The ITGB2 immunomodulatory gene (CD18), enterocolitis, and Hirschsprung's disease.
Hirschsprung's disease (HSCR)-associated enterocolitis (HAEC) remains a major contributor to morbidity and mortality associated with HSCR, being sometimes difficult to diagnose in its subclinical form. Its pathogenesis appears to include impaired local defense mechanisms as well as dysfunctional immune response and leukocyte function. In this context, the ITGB2 (CD18) immunomodulation-related gene is a possible candidate in HAEC pathogenesis as it codes for the beta-subunit of leukocyte adhesion molecule lymphocyte function-associated antigen 1, which has an established role in T-cell development and function. ITGB2/CD18 has also been linked to chronic colitis in both human and animal models involving defense mechanisms within colonic mucosa. There is therefore a fairly compelling case for the potential involvement of the ITGB2 (CD18) in HAEC pathogenesis.


OBJECTIVE
The aim of this study was to investigate the ITGB2 immunomodulatory gene (CD18) in a cohort of patients with HSCR and explore its correlation with enterocolitis.


METHODS
Screening for mutations of the ITGB2 (CD18) gene was performed on DNA extracted from colonic tissue samples and whole blood of 33 HSCR patients controlled by analysis of 60 unaffected individuals from the diverse South African population. Polymerase chain reaction amplification was performed, followed by heteroduplex single-strand conformation polymorphism analysis and bidirectional semiautomated DNA sequencing analysis.


RESULTS
Heteroduplex single-strand conformation polymorphism banding patterns of the ITGB2 gene showed variations in 22 HSCR patients (66%), 13 of whom had severe episodes of HAEC, and 6 others had milder symptoms. Of the 13, 6 (46%) had Down's syndrome-associated HSCR. Genetic variations included 1 mutation (D77N), 2 known (V367, V441), and 4 novel polymorphisms (-111T/C, 24G/T, 295G/A, 892A/G). Significant associations were identified in the exon 5' untranslated promotor region (P < .0001), exon 10 (P < .0007), and the 3' untranslated promotor region at 122G/A (P < .0001) and 370 G/T positions (P = .04). Those regions of the gene most frequently associated with HAEC and severe symptoms were those with more than 1 variant identified in the gene.


CONCLUSIONS
This study shows that impaired CD18 leukocyte and T regulatory cell regulation can probably be linked to a genetic (ITGB2) predisposition to HAEC. It furthermore provides a possible genetic link to HAEC patient selection, identifying a potential molecular target.
Moore
Sam W
SW
Division of Paediatric Surgery, Faculty of Health Sciences, University of Stellenbosch, PO Box 19063, 7505 Tygerberg, South Africa. swm@sun.ac.za <swm@sun.ac.za>
Sidler
Daniel
D
Zaahl
Monique G
MG
D000483:Alleles; D018821:CD18 Antigens / Q000235:genetics*; D016022:Case-Control Studies; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D004760:Enterocolitis / Q000150:complications / Q000235:genetics* / Q000503:physiopathology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D014644:Genetic Variation; D006627:Hirschsprung Disease / Q000150:complications / Q000235:genetics* / Q000503:physiopathology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D016169:Lymphocyte Function-Associated Antigen-1 / Q000235:genetics; D008297:Male; D009154:Mutation; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D011336:Probability; D012016:Reference Values; D012680:Sensitivity and Specificity
D018821:CD18 Antigens; D016169:Lymphocyte Function-Associated Antigen-1