Histopathological Features of Monogenic Inflammatory Bowel Disease: Subanalysis of Systematic Review

Recent advances in genomic technology, such as next-generation sequencing, have made it possible to diagnose patients with a monogenic form of inflammatory bowel disease (IBD) where rare genetic variants appear to be driving the disease process. IBD because of variants transmitted by Mendelian inheritance patterns is described as “monogenic” IBD, as opposed to classical IBD.1Nambu R. et al.Front Pediatr. 2021; 22: 618918Crossref Scopus (2) Google Scholar We have previously reported our findings of a systematic review of monogenic IBD cases, demonstrating that monogenic IBD diagnosis and management is a challenging but important clinical problem across many age groups.2Nambu R. et al.Clin Gastroenterol Hepatol. 2022; 20: e653-e663Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar Several studies have shown that the histopathological features of monogenic IBD in very early onset are different from those of classical IBD.3Parente P. et al.Adv Anat Pathol. 2022; 29: 71-80Crossref PubMed Scopus (3) Google Scholar,4Conrad M.A. et al.J Crohns Colitis. 2019; 13: 615-625Crossref PubMed Scopus (22) Google Scholar In this study, we comprehensively reviewed histopathological features of monogenic IBD as a subanalysis of our systematic review and specifically investigated the relationship between the characteristic histopathological findings and the respective monogenic disorders that cause IBD. From 750 cases in a systematic review, we extracted only those cases in which pathologic findings were mentioned in detail (Supplementary Methods). The 315 included cases with monogenic IBD came from a total of 180 articles (Figure A1A). The cohort included 202 males, 99 females, and 14 with gender not reported. Infantile onset IBD (with disease onset less than 2 years of age) was the most common group (n = 144, 45.7%). On the other hand, 9.5% of patients (n = 30) developed IBD after 18 years of age (Figure A1B). This group covered 54 of the 75 genes known to be associated with monogenic IBD. The most reported gene was CYBB, followed by XIAP, TTC7A, IL10RA, and HPS1 (Figure A1C). The characteristic histopathological findings reported in each case of monogenic IBD are as follows (Figure and Table A1). Characteristic granuloma was reported in 100 cases with a high frequency in chronic granulomatous disease (CGD; n = 40, 72.7%; CYBB, NCF1, NCF4), followed by XIAP deficiency (n = 16, 47.1%; XIAP), Hermansky-Pudlak syndrome (HPS; n = 14, 73.7%; HPS1, HPS4), and Niemann-Pick disease type C (NP-C; n = 7, 87.5%; NPC1). Eosinophilic infiltration was shown in 61 cases and was more frequent in Loeys-Dietz syndrome (n = 4, 80%; TGFBR1, TGFBR2) and TTC7A deficiency (n = 17, 54.8%). In CGD, eosinophilic infiltration was reported in large numbers of cases but not at a high rate (n = 10, 18.1%; CYBB, NCF4). Epithelial cell apoptosis was seen in 55 patients with the highest frequency in TTC7A deficiency (n = 30, 96.7%; TTC7A). In trichohepatoenteric syndrome (n = 5, 60%; SKIV2L, TTC37), Hoyeraal-Hreidarsson syndrome (n = 8, 50%; DKC1, RTEL1), and RIPK1 deficiency (n = 3, 50%; RIPK1), epithelial cell apoptosis was reported at a high rate, whereas in XIAP deficiency (n = 6, 17.6%; XIAP) and IPEX-like syndrome (n = 5, 23.8%; LRBA, IL21, CTLA4) epithelial cell apoptosis was reported in large numbers but not at a high rate. Villous blunting was described in 30 cases with IPEX being the most frequent (n = 4, 50%; FOXP3), followed by IPEX-like syndrome (n = 10, 47.6%; LRBA, CTLA4, MALT1, STAT3 GOF). Pigmented macrophages were reported in 37 cases with CGD (n = 30, 54.5%; CYBB, NCF1) and HPS (n = 7, 36.8%; HPS1, HPS4). In this study, we define the characteristic histopathological findings that have been reported for each case of monogenic IBD by gene. Specific pathological findings may be useful in predicting the existence of monogenic disorder causing IBD when combined with clinical course and the result of molecular tests. Although some review articles have summarized the pathologic features of monogenic IBD, this is the first study to comprehensively analyze all previous reports and to clarify the gene-by-gene distribution of each monogenic IBD gene. Characteristic granuloma can be seen in the classical IBD, as Rubio et al5Rubio C.A. et al.J Clin Pathol. 