Identification of a rare LAMB4 variant associated with familial diverticulitis through exome sequencing

Pathophysiology of Diverticular Disease: From Diverticula Formation to Symptom Generation

Diverticular disease is a common clinical problem, particularly in industrialized countries. In most cases, colonic diverticula remain asymptomatic throughout life and sometimes are found incidentally during colonic imaging in colorectal cancer screening programs in otherwise healthy subjects. Nonetheless, roughly 25% of patients bearing colonic diverticula develop clinical manifestations. Abdominal symptoms associated with diverticula in the absence of inflammation or complications are termed symptomatic uncomplicated diverticular disease (SUDD). The pathophysiology of diverticular disease as well as the mechanisms involved in the shift from an asymptomatic condition to a symptomatic one is still poorly understood. It is accepted that both genetic factors and environment, as well as intestinal microenvironment alterations, have a role in diverticula development and in the different phenotypic expressions of diverticular disease. In the present review, we will summarize the up-to-date knowledge on the pathophysiology of diverticula and their different clinical setting, including diverticulosis and SUDD.

Emerging evidence and recent controversies in diverticulitis: a 5-year review

Diverticulitis is a common gastrointestinal disease that still garners significant attention and study because of its heterogeneity in presentation and outcome. We provide a review of the newest and most controversial topics in diverticulitis. Recent discoveries on the influence of diet and other environmental risk factors are discussed, showing how the epidemiology of the disease process is shifting away from what was previously felt to be a disorder primarily limited to older western populations. Interestingly, as has long been suspected, genetic mutations and variations associated with the development of diverticulitis are being discovered and are summarized here. The data for non-operative and outpatient management of diverticulitis are reviewed, as are pharmacologic agents studied for use in the secondary prevention of diverticulitis. Lastly, we present controversies in the surgical treatment of diverticulitis. This review will provide a synopsis of the last 5 years of literature relating to diverticulitis.

Evaluation of molecular and genetic predisposing parameters at diverticular disease of the colon

BACKGROUND

Diverticular disease (DD) refers to the presence of diverticula throughout the gastrointestinal (GI) tract, mainly along colon. DD might evolve into diverticulitis that is accompanied by severe clinical presentation, which includes abscess formation, perforation, stricture, obstruction and/or fistula.

AIM

The aim of the present review is to summarize the role of molecular and genetic factors in DD development, as well as their possible contribution towards new prognostic indicators, diagnostic algorithms and new therapeutic approaches.

METHODS AND RESULTS

Except from common predisposing parameters, several genetic mutations, immune factors, neurotransmitters, hormones and protein dysfunctions have been associated to the early onset of DD symptoms, pathogenesis and prognosis of the disease. Specific structural changes in the colonic wall, altered matrix composition and compromised motility have been verified as possible pathogenic factors for the development of DD. Dysregulation in peristaltic activity and reduced ability of the longitudinal muscle to relax following contraction has been also associated with DD evolution. In addition, it has been suspected that genetic defects combined with alterations in intestinal microbiota might play an important role in diverticulitis presentation.

Management of colonic diverticulitis

Left sided colonic diverticulitis is a common and costly gastrointestinal disease in Western countries, characterized by acute onset of often severe abdominal pain. Imaging is necessary to make an initial diagnosis and determine disease severity. Colonoscopy should be done six to eight weeks after diagnosis to rule out a missed colon malignancy. Antibiotic treatment is used selectively in immunocompetent patients with mild acute uncomplicated diverticulitis. The clinical course of diverticulitis commonly includes unpredictable recurrences and chronic gastrointestinal symptoms, which are a detriment to quality of life. A better understanding of prognosis has prompted a shift toward non-operative approaches. The decision to undergo prophylactic colon resection should be individualized to consider the severity of diverticulitis, the patient's health and immune status, and the patient's preferences and values, as well as benefits and risks. Because only a section of colon is removed, recurrent diverticulitis remains a risk. Acute diverticulitis with an abscess is treated with antibiotics that cover Gram negative and anaerobic bacteria, with or without percutaneous drainage. Acute diverticulitis with purulent or feculent contamination of the peritoneal cavity is managed with surgery; primary resection and anastomosis is the procedure of choice in stable patients.

