The influence of twinning on cardiac development

Uncovering the Genetic Basis of Congenital Heart Disease: Recent Advancements and Implications for Clinical Management

Congenital heart disease (CHD) is the most prevalent hereditary disorder, affecting approximately 1% of all live births. A reduction in morbidity and mortality has been achieved with advancements in surgical intervention, yet challenges in managing complications, extracardiac abnormalities, and comorbidities still exist. To address these, a more comprehensive understanding of the genetic basis underlying CHD is required to establish how certain variants are associated with the clinical outcomes. This will enable clinicians to provide personalized treatments by predicting the risk and prognosis, which might improve the therapeutic results and the patient's quality of life. We review how advancements in genome sequencing are changing our understanding of the genetic basis of CHD, discuss experimental approaches to determine the significance of novel variants, and identify barriers to use this knowledge in the clinics. Next-generation sequencing technologies are unravelling the role of oligogenic inheritance, epigenetic modification, genetic mosaicism, and noncoding variants in controlling the expression of candidate CHD-associated genes. However, clinical risk prediction based on these factors remains challenging. Therefore, studies involving human-induced pluripotent stem cells and single-cell sequencing help create preclinical frameworks for determining the significance of novel genetic variants. Clinicians should be aware of the benefits and implications of the responsible use of genomics. To facilitate and accelerate the clinical integration of these novel technologies, clinicians should actively engage in the latest scientific and technical developments to provide better, more personalized management plans for patients.

Cardiac findings in newborn twins

AIMS

To evaluate cardiac findings in newborn twins from the general population and investigate if newborn twins may require systematic evaluation of cardiac parameters.

METHODS

Prospective cohort study of newborns with cardiac evaluation performed during the first month of life. Cardiac findings were compared 1:3 with matched singletons.

RESULTS

We included 412 newborn twins (16% monochorionic; 50% boys) and 1236 singletons. Comparing cardiac findings showed twins had an increased prevalence of non-severe structural heart disease (most common: ventricular septal defects in both groups), thinner left ventricular posterior wall in diastole (LVPWd; 1.82 vs. 1.87 mm, p = 0.02), smaller diameter of the left atrium (10.6 vs. 11.1 mm, p = 0.04), higher heart rate (148 vs. 144 bpm, p = 0.04), more left-shifted QRS axis (106 vs. 111°, p < 0.001), and lower maximum R-wave amplitude in V1 (927 vs. 1015 μV, p = 0.02) compared to singletons. After multifactorial adjustment for potential confounders, the effect of twinning on cardiac parameters persisted only for LVPWd (p < 0.05).

CONCLUSION

Despite contemporary surveillance, we found an increased prevalence of non-severe structural heart disease in a population-based cohort of newborn twins. However, the effect of twinning on cardiac parameters was modest and generally did not persist after correction for likely confounding factors.

Epigenetics and Congenital Heart Diseases

Congenital heart disease (CHD) is a frequent occurrence, with a prevalence rate of almost 1% in the general population. However, the pathophysiology of the anomalous heart development is still unclear in most patients screened. A definitive genetic origin, be it single-point mutation or larger chromosomal disruptions, only explains about 35% of identified cases. The precisely choreographed embryology of the heart relies on timed activation of developmental molecular cascades, spatially and temporally regulated through epigenetic regulation: chromatin conformation, DNA priming through methylation patterns, and spatial accessibility to transcription factors. This multi-level regulatory network is eminently susceptible to outside disruption, resulting in faulty cardiac development. Similarly, the heart is unique in its dynamic development: growth is intrinsically related to mechanical stimulation, and disruption of the intrauterine environment will have a direct impact on fetal embryology. These two converging axes offer new areas of research to characterize the cardiac epigenetic regulation and identify points of fragility in order to counteract its teratogenic consequences.