2007; 60: 1268-1272Crossref PubMed Scopus (50) Google Scholar showed that 53.8% of the pediatric patients with CD had granulomas. Conrad et al4Conrad M.A. et al.J Crohns Colitis. 2019; 13: 615-625Crossref PubMed Scopus (22) Google Scholar reported that granulomas are not seen more frequently in very early onset IBD compared with older-onset pediatric IBD. In considering that monogenic IBD is more prevalent under the age of 6 years, when granuloma is seen in younger-onset IBD, molecular diagnostic tests that can differentiate CGD and XIAP deficiency, may be considered. The presence of pigmented macrophages along with granuloma further might help identify CGD (or HPS). Eosinophil infiltration is a common finding in classical IBD but appears to be more related to disease activity than IBD subtype.6Sarin S.K. et al.Dig Dis Sci. 1987; 32: 363-367Crossref PubMed Scopus (65) Google Scholar Epithelial cell apoptosis and villous blunting are generally not seen in classical IBD, but now we can say this is also a finding that can increase suspicion of monogenic IBD.7Gomez A.J. et al.Arch Pathol Lab Med. 2016; 140: 570-577Crossref PubMed Scopus (11) Google Scholar,8Kammermeier J. et al.J Crohns Colitis. 2017; 11: 60-69Crossref PubMed Scopus (82) Google Scholar Villous blunting is rarely seen in Crohn's disease but is more commonly related to celiac disease or congenital diarrhea and enteropathy.9Pallav K. et al.Aliment Pharmacol Ther. 2012; 35: 380-390Crossref PubMed Scopus (69) Google Scholar The mechanism of villous blunting seen among monogenic IBDs is unclear, although it was frequently found in IPEX or IPEX-like syndrome, implying a potential role for regulatory T lymphocytes. Interleukin (IL) 10 and IL-10-receptor-associated colitis, which has the largest number of reports in monogenic IBD, had no characteristic pathologic findings.2Nambu R. et al.Clin Gastroenterol Hepatol. 2022; 20: e653-e663Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar,10Glocker E.O. et al.N Engl J Med. 2009; 361: 2033-2045Crossref PubMed Scopus (1022) Google Scholar In addition, pathologic findings in many monogenic IBDs have simply not been reported or have been reported in very small numbers. Although the characteristic pathologic findings increase the suspicion of a specific monogenic IBD, they cannot be used to rule out the presence of a single genetic abnormality in the case. This study is limited mostly by the nature of systematic reviews. In most reports, negative findings are not described, and histopathology reporting is a non-standardized part of disease evaluation. This can lead to reporting bias. We excluded cases in which the pathologic findings were absent or vaguely described, again leading to potential bias for reporting of highly abnormal, rare findings. If a case was described ambiguously as IBD-like or acute chronic inflammation, the rates of characteristic findings reported in this study might have been overestimated. However, we have shown that certain histopathological findings are associated with some monogenic IBD diseases and can be used to support a suspicion of genetic abnormalities. However, there does not appear to be any pathognomonic or even highly specific histopathologic features that identify specific monogenic IBD diseases. For example, infants with typical pathologic features of CD should alert the clinician to IL-10R deficiency, and infants with atresia or stricturing disease and apoptosis should be screened for TTC7A deficiency. Further case reports and prospective observational studies are still required, but this study supports the need for early next-generation sequencing in patients where monogenic IBD and characteristic pathologic features. Download .docx (.43 MB) Help with docx files Supplemental Methods, Table A1 and Figure A1

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