersensitivity of the bowel, altered bowel motility, inflammation, and stress. Functional gastrointestinal disorders, including irritable bowel syndrome (IBS), represent a significant burden of diseases globally. Irritable bowel syndrome (IBS) is the most common functional gastrointestinal disorder with worldwide prevalence rates ranging between 7%-21%, usually varying significantly between countries according to the diagnostic criteria used. Various diagnostic tools have been employed for the detection of IBS, including the Manning criteria, Rome I criteria and Rome II criteria. Currently, the Rome III criteria are the most common method for diagnosing IBS. Based on the Rome III criteria, the prevalence of IBS has been estimated to range from 10% to 15% in Western countries, whereas that reported in Asian countries ranged from 1% to 10%. According to doctors at King Abdullah Medical Complex in Saudi Arabia, IBS is highly influenced by demographic factors, particularly sex and age. IBS is more prevalent in females than in males and has an onset between late teens to twenties, decreasing with age. Women from developed countries are 2-4 times more likely to have IBS than men. Furthermore, evidence suggests a genetic role in the etiology of IBS, with 33% of patients with IBS reporting a positive family history. In addition to a genetic predisposition, IBS has also been linked to several dietary habits and psychological factors such as stress and anxiety. IBS is a complex functional gastrointestinal disorder that poses a great challenge to both, the affected patients and the physicians treating the ones affected by the prevalence rate of between 10-20 % worldwide.

It is pretty clear that IBS apparently has an impact on quality of life of those who suffer from it, and accounts for substantial amounts of health care resources, both in primary and specialist care. Although most persons with IBS do not consult physicians, the cost to society regarding direct medical expenses such as drug consumption and indirect costs, such as work absenteeism, is considerable. Moreover, IBS poses an economic burden on a country's health care system; the annual cost of diagnosing, treating and managing IBS in a country being in direct costs, and up to in indirect costs. They miss three times as many workdays and are more likely to report that they are too sick to work. IBS is not a grave condition; however, it does considerably reduce the quality of life of people afflicted with this syndrome. It interferes with their education, working ability and social life. 

 Early studies have shown familial aggregation of IBS suggesting shared genetic or environmental factors.

Literature Review

Many studies have evaluated the costly effects of IBS on psychological functioning, health care utilization, and work productivity; relatively few studies have focused on overall daily functioning in patients with IBS. Survey studies have shown that IBS patients report higher levels of difficulty in a broad range of daily activities. Activities that appear to be particularly impaired by IBS include Work, intimacy, recreation, personal relationships, and eating habits. However, these findings typically come from large survey studies. Although most clinicians who work with IBS would agree that many of their patients modify or limit certain activities due to IBS symptoms (or fear of symptoms), this has not been adequately measured or quantified in this population.

Numerous studies have evaluated the relationship between IBS and psychiatric status. Increasing evidence shows that compared with healthy subjects; IBS patients exhibit differences in brain imaging studies, which may suggest the biological association of the psychiatric conditions in IBS. Therefore, psychiatric commonalities may be one of the aspects worthy of IBS-related discussions. According to previous studies, nearly 60% of IBS patients experience major psychosocial problems. Researchers reported that following acute gastroenteritis, prior anxiety and depression might be risk factors for the subsequent development of post-infectious IBS. Also, high anxiety and depression scores have been reported in a post-infectious IBS population following initial infection. Therefore, exploring the psychological aspects of IBS is crucial for an obtaining clearer holistic understanding of the syndrome and for developing effective treatments.

Twin studies of IBS from different parts of the world have shown higher concordance rates among monozygotic twins than dizygotic twins, and thus suggesting a genetic component to this disorder. Multiple studies have tried to link single-nucleotide polymorphisms (SNPs) to IBS, but there is little evidence that these SNPs are functional. Various molecules have been considered and investigated by the researchers. Serotonin, a known neurotransmitter and a local hormone in the enteric nervous system, has been most extensively explored. At this time, the underlying gene pathways, genes and functional variants linked with IBS remain unknown and the promise of genetically-determined risk prediction and personalize medicine remain unfulfilled. However, molecular biological technologies continue to evolve rapidly, and genetic investigations offer much hope in the intervention, treatment, and prevention of IBS.

The expedition to find a genetic basis for IBS has included the vast array of studies ranging from epidemiological familial aggregation studies to gene polymorphism testing studies. Though these studies in several ways have shown the possible hereditary component of IBS, most of the studies have provided only weak evidence between the two. In the last decade, gene search studies have focused more on detecting gene polymorphisms. Historically, underlying pathophysiology is believed to be the interplay of the hypersensitive gut with the main contributions from psychological, social and environmental factors. The field of genetics exploring the underlying potential IBS genes is rapidly evolving. However, huge gaps in our understanding of this complex disorder remain and need further study. Genetic research efforts that are focused on studying the candidate gene polymorphism have so far provided the weak evidence at the best. Gene linkage studies and genome-wide association studies are needed to understand the deficiencies in our current knowledge. In the future studies, it will also be of importance to explore how the environment influences these newly discovered genes.