Human laterality disorders

De novo and inherited micro-CNV at 16p13.11 in 21 Chinese patients with defective cardiac left-right patterning

Objective

Copy number changes at Chromosomal 16p13.11 have been implicated in a variety of human diseases including congenital cardiac abnormalities. The clinical correlation of copy number variants (CNVs) in this region with developmental abnormalities remains controversial as most of the patients inherit the duplication from an unaffected parent.

Methods

We performed CNV analysis on 164 patients with defective left-right (LR) patterning based on whole genome-exome sequencing (WG-ES) followed by multiplex ligation-dependent probe amplification (MLPA) validation. Most cases were accompanied with complex congenital heart disease (CHD).

Results

CNVs at 16p13.11 were identified in a total of 21 cases, accounting for 12.80% (21/164) evaluated cases. We observed a marked overrepresentation of chromosome 16p13.11 duplications in cases when compared with healthy controls according to literature reports (15/164, 9.14% versus 0.09% in controls). Notably, in two independent family trios, de novo 16p13.11 micro-duplications were identified in two patients with laterality defects and CHD. Moreover, 16p13.11 micro-duplication was segregated with the disease in a family trio containing 2 affected individuals. Notably, five coding genes, NOMO1, PKD1P3, NPIPA1, PDXDC1, and NTAN1, were potentially affected by micro-CNV at 16p13.11 in these patients.

Conclusion

Our study provides new family-trio based evidences to support 16p13.11 micro-duplications predispose individuals to defective cardiac left-right patterning and laterality disorder.

Left-sided perforated appendicitis in a patient with situs inversus totalis, a case report

Situs inversus, an uncommon disorder, causes the orientation of asymmetric organs to be opposite to that of normal anatomy. It can be either partial, affecting only the thoracic or abdominal cavities, or full, involving the transposition of both the thoracic and abdominal organs. A 31-year-old Ethiopian male patient presented with migratory abdominal pain in the left lower quadrant for 3 days. Associated with the pain, he experienced symptoms of nausea, vomiting of ingested matter, and loss of appetite. Investigations were consistent with left-sided appendicitis with situs inversus totalis. Therefore, the patient was operated on and discharged with no perioperative complications. Appendicitis is a rare cause of left lower quadrant pain. In order to reduce the delay in patient treatment and avoidable perioperative complications, emergency physicians, radiologists, and surgeons must become more knowledgeable about situs inversus and left side appendicitis.

Investigation of the genetic and clinical features of laterality disorders in prenatal diagnosis: discovery of a novel compound heterozygous mutation in the DNAH11 gene

BACKGROUND

Left-right laterality disorders are a heterogeneous group of disorders caused by an altered position or orientation of the thoracic and intra-abdominal organs and vasculature across the left-right axis. They mainly include situs inversus and heterotaxy. Those disorders are complicated by cardiovascular abnormalities significantly more frequently than situs solitus.

METHODS

In this study, 16 patients with a fetal diagnosis of laterality disorder with congenital heart defects (CHD) were evaluated with a single nucleotide polymorphism array (SNP-arry) combined with whole-exome sequencing (WES).

RESULTS

Although the diagnostic rate of copy number variations was 0 and the diagnostic rate of WES was 6.3% (1/16), the likely pathogenic gene DNAH11 and the candidate gene OFD1 were ultimately identified. In addition, novel compound heterozygous mutations in the DNAH11 gene and novel hemizygous variants in the OFD1 gene were found. Among the combined CHD, a single atrium/single ventricle had the highest incidence (50%, 8/16), followed by atrioventricular septal defects (37.5%, 6/16). Notably, two rare cases of common pulmonary vein atresia (CPVA) were also found on autopsy.

CONCLUSION

This study identified the types of CHD with a high incidence in patients with laterality disorders. It is clear that WES is an effective tool for diagnosing laterality disorders and can play an important role in future research.

The molecular and cellular choreography of early mammalian lung development

Mammalian lung development starts from a specific cluster of endodermal cells situated within the ventral foregut region. With the orchestrating of delicate choreography of transcription factors, signaling pathways, and cell-cell communications, the endodermal diverticulum extends into the surrounding mesenchyme, and builds the cellular and structural basis of the complex respiratory system. This review provides a comprehensive overview of the current molecular insights of mammalian lung development, with a particular focus on the early stage of lung cell fate differentiation and spatial patterning. Furthermore, we explore the implications of several congenital respiratory diseases and the relevance to early organogenesis. Finally, we summarize the unprecedented knowledge concerning lung cell compositions, regulatory networks as well as the promising prospect for gaining an unbiased understanding of lung development and lung malformations through state-of-the-art single-cell omics.

Increased risk of fetal left-right asymmetry disorders associated with maternal SARS-CoV-2 infection during the first trimester

Our center has observed a substantial increase in the detection rate of fetal left-right(LR) asymmetry disorders between March and May 2023. This finding has raised concerns because these pregnant women experienced the peak outbreak of SARS-CoV-2 in China during their first trimester. To explore the relationship between maternal SARS-CoV-2 infection and fetal LR asymmetry disorders. A retrospective collection of clinical and ultrasound data diagnosed as fetal LR asymmetry disorders was conducted from January 2018 to December 2023. The case-control study involved fetuses with LR asymmetry disorders and normal fetuses in a 1:1 ratio. We evaluated and compared the clinical and fetal ultrasound findings in pregnant women with SARS-CoV-2 infection and pregnant women without infection. The Student t-test was utilized to compare continuous variables, while the chi-squared test was employed for univariable analyses. The incidence rate of LR asymmetry disorders from 2018 to 2023 was as follows: 0.17‰, 0.63‰, 0.61‰, 0.57‰, 0.59‰, and 3.24‰, respectively. A total of 30 fetuses with LR asymmetry disorders and 30 normal fetuses were included. This case-control study found that SARS-CoV-2 infection (96.67% vs 3.33%, P = .026) and infection during the first trimester (96.55% vs 3.45%, P = .008) were identified as risk factors. The odds ratio values were 10.545 (95% CI 1.227, 90.662) and 13.067 (95% CI 1.467, 116.419) respectively. In cases of SARS-CoV-2 infection in the first trimester, the majority of infections (88.1%, 37/42) occurred between 5 and 6 weeks of gestation. We found that 43.7% (66/151) of fetuses with LR asymmetry disorder had associated malformations, 90.9% (60/66) exhibited cardiac malformations. SARS-CoV-2 infection during the first trimester significantly increases the risk of fetal LR asymmetry disorders, particularly when the infection occurs between 5 and 6 gestation weeks. The most common associated malformation is heart malformation.

A Case Report of Dextrocardia with Situs Inversus: A Rare Condition and Its Clinical Importance

Situs inversus totalis (SIT) is a rare medical condition characterized by a complete mirror-image reversal of the normal positioning of the internal organs. Aristotle initially described situs inversus in animals, while Fabricius first characterized it in humans. Although the specific cause is uncertain, there is evidence of autosomal recessive and X-linked inheritance. Before seeking treatment for an unrelated ailment, many people with SIT are unaware of their distinct anatomy, as in our case. The presented case is a 30-year-old female patient from Central Ethiopia, presented to Hakim Gizaw Teaching Hospital outpatient department of medicine with the complaint of right-sided anterior chest pain for five days. Clinically, the apical beat was heard in the right 5th intercostal space. After undergoing an electrocardiogram (ECG), echocardiogram, chest X-ray, and abdominal ultrasound, she was diagnosed with situs inversus totalis. The clinical implications of SIT encompass challenges in diagnosis and procedures, potential congenital cardiac abnormalities, considerations for organ transplantation, and clinical decision-making, particularly in emergency scenarios. Key Clinical Messages. This case highlights the clinical implications of dextrocardia with situs inversus totalis, emphasizing the importance of awareness for accurate diagnosis, procedural challenges, and informed clinical decision-making. Understanding this rare condition is crucial for providing appropriate medical care and to navigate potential complications in affected individuals.

