ATP5PO levels regulate enteric nervous system development in zebrafish, linking Hirschsprung disease to Down Syndrome

Hirschsprung disease (HSCR) is a complex genetic disorder characterized by the absence of enteric nervous system (ENS) in the distal region of the intestine. Down Syndrome (DS) patients have a >50-fold higher risk of developing HSCR than the general population, suggesting that overexpression of human chromosome 21 (Hsa21) genes contribute to HSCR etiology. However, identification of responsible genes remains challenging. Here, we describe a genetic screening of potential candidate genes located on Hsa21, using the zebrafish. Candidate genes were located in the DS-HSCR susceptibility region, expressed in the human intestine, were known potential biomarkers for DS prenatal diagnosis, and were present in the zebrafish genome. With this approach, four genes were selected: RCAN1, ITSN1, ATP5PO and SUMO3. However, only overexpression of ATP5PO, coding for a component of the mitochondrial ATPase, led to significant reduction of ENS cells. Paradoxically, in vitro studies showed that overexpression of ATP5PO led to a reduction of ATP5PO protein levels. Impaired neuronal differentiation and reduced mitochondrial ATP production, were also detected in vitro, after overexpression of ATP5PO in a neuroblastoma cell line. Finally, epistasis was observed between ATP5PO and ret, the most important HSCR gene. Taken together, our results identify ATP5PO as the gene responsible for the increased risk of HSCR in DS patients in particular if RET variants are also present, and show that a balanced expression of ATP5PO is required for normal ENS development.

Unbiased characterization of the larval zebrafish enteric nervous system at a single cell transcriptomic level

The enteric nervous system (ENS) regulates many gastrointestinal functions including peristalsis, immune regulation and uptake of nutrients. Defects in the ENS can lead to severe enteric neuropathies such as Hirschsprung disease (HSCR). Zebrafish have proven to be fruitful in the identification of genes involved in ENS development and HSCR pathogenesis. However, composition and specification of enteric neurons and glial subtypes at larval stages, remains mainly unexplored. Here, we performed single cell RNA sequencing of zebrafish ENS at 5 days post-fertilization. We identified vagal neural crest progenitors, Schwann cell precursors, and four clusters of differentiated neurons. In addition, a previously unrecognized elavl3+/phox2bb-population of neurons and cx43+/phox2bb-enteric glia was found. Pseudotime analysis supported binary neurogenic branching of ENS differentiation, driven by a notch-responsive state. Taken together, we provide new insights on ENS development and specification, proving that the zebrafish is a valuable model for the study of congenital enteric neuropathies.

A combinatorial panel for flow cytometry-based isolation of enteric nervous system cells from human intestine

Efficient isolation of neurons and glia from the human enteric nervous system (ENS) is challenging because of their rare and fragile nature. Here, we describe a staining panel to enrich ENS cells from the human intestine by fluorescence-activated cell sorting (FACS). We find that CD56/CD90/CD24 co-expression labels ENS cells with higher specificity and resolution than previous methods. Surprisingly, neuronal (CD24, TUBB3) and glial (SOX10) selective markers appear co-expressed by all ENS cells. We demonstrate that this contradictory staining pattern is mainly driven by neuronal fragments, either free or attached to glial cells, which are the most abundant cell types. Live neurons can be enriched by the highest CD24 and CD90 levels. By applying our protocol to isolate ENS cells for single-cell RNA sequencing, we show that these cells can be obtained with high quality, enabling interrogation of the human ENS transcriptome. Taken together, we present a selective FACS protocol that allows enrichment and discrimination of human ENS cells, opening up new avenues to study this complex system in health and disease.

TFAP2B Haploinsufficiency Impacts Gastrointestinal Function and Leads to Pediatric Intestinal Pseudo-obstruction

Background: Pediatric Intestinal Pseudo-obstruction (PIPO) is a congenital enteric disorder characterized by severe gastrointestinal (GI) dysmotility, without mechanical obstruction. Although several genes have been described to cause this disease, most patients do not receive a genetic diagnosis. Here, we aim to identify the genetic cause of PIPO in a patient diagnosed with severe intestinal dysmotility shortly after birth.

Methods: Whole exome sequencing (WES) was performed in the patient and unaffected parents, in a diagnostic setting. After identification of the potential disease-causing variant, its functional consequences were determined in vitro and in vivo. For this, expression constructs with and without the causing variant, were overexpressed in HEK293 cells. To investigate the role of the candidate gene in GI development and function, a zebrafish model was generated where its expression was disrupted using CRISPR/Cas9 editing.

Results: WES analysis identified a de novo heterozygous deletion in TFAP2B (NM_003221.4:c.602-5_606delTCTAGTTCCA), classified as a variant of unknown significance. In vitro studies showed that this deletion affects RNA splicing and results in loss of exon 4, leading to the appearance of a premature stop codon and absence of TFAP2B protein. Disruption of tfap2b in zebrafish led to decreased enteric neuronal numbers and delayed transit time. However, no defects in neuronal differentiation were detected. tfap2b crispants also showed decreased levels of ednrbb mRNA, a downstream target of tfap2b.

