Linkage heterogeneity for the IBD1 locus in Crohn's disease pedigrees by disease onset and severity.
OBJECTIVE
There is evidence for the IBD1 Crohn's disease (CD) susceptibility locus on chromosome 16 in several but not all populations studied. Genetic and phenotypic heterogeneity may underlie ability to replicate IBD1. We determined if age and severity stratification could identify a clinical subgroup at risk for IBD1.


METHODS
Linkage analysis at microsatellites spanning chromosome 16 was performed in 2 groups of CD pedigrees: group 1, 57 pedigrees with at least one affected relative classified as having "severe" disease, by history of surgical resection or immunomodulator therapy, and with disease diagnosed before age 22; and group 2, 33 pedigrees with no history of early-onset, severe CD.


RESULTS
Group 1 pedigrees demonstrated genomewide significant linkage evidence for the IBD1 locus (nonparametric multipoint logarithm of the odds [Mlod], 3.84; P = 1.3 x 10(-5)) with linkage evidence greater than all 90 pedigrees (Mlod, 2.12; P = 9.0 x 10(-4)). Group 2 pedigrees had near zero nonparametric 2-point and Mlod scores for the IBD1 region. Heterogeneity between groups 1 and 2 was significant (P = 0.002).


CONCLUSIONS
Presence of early-onset, more severe CD identifies pedigrees at high risk for IBD1. These pedigrees will have more power to refine the IBD1 locus and identify the causative gene.
Brant
S R
SR
Harvey M. and Lyn P. Meyerhoff Inflammatory Bowel Disease Center, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Panhuysen
C I
CI
Bailey-Wilson
J E
JE
Rohal
P M
PM
Lee
S
S
Mann
J
J
Ravenhill
G
G
Kirschner
B S
BS
Hanauer
S B
SB
Cho
J H
JH
Bayless
T M
TM
D000328:Adult; D017668:Age of Onset; D002885:Chromosomes, Human, Pair 16 / Q000235:genetics*; D003424:Crohn Disease / Q000453:epidemiology* / Q000235:genetics* / Q000503:physiopathology; D005260:Female; D008040:Genetic Linkage; D014644:Genetic Variation; D006801:Humans; D008126:Lod Score; D008297:Male; D010375:Pedigree; D012720:Severity of Illness Index