Situs inversus totalis in an asymptomatic adolescent - importance of patient education: A case report

BACKGROUND

Situs inversus totalis (SIT) may be an incidental finding in asymptomatic children. Patients may not understand the implications of this condition and the importance of relaying the diagnosis to their healthcare providers.

CASE SUMMARY

We report an asymptomatic seventeen-year-old adolescent with previously-diagnosed SIT who presented for a routine well-child visit. During history taking, he denied any past medical conditions, including cardiovascular conditions. Only when physical exam revealed point of maximal impulse and heart sounds on the right side, did he convey that he had been diagnosed with SIT incidentally at age of 12 years. He was not aware of associated conditions or the potential implications of his diagnosis, nor did he realize it is pertinent medical history to be relayed to healthcare providers. Chest X-ray confirmed dextrocardia and abdominal X-ray showed right-sided stomach. Abdomen sonogram showed left-sided liver and right-sided spleen. Echocardiogram showed normal valvular structure and function. A comprehensive discussion was provided to address the patient's lack of understanding that SIT is a medical diagnosis with potential implications.

CONCLUSION

While SIT is rare and mostly asymptomatic, affected patients may not comprehend the importance of the diagnosis and its potential ramifications. Recognition of the patient's lack of awareness allows the healthcare provider to educate the patient and hopefully can prevent potential medical and surgical complications.

Situs inversus with levocardia in a 15-year-old male adolescent: a case report

BACKGROUND

Situs inversus with levocardia is a rare anomaly in which the heart is present in the left chest but the abdominal viscera are transposed. It is caused by a single incomplete penetration of an autosomal recessive gene. It is unclear what exactly causes situs inversus with levocardia. Even if situs inversus can be identified following a comprehensive physical examination, it is now possible to validate the results and search for further information and pathologies since medical imaging is so widely accessible.

CASE

A 15-year-old Oromo male child from a remote area of Bale Zone presented to the Goba Referral Hospital's medical emergency outpatient department complaining of periumbilical pain that had persisted for 4 months. He frequently came to our hospital and was admitted three times with the same problem. Objectively, there was tenderness over the left lower quadrant and periumbilical area. The sonographic evaluation discovered the transposition of the liver and spleen with cardiac apex on the left side. He received conservative treatment with ceftriaxone 1 g intravenous twice a day and metronidazole 500 mg intravenous for 5 days, and he went home improved.

CONCLUSION

Isolated levocardia is a rare form of situs inversus in which the heart is in the traditional levo position while the abdominal organs are in the dextro position. What causes situs inversus with levocardia is unknown. Despite the fact that situs inversus can be diagnosed after a thorough physical examination, medical imaging has allowed us to confirm the findings as well as understand more about diseases. Due to the severity of an underlying heart defect, situs inversus with levocardia has a dismal prognosis.

Laparoscopic Living Donor Nephrectomy in a Donor With Situs Inversus Totalis: It is Not a Contraindication to Kidney Transplant

Situs inversus totalis (SIT) is a rare anatomic anomaly representing 180° inversion of all internal organs. We report a case of laparoscopic living donor nephrectomy in a donor with SIT. A 55-year-old man volunteered to provide a living kidney source for his son. The donor was in good physical condition, with no clinical history of obesity, hypertension, diabetes, and other abnormalities. Preoperative X-ray thoracic and abdominal scans showed that the donor had a total organ transposition inversus. Computed tomographic renal vascular three-dimensional reconstruction scan showed that the patient had 2 left renal arteries and 1 right renal artery. All data collected comply with the Helsinki Congress and the Declaration of Istanbul. We chose to perform a transabdominal route laparoscopic living donor nephrectomy of the right kidney. The donor did not experience operation-related complications and was discharged on the fourth postoperative day. The recipient did not have a rejection reaction, and the recipient recovered successfully. This case illustrates that laparoscopic living donor nephrectomy is fully feasible in this population.

Identification of novel compound heterozygous variants in the DNAH1 gene of a Chinese family with left-right asymmetry disorder

Most internal organs in humans and other vertebrates exhibit striking left-right asymmetry in position and structure. Variation of normal organ positioning results in left-right asymmetry disorders and presents as internal organ reversal or randomization. Up to date, at least 82 genes have been identified as the causative genetic factors of left-right asymmetry disorders. This study sought to discover potential pathogenic variants responsible for left-right asymmetry disorder present in a Han-Chinese family using whole exome sequencing combined with Sanger sequencing. Novel compound heterozygous variants, c.5690A>G (p.Asn1897Ser) and c.7759G>A (p.Val2587Met), in the dynein axonemal heavy chain 1 gene (DNAH1), were found in the proband and absent in unaffected family members. Conservation analysis has shown that the variants affect evolutionarily conserved residues, which may impact the tertiary structure of the DNAH1 protein. The novel compound heterozygous variants may potentially bear responsibility for left-right asymmetry disorder, which results from a perturbation of left-right axis coordination at the earliest embryonic development stages. This study broadens the variant spectrum of left-right asymmetry disorders and may be helpful for genetic counseling and healthcare management for the diagnosed individual, and promotes a greater understanding of the pathophysiology.

Left-Sided Heart Defects and Laterality Disturbance in Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a complex congenital heart disease characterized by hypoplasia of left-sided heart structures. The developmental basis for restriction of defects to the left side of the heart in HLHS remains unexplained. The observed clinical co-occurrence of rare organ situs defects such as biliary atresia, gut malrotation, or heterotaxy with HLHS would suggest possible laterality disturbance. Consistent with this, pathogenic variants in genes regulating left-right patterning have been observed in HLHS patients. Additionally, Ohia HLHS mutant mice show splenic defects, a phenotype associated with heterotaxy, and HLHS in Ohia mice arises in part from mutation in Sap130, a component of the Sin3A chromatin complex known to regulate Lefty1 and Snai1, genes essential for left-right patterning. Together, these findings point to laterality disturbance mediating the left-sided heart defects associated with HLHS. As laterality disturbance is also observed for other CHD, this suggests that heart development integration with left-right patterning may help to establish the left-right asymmetry of the cardiovascular system essential for efficient blood oxygenation.

Biallelic mutations of TTC12 and TTC21B were identified in Chinese patients with multisystem ciliopathy syndromes

Background

Abnormalities in cilia ultrastructure and function lead to a range of human phenotypes termed ciliopathies. Many tetratricopeptide repeat domain (TTC) family members have been reported to play critical roles in cilium organization and function.

Results

Here, we describe five unrelated family trios with multisystem ciliopathy syndromes, including situs abnormality, complex congenital heart disease, nephronophthisis or neonatal cholestasis. Through whole-exome sequencing and Sanger sequencing confirmation, we identified compound heterozygous mutations of TTC12 and TTC21B in six affected individuals of Chinese origin. These nonsynonymous mutations affected highly conserved residues and were consistently predicted to be pathogenic. Furthermore, ex vivo cDNA amplification demonstrated that homozygous c.1464 + 2 T > C of TTC12 would cause a whole exon 16 skipping. Both mRNA and protein levels of TTC12 were significantly downregulated in the cells derived from the patient carrying TTC12 mutation c.1464 + 2 T > C by real-time qPCR and immunofluorescence assays when compared with two healthy controls. Transmission electron microscopy analysis further identified ultrastructural defects of the inner dynein arms in this patient. Finally, the effect of TTC12 deficiency on cardiac LR patterning was recapitulated by employing a morpholino-mediated knockdown of ttc12 in zebrafish.