Conclusion: We showed that TFAP2B haploinsufficiency leads to reduced neuronal numbers and GI dysmotility, suggesting for the first time, that this gene is involved in PIPO pathogenesis.

Diagnostic accuracy of calretinin and acetylcholinesterase staining of rectal suction biopsies in Hirschsprung disease examined by unexperienced pathologists

Rectal suction biopsy (RSB) is a gold standard for diagnosing Hirschsprung disease (HD). Calretinin staining of RSB is increasingly used by experienced pathologists due to non-complex examination and comparable diagnostic accuracy with acetylcholinesterase (AChE). However, the diagnostic accuracy of calretinin examined by unexperienced pathologists remains to be elucidated. Therefore, we aim to compare diagnostic accuracy of calretinin with AChE on RSB for diagnosing HD when examined by unexperienced pathologists. We prospectively analyzed sections from RSB stained with AChE + HE and calretinin. Blinded examination was done by five unexperienced pathologists (pathology residents) and three experienced pathologists (senior pediatric gastro-enterology pathologists) assessing for the presence of HD. Cases for the study included ones proven to be HD on resection specimens and cases without HD. Diagnostic accuracy was determined calculating area under the curve (AUC), sensitivity, specificity, likelihood ratio, and posttest probability. Fleiss’ kappa analysis was performed to assess interobserver agreement between reviewers. Eleven of 18 included patients (61%) were diagnosed with HD. Comparing the diagnostic accuracy of unexperienced pathologists, calretinin versus AChE + HE showed sensitivity of 80.0% versus 74.5% and specificity of 100% versus 65.4%, AUC of 0.87 (0.78–0.96) versus 0.59 (0.45–0.72). Unexperienced pathologists showed substantial agreement with calretinin (kappa 0.72 [0.61–0.84]) and fair agreement with AChE + HE (kappa 0.34 [0.23–0.44]). We found calretinin having higher diagnostic accuracy in diagnosing HD compared to AChE + HE when examined by unexperienced pathologists. Therefore, we recommend to use calretinin as the standard technique for staining RSB in diagnosing HD.

Size matters: Large copy number losses in Hirschsprung disease patients reveal genes involved in enteric nervous system development

Hirschsprung disease (HSCR) is a complex genetic disease characterized by absence of ganglia in the intestine. HSCR etiology can be explained by a unique combination of genetic alterations: rare coding variants, predisposing haplotypes and Copy Number Variation (CNV). Approximately 18% of patients have additional anatomical malformations or neurological symptoms (HSCR-AAM). Pinpointing the responsible culprits within a CNV is challenging as often many genes are affected. Therefore, we selected candidate genes based on gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics. Next, we used a zebrafish model to investigate whether loss of these genes affects enteric neuron development in vivo.

This study included three groups of patients, two groups without coding variants in disease associated genes: HSCR-AAM and HSCR patients without associated anomalies (HSCR-isolated). The third group consisted of all HSCR patients in which a confirmed pathogenic rare coding variant was identified. We compared these patient groups to unaffected controls. Predisposing haplotypes were determined, confirming that every HSCR subgroup had increased contributions of predisposing haplotypes, but their contribution was highest in isolated HSCR patients without RET coding variants. CNV profiling proved that specifically HSCR-AAM patients had larger Copy Number (CN) losses. Gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics were used to determine plausible candidate genes located within CN losses. Validation in zebrafish using CRISPR/Cas9 targeting confirmed the contribution of UFD1L, TBX2, SLC8A1, and MAPK8 to ENS development. In addition, we revealed epistasis between reduced Ret and Gnl1 expression and between reduced Ret and Tubb5 expression in vivo. Rare large CN losses—often de novo—contribute to HSCR in HSCR-AAM patients. We proved the involvement of six genes in enteric nervous system development and Hirschsprung disease.

Hirschsprung disease is a congenital disorder characterized by the absence of intestinal neurons in the distal part of the intestine. It is a complex genetic disorder in which multiple variations in our genome combined, result in disease. One of these variations are Copy Number Variations (CNVs): large segments of our genome that are duplicated or deleted. Patients often have Hirschsprung disease without other symptoms. However, a proportion of patients has additional associated anatomical malformations and neurological symptoms. We found that CNVs, present in patients with associated anomalies, are more often larger compared to unaffected controls or Hirschsprung patients without other symptoms. Furthermore, Copy Number (CN) losses are enriched for constrained coding regions (CCR; genes usually not impacted by genomic alterations in unaffected controls) of which the expression is higher in the developing intestinal neurons compared to the intestine. We modelled loss of these candidate genes in zebrafish by disrupting the zebrafish orthologues by genome editing. For several genes this resulted in changes in intestinal neuron development, reminiscent of HSCR observed in patients. The results presented here highlight the importance of Copy Number profiling, zebrafish validation and evaluating all CCR expressed in developing intestinal neurons during diagnostic evaluation.

