Mechanisms of Congenital Malformations in Pregnancies with Pre-existing Diabetes

Congenital anomalies in pregnancies with overt and pregestational type 2 diabetes: a gray portrayal from a cohort in Brazil

OBJECTIVE

To describe the frequency and types of congenital anomalies and associated risk factors in Brazilian women with type 2 diabetes.

METHODS

In this retrospective cohort study between 2005 and 2021, we included all pregnant participants with type 2 diabetes from the two major public hospitals in southern Brazil. We collected data from the electronic hospital records. Congenital anomalies were classified by the 10th revised International Classification of Diseases, Q chapter, enhanced by the EUROCAT registry classification, and categorized by type and gravity. We used multiple Poisson regression with robust estimates to estimate risks.

RESULTS

Among 648 participants, we excluded 19, and 62 were lost to follow-up; therefore, we included 567 participants. Overt diabetes arose in 191 participants (33.7%, 95% CI 30.0% - 38.0%). Less than 20% of the participants supplemented folate. Congenital anomalies occurred in 78 neonates (13.8%, CI 11.0 - 16.9%), 73 babies (93.6%) presented major anomalies, and 20 (10.5%) cases occurred in participants with overt diabetes. Cardiac anomalies were the most frequent (43 isolated and 12 combined). Pre-eclampsia was associated with an increased risk in the analyses including all women (adjusted RR 1.87 (95% CI 1.23-2.85), p = 0.003), but not in analyses including only women with an HbA1c measured up to the 14th gestational age. HbA1c, either measured at any time in pregnancy (adjusted RR 1.21 (95% CI 1.10-1.33), p < 0.001) or up to the first 14 weeks (adjusted RR 1.22, 95% CI 1.10-1.35, p < 0.001) was the only sustained risk factor. Risk factors such as maternal age, obesity, diabetes diagnosis, or use of antidiabetic medications were not associated with congenital anomalies.

CONCLUSION

We found a high frequency of congenital anomalies associated with poor maternal glycemic control and revealed an almost universal lack of preconception care. An urgent call to action is mandatory for the reversal of this gray scenario.

p53 inhibitor or antioxidants reduce the severity of ethmoid plate deformities in zebrafish Type 3 Treacher Collins syndrome model

Treacher Collins syndrome-3 (TCS-3) is a rare congenital craniofacial disorder attributed to variants in the RNA pol I subunit C (POLR1C). The pathogenesis of TCS-3 linked to polr1c involves the activation of apoptosis-dependent p53 pathways within neural crest cells (NCCs). This occurs due to disruptions in ribosome biogenesis, and the restoration of polr1c expression in early embryogenesis effectively rescues the observed craniofacial phenotype in polr1c-deficient zebrafish. Clinical variability in TCS patients suggests interactions between genes and factors like oxidative stress. Elevated production of reactive oxygen species (ROS) in epithelial cells may worsen phenotypic outcomes in TCS individuals. Our study confirmed excessive ROS production in facial regions, inducing apoptosis and altering p53 pathways. Deregulated cell-cycle and epithelial-to-mesenchymal transition (EMT) genes were also detected in the TCS-3 model. Utilizing p53 inhibitor (Pifithrin-α; PFT-α) or antioxidants (Glutathione; GSH and N-Acetyl-L-cysteine; NAC) effectively corrected migrated NCC distribution in the pharyngeal arch (PA), suppressed oxidative stress, prevented cell death, and modulated EMT inducers. Crucially, inhibiting p53 activation or applying antioxidants within a specific time window, notably within 30 h post-fertilization (hpf), successfully reversed phenotypic effects induced by polr1c MO.