Conclusions

To the best of our knowledge, this is the first study reporting the association between TTC12 variants and ciliopathies in a Chinese population. In addition to nephronophthisis and laterality defects, our findings demonstrated that TTC21B should also be considered a candidate gene for biliary ciliopathy, such as TTC26, which further expands the phenotypic spectrum of TTC21B deficiency in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-022-00421-z.

Situs inversus totalis with local metastasis of gallbladder carcinoma and variation of the common hepatic artery

Background

Situs inversus totalis (SIT) is a rare congenital anomaly characterized by a complete transposition of all the viscera. SIT cases were usually reported because of the presence of tumors, leading to false association between them. Therefore, any research that advances our understanding on SIT is highly required. This study firstly describes a very rare case of SIT with “jumping” metastasis to pancreas of gallbladder carcinoma.

Case presentation

A 69-year-old female patient presented at our hospital with complaints of one month of epigastric pain was studied. She had not sought for treatment prior the visit. Imaging examinations of this patient revealed SIT and a variation of the common hepatic artery with concomitant tumors of gallbladder and pancreas. However, there was no evidence of distant metastases beyond the abdominal cavity. She underwent a combination of radical cholecystectomy, total pancreatectomy, splenectomy and hepatic artery-splenic artery reconstruction. Histological analyses revealed metastasis of the gallbladder carcinoma in to the pancreas. Although the patient opted against chemotherapy, she survived without tumor for 16 months following the surgery. A review of the current literature on association with SIT and tumor occurrence was presented.

Conclusions

It is a great surgical challenge for the resection of multicenter hepatobiliary and pancreatic tumors in such rare SIT anatomical abnormalities with vascular variants. A reliable surgical plan based on detailed preoperative imaging and intraoperative anatomical exploration is crucial to achieving radical resection.

Clinical and genetic features of primary ciliary dyskinesia in a cohort of consecutive clinically suspect children in western China

BACKGROUND

Primary ciliary dyskinesia (PCD) is a rare, inherited disorder of the motile cilia that exhibits genetic and clinical heterogeneity among different populations. PCD diagnosis remains challenging owing to the heterogeneity of associated clinical features and lack of a gold standard diagnostic test.

OBJECTIVE

The aim of this study was to analyze the clinical and genetic characteristics of a group of children with clinically suspected PCD in one region of China, with the goal of providing a more robust knowledge base regarding the genetic stratification underlying this disease in Chinese populations.

METHODS

We retrospectively analyzed the data from 38 patients with clinically suspected PCD who had undergone next-generation sequencing (NGS) between November 2016 and March 2021 in the respiratory department of a tertiary Children's hospital in Western China. The genetic features of the confirmed cases were summarized by reviewing data associated with other cohorts of Chinese children.

RESULTS

Overall, 16 patients were ultimately diagnosed with PCD with a median age of 8.5 years. All patients presented with a chronic wet cough, 93.75% exhibited chronic or recurrent sinusitis/rhinitis, 43.75% experienced recurrent wheezing, 56.25% reported respiratory symptoms present since infancy, 31.25% had a history of neonatal respiratory distress (NRD), and 25% exhibited otitis media. Only 18.75% of these patients exhibited laterality defects. High frequencies of DNAH11 mutations were detected by integrating data from PCD patient cohorts in China.

CONCLUSION

The high frequency of DNAH11 mutations may limit the utility of transmission electron microscopy (TEM) as a first-line approach to diagnosing PCD in China in the absence of other indicators.

Comparison between Traditional Chinese Medicine Constitution and Blood Biochemical Markers Associated with Left and Right Mammary Hyperplasia in Rural Areas of Southwest China

Background

Hyperplasia of mammary glands (HMG) is the breast disease with the highest clinical incidence. Many traditional Chinese medicine (TCM) doctors suggest that the treatment of HMG should be based on the left and right breast pain difference. However, these views are based on case reports, and an objective basis has not been established for treatment according to left-side and right-side differences.

Methods

We enrolled 150 patients who met the clinical diagnostic criteria of HMG. The incidence bias was determined according to the score difference between bilateral breast pain and mass in patients with HMG. A left group, right group, and bilateral group were included, and TCM constitution was investigated in each group. Blood biochemical indicators were measured for 120 fasting patients. We conducted a network pharmacology study of the key herb qingpi and chenpi, which are used by TCM doctors to treat different lateral HMG.

Results

In patients with biased onset of HMG, the results showed that the frequency and constitution score of stagnant blood in the L group were higher than those of the R group, and the frequency and constitution score of phlegm-dampness in the R group were higher than those of the L group. Both the L and R groups had high proportion of stagnant Qi. The results indicated that the concentration of coagulation factor VIII (FVIII) was higher in the L group than that in the R group, and the concentration of lipoprotein a (Lp-α) was higher in the R group than that in the L group. The results showed that sinensetin and neohesperidin contained in qingpi might interfere with platelet activation, thrombogenesis, prolactin signaling pathway, and atherosclerosis process, in removing “blood stasis” and eventually treating the left-leaning group of HMG patients. Sitosterol and citromitin contained in chenpi could regulate lipid metabolism by interfering with regulation of lipolysis in adipocytes, salivary secretion, estrogen signaling pathway, and thyroid hormone signaling pathway. Chenpi could eliminate “phlegm turbidity” and treat HMG patients in the right-leaning group.

Conclusions

We preliminarily confirmed that the clinical pathogenesis of HMG is not a left-right equilibrium and TCM constitution, coagulation function, and lipid metabolism may be used as the objective basis for the difference between the left and right in HMG pathogenesis. For left-sided HMG patients, the doctor can consider qingpi, herb of activating blood and removing stasis, to treat HMG. However, for right-sided HMG, we think doctors should apply herb of activating Qi and eliminating phlegm, such as chenpi.

Biallelic DNAH9 mutations are identified in Chinese patients with defective left-right patterning and cilia-related complex congenital heart disease

Defective left-right (LR) pattering results in a spectrum of laterality disorders including situs inversus totalis (SIT) and heterotaxy syndrome (Htx). Approximately, 50% of patients with primary ciliary dyskinesia (PCD) displayed SIT. Recessive variants in DNAH9 have recently been implicated in patients with situs inversus. Here, we describe six unrelated family trios and 2 sporadic patients with laterality defects and complex congenital heart disease (CHD). Through whole exome sequencing (WES), we identified compound heterozygous mutations in DNAH9 in the affected individuals of these family trios. Ex vivo cDNA amplification revealed that DNAH9 mRNA expression was significantly downregulated in these patients carrying biallelic DNAH9 mutations, which cause a premature stop codon or exon skipping. Transmission electron microscopy (TEM) analysis identified ultrastructural defects of the outer dynein arms in these affected individuals. dnah9 knockdown in zebrafish lead to the disturbance of cardiac left-right patterning without affecting ciliogenesis in Kupffer's vesicle (KV). By generating a Dnah9 knockout (KO) C57BL/6n mouse model, we found that Dnah9 loss leads to compromised cardiac function. In this study, we identified recessive DNAH9 mutations in Chinese patients with cardiac abnormalities and defective LR pattering.