Genetic Risk Factors for Diverticular Disease-Emerging Evidence

Diverticular disease is traditionally understood as an environmental disease caused by diet and constipation. However, genes are increasing understood to play a role in pathogenesis. Twin studies suggest a substantial component of individual risk is due to heritable factors. Association of diverticular disease with other traits suggests an underlying biological mechanism and recently genome-wide association studies have described the genetic architecture underlying this complex phenotype. These studies suggest a new paradigm for understanding this common surgical disease.

Role of Inflammation in Pathophysiology of Colonic Disease: An Update

Diseases of the colon are a big health burden in both men and women worldwide ranging from acute infection to cancer. Environmental and genetic factors influence disease onset and outcome in multiple colonic pathologies. The importance of inflammation in the onset, progression and outcome of multiple colonic pathologies is gaining more traction as the evidence from recent research is considered. In this review, we provide an update on the literature to understand how genetics, diet, and the gut microbiota influence the crosstalk between immune and non‑immune cells resulting in inflammation observed in multiple colonic pathologies. Specifically, we focus on four colonic diseases two of which have a more established association with inflammation (inflammatory bowel disease and colorectal cancer) while the other two have a less understood relationship with inflammation (diverticular disease and irritable bowel syndrome).

Colonic diverticular disease

Diverticula are outpouchings of the intestinal wall and are common anatomical alterations detected in the human colon. Colonic diverticulosis (the presence of diverticula in the colon; referred to as diverticulosis) remains asymptomatic in most individuals but ~25% of individuals will develop symptomatic diverticulosis, termed colonic diverticular disease (also known as diverticular disease). Diverticular disease can range in severity from symptomatic uncomplicated diverticular disease (SUDD) to symptomatic disease with complications such as acute diverticulitis or diverticular haemorrhage. Since the early 2000s, a greater understanding of the pathophysiology of diverticulosis and diverticular disease, which encompasses genetic alterations, chronic low-grade inflammation and gut dysbiosis, has led to improvements in diagnosis and management. Diagnosis of diverticular disease relies on imaging approaches, such as ultrasonography, CT and MRI, as biomarkers alone are insufficient to establish a diagnosis despite their role in determining disease severity and progression as well as in differential diagnosis. Treatments for diverticular disease include dietary fibre, pharmacological treatments such as antibiotics (rifaximin), anti-inflammatory drugs (mesalazine) and probiotics, alone or in combination, and eventually surgery. Despite being effective in treating primary disease, their effectiveness in primary and secondary prevention of complications is still uncertain.

Structural biology of laminins

Laminins are large cell-adhesive glycoproteins that are required for the formation and function of basement membranes in all animals. Structural studies by electron microscopy in the early 1980s revealed a cross-shaped molecule, which subsequently was shown to consist of three distinct polypeptide chains. Crystallographic studies since the mid-1990s have added atomic detail to all parts of the laminin heterotrimer. The three short arms of the cross are made up of continuous arrays of disulphide-rich domains. The globular domains at the tips of the short arms mediate laminin polymerization; the surface regions involved in this process have been identified by structure-based mutagenesis. The long arm of the cross is an α-helical coiled coil of all three chains, terminating in a cell-adhesive globular region. The molecular basis of cell adhesion to laminins has been revealed by recent structures of heterotrimeric integrin-binding fragments and of a laminin fragment bound to the carbohydrate modification of dystroglycan. The structural characterization of the laminin molecule is essentially complete, but we still have to find ways of imaging native laminin polymers at molecular resolution.

Etiopathogenetic Mechanisms in Diverticular Disease of the Colon

This article reviews epidemiological evidence of heritability and putative mechanisms in diverticular disease, with greatest attention to 3 recent studies of genetic associations with diverticular disease based on genome-wide or whole-genome sequencing studies in large patient cohorts. We provide an analysis of the biological plausibility of the significant associations with gene variants reported and highlight the relevance of ANO1, CPI-17 (aka PPP1R14A), COLQ6, COL6A1, CALCB or CALCA, COL6A1, ARHGAP15, and S100A10 to colonic neuromuscular function and tissue properties that may result in altered compliance and predispose to the development of diverticular disease. Such studies also identify candidate genes for future studies.

