Neuroepithelial cells downregulate their plasma membrane polarity prior to neural tube closure and neurogenesis

Cell differentiation often involves changes in cell polarity. In this study we show that neuroepithelial cells, the progenitors of all neurons and macroglial cells of the vertebrate central nervous system, downregulate the polarized delivery to the apical and basolateral plasma membrane domains during development. Upon infection of the neuroepithelium of mouse embryos with fowl plague virus (FPV), polarized delivery of the viral envelope hemagglutinin, an apical marker, occurred at the neural plate stage (E8), but was downregulated at the open neural tube stage (E9). Upon infection with vesicular stomatitis virus, the viral envelope G protein, a basolateral marker, showed an unpolarized delivery not only at the open neural tube stage, but already at the neural plate stage. These results show that a progressive downregulation of plasma membrane polarity of neuroepithelial cells precedes neural tube closure and the onset of neurogenesis.

Caffeine-induced disturbances of early neurogenesis in whole mouse embryo cultures

In toto mouse embryos were cultivated at embryonic day 8.5 for 26 h with 105, 310 or 620 microM caffeine; 105-310 microM correspond to concentrations transferred by the placenta of heavy caffeine consumers. Failure of neural tube closure, excessive proliferation of neuroepithelial cells and premature evagination of telencephalic vesicles were present in 50% of treated embryos. When reaching the embryonic neural tube before neuronal migration, caffeine regionally modifies the schedule and/or rate of neural cell proliferation.

Disorders of homocysteine metabolism

This review of recent advances covers (1) the metabolism of methionine and its regulation, emphasizing interactions with the three important vitamins folate, cobalamin and pyridoxine; (2) present knowledge of enzymological and moleculargenetic aspects of homozygous deficiencies of the three enzymes which cause elevated homocyst(e)ine; (3) recent clinical findings, post-methionine loading results related to enzyme and mutation studies in obligate heterozygotes for cystathionine beta-synthase deficiency; (4) important new evidence for disturbed homocysteine metabolism in neural tube defects, particularly based on studies of the thermolabile methylene-tetrahydrofolate reductase mutation which is also of importance in vascular disease; (5) the suitability and limitations of animal models that have so far been described.

Vertebral column and spinal cord malformation in children with exstrophy of the cloaca, with emphasis on their functional correlates

Exstrophy of the cloaca is a dramatic malformation whose embryology is poorly understood. While the management of this disorder has received significant attention in the urology and general surgery literature, the neurologic status of these children has been poorly addressed. In order to better characterize the spinal cord and vertebral column malformations found in children with exstrophy of the cloaca, we undertook a clinical review of 26 consecutive children with exstrophy of the cloaca who had been seen at a single institution over 28 years. The prevalence of vertebral malformations in the 25 children who could be evaluated was 25/25 (100%). Twenty (80%) of the children had at least one vertebral fusion, most frequently at T-7. Twenty-two (88%) of the children had at least one vertebra with deficient posterior elements, and the spinal levels most frequently involved were S-2, S-3, S-4 and S-5. Nine (36%) of the children had at least one vertebra with a narrowed interpedicular distance, most frequently at T-7. Nine (36%) of the children had at least one vertebra with atrophic facet anatomy, most frequently at L-3. The prevalence of myelodysplasia in the 19 children for whom spinal magnetic resonance imaging or intraoperative findings were available was 100%. Of these 19 children, 15 (79%) had myelocystocele, 2 (11%) had a lipomeningocele, 2 (11%) had a meningocele, 2 (11%) had hydromyelia, and 4 (21%) had a tethered cord. These data suggest that spinal cord and vertebral column malformations are very common in children with exstrophy of the cloaca.