DNAH11 compound heterozygous variants cause heterotaxy and congenital heart disease

Heterotaxy (HTX), a condition characterized by internal organs not being arranged as expected relative to each other and to the left-right axis, is often accompanied with congenital heart disease (CHD). The purpose was to detect the pathogenic variants in a Chinese family with HTX and CHD. A non-consanguineous Han Chinese family with HTX and CHD, and 200 unrelated healthy subjects were enlisted. Exome sequencing and Sanger sequencing were applied to identify the genetic basis of the HTX family. Compound heterozygous variants, c.3426-1G>A and c.4306C>T (p.(Arg1436Trp)), in the dynein axonemal heavy chain 11 gene (DNAH11) were identified in the proband via exome sequencing and further confirmed by Sanger sequencing. Neither c.3426-1G>A nor c.4306C>T variant in the DNAH11 gene was detected in 200 healthy controls. The DNAH11 c.3426-1G>A variant was predicted as altering the acceptor splice site and most likely affecting splicing. The DNAH11 c.4306C>T variant was predicted to be damaging, which may reduce the phenotype severity. The compound heterozygous variants, c.3426-1G>A and c.4306C>T, in the DNAH11 gene might be the pathogenic alterations resulting in HTX and CHD in this family. These findings broaden the variant spectrum of the DNAH11 gene and increase knowledge used in genetic counseling for the HTX family.

Human Laterality Disorders: Pathogenesis, Clinical Manifestations, Diagnosis, and Management

Human laterality disorders comprise a group of diseases characterized by abnormal location (situs) and orientation of thoraco-abdominal organs and vessels across the left-right axis. Situs inversus totalis is mirror image reversal of thoraco-abdominal organs/great vessels. Situs ambiguus, better known as heterotaxy, is abnormal arrangement of thoraco-abdominal organs across the left-right axis excluding situs inversus totalis. Heterotaxy, also referred to as atrial or atrial appendage isomerism, is characterized by abnormal location of left-sided or right-sided organs with loss of asymmetry of normally paired asymmetric organs. It is associated with a variety of anomalies involving the heart, great vessels, lungs and intra-abdominal organs. Right and left atrial isomerism are associated with multiple complex congenital cardiac and vascular anomalies, many of which are lethal when untreated. Isomerism may also affect the lungs, spleen, liver, gall bladder, and intestines. Innovative surgical therapy of heterotaxy/isomerism has reduced early mortality and markedly improved long-term prognosis.

A novel virtual reality approach for functional lateralization in healthy adults

Functional lateralization relates to a natural asymmetry in the dominance right or left body side, and is a fundamental principle of the brain. The hemispheres of the brain control the contralateral body side, and show subtle, yet striking, anatomical asymmetries and functional lateralization. Innovative technologies, including Virtual Reality (VR), are entering the areas of experimental research, modeling and simulation related to the study of lateralization, with new perspectives of different applications in modern medical practice. Researchers/clinicians note that there are fewer VR studies with healthy participants, and which are important in evaluating/interpreting clinical outcomes, and testing the usefulness, limitations, and sensitivity of VR. The presented influence of the domination of upper/lower limbs on the performance of VR exercises was studied in healthy right-handed adults. Virtual testing sessions were performed independently with both/ dominant/ non-dominant hands, and the similar VR sessions were conduced on a Wii Balance Board (WBB) with the choice of body side, at different levels of the difficulty. The obtained results are consistent with other studies which show that cognitive-motor training in VR with the WBB platform is a very sensitive and promising tool for recognizing/assessing functional asymmetries of the right-left body side not only in disturbed lateralization, but also in the test training of healthy subjects.

Atypical Brain Asymmetry in Human Situs Inversus: Gut Feeling or Real Evidence?

The alignment of visceral and brain asymmetry observed in some vertebrate species raises the question of whether this association also exists in humans. While the visceral and brain systems may have developed asymmetry for different reasons, basic visceral left–right differentiation mechanisms could have been duplicated to establish brain asymmetry. We describe the main phenotypical anomalies and the general mechanism of left–right differentiation of vertebrate visceral and brain laterality. Next, we systematically review the available human studies that explored the prevalence of atypical behavioral and brain asymmetry in visceral situs anomalies, which almost exclusively involved participants with the mirrored visceral organization (situs inversus). The data show no direct link between human visceral and brain functional laterality as most participants with situs inversus show the typical population bias for handedness and brain functional asymmetry, although an increased prevalence of functional crowding may be present. At the same time, several independent studies present evidence for a possible relation between situs inversus and the gross morphological asymmetry of the brain torque with potential differences between subtypes of situs inversus with ciliary and non-ciliary etiologies.

The Axenfeld-Rieger Syndrome Gene FOXC1 Contributes to Left-Right Patterning

Precise spatiotemporal expression of the Nodal-Lefty-Pitx2 cascade in the lateral plate mesoderm establishes the left–right axis, which provides vital cues for correct organ formation and function. Mutations of one cascade constituent PITX2 and, separately, the Forkhead transcription factor FOXC1 independently cause a multi-system disorder known as Axenfeld–Rieger syndrome (ARS). Since cardiac involvement is an established ARS phenotype and because disrupted left–right patterning can cause congenital heart defects, we investigated in zebrafish whether foxc1 contributes to organ laterality or situs. We demonstrate that CRISPR/Cas9-generated foxc1a and foxc1b mutants exhibit abnormal cardiac looping and that the prevalence of cardiac situs defects is increased in foxc1a^−/−; foxc1b^−/− homozygotes. Similarly, double homozygotes exhibit isomerism of the liver and pancreas, which are key features of abnormal gut situs. Placement of the asymmetric visceral organs relative to the midline was also perturbed by mRNA overexpression of foxc1a and foxc1b. In addition, an analysis of the left–right patterning components, identified in the lateral plate mesoderm of foxc1 mutants, reduced or abolished the expression of the NODAL antagonist lefty2. Together, these data reveal a novel contribution from foxc1 to left–right patterning, demonstrating that this role is sensitive to foxc1 gene dosage, and provide a plausible mechanism for the incidence of congenital heart defects in Axenfeld–Rieger syndrome patients.

Performing Endoscopic Retrograde Cholagiopancreatpgraphy and Endoscopic Ultrasound for Management of Malignant Bile Duct Obstruction in a Patient With a Situs Inversus Totalis

Situs inversus totalis (SIT) is a rare anomaly characterized by the transposition of organs. We present a case of a 67-year-old White woman with a history of SIT, who presented with fatigue, jaundice, and abnormal liver enzymes. Endoscopic ultrasound demonstrated a solid lesion at the distal common bile duct (CBD). Subsequent endoscopic retrograde cholangiopancreatography displayed severe stenosis in the CBD. A plastic stent was placed into the CBD, resulting in successful biliary decompression. Biliary brushings and biopsy showed atypical cells, suspicious for carcinoma. Ensuing pancreaticoduodenectomy confirmed cholangiocarcinoma. Although challenging, endoscopic ultrasound and endoscopic retrograde cholangiopancreatography in SIT can be successfully performed in preoperative evaluation for possible pancreaticobiliary cancers.

Side predilection in congenital anomalies of the kidney, urinary and genital tracts

BACKGROUND

There appear to be various patterns of sidedness with relation to the common urogenital malformations observed in pediatric urology. The objective of this statistical review was to synthesize this data and to assess if these patterns are significant.

MATERIALS AND METHODS

Eighteen urogenital conditions were investigated and for each condition the five largest studies that noted laterality were included. The sidedness of each condition was then analysed for statistical significance.