Diverticulosis and nine connective tissue disorders: epidemiological support for an association

Purpose: An underlying connective tissue disorder (CTD) may predispose to formation of intestinal diverticula. We assess the association of diverticulosis with nine selected CTDs, to inform the pathophysiology of diverticula. Methods: A population-based period-prevalence study. Individuals (3.5 million New Zealand residents born 1901-1986) with a health system record 1999-2016 were grouped into those with a hospital diagnosis of diverticulosis or diverticulitis (ICD-10-AM K57), and those without. Also recorded were any hospital diagnoses of nine selected CTDs. The association of exposure to diverticulosis and each CTD was assessed using logistic regressions adjusted for age, gender, ethnicity and region. Results: In all, 85,958 (2.4%) people had a hospital diagnosis of diverticulosis. Hospitalisation with diverticulosis was highly significantly associated with rectal prolapse (adjusted odds ratio [OR] = 3.9), polycystic kidney disease (OR = 3.8), heritable syndromes (Marfan or Ehlers-Danlos) (OR = 2.4), female genital prolapse (OR = 2.3), non-aortic aneurysm (OR = 2.3), aortic aneurysm (OR = 2.2), inguinal hernia (OR = 1.9) and dislocations of shoulder and other joints (OR = 1.7), but not subarachnoid haemorrhage (OR = 1.0). Conclusion: People with diverticulosis are more likely to have colonic extracellular matrix (ECM)/connective tissue alterations in anatomical areas other than the bowel, suggesting linked ECM/connective tissue pathology. Although biases may exist, the results indicate large-scale integrated studies are needed to investigate underlying genetic pathophysiology of colonic diverticula, together with fundamental biological studies to investigate cellular phenotypes and ECM changes.

Epidemiology, Pathophysiology, and Treatment of Diverticulitis

Diverticulitis is a prevalent gastrointestinal disorder that is associated with significant morbidity and health care costs. Approximately 20% of patients with incident diverticulitis have at least 1 recurrence. Complications of diverticulitis, such as abdominal sepsis, are less likely to occur with subsequent events. Several risk factors, many of which are modifiable, have been identified including obesity, diet, and physical inactivity. Diet and lifestyle factors could affect risk of diverticulitis through their effects on the intestinal microbiome and inflammation. Preliminary studies have found that the composition and function of the gut microbiome differ between individuals with vs without diverticulitis. Genetic factors, as well as alterations in colonic neuromusculature, can also contribute to the development of diverticulitis. Less-aggressive and more-nuanced treatment strategies have been developed. Two multicenter, randomized trials of patients with uncomplicated diverticulitis found that antibiotics did not speed recovery or prevent subsequent complications. Elective surgical resection is no longer recommended solely based on number of recurrent events or young patient age and might not be necessary for some patients with diverticulitis complicated by abscess. Randomized trials of hemodynamically stable patients who require urgent surgery for acute, complicated diverticulitis that has not improved with antibiotics provide evidence to support primary anastomosis vs sigmoid colectomy with end colostomy. Despite these advances, more research is needed to increase our understanding of the pathogenesis of diverticulitis and to clarify treatment algorithms.

Altered enteric expression of the homeobox transcription factor Phox2b in patients with diverticular disease

Background

Diverticular disease, a major gastrointestinal disorder, is associated with modifications of the enteric nervous system, encompassing alterations of neurochemical coding and of the tyrosine receptor kinase Ret/GDNF pathway. However, molecular factors underlying these changes remain to be determined.

Objectives

We aimed to characterise the expression of Phox2b, an essential regulator of Ret and of neuronal subtype development, in the adult human enteric nervous system, and to evaluate its potential involvement in acute diverticulitis.