Monochorionic Twin Discordance for Horseshoe Lung and Tricuspid Atresia

Background: The horseshoe lung is a congenital malformation in which the bases of the right and the left lung are fused. Case report: We describe a monochorionic twin gestation with malformation discordance. The abnormal twin had a horseshoe lung with hypoplasia of the right lung, tricuspid atresia, cleft lip, and a pelvic right kidney. Conclusion: The discordance of anomalies in this monochorionic twin suggests that a postzygotic mutation, epigenetic change, or environmental factors may be responsible for these malformations.

Inferior Right Ventricular Wall Thickness by Echocardiogram: A Novel Method of Assessing Hypertrophy in Neonates and Infants

An established echocardiographic (echo) standard for assessing the newborn right ventricle (RV) for hypertrophy has not been thoroughly developed. This is partially due to the RV's complex architecture, which makes quantification of RV mass by echo difficult. Here, we retrospectively evaluate the thickness of the inferior RV wall (iRVWT) by echo in neonates and infants with normal cardiopulmonary physiology. Inferior RVWT was defined at the medial portion of the inferior wall of the RV at the mid-ventricular level, collected from a subxiphoid, short axis view. iRVWT was indexed to body surface area (BSA) to the 0.5 power and normalized to iLVWT to explore the best normalization method. Ninety-eight neonates and 32 infants were included in the final analysis. Mean age for neonates and infants was 2 days and 59 days, respectively. Mean ± SD for neonate and infant end-diastole iRVWT was 2.17 ± 0.35 mm and 1.79 ± 0.28 mm, respectively. There was no residual relationship between the index iRVWT and BSA (r = 0.03, p = NS). In the infant cohort, the iRVWT was significantly lower and iLVWT was significantly higher compared to neonate, consistent with known physiologic changes of RV and LV mass. Thus, iRVWT may serve as a reliable and accurate proxy for RV mass and the parameter warrants further evaluation.

Cardiac Anomalies in Liveborn and Stillborn Monochorionic Twins

BACKGROUND

Cardiovascular anomalies are more common in monochorionic twins, especially with twin-twin transfusion, compared to other twin types and to singletons. Because previous studies are based on fetal and neonatal echocardiography, more information is needed to study prevalence of cardiac anomalies in twin miscarriages, stillbirths, and children after the immediate neonatal period.

METHODS

With specific attention to cardiac anomalies, we reviewed the medical records of 335 selected liveborn twin pairs from the Marshfield Clinic Twin Cohort (enriched for twin-twin transfusion) and all twins (175 pairs) identified in the Wisconsin Stillbirth Service Program cohort of late miscarriages and stillbirths.

RESULTS

Structural cardiac defects occurred in 12% of liveborn monochorionic twin infants and 7.5% of stillborn infants with twin-twin transfusion compared to only 2% of liveborn dizygotic twins and no stillborn dizygotic infants. The most common cardiac lesion in liveborn twins was ventricular septal defect, which was usually isolated and discordant, preferentially affecting the smaller twin in monochorionic pairs. Among stillborn and miscarried monochorionic twins, the most common cardiac lesion was acardia.

CONCLUSIONS

Monochorionic twins, particularly those with TTT, are at increased risk for a spectrum of structural cardiac malformations which we suggest may be related to asymmetry of the inner cell mass resulting in a smaller poorly perfused twin. In severe cases, limited cardiac and circulatory development in the affected twin leads to acardia. In less severe cases, the smaller infant has deficient septal growth that sometimes results in ventricular septal defect.

