Rare copy number variants contribute pathogenic alleles in patients with intestinal malrotation

Developmental regulation of cellular metabolism is required for intestinal elongation and rotation

Malrotation of the intestine is a prevalent birth anomaly, the etiology of which remains poorly understood. Here, we show that late-stage exposure of Xenopus embryos to atrazine, a widely used herbicide that targets electron transport chain (ETC) reactions, elicits intestinal malrotation at high frequency. Interestingly, atrazine specifically inhibits the cellular morphogenetic events required for gut tube elongation, including cell rearrangement, differentiation and proliferation; insufficient gut lengthening consequently reorients the direction of intestine rotation. Transcriptome analyses of atrazine-exposed intestines reveal misexpression of genes associated with glycolysis and oxidative stress, and metabolomics shows that atrazine depletes key glycolytic and tricarboxylic acid cycle metabolites. Moreover, cellular bioenergetics assays indicate that atrazine blocks a crucial developmental transition from glycolytic ATP production toward oxidative phosphorylation. Atrazine-induced defects are phenocopied by rotenone, a known ETC Complex I inhibitor, accompanied by elevated reactive oxygen species, and rescued by antioxidant supplementation, suggesting that malrotation may be at least partly attributable to redox imbalance. These studies reveal roles for metabolism in gut morphogenesis and implicate defective gut tube elongation and/or metabolic perturbations in the etiology of intestinal malrotation.

Polypeptide N-acetylgalactosaminyltransferase-Associated Phenotypes in Mammals

Mucin-type O-glycosylation involves the attachment of glycans to an initial O-linked N-acetylgalactosamine (GalNAc) on serine and threonine residues on proteins. This process in mammals is initiated and regulated by a large family of 20 UDP-GalNAc: polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) (EC 2.4.1.41). The enzymes are encoded by a large gene family (GALNTs). Two of these genes, GALNT2 and GALNT3, are known as monogenic autosomal recessive inherited disease genes with well characterized phenotypes, whereas a broad spectrum of phenotypes is associated with the remaining 18 genes. Until recently, the overlapping functionality of the 20 members of the enzyme family has hindered characterizing the specific biological roles of individual enzymes. However, recent evidence suggests that these enzymes do not have full functional redundancy and may serve specific purposes that are found in the different phenotypes described. Here, we summarize the current knowledge of GALNT and associated phenotypes.

A Heterozygous Missense Variant in MAP2K2 in a Stillborn Romagnola Calf with Skeletal-Cardio-Enteric Dysplasia

Simple Summary

Skeletal dysplasias encompass a clinical-, pathological- and genetically heterogeneous group of disorders characterized by abnormal cartilage and/or bone formation, growth, and remodeling. They may belong to the so-called RASopathies, congenital conditions caused by heterozygous variants in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) cell signaling pathway. Herein, an affected calf of the Italian Romagnola breed was reported showing a skeletal-cardio-enteric dysplasia. We identified a most likely disease-causing mutation in the MAP2K2 gene by whole-genome sequencing (WGS). The MAP2K2 gene is known to be related with dominant inherited cardio-facio-cutaneous syndrome in humans, but it was so far unknown to cause a similar disease in domestic animals. We assume that the identified missense variant that was predicted to impair the function of the protein, occurred either within the germline of the dam or post-zygotically in the embryo. Rare lethal diseases such as the skeletal-cardio-enteric dysplasia in livestock are usually not characterized to the molecular level, mainly because of the lack of funds and diagnostic opportunities. Precise WGS-based diagnostics enables the understanding of rare diseases and supports the value of monitoring cattle breeding populations for fatal genetic defects.

Abstract

RASopathies are a group of developmental disorders caused by dominant mutations in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) cell signaling pathway. The goal of this study was to characterize the pathological phenotype of a Romagnola stillborn calf with skeletal-cardio-enteric dysplasia and to identify a genetic cause by whole-genome sequencing (WGS). The calf showed reduced fetal growth, a short-spine, a long and narrow face, cardiac defects and heterotopy of the spiral colon. Genetic analysis revealed a private heterozygous missense variant in MAP2K2:p.Arg179Trp, located in the protein kinase domain in the calf, and not found in more than 4500 control genomes including its sire. The identified variant affecting a conserved residue was predicted to be deleterious and most likely occurred de novo. This represents the first example of a dominant acting, and most likely pathogenic, variant in MAP2K2 in domestic animals, thereby providing the first MAP2K2-related large animal model, especially in respect to the enteric malformation. In addition, this study demonstrates the utility of WGS-based precise diagnostics for understanding sporadic congenital syndromic anomalies in cattle and the general utility of continuous surveillance for rare hereditary defects in cattle.

Congenital hyperinsulinism: 2 case reports with different rare variants in ABCC8

Congenital hyperinsulinism (CHI) is a rare glucose metabolism disorder characterized by unregulated secretion of insulin that leads to hyperinsulinemic hypoglycemia (HH). Most cases are caused by mutations in the KATP-channel genes ABCC8 and KCNJ11. We report 2 patients that experienced severe HH from the first day of life. Patient 1 developed midgut volvulus after initiating diazoxide and required intestinal resection. He was subsequently managed with a high-dose octreotide and glucose-enriched diet. Consistent with diffuse type CHI by 18F-dihydroxyphenylalanine positron emission tomography-computed tomography, genetic testing revealed a homozygous ABCC8 variant, c.1801G>A, p.(Val601Ile). The rare variant was previously reported to be diazoxide-responsive, and the patient responded well to diazoxide monotherapy, with clinical remission at 2 years of age. Patient 2 responded to diazoxide with spontaneous clinical remission at 15 months of age. However, an oral glucose tolerance test at 7 years of age revealed hyperinsulinism. Genetic testing revealed that the proband and several seemingly healthy family members harbored a novel, heterozygous ABCC8 variant, c.1780T>C, p.(Ser594Pro). Genetic findings identified previously unrecognized HH in the proband's mother. The proband's uncle had been diagnosed with monogenic ABCC8-diabetes and was successfully transitioned from insulin to glibenclamide therapy. We report findings of intestinal malrotation and volvulus occurring 2 days after initiation of diazoxide treatment. We also report a novel, heterozygous ABCC8 variant in a family that exhibited cases of CHI in infancy and HH and monogenic diabetes in adult members. The cases demonstrate the importance and clinical utility of genetic analyses for informing and guiding treatment and care.

