Humans, mice, and mechanisms of intestinal atresias: a window into understanding early intestinal development

A Novel Use of Embryonic Gut Organoid Culture to Investigate Duodenal Atresia

BACKGROUND

The cause of duodenal atresia (DA) is not known. Tandler's "solid cord" hypothesis conflicts with current biological evidence. In humans, a genetic aetiology is supported by the association with Trisomy 21. Interruption of Fgf10 is the strongest genetic link to DA in mice, demonstrating an increased incidence and severity as embryos mature. This project aimed to develop an organoid model to facilitate ex vivo DA research on the FGF10/FGFR2b signalling pathway. We hypothesised that DA morphology represents an evolving spectrum of disease and that Fgf10 knockout organoids would vary in growth pattern compared to wild-type.

METHODS

Organoids were cultured from the duodenum of E12.5 Fgf10 knockout, heterozygous and wild-type embryos, using an air-liquid interface with Growth Factor reduced Matrigel. Organoids were photographed every 48 h to observe growth. Organoids were isolated and fixed after 14 days, then stained with DAPI, KI-67, and cytokeratin to demonstrate proliferation and differentiation.

RESULTS

Wild-type duodenum developed into crypt-forming organoids. Fgf10 heterozygous duodenum failed to progress beyond the development stage of spheroids. Fgf10 knockout duodenum failed to demonstrate any growth. Wholemount staining showed the greatest cell proliferation and differentiation in wild-type tissue.

CONCLUSION

This research presents a novel concept for the growth of embryonic gastrointestinal tissue to inform normal biology. The small sample numbers and restricted culture duration limit longer-term growth analysis. While this model serves as a potential ex vivo setting for future research, that research should consider organoid models with greater standardisation and other gastrointestinal regions.

LEVEL OF EVIDENCE

Animal/laboratory study.

Intrauterine volvulus: systemic review of the literature with pooled analysis

Our objective is to analyse the observations related to intrauterine volvulus and assess how clinical manifestations and treatment strategies impact prognosis. We conducted a comprehensive search on Pubmed and ClinicalTrials.gov from inception to July 2022, using search terms like "intrauterine volvulus" or "foetal volvulus," supplemented by manual scrutiny of reference lists in relevant texts and articles. Our review encompassed 57 case reports/case series, involving 88 cases. The presence of foetal bradycardia during prenatal visits (p = 0.002) and the existence of meconium cyst or pseudocyst (p = 0.038) significantly influence survival rates. Preterm labour occurred more frequently among cases resulting in mortality (54% vs 21%; p = 0.055). Our study's limitations include the inability to access all reported cases and reliance solely on available data. We advocate for vigilant monitoring of foetuses exhibiting signs of intestinal obstruction, and consideration of an emergent caesarean section as a pre-emptive measure before foetal biophysical profile deterioration worsens.

Intestinal atresia and necrotizing enterocolitis: Embryology and anatomy

The primitive gut originates at week 3 of gestation from the endoderm, with posterior incorporation of the remaining embryo layers. Wnt, Notch and TLR4 pathways have been shown to play central roles in the correct development of the intestine. The classical hypothesis for intestinal atresia development consists of failure in bowel recanalization or a vascular accident with secondary bowel reabsorption. These have been challenged due to the high frequency of associated malformations, and furthermore, with the discovery of molecular pathways and genes involved in bowel formation and correlated defects producing atresia. Necrotizing enterocolitis (NEC) has a multifactorial pathogenesis with prematurity being the most important risk factor; therefore, bowel immaturity plays a central role in NEC. Some of the same molecular pathways involved in gut maturation have been found to correlate with the predisposition of the immature bowel to develop the pathological findings seen in NEC.

Delayed development of vacuoles and recanalization in the duodenum: a study in human fetuses to understand susceptibility to duodenal atresia/stenosis

ObjectiveWe compared the cross-sectional areas of the duodenum to the distal small intestine during early gestation to determine if there is a difference in age for recanalization.MethodsSerial sagittal sections of six fetuses of gestational age (GA) 8-10 weeks were examined morphologically to compare the degree of recanalization of the duodenum with to the more distal small intestine.ResultsAt GA 8-9 weeks, the duodenum had more epithelial plugs and vacuoles with no or narrower spaces compared to the distal small bowel. Quantitative assessment at GA 10 weeks showed that the cross-sectional area of the duodenal cavity was significantly less than the distal small bowel.ConclusionThe development and recanalization of vacuoles in the duodenum occurs later than the jejunum and ileum may be involved in the more frequent development of atresia/stenosis of the duodenum compared to more distal gastrointestinal tract.

