IBS -- with symptoms including cramps, abdominal pain, bloating, constipation and diarrhea -- affects twice as many women as men, the agency said in a statement.

Amitiza's safety and effectiveness were evaluated in two studies involving 1,154 people with IBS-C, more than 90 percent of whom were women. More people treated with the drug said their symptoms were moderately or significantly relieved than those who took a non-medicinal placebo.

The effectiveness of the drug in men wasn't conclusively established during clinical testing, the FDA said.

Common side effects included nausea, diarrhea and abdominal pain. More serious yet rarer adverse reactions could include urinary tract infections, dry mouth, fainting, swelling of the extremities, difficulty breathing and heart palpitations, the agency said.

The 8-microgram dose is meant to be taken twice daily with food and water. Amitiza is produced by Maryland-based Sucampo Pharmaceuticals and Illinois-based Takeda Pharmaceuticals North America.

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The FDA has more about this drug's history.

MONDAY, April 28 (HealthDay News) -- The inflammatory bowel diseases ulcerative colitis and Crohn's disease appear to share several genetic variants and risk factors, two new British studies suggest.

Though similar in many ways, the two diseases are distinct, and scientists have been trying to pinpoint the underlying relationship between them to improve their understanding of and treatment for both. The latest findings, expected to be published online in the April 27 issue of Nature Genetics, may be a significant step forward.

Ulcerative colitis and Crohn's disease affect one in 250 individuals of Northern European descent. Ulcerative colitis is a common inflammatory bowel disease, while Crohn's disease is a related, but chronic disorder of the intestine.

In the first study, researchers identified ECM1, a gene variant that encodes a protein secreted by cells to activate a key immune regulator as tied to the risk of colitis. They also found that five genes previously linked to the probability of developing Crohn's disease are also common to ulcerative colitis, while three others are not.

In the second study, several of 50 previously reported susceptibility loci for Crohn's disease were deemed risk variants for both diseases. Three others were found to be specific to Crohn's disease and three specific to ulcerative colitis.

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The American Academy of Family Physicians has more about inflammatory bowel diseases.

Up to 30 percent of people in the United States with inflammatory bowel disease (IBD) have a family history of the condition, and about 25 percent of those families have histories of both Crohn's and ulcerative colitis, according to background information in this multi-center American and Canadian study. People of Ashkenazi Jewish (eastern European) descent are at least twice as likely to develop a form of IBD and are more likely to have a family history of IBD.

Crohn's is most frequently characterized by inflammation of the final section of the small bowel and parts of the colon, while ulcerative colitis involves inflammation of the internal lining of the rectum and colon.

In this study, researchers looked for DNA variations called single nucleotide polymorphisms (SNPs) in 993 families (244 of whom were Ashkenazi Jews) with Crohn's and ulcerative colitis.

Among those of Ashkenazi Jewish descent, the researchers found evidence of genetic markers for familial Crohn's disease on previously identified areas of chromosomes 1 and 3. They also pinpointed a previously unidentified region of chromosome 13 in both Jewish and non-Jewish families with Crohn's.

The researchers also identified areas on chromosomes 2 and 19 that may be related to ulcerative colitis in both groups.

The findings were published in the March issue of Genes and Immunity.

Until now, no gene regions implicated in IBD were specific to Ashkenazi Jews, and there was no genetic evidence to explain why they were twice as likely to develop the disorder, said study senor author Dr. Steven R. Brant, a gastroenterologist at Johns Hopkins.

"This increased risk for some Jewish people makes our study and results especially significant, since this is the first sample size of Jewish families, 244, that was large enough to identify novel gene regions for familial predisposition in this ethnic group," Brant said in a prepared statement.

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The American Academy of Family Physicians has more about IBD.

IBS occurs in about 15 percent of the U.S. population. Some studies have suggested that allergen exposure may lead to IBS symptoms in some patients, but the frequency hadn't been examined.

In this study, researchers looked at 125 adults and found the likelihood of IBS was much higher in patients with allergic eczema (3.85 times) and seasonal allergic rhinitis (2.67) times. They also found that IBS was 2.56 times more likely in people with depression.

"The reported presence of allergic dermatitis was highly correlated to the presence of IBS in our population," the study authors wrote. "In atopic disease, allergic dermatitis is the first step of the 'atopic' march.' In early childhood, AE (allergic eczema) is frequently associated with gastrointestinal dysfunction and food allergy. A clinical history of AE may be a useful marker for patients with gut hypersensitivity and atopic IBS."

The researchers also found that asthma and IBS were reported by 12 of 41 patients (29 percent), similar to findings in a previous study. The researchers proposed that "this subgroup of IBS (atopic IBS) be considered separately from patients with IBS without atopic symptoms, because they may have distinct pathophysiologic features and may benefit from specific therapeutic interventions."

The study was published recently in the Annals of Allergy, Asthma & Immunology.

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The U.S. National Institute of Diabetes and Digestive and Kidney Diseases has more about IBS.

Symptoms of IBS, which affects 10 percent to 15 percent of people in the United States, include gastrointestinal discomfort, diarrhea and constipation.

In this study, researchers from the University of California, Los Angeles, and the University of North Carolina used brain imaging to study female IBS patients and found that those with a background of abuse weren't able to switch off a pain modulation mechanism in the brain as effectively as those with no history of abuse.

The study was published in February's online edition of Gastroenterology.

Previous research has found that more than 50 percent of people with IBS have been physically or sexually abused at some point in their lives. The findings of this new study may help explain why this subset of IBS patients tend to suffer more pain and poorer health outcomes than other IBS patients.

The researchers said their study improves understanding of how IBS develops, and may help lead to new treatments.

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The American Academy of Family Physicians has more about IBS.