A Case Report of Left Atrial Isomerism in a Syndromic Context

The objective of our paper is to underline the importance of assessing microarray genetic analysis for the detection of chromosomal abnormalities in rare cases such as left atrial isomerism, mostly in the context of antenatally detected syndromes. We present the case of a 26-year-old primipara, at 26 weeks of gestation, with prior first trimester normal anomaly scan, who presented in our department accusing lower abdominal pain. An anomaly ultrasound examination of the fetus revealed cardiomegaly with increased size of the right atrium, non-visualization of the atrial septum or the foramen ovale, malalignment of the three-vessel view, location of the superior vena cava above the two-vessel view, slight pericardial effusion, and no interruption of the inferior vena cava nor presence of azygos vein being noted. Associated extracardiac abnormalities, such as small kidneys at the level of the iliac fossa, micrognathia, dolichocephaly with hypoplasia of the cerebellum, increased nuchal fold, and reduced fetal movements were also reported. A diagnostic amniocentesis was performed, and, while the conventional rapid prenatal diagnostic test of the multiplex quantitative fluorescent polymerase chain reaction (PCR) came as normal, the microarray analysis (ChAS, NCBI Built 37 hg 19, detection of microdeletions or microduplications larger than 100 kb) revealed two chromosomal abnormalities: a 22.84 Mb loss of genetic material in the 18q21.31-18q23 chromosomal region and a gain of 22.31 Mb of genetic material in the 20p13-20p11.21 chromosomal region. After the termination of pregnancy, a necropsy of the fetus was performed, confirming heterotaxy syndrome with a common atrium, no atrial septum, superior vena cava draining medianly, and pulmonary veins that drained into the lower segment of the left atrium due to an anatomically enlarged single common atrium. The extracardiac findings consisted of two bilobar lungs, dysmorphic facies, low-set ears, nuchal fold edema, and small kidneys located in the iliac fossa. These findings are conclusive evidence that left atrial isomerism is a more complex syndrome. The genetic tests of the parents did not reveal any translocations of chromosomes 18 and 20 when the Fluorescent in situ Hybridization (FISH) analysis was assessed. The antenatal detection of corroboration between different structural abnormalities using serial ultrasound examinations and cardiac abnormalities, together with the detection of the affected chromosomes, improves the genetic counseling regarding the prognosis of the fetus and the recurrence rate of the condition for siblings.

Pathogenic copy number variants are detected in a subset of patients with gastrointestinal malformations

Background

Gastrointestinal atresias and urological defects are main causes of pediatric surgery in infants. As copy number variants (CNVs) have been shown to be involved in the development of congenital malformations, the aim of our study was to investigate the presence of CNVs in patients with gastrointestinal and urological malformations as well as the possibility of tissue‐specific mosaicism for CNVs in the cohort.

Methods

We have collected tissue and/or blood samples from 25 patients with anorectal malformations, esophageal atresia, or hydronephrosis, and screened for pathogenic CNVs using array comparative genomic hybridization (array‐CGH).

Results

We detected pathogenic aberrations in 2/25 patients (8%) and report a novel possible susceptibility region for esophageal atresia on 15q26.3. CNV analysis in different tissues from the same patients did not reveal evidence of tissue‐specific mosaicism.

Conclusion

Our study shows that it is important to perform clinical genetic investigations, including CNV analysis, in patients with congenital gastrointestinal malformations since this leads to improved information to families as well as an increased understanding of the pathogenesis.

Rare copy number variants contribute pathogenic alleles in patients with intestinal malrotation

BACKGROUND

Intestinal malrotation is a potentially life-threatening congenital anomaly due to the risk of developing midgut volvulus. The reported incidence is 0.2%-1% and both apparently hereditary and sporadic cases have been reported. Intestinal malrotation is associated with a few syndromes with known genotype but the genetic contribution in isolated intestinal malrotation has not yet been reported. Rare copy number variants (CNVs) have been implicated in many congenital anomalies, and hence we sought to investigate the potential contribution of rare CNVs in intestinal malrotation.

METHODS

Analysis of array comparative genomic hybridization (aCGH) data from 47 patients with symptomatic intestinal malrotation was performed.

RESULTS

We identified six rare CNVs in five patients. Five CNVs involved syndrome loci: 7q11.23 microduplication, 16p13.11 microduplication, 18q terminal deletion, HDAC8 (Cornelia de Lange syndrome type 5 and FOXF1) as well as one intragenic deletion in GALNT14, not previously implicated in human disease.

CONCLUSION

In the present study, we identified rare CNVs contributing pathogenic or potentially pathogenic alleles in five patients with syndromic intestinal malrotation, suggesting that CNV screening is indicated in intestinal malrotation with associated malformations or neurological involvements. In addition, we identified intestinal malrotation in two known syndromes (Cornelia de Lange type 5 and 18q terminal deletion syndrome) that has not previously been associated with gastrointestinal malformations.