The pro-apoptotic Bax gene modifies susceptibility to craniofacial dysmorphology following gastrulation-stage alcohol exposure

BACKGROUND

During early development, alcohol exposure causes apoptotic cell death in discrete regions of the embryo which are associated with distinctive patterns of later-life abnormalities. In gastrulation, which occurs during the third week of human pregnancy, alcohol targets the ectoderm, the precursor of the eyes, face, and brain. This midline tissue loss leads to the craniofacial dysmorphologies, such as microphthalmia and a smooth philtrum, which define fetal alcohol syndrome (FAS). An important regulator of alcohol-induced cell death is the pro-apoptotic protein Bax. The current study determines if mice lacking the Bax gene are less susceptible to the pathogenic effects of gastrulation-stage alcohol exposure.

METHODS

Male and female Bax^+/- mice mated to produce embryos with full (^-/- ) or partial (^+/- ) Bax deletions, or Bax^+/+ wild-type controls. On Gestational Day 7 (GD 7), embryos received two alcohol (2.9 g/kg, 4 hr apart), or control exposures. A subset of embryos was collected 12 hr later and examined for the presence of apoptotic cell death, while others were examined on GD 17 for the presence of FAS-like facial features.

RESULTS

Full Bax deletion reduced embryonic apoptotic cell death and the incidence of fetal eye and face malformations, indicating that Bax normally facilitates the development of alcohol-induced defects. An RNA-seq analysis of GD 7 Bax^+/+ and Bax^-/- embryos revealed 63 differentially expressed genes, some of which may interact with the Bax deletion to further protect against apoptosis.

CONCLUSIONS

Overall, these experiments identify that Bax is a primary teratogenic mechanism of gastrulation-stage alcohol exposure.

Update on the gestational effects of maternal hyperthermia

OBJECTIVES

I plan to review the types of defects caused by gestational hyperthermia. Hyperthermia-induced malformations in animals and humans involve many organs and structures, particularly the central nervous system, as well as other defects. The type of defect is related to the timing of the hyperthermic insult, and the underlying mechanisms include cell death, membrane disruption, vascular disruption, and placental infarction.

METHODS

Review of recent epidemiologic studies (2005-2020) has confirmed an association between gestational hyperthermia and birth defects.

RESULTS

There are strong associations between neural tube defects and maternal fever, and other studies have demonstrated associations between first trimester hyperthermia and an increased risk for cardiovascular defects, oral clefts, isolated congenital ear defects, cataracts, hypospadias, renal anomalies, possibly anorectal malformations, and congenital anomalies in general, suggesting that this association between maternal hyperthermia and birth defects in humans is causal. The first prospective evaluation of maternal fever was reported in 1998, and this study confirmed findings from previous case-control studies and case series regarding the magnitude and duration of elevated maternal body temperature in relation to an increased risk for neural tube defects as well as a specific pattern of malformation.

CONCLUSIONS

The consistency of findings across these different study designs supports the causal nature of the relationship between maternal fever and specific birth defects. This review summarizes the recent human evidence documenting the gestational effects of maternal hyperthermia.

De Novo Pathogenic Variants in N-cadherin Cause a Syndromic Neurodevelopmental Disorder with Corpus Collosum, Axon, Cardiac, Ocular, and Genital Defects

Cadherins constitute a family of transmembrane proteins that mediate calcium-dependent cell-cell adhesion. The extracellular domain of cadherins consists of extracellular cadherin (EC) domains, separated by calcium binding sites. The EC interacts with other cadherin molecules in cis and in trans to mechanically hold apposing cell surfaces together. CDH2 encodes N-cadherin, whose essential roles in neural development include neuronal migration and axon pathfinding. However, CDH2 has not yet been linked to a Mendelian neurodevelopmental disorder. Here, we report de novo heterozygous pathogenic variants (seven missense, two frameshift) in CDH2 in nine individuals with a syndromic neurodevelopmental disorder characterized by global developmental delay and/or intellectual disability, variable axon pathfinding defects (corpus callosum agenesis or hypoplasia, mirror movements, Duane anomaly), and ocular, cardiac, and genital anomalies. All seven missense variants (c.1057G>A [p.Asp353Asn]; c.1789G>A [p.Asp597Asn]; c.1789G>T [p.Asp597Tyr]; c.1802A>C [p.Asn601Thr]; c.1839C>G [p.Cys613Trp]; c.1880A>G [p.Asp627Gly]; c.2027A>G [p.Tyr676Cys]) result in substitution of highly conserved residues, and six of seven cluster within EC domains 4 and 5. Four of the substitutions affect the calcium-binding site in the EC4-EC5 interdomain. We show that cells expressing these variants in the EC4-EC5 domains have a defect in cell-cell adhesion; this defect includes impaired binding in trans with N-cadherin-WT expressed on apposing cells. The two frameshift variants (c.2563_2564delCT [p.Leu855Valfs^∗4]; c.2564_2567dupTGTT [p.Leu856Phefs^∗5]) are predicted to lead to a truncated cytoplasmic domain. Our study demonstrates that de novo heterozygous variants in CDH2 impair the adhesive activity of N-cadherin, resulting in a multisystemic developmental disorder, that could be named ACOG syndrome (agenesis of corpus callosum, axon pathfinding, cardiac, ocular, and genital defects).

