Familial Risk of Inflammatory Bowel Disease Continues to Third Generation

By Anne Harding

NEW YORK (Reuters Health) - First-, second-, and third-degree relatives of people with inflammatory bowel disease (IBD) have a significantly increased risk of developing the disease themselves, according to a new study of the entire Danish population.

"In general, first-degree relatives of IBD cases had seven to eight times increased risk of contracting IBD, compared with sporadic cases," Dr. Frederik Trier Moller, of Statens Serum Institute in Copenhagen, told Reuters Health by email. "Further, this risk was most increased in early life."

Studies looking at familial IBD risk have found an increased likelihood of the disease in first-degree relatives of patients, but the size of this increase and the risk for more distant relatives is not as clear, Dr. Moller and colleagues note in their report, published online March 24 in the American Journal of Gastroenterology.

The researchers looked at data for the entire population of Denmark for 1977-2011, nearly 8.3 million people, including 45,780 people with IBD. The study period spanned 200 million person-years.

First-degree relatives of patients with Crohn's disease (CD) had an incidence rate ratio (IRR) of 7.77 of having the disease themselves. The IRR came to 2.44 for second-degree relatives of patients with CD and 1.88 for third-degree relatives. The increased risk of ulcerative colitis (UC) was less pronounced for relatives of people with CD.

Among UC patients, the IRR was 4.08 for their first-degree relatives, 1.85 for their second-degree relatives, and 1.51 for their third-degree relatives. The UC patients' relatives' increased risk for CD was not as pronounced.

Up to 12% of people with CD and 9% of those with UC have a relative with the same disease, Dr. Moller and his team wrote. Family members' risk was particularly high for younger relatives, they add, which suggests that shared environment may also contribute to this risk, as well as genetic factors.

"While the rate ratios presented may be more generalizable, the presented absolute risk estimates are applicable mainly in a setting with prevalence and incidence data similar to the Danish numbers," Dr. Moller said.

According to the researchers, the findings may help pave the way for efforts to prevent IBD in high-risk individuals. "Making statements about the future is always precarious," Dr. Moller noted. "Nevertheless, I believe studies such as the GEM study, IBD Character, as well as emerging twin studies and international IBD consortiums, are likely to produce targets for metagenomic prevention approaches in a not-so-distant future."

This study was supported by Region of Southern Denmark, University of Southern Denmark, Hospital of Southern Jutland and Beckett foundation. One author reported being an adviser for member of advisory board for MSD/Merck and Janssen.

SOURCE: https://bit.ly/1cdxu8w

Am J Gastroenterol 2015.

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