Analysis of Gut Characteristics and Microbiota Changes with Maternal Supplementation in a Neural Tube Defect Mouse Model

Adequate nutrient supply is crucial for the proper development of the embryo. Although nutrient supply is determined by maternal diet, the gut microbiota also influences nutrient availability. While currently there is no cure for neural tube defects (NTDs), their prevention is largely amenable to maternal folic acid and inositol supplementation. The gut microbiota also contributes to the production of these nutrients, which are absorbed by the host, but its role in this context remains largely unexplored. In this study, we performed a functional and morphological analysis of the intestinal tract of loop-tail mice (Vangl2 mutants), a mouse model of folate/inositol-resistant NTDs. In addition, we investigated the changes in gut microbiota using 16S rRNA gene sequencing regarding (1) the host genotype; (2) the sample source for metagenomics analysis; (3) the pregnancy status in the gestational window of neural tube closure; (4) folic acid and (5) D-chiro-inositol supplementation. We observed that Vangl2+/Lp mice showed no apparent changes in gastrointestinal transit time or fecal output, yet exhibited increased intestinal length and cecal weight and gut dysbiosis. Moreover, our results showed that the mice supplemented with folic acid and D-chiro-inositol had significant changes in their microbiota composition, which are changes that could have implications for nutrient absorption.

Effects of dietary polyphenols on maternal and fetal outcomes in maternal diabetes

The incidences of short-term or long-term adverse maternal and fetal outcomes caused by maternal diabetes are increasing. Due to toxicity or side effects, economic pressures, and other problems associated with injections or oral hypoglycemic drugs, many researchers have investigated natural treatment methods. Polyphenols can protect against chronic pathologies by regulating numerous physiological processes and provide many health benefits. Moreover, polyphenols have anti-diabetic properties and can be used to treat diabetic complications. Diets rich in polyphenols are beneficial to pregnant women with diabetes. Here, we review the epidemiological and experimental evidence on the impact of dietary polyphenols on maternal and fetal outcomes in pregnant women with diabetes, and the effects of polyphenols on biological changes and possible mechanisms. Previous data (mainly from in vitro and animal experiments) showed that polyphenols can alleviate gestational diabetes mellitus and diabetic embryopathy by reducing maternal hyperglycemia and insulin resistance, alleviating inflammation and oxidative stress, and regulating related signaling pathways. Although polyphenols have shown many health benefits, further research is needed to better understand the complex interactions between polyphenols and maternal diabetes.

Pre-gestational diabetes and the risk of congenital heart defects in the offspring: A French nationwide study

AIM

To compare the frequencies and types of congenital heart defects for infants of women without and with pre-gestational diabetes, type 1 and type 2 diabetes (T1DM, T2DM) and to identify risk factors.

METHODS

All live births between 2012 and 2020 were screened for maternal diabetes and infant congenital heart defects using the French Medical Information System Program in Medicine, Surgery and Obstetrics database (PMSI-MCO). Incidences of these defects were estimated, and a logistic model evaluated maternal and fetal prognostic risk factors.

RESULTS

Overall, 6,038,703 mothers did not have pre-gestational diabetes (no-diabetes), 23,147 had T1DM, and 14,401 had T2DM. The incidence of infant congenital disease was 6.2% for the no-diabetes group, 8.0%, for women with T1DM, and 8.4% for women with T2DM (P < 0.001); for congenital heart defects, incidences were respectively 0.8%, 3.0% and 2.7% (P < 0.001). In comparison with the no-diabetes group, the odds ratios (95%CI) of coronary heart defects were 2.07 (1.91;2.24) (P < 0.001) for women with T1DM and 2.20 (1.99;2.44) (P < 0.001) for women with T2DM, with no difference between T1DM and T2DM (P = 0.336). cesarian section, small and large for gestational age, and prematurity were also associated with an increased risk of congenital heart defects.

CONCLUSION

In this study we observed higher incidences of congenital heart defects in infants of women with pre-gestational diabetes compared to women without pre-gestational diabetes, with no difference between women with T1DM or T2DM. These data call for intensifying preconception care and justify systematic cardiac echography in selected fetuses.