Epidemiology of anophthalmia and microphthalmia: Prevalence and patterns in Texas, 1999-2009

Anophthalmia and microphthalmia are a set of rare, yet severe, birth defects considered to be part of a spectrum of developmental ocular malformations ranging from smaller than average to completely absent eyes. Despite their clinical significance, little is known about the etiologies of these conditions. The goal of this study was to expand our understanding of the epidemiology of anophthalmia and microphthalmia. Data for this population-based assessment were obtained from the Texas Birth Defects Registry (TBDR) and Center for Health Statistics for the period 1999-2009. Descriptive analyses and estimates of birth prevalence and prevalence ratios (PR) were determined for this defect. There were 1,262 definite anophthalmia and microphthalmia patients identified in the TBDR, with an overall combined prevalence of 3.0 per 10,000 live births. More than half (55.7%) of the patients had at least one chromosome abnormality or syndrome. In addition, 92.4% of nonsyndromic patients (i.e., have no recorded chromosome abnormalities or syndromes) had at least one additional birth defect. After adjustment for multiple factors, the prevalence of nonsyndromic anophthalmia and microphthalmia was higher among mothers who had ≥2 previous fetal deaths (PR = 1.43, 95% confidence interval [CI]: 1.03-1.97) and among mothers with any reported diabetes (PR = 2.08, 95% CI: 1.49-2.90). Our results confirm that children with anophthalmia and microphthalmia frequently have genetic syndromes or are born with other major birth defects. Our findings add to the limited body of literature on anophthalmia and microphthalmia as well as help define subgroups of women who are more likely to have children with this malformation.

Remote examination of exudates-impact of macular oedema

One of the major causes of eye blindness is identified to be as diabetic retinopathy, which if not detected in earlier stage would cause a serious issue. Long-term diabetes causes diabetic retinopathy. The significant key factor leading to diabetic retinopathy is exudates which affect the retina part and causes eye defects. Thus the first and foremost task in the automated detection of macular oedema is to detect the presence of these exudates. The authors use image processing techniques to detect the optic disc, exudates and the presence of macular oedema. Their method has the sensitivity 96.07%, selectivity 97.36%, and accuracy 96.62% for the exudates detection and in the case of macular oedema detection the sensitivity 97.75%, selectivity 100%, and accuracy 98.86% is achieved. The performance comparison with other methods reveals that their method can be used as a screening process for diabetic retinopathy. In addition to that, the algorithm can help to detect macular oedema.

Mannose supplements induce embryonic lethality and blindness in phosphomannose isomerase hypomorphic mice

Patients with congenital disorder of glycosylation (CDG), type Ib (MPI-CDG or CDG-Ib) have mutations in phosphomannose isomerase (MPI) that impair glycosylation and lead to stunted growth, liver dysfunction, coagulopathy, hypoglycemia, and intestinal abnormalities. Mannose supplements correct hypoglycosylation and most symptoms by providing mannose-6-P (Man-6-P) via hexokinase. We generated viable Mpi hypomorphic mice with residual enzymatic activity comparable to that of patients, but surprisingly, these mice appeared completely normal except for modest (~15%) embryonic lethality. To overcome this lethality, pregnant dams were provided 1-2% mannose in their drinking water. However, mannose further reduced litter size and survival to weaning by 40 and 66%, respectively. Moreover, ~50% of survivors developed eye defects beginning around midgestation. Mannose started at birth also led to eye defects but had no effect when started after eye development was complete. Man-6-P and related metabolites accumulated in the affected adult eye and in developing embryos and placentas. Our results demonstrate that disturbing mannose metabolic flux in mice, especially during embryonic development, induces a highly specific, unanticipated pathological state. It is unknown whether mannose is harmful to human fetuses during gestation; however, mothers who are at risk for having MPI-CDG children and who consume mannose during pregnancy hoping to benefit an affected fetus in utero should be cautious.