Hirschsprung’s disease: clinical dysmorphology, genes, micro-RNAs, and future perspectives

Review nature publishing group Hirschsprung’s disease: clinical dysmorphology, genes, micro-RNAs, and future perspectives Consolato Maria Sergi1,2,3, Oana Caluseriu3,4, Hunter McColl3 and David D. Eisenstat3,4 On the occasion of the 100th anniversary of Dr. Harald Hirschsprung’s death, there is a worldwide significant research effort toward identifying and understanding the role of genes and biochemical pathways involved in the pathogenesis as well as the use of new therapies for the disease harboring his name (Hirschsprung disease, HSCR). HSCR (aganglionic megacolon) is a frequent diagnostic and clinical challenge in perinatology and pediatric surgery, and a major cause of neonatal intestinal obstruction. HSCR is characterized by the absence of ganglia of the enteric nervous system, mostly in the distal gastrointestinal tract. This review focuses on current understanding of genes and pathways associated with HSCR and summarizes recent knowledge related to micro RNAs (miRNAs) and HSCR pathogenesis. While commonly sporadic, Mendelian patterns of inheritance have been described in syndromic cases with HSCR. Although only half of the patients with HSCR have mutations in specific genes related to early embryonic development, recent pathway-based analysis suggests that gene modules with common functions may be associated with HSCR in different populations. This comprehensive profile of functional gene modules may serve as a useful resource for future developmental, biochemical, and genetic studies providing insights into the complex nature of HSCR. T he enteric nervous system (ENS) is recognized as a distinct third portion of the autonomic nervous system, which also includes the sympathetic and parasympathetic systems (1). The ENS is involved in peristalsis and, singularly, other spontaneous movements still persist following its isolation from all nervous inputs (2–4). The interstitial cells of Cajal are crucial in mediating nervous impulse onto smooth muscle cells acting as the intrinsic pacemaker of the bowel, while the ENS controls the continuous influence of the sympathetic and parasympathetic systems. The cholinergic (postganglionic) parasympathetic neurons increase peristalsis, secretions, and vasodilation, while the noradrenergic (postganglionic) sympathetic fibers project onto the submucosal and myenteric plexuses, where they play an inhibitory effect on the cholinergic neurons promoting an inhibition of peristalsis and secretions and stimulation of vasoconstriction (5). Parasympathetic fibers reach the gut via vagal nerves to celiac and superior mesenteric plexuses to over the mid-transverse colon, while the rest of the gut is supplied by fibers arising from pelvic splanchnic nerves via the sacral nerves 2–4 going through the pelvic plexus (5). Hirschprung’s disease (HSCR; MIM# 142623), one disorder of the ENS, is a rare congenital developmental disorder of the gastrointestinal tract characterized by a failure of vagal system derived enteric neural crest (NC) cells (ENCC) (neurocristopathy) to fully migrate cranio-caudally during embryonic development and adequately colonize the entire gut, leaving an aganglionic portion of variable length (6–9). Although original studies suggested colonization of the entire length of the human gut by enteric neural precursors is not complete until the 12th week of gestation, more recent studies seem to support complete colonization by the 7th week, which corresponds more closely with data obtained from animal models as well (10). HSCR is named after Dr. Harald Hirschsprung who first described this phenotype at “The Queen Louise Hospital for Children” in Copenhagen, Danemark. Aganglionosis is defined as the absence of ganglion cells in the myenteric and submucosal plexuses of the intestinal wall with concomitant hypertrophy of parasympathetic nerve fibers (11,12) (Figure 1). When suspected, HSCR is diagnosed by standard histopathological evaluation with or without auxiliary special stains or immunohistochemistry that confirms the diagnosis following biopsy of the distal rectum (Figure 1a–c). Expression of calretinin, a vitamin D–dependent calcium-binding protein found in ganglion cells and nerves, has been described as an adjunctive or primary diagnostic test on gut biopsy specimens in HSCR with lack of specific calretinin staining confirming the diagnosis of aganglionosis (Figure 1d) (8). Classifying HSCR clinically is not an easy task, because the nervous system colonization failure may be variable or discontinuous (9,13–15). Three phenotypes are usually recognized, including (i) total colonic aganglionosis (TCA), which involves the entire colon which is aganglionic with a potential proximal extension into varying lengths of small bowel (usually no more than 50 cm of The first two authors contributed equally to this work. 1 Department of Orthopedics, Wuhan University of Science and Technology, Hubei, P.R. China; 2Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada; 3Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada; 4Department of Medical Genetics, University of Alberta, Edmonton, Alberta, Canada. Correspondence: Consolato Maria Sergi () Received 24 June 2016; accepted 5 September 2016; advance online publication 2 November 2016. doi:10.1038/pr.2016.202 Copyright © 2017 International Pediatric Research Foundation, Inc. Volume 81 | Number 1 | January 2017      Pediatric Research  177 Review Sergi et al. a b c d Figure 1. Ganglion cell maturation and Hirschsprung’s disease. (a) The myenteric plexus of the distal intestinal tract of a baby of 23 wk of gestation highlighting the high nucleus to cytoplasm ratio of the premature ganglion cells (400×, hematoxylin-eosin staining, bar: 400 μm), while panel b shows the relatively more mature ganglion cells of a term newborn baby at level of the submucosa of the lower intestinal tract (400×, hematoxylin-eosin staining, bar: 630 μm). (c) The lack of ganglion cells and hypertrophy of nerve fibers of a baby born at term (50×, hematoxylin-eosin staining, bar: 50 μm), while panel d shows Hirschsprung’s disease in a newborn baby confirming the absence of ganglion cells using a monoclonal antibody against calretinin, a calcium-binding protein of 29 kDa and calcium-dependent regulator with positive staining in the perivascular cells of blood vessels (internal control). Moreover, positive calretinin staining may be recognized in the lower right corner showing characteristic dark-brown granular nerve twigs in the muscularis mucosae. No calretinin staining is identified in nerve fibers at the center of the microphotograph (200×, anti-calretinin immunohistochemical staining, avidin-biotin complex, bar: 200 μm). small bowel proximal to the ileocaecal valve), (ii) total colonic and small bowel aganglionosis, which may involve very long segments of small bowel aganglionosis, and (iii) the more frequent rectal or rect (...truncated)