Prenatal detection of chromosomal abnormalities and copy number variants in fetuses with congenital gastrointestinal obstruction

Background

Congenital gastrointestinal obstruction (CGIO) mainly refers to the stenosis or atresia of any part from the esophagus to the anus and is one of the most common surgical causes in the neonatal period. The concept of genetic factors as an etiology of CGIO has been accepted, but investigations about CGIO have mainly focused on aneuploidy, and the focus has been on duodenal obstruction. The objective of this study was to evaluate the risk of chromosome aberrations (including numeric and structural aberrations) in different types of CGIO. A second objective was to assess the risk of abnormal CNVs detected by copy number variation sequencing (CNV-seq) in fetuses with different types of CGIO.

Methods

Data from pregnancies referred for invasive testing and CNV-seq due to sonographic diagnosis of fetal CGIO from 2015 to 2020 were obtained retrospectively from the computerized database. The rates of chromosome aberrations and abnormal CNV-seq findings for isolated CGIOs and complicated CGIOs and different types of CGIOs were calculated.

Results

Of the 240 fetuses with CGIO that underwent karyotyping, the detection rate of karyotype abnormalities in complicated CGIO was significantly higher than that of the isolated group (33.8% vs. 10.8%, p < 0.01). Ninety-three cases with normal karyotypes further underwent CNV-seq, and CNV-seq revealed an incremental diagnostic value of 9.7% over conventional karyotyping. In addition, the incremental diagnostic yield of CNV-seq analysis in complicated CGIOs (20%) was higher than that in isolated CGIOs (4.8%), and the highest prevalence of pathogenic CNVs/likely pathogenic CNVs was found in the duodenal stenosis/atresia group (17.5%), followed by the anorectal malformation group (15.4%). The 13q deletion, 10q26 deletion, 4q24 deletion, and 2p24 might be additional genetic etiologies of duodenal stenosis/atresia.

Conclusions

The risk of pathogenic chromosomal abnormalities and CNVs increased in the complicated CGIO group compared to that in the isolated CGIO group, especially when fetuses presented duodenal obstruction (DO) and anorectal malformation. CNV-seq was recommended to detect submicroscopic chromosomal aberrations for DO and anorectal malformation when the karyotype was normal. The relationship between genotypes and phenotypes needs to be explored in the future to facilitate prenatal diagnosis of fetal CGIO and yield new clues into their etiologies.

Chromosomal Abnormalities and Pregnancy Outcomes for Fetuses With Gastrointestinal Tract Obstructions

Fetal gastrointestinal tract obstruction (GITO) is the most frequently encountered gastrointestinal defect in the prenatal period. This study aimed to investigate the genetic disorders and pregnancy outcomes of fetal GITO. We reviewed data from 70 pregnancies that were referred for invasive prenatal testing because of fetal GITO. According to the level of obstruction, they were classified into esophageal atresia/stenosis, duodenal atresia/stenosis, jejunal or ileal atresia/stenosis, or anal atresia. Traditional karyotyping was performed on all the 70 pregnancies, and chromosomal microarray analysis (CMA) was performed on 32 of them in parallel. Traditional karyotyping revealed twelve (17.1%) chromosomal abnormalities, including 11 cases of trisomy 21 (Down syndrome), and one case of a supernumerary marker chromosome related to Cat eye syndrome. According to the absence or presence of other ultrasound anomalies, they were categorized into isolated GITO (n = 36) and non-isolated GITO (n = 34). The rate of chromosomal abnormalities in the non-isolated GITO pregnancies was significantly higher than that in the isolated GITO pregnancies (29.4 vs. 5.5%, p < 0.05); the survival rate in the isolated group was significantly higher than that in the non-isolated group (67.6 vs. 34.4%, p < 0.05). Among the 32 cases where CMA was performed, an additional one (3.1%) copy number variant with clinical significance was noted in a fetus with normal karyotype. The microduplication on 7q12 was considered to be the genetic etiology of duodenal stenosis, although it was inherited from a phenotypically normal mother. Our study supports the strong association between Down syndrome and fetal GITO, especially duodenal stenosis. Our findings suggested that the risk of chromosomal abnormalities was increased when GITO was accompanied by other ultrasound anomalies; thus, chromosomal abnormalities and fetal anatomy should be carefully evaluated for pregnancy management of fetal GITO.