Folate Supplementation in Women with Pre-Existing Diabetes

Folate supplementation in the periconceptual period is the standard of care for the prevention of neural tube defects. To support dietary folate intake, some countries have introduced mandatory folic acid fortification of food products. Robust evidence supports the additional use of a low-dose folic acid supplement (0.4 mg/day) in all women from 2-3 months preconception until the end of the 12th week of gestation. For women with pre-existing diabetes, high-dose folic acid supplementation (5 mg/day) is recommended in some, but not all international guidelines. The recommendation is made based on consensus opinion and reflects the increased risk of neural tube defects in pregnant women with pre-existing diabetes. However, there is limited evidence to clarify the high-risk groups that benefit from high-dose folic acid versus those that do not. There are also some data to suggest that high-dose folic acid may be harmful to mothers and offspring, although this issue remains controversial. This narrative review explores the evidence that supports the recommendation for women with pre-existing diabetes to take high-dose folic acid in the periconceptual period. It explores the potential benefits of high-dose supplemental folate beyond the prevention of neural tube defects, and also the potential adverse impacts of high-dose folate use. These topics are considered with a specific focus on the issues that are pertinent to women with pre-existing diabetes. Based on the available evidence, a pragmatic approach to the use of folic acid supplements in women with pre-existing diabetes during the periconception period is suggested. The need for comprehensive preconception care that optimises glycaemic control and addresses other modifiable risk factors before pregnancy is emphasized.

High glucose causes developmental abnormalities in neuroepithelial cysts with actin and HK1 distribution changes

It has been reported that the offspring of diabetic pregnant women have an increased risk for neural tube defects. Previous studies in animal models suggested that high glucose induces cell apoptosis and epigenetic changes in the developing neural tube. However, effects on other cellular aspects such as the cell shape changes were not fully investigated. Actin dynamics plays essential roles in cell shape change. Disruption on actin dynamics is known to cause neural tube defects. In the present study, we used a 3D neuroepithelial cyst model and a rosette model, both cultured from human embryonic stem cells, to study the cellular effects caused by high glucose. By using these models, we observed couple of new changes besides increased apoptosis. First, we observed that high glucose disturbed the distribution of pH3 positive cells in the neuroepithelial cysts. Secondly, we found that high glucose exposure caused a relatively smaller actin inner boundary enclosed area, which was unlikely due to osmolarity changes. We further investigated key glucose metabolic enzymes in our models and the results showed that the distribution of hexokinase1 (HK1) was affected by high glucose. We observed that hexokinase1 has an apical-basal polarized distribution and is highest next to actin at the boundaries. hexokinase1 was more diffused and distributed less polarized under high glucose condition. Together, our observations broadened the cellular effects that may be caused by high glucose in the developing neural tube, especially in the secondary neurulation process.

Glycemic and nonglycemic mechanisms of congenital malformations in hyperglycemic pregnancies: a narrative review

Congenital malformations are more frequently found among children born to mothers with diabetes than in the background population. There are several complex mechanisms involved in the development of congenital malformations in the offspring of mothers with hyperglycemia, such as the overexpression of glucose transporters (GLUTs) 1 and 2, the increased activity of the hexosamine biosynthetic pathway and the reduced expression of the PAX3 gene with a consequent increase in p53 protein expression. These alterations can lead to increased glucose and free radical concentrations in the embryo, thus promoting the process of apoptosis and causing malformation. The most frequent malformations found in the offspring of mothers with diabetes are heart and neural tube defects, urinary tract and kidney malformations, and cleft lip with or without cleft palate. Strict glycemic control should be obtained before and during pregnancy, aiming to avoid or minimize the risk of congenital malformations in the offspring. Beyond hyperglycemia, several factors may also be associated with increased risks of malformations in the offspring of these women, such as obesity, multiple pregnancies, advanced maternal age, folic acid deficiency, use of angiotensin converting enzyme inhibitors and angiotensin receptor blockers, assisted reproduction techniques, and exposure to different types of environmental pollutants.