Methods

Site-specific gene expression of Phox2b in the adult colon was analysed by quantitative polymerase chain reaction. Colonic specimens of adult controls and patients with diverticulitis were subjected to quantitative polymerase chain reaction for Phox2b and dual-label immunochemistry for Phox2b and the neuronal markers RET and tyrosine hydroxylase or the glial marker S100β.

Results

The results indicate that Phox2b is physiologically expressed in myenteric neuronal and glial subpopulations in the adult enteric nervous system. Messenger RNA expression of Phox2b was increased in patients with diverticulitis and both neuronal, and glial protein expression of Phox2b were altered in these patients.

Conclusions

Alterations of Phox2b expression may contribute to the enteric neuropathy observed in diverticular disease. Future studies are required to characterise the functions of Phox2b in the adult enteric nervous system and to determine its potential as a therapeutic target in gastrointestinal disorders.

Progress and challenges in the management of diverticular disease: which treatment?

Diverticular disease of the colon (DDC) includes a spectrum of conditions from asymptomatic diverticulosis to symptomatic uncomplicated diverticulosis, segmental colitis associated with diverticulosis, and acute diverticulitis without or with complications that may have serious consequences. Clinical and scientific interest in DDC is increasing because of the rising incidence of all conditions within the DDC spectrum, a better, although still limited understanding of the pathogenic mechanisms involved; the increasing socioeconomic burden; and the new therapeutic options being tested. The goals of treatment in DDC are symptom and inflammation relief and preventing disease progression or recurrence. The basis for preventing disease progression remains a high-fiber diet and physical exercise, although evidence is poor. Other current strategies do not meet expectations or lack a solid mechanistic foundation; these strategies include modulation of gut microbiota or dysbiosis with rifaximin or probiotics, or using mesalazine for low-grade inflammation in uncomplicated symptomatic diverticulosis. Most acute diverticulitis is uncomplicated, and the trend is to avoid hospitalization and unnecessary antibiotic therapy, but patients with comorbidities, sepsis, or immunodeficiency should receive broad spectrum and appropriate antibiotics. Complicated acute diverticulitis may require interventional radiology or surgery, although the best surgical approach (open versus laparoscopic) remains a matter of discussion. Prevention of acute diverticulitis recurrence remains undefined, as do therapeutic strategies. Mesalazine with or without probiotics has failed to prevent diverticulitis recurrence, whereas new studies are needed to validate preliminary positive results with rifaximin. Surgery is another option, but the number of acute events cannot guide this indication. We need to identify risk factors and disease progression or recurrence mechanisms to implement appropriate preventive strategies.

Recent advances in understanding and managing diverticulitis

In the past few decades, the increasing socioeconomic burden of acute diverticulitis (AD) has become evident, and with the growth of the population age, this significant economic impact will likely continue to rise. Furthermore, recent evidence showed an increased rate of hospital admissions especially evident among women and younger individuals. The natural history and pathophysiology of this clinical condition is still to be fully defined, and efforts continue to be made in the identification of risk factors and the establishment of relative preventive strategies. The actual therapeutic strategies aimed to modulate gut microbiota, such as rifaximin or probiotics, or to reduce mucosal inflammation, such as mesalazine, present a relatively poor efficacy for both the prevention of the first AD episode (primary prevention) and its recurrence (secondary prevention). In the last few years, the main goal achieved has been in the management of AD in that uncomplicated AD can, to a larger extent, be managed in an outpatient setting with no or little supportive therapy, a strategy that will certainly impact on the health costs of this disease. The problem of AD recurrence remains a topic of debate. The aim of this review is to present updated evidence on AD epidemiology and relative open clinical questions and to analyze in detail predisposing and protective factors with an attempt to integrate their possible modes of action into the several pathogenic mechanisms that have been suggested to contribute to this multifactorial disease. A unifying hypothesis dealing with the colonic luminal and extra-luminal microenvironments separately is provided. Finally, evidence-based changes in therapeutic management will be summarized. Because of an ascertained multifactorial pathogenesis of uncomplicated and complicated AD, it is probable that a single 'causa prima' will not be identifiable, and a better stratification of patients could allow one to pursue tailored therapeutic algorithm strategies.