Discordant malformations in monochorionic twins: a retrospective cohort study in La Reunion Island

Background: Discordant malformation between monochorionic twins is a rare and unknown phenomenon.Objectives: To estimate the incidence of discordant monochorionic twins and to describe their characteristics.Study design: A retrospective multicenter cohort of pregnancies between 2002 and 2015 in La Reunion Island was analyzed, thanks to a population-based register. Only monochorionic pregnancies were included in order to analyze specifically monozygotic twins. We defined as discordant twin pairs those in which different malformations were identified for each twin and those with only one fetus showing a malformation.Results: During the study period, 203,807 births occurred, including 410 monochorionic twin pairs. Congenital anomalies rate for monochorionic twin pairs was 10.7%. We included 38 monochorionic twin pairs with discordant phenotypes, which represent 9.3% of monochorionic twin pairs and 86.4% of monochorionic twin pairs affected by congenital anomalies. Among them, both twins were affected by different congenital anomalies in 7 pairs (18.4%), and only one twin was affected in 31 pairs (81.6%). We identified 20 congenital heart anomalies (44.4%), 5 brain anomalies (11.1%), 5 genital anomalies (11.1%), 4 axial bones and skull anomalies (8.9%), 4 limb anomalies (8.9%), 4 facial anomalies (8.9%), 3 urological anomalies (6.6%), 2 thoracic anomalies (4.4%), 1 bile duct anomaly (2,2%), 1 abdominal parietal defect (2.2%), and 1 aneuploidy (2.2%). Among them, 3 (6.6%) fetuses had an association of malformations. Among the 45 fetuses with malformations, 37 fetuses (82.2%) were born alive and 21 (46.6%) had postnatal surgery.Conclusions: Despite a supposed identical genome, discordant congenital anomalies in monochorionic twin pregnancies are not exceptional and related to genetic and epigenetic mechanisms. Sonographers and pediatricians should know that in monochorionic twin a pair, the occurrence of discordant phenotypes is high (9.3%).

The burden to be second twin: a population-based study of 2686 twins: (2124 dichorionic). Proposal of the concept of mobility

Objectives: To identify if there is a specific neonatal morbidity/mortality among second twins relative to first twins.Study design: A 17-year (2001-2017) population-based observational cohort of all twin newborns born in the South of Reunion island after 21 weeks.Results: Among 1062 dichorionic (DTP) and 281 monochorionic twin pregnancies (2686 newborns), twin 2 have a doubled risk to be in breech presentation and a bad Apgar at 1 mn (≤6) in vaginal deliveries. Specific to dichorionic pregnancies, twin 2 were lighter by 50-60 g than twin 1, had higher rates of intrauterine growth retardation (IUGR), OR 1.33, p = .007, a doubled risk to have congenital abnormalities OR 2.1, p = .006.Conclusion: In dichorionic twin pregnancies, second twins having a doubled prevalence of severe congenital abnormalities are not completely elucidated and deserves further research. (1) We propose that twin 2 presenting higher risks of being IUGR and much higher risks of severe malformations suggest that during pregnancy, the less mobile of the two twins is "relegated" to the back of the uterus. (2) For interventions in the delivery room, systematically the most experimented neonatologist should plan to manage the second twin because significantly twin 2 presents higher problems than twin 1.

Copy Number Variants and Exome Sequencing Analysis in Six Pairs of Chinese Monozygotic Twins Discordant for Congenital Heart Disease

Congenital heart disease (CHD) is one of the most common birth defects. More than 200 susceptibility loci have been identified for CHDs, yet a large part of the genetic risk factors remain unexplained. Monozygotic (MZ) twins are thought to be completely genetically identical; however, discordant phenotypes have been found in MZ twins. Recent studies have demonstrated genetic differences between MZ twins. We aimed to test whether copy number variants (CNVs) and/or genetic mutation differences play a role in the etiology of CHDs by using single nucleotide polymorphism (SNP) genotyping arrays and whole exome sequencing of twin pairs discordant for CHDs. Our goal was to identify mutations present only in the affected twins, which could identify novel candidates for CHD susceptibility loci. We present a comprehensive analysis for the CNVs and genetic mutation results of the selected individuals but detected no consistent differences within the twin pairs. Our study confirms that chromosomal structure or genetic mutation differences do not seem to play a role in the MZ twins discordant for CHD.