Diabetic Embryopathies

Diabetic embryopathy is defined as congenital anomalies that are linked to maternal diabetes. The association between diabetes and fetal, neonatal, and long-term complications is well-established. These complications include organ or structural maldevelopment, fetal growth abnormalities, and learning/psychiatric comorbidities. Recent studies have elucidated the pathophysiology behind these conditions and outlined new management approaches. Caudal regression syndrome, also known as sacral agenesis, is a well-known but less described complication of maternal diabetes. The purpose of this review is to summarize existing research on common neonatal morbidities in infants of mothers with diabetes with a focus on caudal regression syndrome and its long-term associations.

Pathogenesis of neural tube defects: The regulation and disruption of cellular processes underlying neural tube closure

Neural tube closure (NTC) is crucial for proper development of the brain and spinal cord and requires precise morphogenesis from a sheet of cells to an intact three-dimensional structure. NTC is dependent on successful regulation of hundreds of genes, a myriad of signaling pathways, concentration gradients, and is influenced by epigenetic and environmental cues. Failure of NTC is termed a neural tube defect (NTD) and is a leading class of congenital defects in the United States and worldwide. Though NTDs are all defined as incomplete closure of the neural tube, the pathogenesis of an NTD determines the type, severity, positioning, and accompanying phenotypes. In this review, we survey pathogenesis of NTDs relating to disruption of cellular processes arising from genetic mutations, altered epigenetic regulation, and environmental influences by micronutrients and maternal condition. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Stem Cells and Development.

Systems biology analysis of human genomes points to key pathways conferring spina bifida risk

Genetic investigations of most structural birth defects, including spina bifida (SB), congenital heart disease, and craniofacial anomalies, have been underpowered for genome-wide association studies because of their rarity, genetic heterogeneity, incomplete penetrance, and environmental influences. Our systems biology strategy to investigate SB predisposition controls for population stratification and avoids much of the bias inherent in candidate gene searches that are pervasive in the field. We examine both protein coding and noncoding regions of whole genomes to analyze sequence variants, collapsed by gene or regulatory region, and apply machine learning, gene enrichment, and pathway analyses to elucidate molecular pathways and genes contributing to human SB.

Spina bifida (SB) is a debilitating birth defect caused by multiple gene and environment interactions. Though SB shows non-Mendelian inheritance, genetic factors contribute to an estimated 70% of cases. Nevertheless, identifying human mutations conferring SB risk is challenging due to its relative rarity, genetic heterogeneity, incomplete penetrance, and environmental influences that hamper genome-wide association studies approaches to untargeted discovery. Thus, SB genetic studies may suffer from population substructure and/or selection bias introduced by typical candidate gene searches. We report a population based, ancestry-matched whole-genome sequence analysis of SB genetic predisposition using a systems biology strategy to interrogate 298 case-control subject genomes (149 pairs). Genes that were enriched in likely gene disrupting (LGD), rare protein-coding variants were subjected to machine learning analysis to identify genes in which LGD variants occur with a different frequency in cases versus controls and so discriminate between these groups. Those genes with high discriminatory potential for SB significantly enriched pathways pertaining to carbon metabolism, inflammation, innate immunity, cytoskeletal regulation, and essential transcriptional regulation consistent with their having impact on the pathogenesis of human SB. Additionally, an interrogation of conserved noncoding sequences identified robust variant enrichment in regulatory regions of several transcription factors critical to embryonic development. This genome-wide perspective offers an effective approach to the interrogation of coding and noncoding sequence variant contributions to rare complex genetic disorders.

