Genetic susceptibility in IBD: overlap between ulcerative colitis and Crohn's disease.
BACKGROUND
The etiology of ulcerative colitis (UC) and Crohn's disease (CD) involves both genetic and environmental components. Multiple UC and CD susceptibility genes have been identified through genome-wide association studies and subsequent meta-analyses. These studies have also highlighted the presence of genes common to both diseases, and shared with several other autoimmune disorders. The aim of this study was to identify single nucleotide polymorphisms (SNPs) recently identified by the International IBD Genetics Consortium (IIBDGC) demonstrating that highly significant associations with CD could also confer genetic susceptibility to UC.


METHODS
Statistical modeling was performed on 29 CD-associated SNPs. The study comprised of 1652 UC cases from the Australia and New Zealand IBD Consortium and 2363 Australian population-based controls.


RESULTS
After adjustment for multiple comparisons, only one SNP, rs3024505, was significantly associated with UC (P = 0.001). Independent chi-square analyses identified odds ratios of 2.22 (1.48-3.37) for the rare homozygous genotype, and 1.20 (1.06-1.35) for the minor allele. Five other SNPs demonstrated moderate to weak associations with UC.


CONCLUSIONS
Of the 29 SNPs conferring high genetic susceptibility to CD, 28 were not associated with UC, thus indicating that for this SNP set there is a low level of overlap between the two major forms of IBD. Only one SNP, rs3024505 (Chr 1q32.1, upstream of IL10), was associated with susceptibility to UC. The identification of this SNP replicates a finding from Franke et al (2008), where the rs3024505 SNP was strongly associated with UC across multiple European populations.
The Australian E-Health Research Centre, Queensland, Australia.
James D
JD
Doecke
Lisa A
LA
Simms
Zhen Zhen
ZZ
Zhao
Ning
N
Huang
Katherine
K
Hanigan
Krupa
K
Krishnaprasad
Rebecca L
RL
Roberts
Jane M
JM
Andrews
Gillian
G
Mahy
Peter
P
Bampton
Peter
P
Lewindon
Timothy
T
Florin
Ian C
IC
Lawrance
Richard B
RB
Gearry
Grant W
GW
Montgomery
Graham L
GL
Radford-Smith
D001315:Australia; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D003093:Colitis, Ulcerative / Q000235:genetics*; D003424:Crohn Disease / Q000235:genetics*; D056726:Genetic Association Studies; D005819:Genetic Markers; D020022:Genetic Predisposition to Disease; D006801:Humans; D016753:Interleukin-10 / Q000235:genetics; D016014:Linear Models; D015999:Multivariate Analysis; D009520:New Zealand; D016017:Odds Ratio; D020641:Polymorphism, Single Nucleotide
D005819:Genetic Markers; C508609:IL10 protein, human; D016753:Interleukin-10