The changing epidemiology of Ebstein's anomaly and its relationship with maternal mental health conditions: a European registry-based study

OBJECTIVES

The aim of this study was to describe the epidemiology of Ebstein's anomaly in Europe and its association with maternal health and medication exposure during pregnancy.

DESIGN

We carried out a descriptive epidemiological analysis of population-based data.

SETTING

We included data from 15 European Surveillance of Congenital Anomalies Congenital Anomaly Registries in 12 European countries, with a population of 5.6 million births during 1982-2011. Participants Cases included live births, fetal deaths from 20 weeks gestation, and terminations of pregnancy for fetal anomaly. Main outcome measures We estimated total prevalence per 10,000 births. Odds ratios for exposure to maternal illnesses/medications in the first trimester of pregnancy were calculated by comparing Ebstein's anomaly cases with cardiac and non-cardiac malformed controls, excluding cases with genetic syndromes and adjusting for time period and country.

RESULTS

In total, 264 Ebstein's anomaly cases were recorded; 81% were live births, 2% of which were diagnosed after the 1st year of life; 54% of cases with Ebstein's anomaly or a co-existing congenital anomaly were prenatally diagnosed. Total prevalence rose over time from 0.29 (95% confidence interval (CI) 0.20-0.41) to 0.48 (95% CI 0.40-0.57) (p<0.01). In all, nine cases were exposed to maternal mental health conditions/medications (adjusted odds ratio (adjOR) 2.64, 95% CI 1.33-5.21) compared with cardiac controls. Cases were more likely to be exposed to maternal β-thalassemia (adjOR 10.5, 95% CI 3.13-35.3, n=3) and haemorrhage in early pregnancy (adjOR 1.77, 95% CI 0.93-3.38, n=11) compared with cardiac controls.

CONCLUSIONS

The increasing prevalence of Ebstein's anomaly may be related to better and earlier diagnosis. Our data suggest that Ebstein's anomaly is associated with maternal mental health problems generally rather than lithium or benzodiazepines specifically; therefore, changing or stopping medications may not be preventative. We found new associations requiring confirmation.

Congenital heart disease in twins: The contribution of type of conception and chorionicity

BACKGROUND

Increased incidence of congenital heart disease (CHD) has been reported in the offspring of monochorionic twin gestations. Assisted reproductive technology (ART), which is related to increased rates of twinning, has also been associated with higher risk of birth defects. We studied the incidence of CHD in a cohort of twins to clarify the contribution of type of conception and chorionicity.

METHODS

Data concerning 874 live-born twins of which at least one was admitted in our Neonatal Unit during 1995-2012 were analysed. Forty-five % (N=197) of the gestations resulted from ART (in vitro fertilisation or intracytoplasmic sperm insertion).

RESULTS

In the ART group 32/389 (8.2%) had CHD compared to 21/485 (4.3%) infants conceived naturally (OR 1.90, 95%CI 1.08-3.34, p=0.024). Spontaneous-conception gestations had higher incidence of monochorionic placentation (47/245 versus 4/197, p<0.001), and included younger mothers (29.1±5.2 versus 33.9±5.5years, p<0.001) who had higher parity (median 2 [range 1-7] versus 1 Pinborg (2005), Blondel and Kaminski (2002), Knopman et al. (2014), Kyvik and Derom (2006) ; p<0.001). Multivariable logistic regression analysis showed that ART (OR 2.60, 95% CI 1.24-5.45) and monochorionicity (OR 3.49, 95% CI 1.57-7.77) were significant determinants of CHD, independently of maternal age, parity, and the gender of the offspring.

CONCLUSIONS

We confirmed that monochorionic twins have increased risk of CHD and we documented a higher incidence of CHD in ART twins independently of chorionicity. We suggest improvement of echocardiographic skills of health care professionals involved in prenatal screening and foetal cardiology referral of ART dichorionic twins with suspicious findings at screening, in addition to all monochorionic gestations.