Unraveling the complex genetics of neural tube defects: From biological models to human genomics and back

Neural tube defects (NTDs) are a classic example of preventable birth defects for which there is a proven-effective intervention, folic acid (FA); however, further methods of prevention remain unrealized. In the decades following implementation of FA nutritional fortification programs throughout at least 87 nations, it has become apparent that not all NTDs can be prevented by FA. In the United States, FA fortification only reduced NTD rates by 28-35% (Williams et al., 2015). As such, it is imperative that further work is performed to understand the risk factors associated with NTDs and their underlying mechanisms so that alternative prevention strategies can be developed. However, this is complicated by the sheer number of genes associated with neural tube development, the heterogeneity of observable phenotypes in human cases, the rareness of the disease, and the myriad of environmental factors associated with NTD risk. Given the complex genetic architecture underlying NTD pathology and the way in which that architecture interacts dynamically with environmental factors, further prevention initiatives will undoubtedly require precision medicine strategies that utilize the power of human genomics and modern tools for assessing genetic risk factors. Herein, we review recent advances in genomic strategies for discovering genetic variants associated with these defects, and new ways in which biological models, such as mice and cell culture-derived organoids, are leveraged to assess mechanistic functionality, the way these variants interact with other genetic or environmental factors, and their ultimate contribution to human NTD risk.

Zuogui Wan alleviated maternal kidney-yin deficiency-induced thymic epithelial cell dysfunction in newborn rats through Wnt/β-catenin signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Kidney-yin deficiency (KYD) during pregnancy is common and associated with possibility of thymus hypoplasia in neonates. Zuogui Wan (ZGW) is a classic traditional medicine to treat KYD.

AIM OF STUDY

The Wnt/β-catenin signaling pathway is essential for thymic epithelial cell (TEC) viability, function and for thymus integrity. We evaluated whether maternal diets with ZGW in KYD rats ameliorates epithelial cell dysfunction in the fetal thymus, and investigated its underlying mechanism in which the Wnt/β-catenin signaling pathway is involved.

MATERIALS AND METHODS

Rats were randomly assigned to four groups (n = 8). Two experimental groups received KYD induction with or without ZGW supplementation. The other 2 vehicle groups were sham operated and administrated with normal saline or ZGW. KYD was established using periodically chronic shaken stimulus and threaten stress. Success of the model induction was evaluated by the general observation, changing of the body weight and plasma thyroxine level. Then, pregnant of vehicle and KYD rats were fed with or without ZGW-supplemented diet throughout the F1 gestation. Postnatal thymi samples were obtained after delivery for histological examination. In vitro, TECs of the newborn rats whose mother suffered KYD were isolated, and cultured using the serum containing ZGW with or without the supplement of Wnt4/β-catenin pathway inhibitor ICG-001. Cell viability was evaluated by CCK-8 assay. Meanwhile, the thymi tissues and TECs were collected for biochemical analysis. Levels of thymosin β4 (TMSβ4) and thymosin α1 (Tα1) were detected by ELISA assay. The mRNA and protein expression of Wnt4, β-catenin, and Foxn1 were determined by RT-qPCR and Western blot respectively.

RESULTS

In vivo, KYD resulted in significantly increased apoptosis of TECs and atrophy of the thymi, especially in the medullary zone. The morphological changes observed in KYD rats were ameliorated by ZGW treatment. Meanwhile, the decreased TMSβ4, Tα1, Wnt4, β-catenin, and Foxn1 levels in KYD rats were also significantly alleviated by ZGW administration. In vitro, elevated TMSβ4 and Tα1 levels accompanied with upregulated Wnt4, β-catenin, and Foxn1 expressions in the TECs were observed after ZGW intervention, however, which were significantly downregulated by ICG-001 supplement.

CONCLUSIONS

Maternal kidney-yin deficiency could result in TEC dysfunction in newborn rats. ZGW was able to improve the growth and development of TEC, potentially by regulating the Wnt/β-catenin pathway.