RESULTS

Three conditions had a statistically significant higher proportion on the right side: palpable undescended testis (63%, p = 0.0002), inguinal hernia (59%, p = 0.0001) and hydrocele (60%, p = 0.003). Three conditions were significantly more common on the left side: impalpable undescended testis (59%, p = 0.0008), renal agenesis (54%, p = 0.02) and vesico-ureteric junction obstruction (71%, p < 0.0001) while both pelvi-ureteric junction obstruction (62%, p = 0.09) and absent vas deferens (61%, p = 0.11) were trending towards significance.

CONCLUSIONS

Various urogenital malformations display a predilection for one side. Proximal malformations tend to be more frequently seen on the left side, where as inguinoscrotal malformations are more frequently observed on the right. There is an increasing body of literature regarding aetiological factors for these conditions. However, our current understanding of the pathophysiology of these conditions does not completely explain this pattern of observation.

Biallelic loss of function NEK3 mutations deacetylate α-tubulin and downregulate NUP205 that predispose individuals to cilia-related abnormal cardiac left-right patterning

Defective left–right (LR) organization involving abnormalities in cilia ultrastructure causes laterality disorders including situs inversus (SI) and heterotaxy (Htx) with the prevalence approximately 1/10,000 births. In this study, we describe two unrelated family trios with abnormal cardiac LR patterning. Through whole-exome sequencing (WES), we identified compound heterozygous mutations (c.805-1G >C; p. Ile269GlnfsTer8/c.1117dupA; p.Thr373AsnfsTer19) (c.29T>C; p.Ile10Thr/c.356A>G; p.His119Arg) of NEK3, encoding a NIMA (never in mitosis A)-related kinase, in two affected individuals, respectively. Protein levels of NEK3 were abrogated in Patient-1 with biallelic loss-of function (LoF) NEK3 mutations that causes premature stop codon. Subsequence transcriptome analysis revealed that NNMT (nicotinamide N-methyltransferase) and SIRT2 (sirtuin2) was upregulated by NEK3 knockdown in human retinal pigment epithelial (RPE) cells in vitro, which associates α-tubulin deacetylation by western blot and immunofluorescence. Transmission electron microscopy (TEM) analysis further identified defective ciliary ultrastructure in Patient-1. Furthermore, inner ring components of nuclear pore complex (NPC) including nucleoporin (NUP)205, NUP188, and NUP155 were significantly downregulated in NEK3-silenced cells. In conclusion, we identified biallelic mutations of NEK3 predispose individual to abnormal cardiac left–right patterning via SIRT2-mediated α-tubulin deacetylation and downregulation of inner ring nucleoporins. Our study suggested that NEK3 could be a candidate gene for human ciliopathies.

Monoallelic Mutations in CC2D1A Suggest a Novel Role in Human Heterotaxy and Ciliary Dysfunction

BACKGROUND

Human heterotaxy is a group of congenital disorders characterized by misplacement of one or more organs according to the left-right axis. The genetic causes of human heterotaxy are highly heterogeneous.

METHODS

We performed exome sequencing in a cohort of 26 probands with heterotaxy followed by gene burden analysis for the enrichment of novel rare damaging mutations. Transcription activator-like effector nuclease was used to generate somatic loss-of-function mutants in a zebrafish model. Ciliary defects were examined by whole-mount immunostaining of acetylated α-tubulin.

RESULTS

We identified a significant enrichment of novel rare damaging mutations in the CC2D1A gene. Seven occurrences of CC2D1A mutations were found to affect 4 highly conserved amino acid residues of the protein. Functional analyses in the transcription activator-like effector nuclease-mediated zebrafish knockout models were performed, and heterotaxy phenotypes of the cardiovascular and gastrointestinal systems in both somatic and germline mutants were observed. Defective cilia were demonstrated by whole-mount immunostaining of acetylated α-tubulin. These abnormalities were rescued by wild-type cc2d1a mRNA but not cc2d1a mutant mRNA, strongly suggesting a loss-of-function mechanism. On the other hand, overexpression of cc2d1a orthologous mutations cc2d1a P559L and cc2d1a G808V (orthologous to human CC2D1A P532L and CC2D1A G781V) did not affect embryonic development.

CONCLUSIONS

Using a zebrafish model, we were able to establish a novel association of CC2D1A with heterotaxy and ciliary dysfunction in the F2 generation via a loss-of-function mechanism. Future mechanistic studies are needed for a better understanding of the role of CC2D1A in left-right patterning and ciliary dysfunction.

Initial morphological symmetry breaking in the foregut and development of the omental bursa in human embryos

Bilaterally symmetrical primordia of visceral organs undergo asymmetrical morphogenesis leading to typical arrangement of visceral organs in the adult. Asymmetrical morphogenesis within the upper abdomen leads, among others, to the formation of the omental bursa dorsally to the rotated stomach. A widespread view of this process assumes kinking of thin mesenteries as a main mechanism. This view is based on a theory proposed already by Johannes Müller in 1830 and was repeatedly criticized, but some of the most plausible alternative views (initially proposed by Swaen in 1897 and Broman in 1904) still remain to be proven. Here, we analyzed serial histological sections of human embryos between stages 12 and 15 at high light microscopical resolution to reveal the succession of events giving rise to the development of the omental bursa and its relation to the emerging stomach asymmetry. Our analysis indicates that morphological symmetry breaking in the upper abdomen occurs within a wide mesenchymal plate called here mesenteric septum and is based on differential behavior of the coelomic epithelium which causes asymmetric paragastric recess formation and, importantly, precedes initial rotation of stomach. Our results thus provide the first histological evidence of breaking the symmetry of the early foregut anlage in the human embryo and pave the way for experimental studies of left-right symmetry breaking in the upper abdomen in experimental model organisms.

The Spectrum of Cardiac Anomalies Associated with Heterotaxy: A Single-Center Study of a Large Series Based on Computed Tomography

The aim of the study was to identify and correlate the anatomical variants of cardiac structures among patients with heterotaxy. In this retrospective cross-sectional analysis of 13 years duration, 302 patients of congenital heart diseases associated with heterotaxy were studied. All these patients had undergone a meticulous clinical evaluation, echocardiography, and cardiac computed tomography. The mean age of the cohort was 38.4 months, with 180 males and 122 females. The cohort had 184 patients of right isomerism and 118 of left isomerism. More than half of the cohort had abnormal pulmonary veins. Over 75% of the cohort had low pulmonary blood flow. Abnormal relationship of great arteries was seen in nearly 69% of the cohort. Atrio-venticular canal defect was the commonest anatomical variant. Overall, 43% of the cohort had single ventricle physiology, predominantly associated with right isomerism. Heterotaxy forms a difficult anatomical subset to comprehend due to the plethora of possible abnormalities. However, unless the cardiac and visceral anatomy is delineated well, the surgical plan becomes suboptimal and often elusive, leaving tough choices for cardiac surgeon. It is essential to obtain all the possible anatomical information using additional imaging modalities to devise a basis for a comprehensive plan for medical and surgical management. A better understanding of the genetic and molecular factors in the etiology, coupled with the application of state-of-the-art imaging techniques, is likely to add to our knowledge of heterotaxy to bring about improved surgical outcomes and a better quality of life for patients suffering from this complex entity.

Invasive Cardiac Lipoma Complicating Visceral Inversion

We report a case of cardiac lipoma with intramyocardial invasion complicated by visceral inversion, which, to the best of our knowledge, has not been reported before. Multimodality imaging played an important role in differential diagnosis and determination of the management strategy. (Level of Difficulty: Advanced.)