Lack of discreet colocalization of epithelial apoptosis to the atretic precursor in the colon of the Fibroblast growth factor receptor 2IIIb mouse and staining consistent with cellular movement suggest a revised model of atresia formation

BACKGROUND

Colonic atresias in the Fibroblast growth factor receptor 2IIIb (Fgfr2IIIb) mouse model have been attributed to increased epithelial apoptosis and decreased epithelial proliferation at embryonic day (E) 10.5. We therefore hypothesized that these processes would colocalize to the distal colon where atresias occur (atretic precursor) and would be excluded or minimized from the proximal colon and small intestine.

RESULTS

We observed a global increase in intestinal epithelial apoptosis in Fgfr2IIIb -/- intestines from E9.5 to E10.5 that did not colocalize to the atretic precursor. Additionally, epithelial proliferations rates in Fgfr2IIIb -/- intestines were statistically indistinguishable to that of controls at E10.5 and E11.5. At E11.5 distal colonic epithelial cells in mutants failed to assume the expected pseudostratified columnar architecture and the continuity of the adjacent basal lamina was disrupted. Individual E-cadherin-positive cells were observed in the colonic mesenchyme.

CONCLUSIONS

Our observations suggest that alterations in proliferation and apoptosis alone are insufficient to account for intestinal atresias and that these defects may arise from both a failure of distal colonic epithelial cells to develop normally and local disruptions in basal lamina architecture.

The Role of Fibroblast Growth Factor 10 Signaling in Duodenal Atresia

Introduction

Duodenal atresia (DA) is a congenital bowel obstruction requiring major surgery in the first week of life. Three morphological phenotypes are described, reflecting increasing degrees of obstruction and discontinuity of the duodenum. The cause of DA is not known. Tandler’s original “solid cord” hypothesis conflicts with recent biological evidence, and is unable to account for differing DA types. In humans, a genetic etiology is supported by the association between Trisomy 21 and DA, and reports of familial inheritance patterns. Interruption of FGF10/FGFR2b signaling is the best demonstrated genetic link to DA in mice, with 35–75% of homozygous knockout embryos developing DA.

Purpose

This review examines the current evidence surrounding the etiology of DA. We focus on research regarding FGF10/FGFR2b signaling and its role in duodenal and other intestinal atresia. Further, we outline planned future research in this area, that we consider necessary to validate and better understand this murine model in order to successfully translate this research into clinical practice.

Conclusion

Determining the etiology of DA in humans is a clinical and scientific imperative. Fgf10/Fgfr2b murine models represent current science’s best key to unlocking this mystery. However, further research is required to understand the complex role of FGF10/FGFR2b signaling in DA development. Such complexity is expected, given the lethality of their associated defects makes ubiquitous interruption of either Fgf10 or Fgfr2b genes an unlikely cause of DA in humans. Rather, local or tissue-specific mutation in Fgf10, Fgfr2b, or their downstream targets, is the hypothesized basis of DA etiology.

FGF10 and the Mystery of Duodenal Atresia in Humans

Background: Duodenal atresia (DA) is a congenital obstruction of the duodenum, which affects 1 in 7000 pregnancies and requires major surgery in the 1st days of life. Three morphological DA types are described. In humans, the association between DA and Down syndrome suggests an underlying, albeit elusive, genetic etiology. In mice, interruption of fibroblast growth factor 10 (Fgf10) gene signaling results in DA in 30–50% of embryos, supporting a genetic etiology. This study aims to validate the spectrum of DA in two novel strains of Fgf10 knock-out mice, in preparation for future and translational research.

Methods: Two novel CRISPR Fgf10 knock-out mouse strains were derived and embryos generated by heterozygous plug-mating. E15.5–E19.5 embryos were genotyped with respect to Fgf10 and micro-dissected to determine the presence and type of DA.