Special Considerations Regarding Antenatal Care and Pregnancy Complications in Dichorionic Twin Pregnancies

Twin pregnancies account for about 3.3% of all deliveries in the United States with the majority of them being dichorionic diamniotic (DCDA). Maternal physiological adaption in twin pregnancies is exaggerated and the rate of almost every maternal and fetal complication is higher when compared to singleton pregnancies. Therefore, twin pregnancies necessitate closer antenatal surveillance by care providers who are familiar with the specific challenges unique to these pregnancies, and there is evidence that following women with twins in a specialized twin clinic can result in improved obstetrical outcomes. The importance of the first antenatal visit in twin pregnancies cannot be over emphasized and should preferably take place early in gestation as it is the optimal period to correctly identify the number of fetuses and the type of placentation (chorionicity and amnionicity). This will allow the patients, families, and caregivers to make the appropriate modifications and to tailor an optimal antenatal follow-up plan. This plan should focus on general recommendations such as weight gain and level of activity, education regarding complications specific to twin pregnancies along with the relevant symptoms and indications to seek care, as well as on close maternal and fetal monitoring. In this review, we summarize available evidence and current guidelines regarding antenatal care in DCDA twin pregnancies.

Skeletal malformations and growth disturbances in fetuses of mild diabetic rats

Introducción.

En la actualidad, la diabetes mellitus representa una de las condiciones médicas que complica el embarazo con mayor frecuencia, lo que afecta el crecimiento y el desarrollo fetal.

Objetivo.

Determinar las malformaciones esqueléticas y alteraciones en el crecimiento en fetos de ratas Wistar diabéticas.

Materiales y métodos.

Se utilizó un modelo de diabetes moderada inducida neonatalmente con estreptozotocina (STZ 100 mg/kg de peso corporal, por vía subcutánea) en ratas Wistar. En la adultez, las ratas sanas y diabéticas se aparearon con machos sanos de la misma edad y cepa. El día 20 de gestación se practicó la cesárea bajo anestesia. Se extrajeron los fetos, se pesaron y clasificaron como pequeños (PAG), adecuados (AEG) o grandes (GEG) para la edad gestacional. Los fetos seleccionados se procesaron para el análisis de anomalías esqueléticas y sitios de osificación.

Resultados.

En la descendencia de las ratas diabéticas, hubo un mayor porcentaje de fetos clasificados como pequeños o grandes y un menor porcentaje de fetos con peso adecuado; el promedio de peso fetal fue menor y había menos sitios de osificación. Se observaron alteraciones en la osificación de cráneo, esternón, columna vertebral, costillas y extremidades anteriores y posteriores; y también, hubo una correlación directa entre el peso y el grado de osificación fetal.

Hubo malformaciones congénitas asociadas con la fusión y bifurcación de las costillas, así como cambios indicativos de hidrocefalia, como la forma de domo del cráneo, una amplia distancia entre los parietales y la anchura de las fontanelas anterior y posterior.

Conclusión.

La diabetes moderada durante la gestación altera el crecimiento y el desarrollo fetal, que se ve afectado tanto por macrosomía y la restricción del crecimiento intrauterino como por malformaciones esqueléticas.

Organisational alteration of cardiac myofilament proteins by hyperglycaemia in mouse embryonic stem cell-derived cardiomyocytes

The exposure of the developing foetal heart to hyperglycaemia in mothers with diabetes mellitus is a major risk factor for foetal cardiac complications that lead to heart failure. We studied the effects of hyperglycaemia on the layout of cardiac myofilament proteins in stem cell-derived cardiomyocytes and their possible underlying mechanisms. Mouse embryonic stem cells (mESCs) were differentiated into cardiac-like cells and cultured in media containing baseline- or high glucose concentrations. Cellular biomarkers were detected using Western blot analysis, immunocytochemistry, 5-ethynyl-2'-deoxyuridine (EdU) cell proliferation assay, and terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) assay. High glucose decreased the proportion of cardiac troponin T and α-actinin 2 positive mESCs as well as disrupted the α-actinin 2 striated pattern and the distribution of the cardiac myosin heavy chain α- and β isoforms. However, there was no alteration of the cellular EdU uptake nor the expression of the receptor of advanced glycation end-product (RAGE). High glucose also increased the presence of the oxidative stress marker nitrotyrosine as well as the number of TUNEL-stained nuclei in cardiac-like cells. Treatment with the antioxidant N-acetyl cysteine decreased the number of TUNEL-stained cells in high glucose and improved the α-actinin 2 striated pattern. Hyperglycaemia negatively impacted the expression and cellular organisation of cardiac myofilament proteins in mESC-derived cardiomyocytes through oxidative stress. The results add further insights into the pathophysiological mechanisms of cardiac contractile dysfunction in diabetic cardiac developmental disease.