Comorbidities in situs inversus totalis: A hospital-based study

BACKGROUND AND OBJECTIVE

Few studies have assessed the comorbid diseases in situs inversus totalis (SIT) comprehensively. The aim of this study was to provide insight into the spectrum and prevalence of comorbidities in SIT.

METHODS

Children ≤18 years of age with SIT were enrolled in this retrospective observational study. Situs status and comorbidities were independently confirmed by two physicians, based on review of radiologic, ultrasonic examination, operative records, and case notes.

RESULTS

A total of 155 children (median age: 1.24 years; range: 1 day-17.8 years) confirmed to have SIT were recruited between January 2008 and December 2018. Associated conditions were diagnosed in 114 children (73.5%). Among them, 25 children (16.1%) had multiple anomalies affecting two or more organ systems. The most commonly associated conditions were congenital heart defects (n = 72, 46.5%) followed by primary ciliary dyskinesia (n = 19, 12.3%), renal disorders (n = 12, 7.7%), biliary atresia (n = 7, 4.5%), skeletal dysplasia (n = 8, 5.2%), and mental retardation (n = 4, 2.6%).

CONCLUSION

A substantial proportion of children with SIT have comorbidities affecting multiple systems, especially cardiovascular and respiratory abnormalities. Children with SIT warrant careful examination for the presence of congenital and acquired abnormalities.

Genome sequencing for rightward hemispheric language dominance

Most people have left-hemisphere dominance for various aspects of language processing, but only roughly 1% of the adult population has atypically reversed, rightward hemispheric language dominance (RHLD). The genetic-developmental program that underlies leftward language laterality is unknown, as are the causes of atypical variation. We performed an exploratory whole-genome-sequencing study, with the hypothesis that strongly penetrant, rare genetic mutations might sometimes be involved in RHLD. This was by analogy with situs inversus of the visceral organs (left-right mirror reversal of the heart, lungs and so on), which is sometimes due to monogenic mutations. The genomes of 33 subjects with RHLD were sequenced and analyzed with reference to large population-genetic data sets, as well as 34 subjects (14 left-handed) with typical language laterality. The sample was powered to detect rare, highly penetrant, monogenic effects if they would be present in at least 10 of the 33 RHLD cases and no controls, but no individual genes had mutations in more than five RHLD cases while being un-mutated in controls. A hypothesis derived from invertebrate mechanisms of left-right axis formation led to the detection of an increased mutation load, in RHLD subjects, within genes involved with the actin cytoskeleton. The latter finding offers a first, tentative insight into molecular genetic influences on hemispheric language dominance.

Selective Serotonin Reuptake Inhibitor Use During Pregnancy and Major Malformations: The Importance of Serotonin for Embryonic Development and the Effect of Serotonin Inhibition on the Occurrence of Malformations

Bioelectric signaling is transduced by neurotransmitter pathways in many cell types. One of the key mediators of bioelectric control mechanisms is serotonin, and its transporter SERT, which is targeted by a broad class of blocker drugs (selective serotonin reuptake inhibitors [SSRIs]). Studies showing an increased risk of multiple malformations associated with gestational use of SSRI have been accumulating but debate remains on whether SSRI as a class has the potential to generate these malformations. This review highlights the importance of serotonin for embryonic development; the effect of serotonin inhibition during early pregnancy on the occurrence of multiple diverse malformations that have been shown to occur in human pregnancies; that the risks outweigh the benefits of SSRI use during gestation in populations of mild to moderately depressed pregnant women, which encompass the majority of pregnant depressed women; and that the malformations seen in human pregnancies constitute a pattern of malformations consistent with the known mechanisms of action of SSRIs. We present at least three mechanisms by which SSRI can affect development. These studies highlight the relevance of basic bioelectric and neurotransmitter mechanism for biomedicine.

DNAAF1 links heart laterality with the AAA+ ATPase RUVBL1 and ciliary intraflagellar transport

DNAAF1 (LRRC50) is a cytoplasmic protein required for dynein heavy chain assembly and cilia motility, and DNAAF1 mutations cause primary ciliary dyskinesia (PCD; MIM 613193). We describe four families with DNAAF1 mutations and complex congenital heart disease (CHD). In three families, all affected individuals have typical PCD phenotypes. However, an additional family demonstrates isolated CHD (heterotaxy) in two affected siblings, but no clinical evidence of PCD. We identified a homozygous DNAAF1 missense mutation, p.Leu191Phe, as causative for heterotaxy in this family. Genetic complementation in dnaaf1-null zebrafish embryos demonstrated the rescue of normal heart looping with wild-type human DNAAF1, but not the p.Leu191Phe variant, supporting the conserved pathogenicity of this DNAAF1 missense mutation. This observation points to a phenotypic continuum between CHD and PCD, providing new insights into the pathogenesis of isolated CHD. In further investigations of the function of DNAAF1 in dynein arm assembly, we identified interactions with members of a putative dynein arm assembly complex. These include the ciliary intraflagellar transport protein IFT88 and the AAA+ (ATPases Associated with various cellular Activities) family proteins RUVBL1 (Pontin) and RUVBL2 (Reptin). Co-localization studies support these findings, with the loss of RUVBL1 perturbing the co-localization of DNAAF1 with IFT88. We show that RUVBL1 orthologues have an asymmetric left-sided distribution at both the mouse embryonic node and the Kupffer's vesicle in zebrafish embryos, with the latter asymmetry dependent on DNAAF1. These results suggest that DNAAF1-RUVBL1 biochemical and genetic interactions have a novel functional role in symmetry breaking and cardiac development.

Lineage-Specific Chiral Biases of Human Embryonic Stem Cells during Differentiation

Left-right symmetry breaking is a complex developmental process and an important part of embryonic axis development. As of yet, the biophysical mechanism behind LR asymmetry establishment remains elusive for the overall asymmetry of embryos as well as for the organ-specific asymmetry. Here, we demonstrate that inherent cellular chirality is observable in the cells of early embryonic stages using a 3D Matrigel bilayer system. Differentiation of human embryonic stem cells to three lineages corresponding to heart, intestine, and neural tissues demonstrates phenotype-specific inherent chiral biases, complementing the current knowledge regarding organ development. The existence of inherent cellular chirality early in development and its correlation with organ asymmetry implicate cell chirality as a possible regulator in LR symmetry breaking.

Development of mesenteric tissues

Mesothelial, neurovascular, lymphatic, adipose and mesenchymal tissues make up the mesentery. These tissues are pathobiologically important for numerous reasons. Collectively, they form a continuous, discrete and substantive organ. Additionally, they maintain abdominal digestive organs in position and in continuity with other systems. Furthermore, as they occupy a central position, they mediate transmission of signals between the abdominal digestive system and the remainder of the body. Despite this physiologic centrality, mesenteric tissue development has received little investigatory focus. However, recent advances in our understanding of anatomy demonstrate continuity between all mesenteric tissues, thereby linking previously unrelated studies. In this review, we examine the development of mesenteric tissue in normality and in the setting of congenital abnormalities.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

A case report of congenital scoliosis associated with situs inversus totalis

RATIONALE

Situs inversus totalis is a rare anomaly disease in which the organs in the chest and abdomen are positioned in a mirror image reversal of normal positions. Although this has been confirmed to be associated with spinal abnormalities, reports about situs inversus totalis with congenital scoliosis remain limited.

PATIENT CONCERNS

We present a 9-year-old girl having congenital scoliosis associated with situs inversus totalis.