Managing Monoamniotic Twin Pregnancies

Monoamniotic twins comprise a rare but important subset of twins at risk of unique and serious complications, placing them at the highest risk of perinatal mortality of all twin gestations. In addition to risks faced by all twins (prematurity, selective growth restriction), all monochorionic twins (twin-twin transfusion syndrome), and all monozygotic twins (congenital anomalies), monoamniotic twins face the unique risk of cord entanglement. Accordingly, early diagnosis, screening for fetal anomalies, surveillance for twin-twin transfusion syndrome, decisions related to monitoring after viability, and timing and route of delivery are all critical. Herein, we present recommendations for optimal management.

The management of conjoined twins: Cardiology assessment

Structural cardiac defects occur in at least 1 twin in about 75% of conjoined twins with thoracic level fusion. Outcomes after surgical separation of thoracic level conjoined twins have been favorable when the hearts have been separate. However, even in this situation, the outlook is poor for an individual twin with an important cardiac defect. Arterial anastomosis between twin circulations is an important additional consideration, with poor outcomes for perfusion recipient twins. Surgical separation is contraindicated when ventricular level cardiac fusion exists. Cardiac assessment is a key component of prenatal counseling.

Cardiac function in 10-year-old twins following different fetal therapies for twin-twin transfusion syndrome

OBJECTIVES

To compare cardiac function at 10 years of age in four groups of monochorionic diamniotic (MCDA) twin pairs: uncomplicated MCDA twins (n = 6) (Group 1); twins that had had twin-twin transfusion syndrome (TTTS) managed by amnioreduction (TTTS-amnio, n = 9) (Group 2) or laser photocoagulation (TTTS-laser, n = 10) (Group 3); and dichorionic diamniotic controls (DCDA, n = 6) (Group 4).

METHODS

Echocardiograms optimizing apical four-chamber and short-axis left ventricular views were stored for offline speckle-tracking analysis, blinded to twin type. Myocardial long-axis shortening and lengthening velocities were measured using pulsed Doppler ultrasound at the cardiac base. M-mode measurements of fractional shortening (short axis) and maximal excursion of the atrioventricular annulus (four-chamber) were recorded. Syngo Vector Velocity Imaging software tracked left ventricular myocardial motion offline to produce free wall strain, strain rate and rotation. Intertwin pair and group differences were investigated using ANOVA.

RESULTS

Cardiac measurements were within the normal ranges for 10-year-olds. No significant within-twin-pair and intergroup differences were found in current size, heart rates, strain or strain rate. Compared to DCDA controls, TTTS twins showed less cardiac rotation (TTTS-laser, P < 0.001 and TTTS-amnio, P = 0.054) with significant intertwin reduction in the ex-recipient (TTTS-amnio, P = 0.006) and larger MCDA twins (P = 0.027) compared with their cotwins. A similar pattern was seen in left ventricular early diastolic mitral valve tissue velocity (MVE') in all monochorionic groups, but only achieving significance in TTTS-amnio twins (P = 0.037). Intrapair differences in rotation and MVE' were significantly different following treatment at Quintero stages III or IV.

CONCLUSIONS

Within-twin-pair patterns of left ventricular rotation and diastolic function differ at 10 years of age in ex-recipients of TTTS twins treated with amnioreduction compared with those treated by laser photocoagulation and controls. .

Assessing the role of multiple pregnancies in the association between tetralogy of Fallot and assisted reproductive techniques: a path-analysis approach

Background

Assisted reproductive techniques (ART) are associated with a higher risk of tetralogy of Fallot (TOF) and multiple pregnancies may be associated with a higher risk of congenital anomalies. We assessed the extent to which the association between ART and risk of TOF may be mediated by the higher risk of multiple pregnancies associated with ART.