Heterogeneity of spina bifida

Splitting birth defects into dysmorphologically homogeneous groups might improve the ability to detect a genetic risk factor or teratogenic exposure. With regard to spina bifida, recent studies suggest that etiologic heterogeneity exists within the group of spina bifida, although exogenous risk factors have been sparsely evaluated for subgroups. In the present study, 210 spina bifida patients were classified into relatively homogeneous groups, based on retrospective information on appearance and functional aspects of the lesion abstracted from medical records of the patients. We compared high with low spina bifida, and open with closed spina bifida, and investigated whether risk factors for spina bifida such as maternal age, antiepileptic drug use, parental occupation, and genetic factors were specifically associated with these homogeneous subclasses. For these comparisons, a referent group of 671 children was used. Although classifying spina bifida into homogeneous subclasses presented some difficulties and numbers were small, this study provides some evidence for different risk profiles for subclasses of spina bifida. The sex ratio, the proportion of miscarriages of siblings, and maternal age did not differ among the different subclasses of spina bifida. However, children with a positive family history of neural tube defects (NTDs) had a higher risk of high spina bifida [odds ratio (OR) = 6.3, 95% confidence interval (CI): 1.7-19.2] than of low spina bifida (OR = 2.1, 95% CI: 1.0-4.2). Siblings with NTDs were more common in cases with high spina bifida and cases with open spina bifida. A strongly increased risk of high spina bifida was found for male welders (OR = 12.1, 95% CI: 1.5-64.2), whereas the risk of low spina bifida was much lower (OR = 1.6, 95% CI: 0.2-7.9). For mothers with agricultural occupations, a strongly increased risk was observed for open spina bifida (OR = 14.3, 95% CI: 2.9-77.7), whereas none of 107 cases with closed spina bifida had a mother with an occupation in agriculture. Due to small numbers, the results must be interpreted with caution.

Synergistic interactions between XPC and p53 mutations in double-mutant mice: neural tube abnormalities and accelerated UV radiation-induced skin cancer

The significance of DNA repair to human health has been well documented by studies on xeroderma pigmentosum (XP) patients, who suffer a dramatically increased risk of cancer in sun-exposed areas of their skin [1,2]. This autosomal recessive disorder has been directly associated with a defect in nucleotide excision-repair (NER) [1,2]. Like human XP individuals, mice carrying homozygous mutations in XP genes manifest a predisposition to skin carcinogenesis following exposure to ultraviolet (UV) radiation [3-5]. Recent studies have suggested that, in addition to roles in apoptosis [6] and cell-cycle checkpoint control [7] in response to DNA damage, p53 protein may modulate NER [8]. Mutations in the p53 gene have been observed in 50% of all human tumors [9] and have been implicated in both the early [10] and late [11] stages of skin cancer. To examine the consequences of a combined deficiency of the XPC and the p53 proteins in mice, we generated double-mutant animals. We document a spectrum of neural tube defects in XPC p53 mutant embryos. Additionally, we show that, following exposure to UV-B radiation, XPC p53 mutant mice have more severe solar keratosis and suffer accelerated skin cancer compared with XPC mutant mice that are wild-type with respect to p53.

p53-dependent apoptosis suppresses radiation-induced teratogenesis

About half of human conceptions are estimated not to be implanted in the uterus, resulting in unrecognizable spontaneous abortions, and about 5% of human births have a recognizable malformation. In order to find clues to the mechanisms of malformation and abortion, we compared the incidences of radiation-induced malformations and abortions in p53 null (p53-/-) and wild-type (p53+/+) mice. After X-irradiation with 2 Gy on day 9.5 of gestation, p53-/- mice showed a 70% incidence of anomalies and a 7% incidence of deaths, whereas p53+/+ mice had a 20% incidence of anomalies and a 60% incidence of deaths. Similar results were obtained after irradiation on day 3.5 of gestation. This reciprocal relationship of radiosensitivity to anomalies and to embryonic or fetal lethality supports the notion that embryonic or fetal tissues have a p53-dependent "guardian" of the tissue that aborts cells bearing radiation-induced teratogenic DNA damage. In fact, after X-irradiation, the number of cells with apoptotic DNA fragments was greatly increased in tissues of the p53+/+ fetuses but not in those of the p53-/- fetuses.

Folic acid absorption in women with a history of pregnancy with neural tube defect

Folic acid absorption was compared in nonpregnant women with a history of pregnancy with a neural tube defect (cases)(n = 10) with that of control women (n = 10) with a normal pregnancy history. [2H4]folic acid was administered in an oral dose (400 micrograms) to fasting case and control subjects after a 30-d saturation protocol involving daily ingestion of two 1-mg folic acid supplements. Serum and red blood cell folate concentrations were not different for case and control subjects before or during the saturation protocol (P > 0.05). The percentage (x +/- SD) of the oral dose of [2H4]folic acid excreted in 24-h urine collections postdose was not different (P > 0.05) for case compared with control subjects (9.05 +/- 2.25% and 11.10 +/- 3.41%, respectively). These data suggest that the absorption of folic acid routinely consumed in supplements and fortified food products is not impaired in women with a history of a pregnancy with a neural tube defect. Further case-controlled studies are needed to compare the absorption of the predominant dietary form of the vitamin.