DIAGNOSES

She also had other associated anomalies: ventricular septal defect, mild restrictive ventilatory dysfunction, hydronephrosis, and syringomyelia. Her preoperative Cobb angle (T11-L3) was 78°.

INTERVENTIONS

She received single growing rods treatment and subsequent posterior spinal fusion correction surgery for her scoliosis.

OUTCOMES

The coronal Cobb angle of the main curve was corrected to 20° postoperatively and no obvious loss of spinal corrective angle was identified 1 year after the correction surgery.

LESSONS

Growing rods technique could be a safe and effective alternative for the treatment of scoliosis associated with situs inversus totalis. In the correction of left-sided lumbar curve of this kind of patients, the risks of aorta impingements should not be neglected when placing pedicle screws on the concave sides.

Situs Inversus Totalis in Twins: A Brief Review and a Life History / Twin Research: Twin Studies of Trisomy 21; Monozygotic Twin Concordance for Bilateral Coronoid Hyperplasia; Prenatal Hormonal Effects in Mixed-Sex Non-Human Primate Litters; Insurance Mandates and Twinning After In Vitro Fertilization / News Reports: First Report of Identical Twin Puppies; Twins Sisters Turn 100; Remembering an Identical Twin Production Designer; New York City Marathon Quadruplets

The presence of situs inversus totalis (full reversal of internal organs) in twins is briefly reviewed. Information gathered from 35-year-old monozygotic (MZ) female twin pair discordant for this condition is presented. This is followed by summaries of research on the frequency of trisomy 21 (Down syndrome) in twins, the first case of MZ twin concordance for bilateral coronoid hyperplasia, prenatal hormonal effects in mixed-sex non-human primate litters, and links between insurance mandates and twinning following in vitro fertilization. The final section of this article describes twin-related events reported in the news, namely, the first recorded birth of identical twin puppies; the 100th birthday celebration of a pair of fraternal female twins, the passing of an award-winning identical twin production designer, and the first running of the New York City Marathon by a set of quadruplets.

HCN4 ion channel function is required for early events that regulate anatomical left-right patterning in a nodal and lefty asymmetric gene expression-independent manner

Laterality is a basic characteristic of all life forms, from single cell organisms to complex plants and animals. For many metazoans, consistent left-right asymmetric patterning is essential for the correct anatomy of internal organs, such as the heart, gut, and brain; disruption of left-right asymmetry patterning leads to an important class of birth defects in human patients. Laterality functions across multiple scales, where early embryonic, subcellular and chiral cytoskeletal events are coupled with asymmetric amplification mechanisms and gene regulatory networks leading to asymmetric physical forces that ultimately result in distinct left and right anatomical organ patterning. Recent studies have suggested the existence of multiple parallel pathways regulating organ asymmetry. Here, we show that an isoform of the hyperpolarization-activated cyclic nucleotide-gated (HCN) family of ion channels (hyperpolarization-activated cyclic nucleotide-gated channel 4, HCN4) is important for correct left-right patterning. HCN4 channels are present very early in Xenopus embryos. Blocking HCN channels (Ih currents) with pharmacological inhibitors leads to errors in organ situs. This effect is only seen when HCN4 channels are blocked early (pre-stage 10) and not by a later block (post-stage 10). Injections of HCN4-DN (dominant-negative) mRNA induce left-right defects only when injected in both blastomeres no later than the 2-cell stage. Analysis of key asymmetric genes' expression showed that the sidedness of Nodal, Lefty, and Pitx2 expression is largely unchanged by HCN4 blockade, despite the randomization of subsequent organ situs, although the area of Pitx2 expression was significantly reduced. Together these data identify a novel, developmental role for HCN4 channels and reveal a new Nodal-Lefty-Pitx2 asymmetric gene expression-independent mechanism upstream of organ positioning during embryonic left-right patterning.

Clinical care for primary ciliary dyskinesia: current challenges and future directions

Primary ciliary dyskinesia (PCD) is a rare genetic disease that affects the motility of cilia, leading to impaired mucociliary clearance. It is estimated that the vast majority of patients with PCD have not been diagnosed as such, providing a major obstacle to delivering appropriate care. Challenges in diagnosing PCD include lack of disease-specific symptoms and absence of a single, "gold standard", diagnostic test. Management of patients is currently not based on high-level evidence because research findings are mostly derived from small observational studies with limited follow-up period. In this review, we provide a critical overview of the available literature on clinical care for PCD patients, including recent advances. We identify barriers to PCD research and make suggestions for overcoming challenges.

Epigenetic regulation of left-right asymmetry by DNA methylation

DNA methylation is a major epigenetic modification; however, the precise role of DNA methylation in vertebrate development is still not fully understood. Here, we show that DNA methylation is essential for the establishment of the left-right (LR) asymmetric body plan during vertebrate embryogenesis. Perturbation of DNA methylation by depletion of DNA methyltransferase 1 (dnmt1) or dnmt3bb.1 in zebrafish embryos leads to defects in dorsal forerunner cell (DFC) specification or collective migration, laterality organ malformation, and disruption of LR patterning. Knockdown of dnmt1 in Xenopus embryos also causes similar defects. Mechanistically, loss of dnmt1 function induces hypomethylation of the lefty2 gene enhancer and promotes lefty2 expression, which consequently represses Nodal signaling in zebrafish embryos. We also show that Dnmt3bb.1 regulates collective DFC migration through cadherin 1 (Cdh1). Taken together, our data uncover dynamic DNA methylation as an epigenetic mechanism to control LR determination during early embryogenesis in vertebrates.

Establishment of lateral organ asymmetries in the invertebrate chordate, Ciona intestinalis

BACKGROUND

The evolutionary emergence and diversification of the chordates appear to involve dramatic changes in organ morphogenesis along the left/right axis. However, the ancestral chordate mechanism for establishing lateral asymmetry remains ambiguous. Additionally, links between the initial establishment of lateral asymmetry and subsequent asymmetries in organ morphogenesis are poorly characterized.

RESULTS

To explore asymmetric organ morphogenesis during chordate evolution, we have begun to characterize left/right patterning of the heart and endodermal organs in an invertebrate chordate, Ciona intestinalis. Here, we show that Ciona has a laterally asymmetric, right-sided heart. Our data indicate that cardiac lateral asymmetry requires H+/K+ ion flux, but is independent of Nodal signaling. Our pharmacological inhibitor studies show that ion flux is required for polarization of epidermal cilia and neurula rotation and suggest that ion flux functions synergistically with chorion contact to drive cardiac laterality. Live imaging analysis revealed that larval heart progenitor cells undergo a lateral shift without displaying any migratory behaviors. Furthermore, we find that this passive shift corresponds with the emergence of lateral asymmetry in the endoderm, which is also ion flux dependent.

CONCLUSIONS

Our data suggest that ion flux promotes laterally asymmetric morphogenesis of the larval endoderm rudiment leading to a passive, Nodal-independent shift in the position of associated heart progenitor cells. These findings help to refine hypotheses regarding ancestral chordate left/right patterning mechanisms and how they have diverged within invertebrate and vertebrate chordate lineages.

Cardiac Embryology and Molecular Mechanisms of Congenital Heart Disease: A Primer for Anesthesiologists

Congenital heart disease is diagnosed in 0.4% to 5% of live births and presents unique challenges to the pediatric anesthesiologist. Furthermore, advances in surgical management have led to improved survival of those patients, and many adult anesthesiologists now frequently take care of adolescents and adults who have previously undergone surgery to correct or palliate congenital heart lesions. Knowledge of abnormal heart development on the molecular and genetic level extends and improves the anesthesiologist's understanding of congenital heart disease. In this article, we aim to review current knowledge pertaining to genetic alterations and their cellular effects that are involved in the formation of congenital heart defects. Given that congenital heart disease can currently only occasionally be traced to a single genetic mutation, we highlight some of the difficulties that researchers face when trying to identify specific steps in the pathogenetic development of heart lesions.