Methods

We conducted a case–control study using population-based data from the Paris Registry of Congenital Malformations for the period 1987–2009 and a cohort study of congenital heart defects (EPICARD). The study population included 395 cases of TOF and 4104 malformed controls with no known associations with ART. The analysis was based on a path-analysis model using a counterfactual approach, which allows decomposition of the total effect of ART into an indirect effect (that mediated by the association between ART and multiple pregnancies) and a direct effect.

Results

ART (all methods combined) were associated with a 2.6-fold higher odds of TOF after adjustment for maternal and paternal characteristics and year of birth (adjusted OR 2.6, 95% CI, 1.5-4.5). Most (79%) of the effect associated with ART was a direct effect (i.e., not mediated by multiple pregnancies), whereas 21% of the effect of ART was due to its association with multiple pregnancies (i.e., the indirect effect). In vitro fertilization with intracytoplasmic sperm injection was associated with a 3.5-fold higher odds of TOF (adjusted OR 3.5, 95% CI, 1.1-11.2); 11% of this effect was mediated through the association of ICSI with multiple pregnancies.

Conclusions

By far, most of the higher risk of TOF associated with ART is a direct effect and only a small proportion of the effect may be mediated by multiple pregnancies.

Association of twinning and maternal age with major structural birth defects in Utah, 1999 to 2008

BACKGROUND

Twinning is a risk factor for birth defects. Using population-based data from the Utah Birth Defect Network and the Utah Department of Health Vital Records, we investigated whether twinning increases the risk of major structural birth defects in live-born opposite-sex (OS) and same-sex (SS) twins as proxies for monozygotic and dizygotic twins, respectively. We also assessed whether maternal age modified the association between twinning and birth defects.

METHODS

All resident live-born singleton (n = 492,143) and twin (n = 13,596) infants issued a Utah birth certificate and delivered from 1999 through 2008 were included. Unadjusted and adjusted odds ratios (aORs) with 95% confidence intervals were calculated for each birth defect using unconditional logistic regression.

RESULTS

Birth defects were slightly more likely to occur in SS (aOR = 1.94; 95% confidence interval, 1.70-2.21) than OS (aOR = 1.55; 95% confidence interval, 1.27-1.90) twins. The aORs stratified by maternal age did not show a trend for any twin type when calculated for all birth defects combined. However, trends were observed for coarctation, pyloric stenosis, and shaft or penoscrotal hypospadias in OS twins; microcephaly, anotia/microtia, conotruncal defects, membranous ventricular septal defects, pyloric stenosis, all hypospadias, and craniosynostosis in SS twins; and tetralogy of Fallot, right ventricular outflow tract obstructions, renal agenesis/hypoplasia, and craniosynostosis in all twins.

CONCLUSION

All twin types have an increased risk for birth defects compared with singletons. SS twins have the highest risk, presumably due to the influence of monozygotic twins. The risk for birth defects in twins was not significantly modified by the mother's age.

Epigenetic epidemiology in psychiatry: A translational neuroscience perspective

Accumulating evidence from the field of neuroscience indicates a crucial role for epigenetic regulation of gene expression in development and aging of nervous system and suggests that aberrations in the epigenetic machinery are involved in the etiology of psychiatric disorders. Epidemiologic evidence on epigenetics in psychiatry, however, is currently very sparsely available, but is consistent with a mediating role for epigenetic mechanisms in bringing together inherited and acquired risk factors into a neurodevelopmental etiological model of psychiatric disorders. Here, we review evidence from the epidemiological and neuroscience literature, and aim to converge the evidence into an etiological model of psychiatric disorders that encompasses environmental, genetic and epigenetic contributions. Given the dynamic nature of the epigenetic machinery and the potential reversibility of epigenetic modifications, future well-designed interdisciplinary and translational studies will be of key importance in order to identify new targets for prevention and therapeutic strategies.