Results: One twenty seven embryos (32 wild-type, 34 heterozygous, 61 null) were analyzed. No wild-type or heterozygous embryos had DA. However, 74% of Fgf10 null embryos had DA (49% type 1, 18% type 2, and 33% type 3).

Conclusion: Our CRISPR-derived strains showed higher penetrance of DA due to single-gene deletion of Fgf10 in mice than previously reported. Further, the DA type distribution in these mice more closely reiterated that observed in humans. Future experiments will document RNA and protein expression of FGF10 and its key downstream signaling targets in normal and atretic duodenum. This includes exploitation of modern, high-fidelity developmental tools, e.g., Fgf10^flox/+–tomato^flox/flox mice.

Fish consumption in early pregnancy and congenital gastrointestinal tract atresia in the Japan Environment and Children's Study

Current evidence suggests that the aetiology of congenital gastrointestinal (GI) tract atresia is multifactorial, and not based solely on genetic factors. However, there are no established modifiable risk factors for congenital GI tract atresia. We used data from a Japanese nationwide birth cohort study launched in 2011, and examined whether fish consumption in early pregnancy was associated with congenital GI tract atresia. We analysed data of 89 495 women (mean age at delivery=31·2 years) who delivered singleton live births without chromosomal anomalies. Based on the results of the FFQ, we estimated the daily intake of fish and n-3 PUFA consumption in early pregnancy. We defined a composite outcome (oesophageal atresia, duodenal atresia, jejunoileal atresia and/or anorectal malformation) as congenital GI tract atresia. In this population, median fish intake was 31·9 g/d, and seventy-four cases of congenital GI tract atresia were identified. Fish consumption in early pregnancy was inversely associated with the composite outcome (multivariable-adjusted OR for the high v. low consumption category=0·5, 95 % CI 0·3, 1·0). For all the specific types of atresia, decreased OR were observed in the high consumption category, although not statistically significant. Reduced atresia occurrence was observed even beyond the US Food and Drug Administration's recommended consumption of no more than 340 g/week. Also, n-3 PUFA-rich fish and n-3 PUFA consumptions tended to be inversely associated with atresia. Fish consumption in early pregnancy may be a preventive factor for congenital GI tract atresia.

An unusual colon atresia in a calf: at the junction of the distal loop and transverse colon. A brief overview

Congenital defects are those abnormalities present at birth. During embryogenesis, many anomalies can occur. The primitive gut tube lengthens quickly and rotates, allowing the gastrointestinal tract acquire its final position and orientation. Because the colon of large animals is complex, most changes occur in this segment. Thus, in ruminants, colon atresia is the most frequent malformation, affecting mainly ascending colon, at the level of the spiral loop. There are no previous references about a very atypical colon atresia at the junction of distal loop and transverse colon, such we have described in a 5-day-old calf, after a history of abdominal distention and absence of feces at birth, even with a patent anal opening. Atresia coli was detected at distal position of the typical colon atresia, at the junction of distal loop and transverse colon. In addition, the distal blind end was bent into a U-shape supported by the mesocolon. Besides the anatomical findings of this worthwhile atresia coli we discuss its possible etiology, in which local factors, such as a compromised blood supply during embryogenesis, are more consistent than genetic factors. Finding out the causes of atresia coli would help to reduce its incidence, lessen animal suffering and economic loss.

Recent advances in the molecular and genetic understanding of congenital gastrointestinal malformations

Major developmental paradigms are highly conserved among vertebrates. The contribution of developmental biology to the understanding of human disease and regeneration has soared recently. We review advances in the molecular and genetic understanding of gastrointestinal development using evidence from both mammalian and nonmammalian models. When appropriate, we highlight relevance and applicability to human disease.

Intestinal atresia occurring in association with placental fetal thrombotic vasculopathy: a case report with literature review

Fetal thrombotic vasculopathy (FTV) is a thrombo-occlusive disorder of the placenta that has been reported in association with perinatal conditions such as cardiac abnormalities, neurological injury, and perinatal liver disease. These complications are related to fetal circulation vascular compromise. We herein report a previously undocumented association of congenital intestinal atresia and placental FTV. Vascular occlusion of the fetal mesenteric vessels has been hypothesized to result in congenital intestinal atresia. Our report provides support for this vascular hypothesis and illustrates the value of formal pathological examination of the placenta in explaining this occurrence of congenital intestinal atresia.