Risk, autonomy, and responsibility: informed consent for prenatal testing

Why is informed consent required for prenatal testing? Consent is routinely sought, but examination of the theory behind and the implementation of informed consent for prenatal testing suggests that we need to reconceptualize both the risks and the responsibilities involved in offering and accepting such prenatal tests.

Symptomatic Chiari malformation and associated pathophysiology in pediatric and adult patients without myelodysplasia

The clinical characteristics of eight pediatric and five adult patients with Chiari malformation were evaluated. Six pediatric and five adult patients had associated syringomyelia. All patients initially underwent a suboccipital craniectomy with upper cervical (C-1 and/or C-2) laminectomy and duraplasty, and/or shunting procedures. The clinical characteristics of the pediatric and adult groups were compared. The mean interval between onset of symptoms and operation was shorter in the pediatric group (3 yrs 6 mos) than in the adult group (7 yrs 1 mo). Pediatric patients without syringomyelia had the shortest mean interval of 1 year 8 months. Preoperatively, the clinical features were more severe in the adult patients than in the pediatric patients. Postoperatively, seven of eight pediatric patients improved and one stabilized, while two of five adult patients improved, one stabilized, and in two the disease continued to progress despite multiple corrective procedures. Cine magnetic resonance imaging revealed correction of the abnormal cerebrospinal fluid (CSF) flow at the craniovertebral junction and decreased to-and-fro movement in the syrinx after posterior fossa decompression, which were closely correlated with the improvement of clinical features in pediatric patients. However, adult patients required further procedures because of the multifactorial nature of the disease. Evaluation of abnormal CSF pathways at the craniovertebral junction is important for investigating the pathogenesis of Chiari malformation and associated syringomyelia.

Embryogenesis in cultured whole rat embryos after combined exposures to 3,3',5-triiodo-L-thyronine (T3) plus all-trans-retinoic acid and to T3 plus 9-cis-retinoic acid

Retinoid-induced malformations of the jaw, ears, face, skull, eyes, and heart in humans and rodents are well known. Data on nuclear receptors and developmental toxicity bioassays indicate that thyroid hormones can modulate the biologic activity of retinoids. The present investigation concerned the potential for interactions of all-trans-retinoic acid (RA) with 3,3'5-triiodo-L-thyronine (T3) and of 9-cis-retinoic acid (9-cis-RA) with T3 in the morphogenesis of cultured whole rat embryos. Varying concentrations of retinoids or T3 were microinjected into the amniotic fluid or placed in the culture medium alone or in combinations of T3 with each retinoid. At 200 ng/ml, T3 increased the incidence of branchial arch defects produced by either RA or 9-cis-RA but did not elicit branchial arch defects alone except at concentrations significantly compromising survival (2,000 ng/ml; 32% mortality). Similarly high culture medium concentrations of T3 alone were associated with failure of neural tube closure in the rhombencephalon (rhombencephalic schisis). At this concentration, other dysmorphia were minimal and at 670 ng/ml T3, no dysmorphogenic or embryotoxic effects could be detected. Modulation of T3 effects by the yolk sac placenta was suggested by failure of microinjected T3 to elicit dysmorphia at very high amniotic fluid concentrations. RA (300 ng/ml) or 9-cis-RA (600 ng/ml) alone elicited no or minimal rhombencephalic schisis at the highest concentrations studied. RA plus T3 produced a much greater than additive effect on rhombencephalic schisis, whereas 9-cis-RA plus T3 produced a less than additive effect. Conversely, much greater than additive effects on anterior schisis were observed for 9-cis-RA plus T3 whereas combined effects of RA and T3 were approximately additive. For most other dysmorphia, the combined effects of each retinoid with T3 were greater than additive and were particularly striking for cephalic defects.