No major role for X-inactivation in variations of intelligence and behavioral problems at middle childhood

Although members of monozygotic (MZ) twin pairs are identical in genomic sequence, epigenetic mechanisms may occasion difference in gene expression and, consequently, twin discordance in complex traits. Recent work suggests that the epigenetic process of X-inactivation in female individuals may impact on intelligence and child behavioral problems. The timing of X-inactivation has been linked to chorionic splitting in MZ twins. Dichorionic monozygotic (DC-MZ) twinning, unlike monochorionic monozygotic (MC-MZ) twinning, occurs prior to the time of X-inactivation in female organisms. Therefore, the hypothesis of a causal role of X-inactivation in intelligence and behavioral problems can be analyzed by modeling the statistical interaction between sex and chorion type for within-pair differences in these traits in MZ twins. In this study, the effect of X-inactivation on childhood behavioral problems, measured with the CBCL, was studied in a sample of 324 MZ twin pairs from the EFPTS and the effect of X-inactivation on IQ was studied in a sample of 272 twin pairs from the same twin survey. Information on chorion type, gestational age, and birth weight was additionally collated. No significant statistical interaction was found between sex and chorion type, indicating that X-inactivation is not likely involved in variations in intelligence or behavioral problems in middle childhood. Further studies are required to replicate these findings and may explore the role of X-inactivation at different ages or at the extreme scores in the spectrum of intelligence and behavioral problems or may focus on other epigenetic mechanisms.

Consistent left-right asymmetry cannot be established by late organizers in Xenopus unless the late organizer is a conjoined twin

How embryos consistently orient asymmetries of the left-right (LR) axis is an intriguing question, as no macroscopic environmental cues reliably distinguish left from right. Especially unclear are the events coordinating LR patterning with the establishment of the dorsoventral (DV) axes and midline determination in early embryos. In frog embryos, consistent physiological and molecular asymmetries manifest by the second cell cleavage; however, models based on extracellular fluid flow at the node predict correct de novo asymmetry orientation during neurulation. We addressed these issues in Xenopus embryos by manipulating the timing and location of dorsal organizer induction: the primary dorsal organizer was ablated by UV irradiation, and a new organizer was induced at various locations, either early, by mechanical rotation, or late, by injection of lithium chloride (at 32 cells) or of the transcription factor XSiamois (which functions after mid-blastula transition). These embryos were then analyzed for the position of three asymmetric organs. Whereas organizers rescued before cleavage properly oriented the LR axis 90% of the time, organizers induced in any position at any time after the 32-cell stage exhibited randomized laterality. Late organizers were unable to correctly orient the LR axis even when placed back in their endogenous location. Strikingly, conjoined twins produced by late induction of ectopic organizers did have normal asymmetry. These data reveal that although correct LR orientation must occur no later than early cleavage stages in singleton embryos, a novel instructive influence from an early organizer can impose normal asymmetry upon late organizers in the same cell field.

Health care supervision for twin pairs

Twins are at increased risk for congenital anomalies and have particular health care needs, but twin management guidelines do not exist. This review attempts to integrate the latest research findings and evidence-based medicine on twins into basic clinical recommendations for general pediatricians.

Long segment congenital tracheal stenosis in twins successfully treated by slide tracheoplasty

Long segment congenital tracheal stenosis (LSCTS), associated with complete tracheal rings, is a rare condition, difficult to manage and historically associated with high mortality rate. We report two pairs of identical twins all affected by LSCTS successfully treated by sliding tracheoplasty. All had severe respiratory distress. Three infants had left pulmonary artery (LPA) sling and one intra-cardiac malformation. Slide tracheoplasty was done under cardiopulmonary bypass, and cardiovascular malformations were corrected at the same time. One child needed plication of paralyzed right hemi-diaphragm and another distal tracheal Palmaz stent insertion due severe tracheobronchomalacia. All children are doing well during 6 months follow-up. Slide tracheoplasty seems to produce the same good early results in twins as for singletons with LSCTS.