Identification of Novel Molecular Defects in Chronic Intestinal Pseudo-Obstruction (CIPO). G. Romeo1, E. Bonora1, F. Bianco1, L. Cordeddu2, M. D'Amato2, G. Lindberg2, M. Bamshad3, D. Nickerson3, Z. Mungan4, K. Cefle4, S. Palanduz4, S. Ozturk4, T. Ozcelik5, A. Gedikbasi6, V. Stanghellini1, R. Cogliandro1, E. Boschetti1, C. Graziano1, M. Seri1, R. De Giorgio1, University of Washington Center for Mendelian Genomics (UW CMG) 1) Medical Gen Unit, Univ Bologna, Bologna, Italy; 2) Karolinska Institutet, Stockholm, Sweden; 3) University of Washington, Seattle, U.S.A; 4) University of Istanbul, Istanbul, Turkey; 5) Bilkent University, Ankara, Turkey; 6) Bakirkoy Sadi Konuk Hospital, Istanbul, Turkey.
INTRODUCTION: CIPO is characterized by severe impairment of gut motility mimicking a mechanical sub-occlusion in the absence of occluding causes. Although most patients are sporadic, some CIPO cases show familial clustering with a likely genetic origin. We wanted to identify the gene involved in a previously studied large Turkish consanguineous pedigree with recurrence of CIPO together with megaduodenum, Barret esophagus and cardiac anomalies (MIM # 611376) and test at the same time whether the genetic alterations found in that pedigree may have any implication in sporadic CIPO. RESULTS: WES analysis revealed a novel homozygous mutation, c.1864 G>A, p.622 Ala>Thr in RAD21 in the consanguineous Turkish pedigree where we had previously mapped CIPO on 8q23-q24 using homozygosity mapping 1. RAD21 belongs to the cohesin complex regulating cell replication and gene expression. The reported change cosegregated with the disease and was not detected in 1000 Turkish control chromosomes. PolyPhen-2 predicted it as probably damaging (HumDiv score: 0.999), since it resides in a conserved position. RAD21 screening in 12 Swedish and 24 Italian well-characterized sporadic CIPO patients did not show any coding mutation. However, we established a relationship between RAD21 and sporadic CIPO starting from our finding related to the expression of APOB 2. APOB mRNA and protein levels were found to be increased in CIPO patients vs. controls. In silico analysis of the human APOB promoter identified three RAD21-putative binding sites. EMSA with anti-RAD21 antibodies showed that RAD21 binds to these regions. A significant increase in APOB and RAD21 immunoreactive cells was also detected in the lamina propria of gut biopsies of CIPO patients vs. controls. CONCLUSION: We identified a novel mutation of RAD21 in a familial syndromic form of CIPO and an altered expression of RAD21 and APOB in sporadic CIPO. These previously uncharacterized pathways contribute to clarify the pathogenesis of CIPO and bear clinical implications for the diagnosis and prognosis of this disabling condition. ACKNOWLWDGEMENT: Sequencing was provided by the University of Washington Center for Mendelian Genomics (UW CMG) funded by NIH grant 1U54HG006493 to Drs. Debbie Nickerson, Jay Shendure and Michael Bamshad. REFERENCES: 1. Degl'Incerti et al Eur J Hum Genet 15, 889-897, 2007; 2. Evangelisti et al Neurogastroenterology & Motility, 24, 497-508, 2012.
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