Ileocolic Intussusception as the Presenting Symptom of Primary Enteric Varicella-Zoster Virus Infection in a 7-Month-Old Infant

Ileocolic intussusception is the invagination of ileum into the colon. In a subset of patients, the disease is caused by mesenteric lymphadenopathy in response to (viral) infection. We present a case of an ileocolic intussusception necessitating surgery in a 7-month-old immunocompetent infant with concurrent primary wild-type varicella-zoster virus (VZV) infection, in whom chickenpox rash developed 2 days after surgery. Detailed in situ analyses of resected intestine for specific cell type markers and VZV RNA demonstrated VZV-infected lymphocytes and neurons in the gut wall and in ganglion cells of the myenteric plexus.

Does a Dose Calculator as an Add-On to a Web-Based Paediatric Formulary Reduce Calculation Errors in Paediatric Dosing? A Non-Randomized Controlled Study

OBJECTIVES

The structured digital dosing guidelines of the web-based Dutch Paediatric Formulary provided the opportunity to develop an integrated paediatric dose calculator. In a simulated setting, we tested the ability of this calculator to reduce calculation errors.

METHODS

Volunteer healthcare professionals were allocated to one of two groups, manual calculation versus the use of the dose calculator. Professionals in both groups were given access to a web-based questionnaire with 14 patient cases for which doses had to be calculated. The effect of group allocation on the probability of making a calculation error was determined using generalized estimated equations (GEE) logistic regression analysis. The causes of all the erroneous calculations were evaluated.

RESULTS

Seventy-seven healthcare professionals completed the web-based questionnaire: thirty-seven were allocated to the manual group and 40 to the calculator group. Use of the dose calculator resulted in an estimated mean probability of a calculation error of 24.4% (95% CI 16.3-34.8) versus 39.0% (95% CI 32.4-46.1) with use of manual calculation. The mean difference of probability of calculation error between groups was 14.6% (95% CI 3.1-26.2; p = 0.013). In a secondary analysis where calculation error was defined as a 10% or greater deviation from the correct answer, the corresponding figures were 19.5% (95% CI 13-28.2) versus 26.5% (95% CI 21.6-32.1) with a mean difference of 7% between groups (95% CI 2.2-16.3; p = 0.137). Juxtaposition, typo/transcription errors and non-specified errors were more frequent as cause of error in the calculator group; exceeding the maximum dose and wrong correction for age were more frequent in the manual group. The percentage of tenfold errors was 3.1% in the manual group and 3.7% in the calculator group.

CONCLUSIONS

Our study shows that the use of a dose calculator as an add-on to a web-based paediatric formulary can reduce calculation errors. Furthermore, it shows that technologies may introduce new errors through transcription errors and wrongly selecting parameters from drop-down lists. Therefore, dosing calculators should be developed and used with special attention for selection and transcription errors.

Proteomic Analysis of the Developmental Trajectory of Human Hepatic Membrane Transporter Proteins in the First Three Months of Life

Human hepatic membrane-embedded transporter proteins are involved in trafficking endogenous and exogenous substrates. Even though impact of transporters on pharmacokinetics is recognized, little is known on maturation of transporter protein expression levels, especially during early life. We aimed to study the protein expression of 10 transporters in liver tissue from fetuses, infants, and adults. Transporter protein expression levels [ATP-binding cassette transporter (ABC)B1, ABCG2, ABCC2, ABCC3, bile salt efflux pump, glucose transporter 1, monocarboxylate transporter 1, organic anion transporter polypeptide (OATP)1B1, OATP2B1, and organic cation/carnitine transporter 2) were quantified using ultraperformance liquid chromatography tandem mass spectrometry in snap-frozen postmortem fetal, infant, and adult liver samples. Protein expression was quantified in isolated crude membrane fractions. The possible association between postnatal and postmenstrual age versus protein expression was studied. We studied 25 liver samples, as follows: 10 fetal [median gestational age 23.2 wk (range 16.4-37.9)], 12 infantile [gestational age at birth 35.1 wk (27.1-41.0), postnatal age 1 wk (0-11.4)], and 3 adult. The relationship of protein expression with age was explored by comparing age groups. Correlating age within the fetal/infant age group suggested four specific protein expression patterns, as follows: stable, low to high, high to low, and low-high-low. The impact of growth and development on human membrane transporter protein expression is transporter-dependent. The suggested age-related differences in transporter protein expression may aid our understanding of normal growth and development, and also may impact the disposition of substrate drugs in neonates and young infants.