The determination factors of left-right asymmetry disorders- a short review

Laterality defects in humans, situs inversus and heterotaxy, are rare disorders, with an incidence of 1:8000 to 1:10 000 in the general population, and a multifactorial etiology. It has been proved that 1.44/10 000 of all cardiac problems are associated with malformations of left-right asymmetry and heterotaxy accounts for 3% of all congenital heart defects. It is considered that defects of situs appear due to genetic and environmental factors. Also, there is evidence that the ciliopathies (defects of structure or function) are involved in development abnormalities. Over 100 genes have been reported to be involved in left-right patterning in model organisms, but only a few are likely to candidate for left-right asymmetry defects in humans. Left-right asymmetry disorders are genetically heterogeneous and have variable manifestations (from asymptomatic to serious clinical problems). The discovery of the right mechanism of left-right development will help explain the clinical complexity and may contribute to a therapy of these disorders.

Mechanism for generation of left isomerism in Ccdc40 mutant embryos

Leftward fluid flow in the mouse node is generated by cilia and is critical for initiating asymmetry of the left-right axis. Coiled-coil domain containing-40 (Ccdc40) plays an evolutionarily conserved role in the assembly of motile cilia and establishment of the left-right axis. Approximately one-third of Ccdc40^lnks mutant embryos display situs defects and here we investigate the underlying mechanism. Ccdc40^lnks mutants show delayed induction of markers of the left-lateral plate mesoderm (L-LPM) including Lefty1, Lefty2 and Nodal. Consistent with defective cilia motility compromising fluid flow across the node, initiation of asymmetric perinodal Cerberus like-2 (Cerl2) expression is delayed and then randomized. This is followed by delayed and then randomized asymmetric Nodal expression around the node. We propose a model to explain how left isomerism arises in a proportion of Ccdc40^lnks mutants. We postulate that with defective motile cilia, Cerl2 expression remains symmetric and Nodal is antagonized equally on both sides of the node. This effectively reduces Nodal activation bilaterally, leading to reduced and delayed activation of Nodal and its antagonists in the LPM. This model is further supported by the failure to establish Nodal expression in the left-LPM with reduced Nodal gene dosage in Ccdc40^lnks/lnks;Nodal^LacZ/+ mutants causing a predominance of right not left isomerism. Together these results suggest a model where cilia generated fluid flow in the node functions to ensure robust Nodal activation and a timely left-sided developmental program in the LPM.

Cilia in vertebrate left-right patterning

Understanding how left-right (LR) asymmetry is generated in vertebrate embryos is an important problem in developmental biology. In humans, a failure to align the left and right sides of cardiovascular and/or gastrointestinal systems often results in birth defects. Evidence from patients and animal models has implicated cilia in the process of left-right patterning. Here, we review the proposed functions for cilia in establishing LR asymmetry, which include creating transient leftward fluid flows in an embryonic 'left-right organizer'. These flows direct asymmetric activation of a conserved Nodal (TGFβ) signalling pathway that guides asymmetric morphogenesis of developing organs. We discuss the leading hypotheses for how cilia-generated asymmetric fluid flows are translated into asymmetric molecular signals. We also discuss emerging mechanisms that control the subcellular positioning of cilia and the cellular architecture of the left-right organizer, both of which are critical for effective cilia function during left-right patterning. Finally, using mosaic cell-labelling and time-lapse imaging in the zebrafish embryo, we provide new evidence that precursor cells maintain their relative positions as they give rise to the ciliated left-right organizer. This suggests the possibility that these cells acquire left-right positional information prior to the appearance of cilia.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.

Conserved roles for cytoskeletal components in determining laterality

Consistently-biased left-right (LR) patterning is required for the proper placement of organs including the heart and viscera. The LR axis is especially fascinating as an example of multi-scale pattern formation, since here chiral events at the subcellular level are integrated and amplified into asymmetric transcriptional cascades and ultimately into the anatomical patterning of the entire body. In contrast to the other two body axes, there is considerable controversy about the earliest mechanisms of embryonic laterality. Many molecular components of asymmetry have not been widely tested among phyla with diverse bodyplans, and it is unknown whether parallel (redundant) pathways may exist that could reverse abnormal asymmetry states at specific checkpoints in development. To address conservation of the early steps of LR patterning, we used the Xenopus laevis (frog) embryo to functionally test a number of protein targets known to direct asymmetry in plants, fruit fly, and rodent. Using the same reagents that randomize asymmetry in Arabidopsis, Drosophila, and mouse embryos, we show that manipulation of the microtubule and actin cytoskeleton immediately post-fertilization, but not later, results in laterality defects in Xenopus embryos. Moreover, we observed organ-specific randomization effects and a striking dissociation of organ situs from effects on the expression of left side control genes, which parallel data from Drosophila and mouse. Remarkably, some early manipulations that disrupt laterality of transcriptional asymmetry determinants can be subsequently "rescued" by the embryo, resulting in normal organ situs. These data reveal the existence of novel corrective mechanisms, demonstrate that asymmetric expression of Nodal is not a definitive marker of laterality, and suggest the existence of amplification pathways that connect early cytoskeletal processes to control of organ situs bypassing Nodal. Counter to alternative models of symmetry breaking during neurulation (via ciliary structures absent in many phyla), our data suggest a widely-conserved role for the cytoskeleton in regulating left-right axis formation immediately after fertilization of the egg. The novel mechanisms that rescue organ situs, even after incorrect expression of genes previously considered to be left-side master regulators, suggest LR patterning as a new context in which to explore multi-scale redundancy and integration of patterning from the subcellular structure to the entire bodyplan.

Bi-allelic Mutations in PKD1L1 Are Associated with Laterality Defects in Humans

Disruption of the establishment of left-right (L-R) asymmetry leads to situs anomalies ranging from situs inversus totalis (SIT) to situs ambiguus (heterotaxy). The genetic causes of laterality defects in humans are highly heterogeneous. Via whole-exome sequencing (WES), we identified homozygous mutations in PKD1L1 from three affected individuals in two unrelated families. PKD1L1 encodes a polycystin-1-like protein and its loss of function is known to cause laterality defects in mouse and medaka fish models. Family 1 had one fetus and one deceased child with heterotaxy and complex congenital heart malformations. WES identified a homozygous splicing mutation, c.6473+2_6473+3delTG, which disrupts the invariant splice donor site in intron 42, in both affected individuals. In the second family, a homozygous c.5072G>C (p.Cys1691Ser) missense mutation was detected in an individual with SIT and congenital heart disease. The p.Cys1691Ser substitution affects a highly conserved cysteine residue and is predicted by molecular modeling to disrupt a disulfide bridge essential for the proper folding of the G protein-coupled receptor proteolytic site (GPS) motif. Damaging effects associated with substitutions of this conserved cysteine residue in the GPS motif have also been reported in other genes, namely GPR56, BAI3, and PKD1 in human and lat-1 in C. elegans, further supporting the likely pathogenicity of p.Cys1691Ser in PKD1L1. The identification of bi-allelic PKD1L1 mutations recapitulates previous findings regarding phenotypic consequences of loss of function of the orthologous genes in mice and medaka fish and further expands our understanding of genetic contributions to laterality defects in humans.