Acalvaria: a unique congenital anomaly

Acalvaria is a rare malformation usually regarded as a postneurulation defect. It consists of absence of the calvarial bones, dura mater and associated muscles in the presence of a normal skull base and normal facial bones. The condition is frequently confused by prenatal ultrasonography with anencephaly or an encephalocele. Whereas the cerebral hemispheres are absent in anencephaly, the cranial contents in acalvaria are generally complete, though some neuropathological abnormality is often present. The presumed pathogenesis of acalvaria is faulty migration of the membranous neurocranium with normal placement of the embryonic ectoderm, resulting in absence of the calvaria but an intact layer of skin over the brain parenchyma. We describe 2 cases of acalvaria, one misdiagnosed ultrasonographically as an occipital encephalocele prenatally. The brain in one fetus demonstrated semilobar holoprosencephaly and micropolygyria, but in the other, was structurally and histologically normal with the exception of hydrocephalus.

The choices women make about prenatal diagnosis

Despite the rapid advancement and increasing utilization of prenatal diagnostic technologies, there has been a paucity of investigation into the psychological, socioeconomic, and demographic features associated with the choices women make about both the uptake of services, and the actions taken after fetal abnormalities are discovered. From 1986 through 1991 we have completed four studies initiating a proposed comprehensive evaluation of these factors. The first two studies concentrated on patient features influencing uptake of prenatal diagnostic procedures in both a priori 'high risk' pregnancies (advanced maternal age) as well as in previously 'low risk' pregnancies which had become 'high risk' by virtue of abnormal maternal alpha-fetoprotein (MSAFP) screening. The second two studies evaluated features influencing abortion decisions after the discovery of either chromosomal anomalies, or non-aneuploid ultrasonographically detected structural abnormalities. Data suggested that (1) older and more highly educated women tended to choose CVS over amniocentesis; (2) perceptions of genetic risk within couples was most influenced by attributes of their partners; (3) anxiety and perception of risk was higher in young women having abnormal screening MSAFP, than in the advanced maternal age group although this difference appeared to be commensurate with actual risks; (4) for fetal aneuploidy, the specific karyotype and, to a lesser extent, coexistent structural anomalies are the major determinants of decisions to abort; (5) for euploid fetal structural abnormalities the prognostic severity and potential for beneficial medical intervention (either antenatally or postnatally) as counselled by the physician were the principal determinants influencing abortion decisions. Further study is needed and important questions still to be addressed are discussed.

A survey of Calgary paediatricians' attitudes regarding the treatment of defective newborns: a report from Canada

... Premature infants and those born with severe abnormalities have stimulated the creation of neonatal units, but advances in medicine have created the dilemma of whether to sustain life in neonates who would otherwise die from their abnormalities. Often these methods are sophisticated and costly, and carry their own share of iatrogenic complications... It is crucial that the infant -- unable to be directly involved -- have an advocate, whose role it is to act in the best interests of the patient in determinations of the latter's treatment. Under most circumstances that role is occupied by the child's physician and family... For this reason, it is imperative to discern physicians' -- and specifically pediatricians' -- attitudes towards the treatment of defective newborns. To accomplish this, a survey was taken in Calgary... It is the purpose of this paper to provide information regarding local physicians' views and how they compare with the opinions of their colleagues from other countries.

Musculoskeletal problems in association with cloacal exstrophy

The records of all thirteen patients for whom a diagnosis of cloacal exstrophy had been recorded in our hospitals were analyzed for evidence of musculoskeletal problems. All thirteen patients had spina bifida, four had congenital scoliosis, two had congenital kyphosis, and three had non-congenital scoliosis. All had a lipomeningocele, and eleven had paralysis of the lower extremities. Hydrocephalus and its associated problems were not found, but tethered-cord syndrome was diagnosed in eleven patients. Persistent diastasis of the symphysis pubis was found in all patients. Abduction and external rotation of the hips were more than normal. Mild dysplasia was seen in six of the twenty-six hips. Deformities of the foot were common, and twelve feet had been operated on for correction. Recurrent equinovarus deformity of the foot was associated with tethered-cord syndrome in two patients.

Spondylocostal dysplasia and neural tube defects

Spondylocostal dysplasia (Jarcho-Levin syndrome) comprises multiple malformations of the vertebrae and ribs coupled with a characteristic clinical picture of short neck, scoliosis, short trunk, and deformity of the rib cage. We describe a patient with the syndrome who also had spina bifida and diastematomyelia. We surmise that this association is not coincidental. Additional evidence is needed to support the hypothesis that spondylocostal dysplasia and neural tube defects are aetiologically related.