Diabetic Embryopathy Susceptibility in Mice Is Associated with Differential Dependence on Glucosamine and Modulation of High Glucose-Induced Oxidative Stress

The high K_M glucose transporter, GLUT2 (SLC2A2), is expressed by embryos and causes high rates of glucose transport during maternal hyperglycemic episodes in diabetic pregnancies and causes congenital malformations (diabetic embryopathy). GLUT2 is also a low K_M transporter of the amino sugar, glucosamine (GlcN), which enters the hexosamine biosynthetic pathway (HBP) and provides substrate for glycosylation reactions. Exogenous GlcN also increases activity of the pentose phosphate pathway (PPP), which increases production of NADPH reducing equivalents. GLUT2-transported GlcN is inhibited by high glucose concentrations. Not all mouse strains are susceptible to diabetic embryopathy. The aim of this study was to test the hypothesis that susceptibility to diabetic embryopathy is related to differential dependence on exogenous GlcN for glycosylation or stimulation of the PPP. We tested this using murine embryonic stem cell (ESC) lines that were derived from embryopathy-susceptible FVB/NJ (FVB), and embryopathy-resistant C57Bl/6J (B6), embryos in the presence of low or high glucose, and in the presence or absence of GlcN. There were no significant differences in Glut2 expression, or of glucose or GlcN transport, between FVB and B6 ESC. GlcN effects on growth and incorporation into glycoproteins indicated that FVB ESC are more dependent on exogenous GlcN than are B6 ESC. GlcN stimulated PPP activity in FVB but not in B6 ESC. High glucose induced oxidative stress in FVB ESC but not in B6 ESC. These results indicate that FVB embryos are more dependent on exogenous GlcN for glycosylation, but also for stimulation of the PPP and NADPH production, than are B6 embryos, thereby rendering FVB embryos more susceptible to high glucose to induce oxidative stress.

Diabetes, Oxidative Stress, and DNA Damage Modulate Cranial Neural Crest Cell Development and the Phenotype Variability of Craniofacial Disorders

Craniofacial malformations are among the most common birth defects in humans and they often have significant detrimental functional, aesthetic, and social consequences. To date, more than 700 distinct craniofacial disorders have been described. However, the genetic, environmental, and developmental origins of most of these conditions remain to be determined. This gap in our knowledge is hampered in part by the tremendous phenotypic diversity evident in craniofacial syndromes but is also due to our limited understanding of the signals and mechanisms governing normal craniofacial development and variation. The principles of Mendelian inheritance have uncovered the etiology of relatively few complex craniofacial traits and consequently, the variability of craniofacial syndromes and phenotypes both within families and between families is often attributed to variable gene expression and incomplete penetrance. However, it is becoming increasingly apparent that phenotypic variation is often the result of combinatorial genetic and non-genetic factors. Major non-genetic factors include environmental effectors such as pregestational maternal diabetes, which is well-known to increase the risk of craniofacial birth defects. The hyperglycemia characteristic of diabetes causes oxidative stress which in turn can result in genotoxic stress, DNA damage, metabolic alterations, and subsequently perturbed embryogenesis. In this review we explore the importance of gene-environment associations involving diabetes, oxidative stress, and DNA damage during cranial neural crest cell development, which may underpin the phenotypic variability observed in specific craniofacial syndromes.