The time has come for NOD2/CARD15 testing for families with Crohn's disease: pro

Estimating risks of common complex diseases across genetic and environmental factors: the example of Crohn disease

BACKGROUND

Progress has been made in identifying mutations that confer susceptibility to complex diseases, with the prospect that these genetic risks might be used in determining individual disease risk.

AIM

To use Crohn disease (CD) as a model of a common complex disorder, and to develop methods to estimate disease risks using both genetic and environmental risk factors.

METHODS

The calculations used three independent risk factors: CARD15 genotype (conferring a gene dosage effect on risk), smoking (twofold increased risk for smokers), and residual familial risk (estimating the effect of unidentified genes, after accounting for the contribution of CARD15). Risks were estimated for high-risk people who are siblings, parents and offspring of a patient with CD.

RESULTS

The CD risk to the sibling of a patient with CD who smokes and carries two CARD15 mutations is approximately 35%, which represents a substantial increase on the population risk of 0.1%. In contrast, the risk to a non-smoking sibling of a patient with CD who carries no CARD15 mutations is 2%. Risks to parents and offspring were lower.

CONCLUSIONS

High absolute risks of CD disease can be obtained by incorporating information on smoking, family history and CARD15 mutations. Behaviour modification through smoking cessation may reduce CD risk in these people.

Attitudes toward genetic testing in patients with inflammatory bowel disease

OBJECTIVES

Significant progress has been observed in our understanding of the role of genetics in inflammatory bowel disease susceptibility and phenotype. The clinical role of genetic testing for inflammatory bowel disease is not well developed, but may become important as more susceptibility genes are found. The aim of this study was to evaluate the attitudes of patients with inflammatory bowel disease toward genetic testing.

METHODS

Two hundred and fifty patients (108 ulcerative colitis, 142 Crohn's disease) attending the outpatient clinic completed a questionnaire regarding clinical and family history data, as well as their attitudes toward genetic testing for inflammatory bowel disease.

RESULTS

Ninety percent (225/250) of all patients expressed an interest in undergoing genetic testing themselves, with 87.6% (219/250) also expressing a desire for their children to be tested. Although the proportion of ulcerative colitis and Crohn's disease patients interested in testing was similar, levels of interest decreased as the predictive value of a putative genetic test decreased. A comparable proportion of those with [80/86 (93.0%)] and those without [145/164 (88.4%)] a family history of inflammatory bowel disease expressed an interest in genetic testing. More patients who had received immunomodulating or biologic therapies [123/128 (96.1%)], however, wished to undergo testing than those who had not received these medications [78/93 (83.9%; P<0.01)].

CONCLUSION

Patients with inflammatory bowel disease have a high level of interest in genetic testing, both for themselves and for their children, and this will have an impact upon the provision of genetic services as progress is made toward defining a clinical role for inflammatory bowel disease susceptibility genes.

A population-based case-control study of CARD15 and other risk factors in Crohn's disease and ulcerative colitis

OBJECTIVES

Multiple established Crohn's disease (CD) and ulcerative colitis (UC) risk factors including family history, tobacco use, Jewish ethnicity, urban residency, and CARD15/NOD2 mutations have been evaluated singly and in hospital-based observational studies. The goal of this study was to assess the relative contributions of all these risk factors jointly in a nonreferral, population-based cohort derived from a population epidemiologic database.

METHODS

CD (N = 232) and UC (N = 121) subjects were ascertained from our population-based IBD Registry derived from Manitoba Health, the single provincial insurer. Healthy controls (HC) (N = 336) were recruited via a 10:1 mailing matched for age, sex, and postal code. Ethnicity, tobacco use, family history, residency, and CARD15/NOD2 genotype status were determined.

RESULTS

In both univariate analyses and analyses adjusted for all risk factors, CD was influenced independently by CARD15/NOD2 heterozygote and homozygote/compound-heterozygote status (adjusted odds ratios [OR] 3.7 and 40.0, respectively), Jewish ethnicity (OR 18.5), CD family history (OR 6.2), and smoking (OR 3.0 current and 1.7 ex-smoker, respectively). Penetrance for homozygote/compound-heterozygotes was 4.9%, heterozygotes 0.54%, and wild types 0.184%. Population attributable risk for CARD15 was 26.7% and current tobacco use was 46.8%. A tobacco-CARD15 interaction was not observed. UC was influenced by Jewish ethnicity (OR 37.1), and by family history (OR 2.6), ex-smoker status (OR 1.9), and CARD15/NOD2 heterozygote or homozygote/compound-heterozygote status (OR 1.9 and 6.4, respectively) in adjusted analyses only.

CONCLUSIONS

CARD15/NOD2, family history, smoking, and Jewish ethnicity are independent risk factors for CD. Examination of these risk factors together in a single population-based cohort has provided initial data for population epidemiological characterization and genetic counseling uses.