Congenital malformations of the central nervous system in spontaneous abortions

Risk factors associated with congenital central nervous system abnormalities in the National Hospital of Zinder, Niger

INTRODUCTION

Congenital malformations of the central nervous system (CNS) are morphological abnormalities of the brain and spinal cord that occur during fetal development. They constitute the second most common congenital disability, after congenital cardiac defects. Many risk factors have been identified; however, these studies included various types of congenital abnormality. Furthermore, there is a lack of information on risk factors for congenital CNS malformation, and notably in the Zinder region of Niger.

OBJECTIVE

This study aimed to identify the risk factors associated with congenital CNS malformations in the Zinder region.

METHODS

In a case-control design, patients with congenital CNS malformation were enrolled between June 2022 and April 2023 in the Department of Neurosurgery of the National Hospital of Zinder.

RESULTS

Family history of malformation (aOR:3.31, 95% CI:1.25-8.78) and consanguine marriage (aOR:2.28, 95% CI:1.23-4.20) were significantly associated with congenital CNS malformation. In contrast, folic acid supplementation (aOR:0.34, 95% CI:0.13, 0.89), multiparity (aOR:0.34, 95% CI:0.13, 0.89), and grand multiparity (aOR, 0.47; 95% CI:0.23, 0.97) had a protective effect.

CONCLUSION

Risk factors such as family malformation history and consanguine marriage increased the risk of developing congenital malformations of the central nervous system. In contrast, folic acid supplementation in the index period and multiparity had a significant protective effect.

A topographical analysis of encephalocele locations: generation of a standardised atlas and cluster analysis

OBJECTIVE

Encephaloceles are considered to result from defects in the developing skull through which meninges, and potentially brain tissue, herniate. The pathological mechanism underlying this process is incompletely understood. We aimed to describe the location of encephaloceles through the generation of a group atlas to determine whether they occur at random sites or clusters within distinct anatomical regions.

METHODS

Patients diagnosed with cranial encephaloceles or meningoceles were identified from a prospectively maintained database between 1984 and 2021. Images were transformed to atlas space using non-linear registration. The bone defect, encephalocele and herniated brain contents were manually segmented allowing for a 3-dimensional heat map of encephalocele locations to be generated. The centroids of the bone defects were clustered utilising a K-mean clustering machine learning algorithm in which the elbow method was used to identify the optimal number of clusters.

RESULTS

Of the 124 patients identified, 55 had volumetric imaging in the form of MRI (48/55) or CT (7/55) that could be used for atlas generation. Median encephalocele volume was 14,704 (IQR 3655-86,746) mm3 and the median surface area of the skull defect was 679 (IQR 374-765) mm2. Brain herniation into the encephalocele was found in 45% (25/55) with a median volume of 7433 (IQR 3123-14,237) mm3. Application of the elbow method revealed 3 discrete clusters: (1) anterior skull base (22%; 12/55), (2) parieto-occipital junction (45%; 25/55) and (3) peri-torcular (33%; 18/55). Cluster analysis revealed no correlation between the location of the encephalocele with gender (χ2 (2, n = 91) = 3.86, p = 0.15). Compared to expected population frequencies, encephaloceles were relatively more common in Black, Asian and Other compared to White ethnicities. A falcine sinus was identified in 51% (28/55) of cases. Falcine sinuses were more common (χ2 (2, n = 55) = 6.09, p = 0.05) whilst brain herniation was less common (χ2 (2, n = 55) = .16.24, p < 0.0003) in the parieto-occipital location.

CONCLUSION

This analysis revealed three predominant clusters for the location of encephaloceles, with the parieto-occipital junction being the most common. The stereotypic location of encephaloceles into anatomically distinct clusters and the coexistence of distinct venous malformations at certain sites suggests that their location is not random and raises the possibility of distinct pathogenic mechanisms unique to each of these regions.

Evaluation of prenatal central nervous system anomalies: obstetric management, fetal outcomes and chromosome abnormalities

Objective

To study the outcomes of fetuses who were diagnosed with central nervous system (CNS) anomalies during prenatal period and to describe the obstetric management of those pregnancies.

Methods

In this retrospective study, fetuses who were detected to have central nervous system anomalies by prenatal ultrasound from January 2010 to December 2019 were recruited. Data regarding prenatal diagnosis and obstetric outcomes were retrieved from maternal and paediatric records. The prognosis of fetuses who were born alive was classified based on their neurodevelopmental outcome within two years of life.

Results

There were a total of 365 fetuses with CNS anomalies within the 10-year study period, with a mean gestational age of 24.65±7.37 weeks at diagnosis. Ventriculomegaly (23.36%) was the commonest CNS anomalies seen. 198 (54.20%) of these fetuses had associated extra-CNS anomalies, with cardiovascular being the most common system involved. Fetal karyotyping was performed in 111 pregnancies, with chromosomal aberrations detected in 53 (49.07%) cases and culture failure in 3 cases. Majority of the chromosomal abnormalities were Edward syndrome (trisomy 18) and Patau syndrome (trisomy 13). Fetuses with congenital CNS anomalies and abnormal chromosomal karyotyping were more likely to be diagnosed earlier by prenatal ultrasound and tend to have poorer obstetric and neurocognitive prognosis. Prenatally, 86 (23.56%) of the cases were lost to follow up and likely to deliver elsewhere. Among the 279 cases whom their pregnancy outcomes were available, 139 (49.82%) pregnancies resulted in live births, 105 (37.63%) pregnancies were electively terminated, while the remaining 35 (12.54%) pregnancies ended in spontaneous loss. The decision of termination of pregnancy largely depends on mean diagnostic gestational age, presence of chromosomal aberrations and abnormal amniotic fluid volume in those fetuses. Two years after delivery, only 75 (53.96%) children out of 139 live births were still alive, 43 (30.93%) died and 21 (15.11%) cases were lost to follow-up. 32 (23.02%) children with prenatally diagnosed CNS anomalies had normal neurodevelopmental outcome. The presence of multiple CNS anomalies and involvement of extra-CNS anomalies indicated a poorer neurodevelopmental prognosis.

Conclusion

Less than 50% of fetuses with prenatally diagnosed CNS anomalies resulted in live births. Even if they survive till delivery, 36.45% of them passed away within 2 years and 62.79% of children who survived till 2 years old had neurodevelopmental disability.

Hepatocyte Polyploidy: Driver or Gatekeeper of Chronic Liver Diseases

Polyploidy, also known as whole-genome amplification, is a condition in which the organism has more than two basic sets of chromosomes. Polyploidy frequently arises during tissue development and repair, and in age-associated diseases, such as cancer. Its consequences are diverse and clearly different between systems. The liver is a particularly fascinating organ in that it can adapt its ploidy to the physiological and pathological context. Polyploid hepatocytes are characterized in terms of the number of nuclei per cell (cellular ploidy; mononucleate/binucleate hepatocytes) and the number of chromosome sets in each nucleus (nuclear ploidy; diploid, tetraploid, octoploid). The advantages and disadvantages of polyploidy in mammals are not fully understood. About 30% of the hepatocytes in the human liver are polyploid. In this review, we explore the mechanisms underlying the development of polyploid cells, our current understanding of the regulation of polyploidization during development and pathophysiology and its consequences for liver function. We will also provide data shedding light on the ways in which polyploid hepatocytes cope with centrosome amplification. Finally, we discuss recent discoveries highlighting the possible roles of liver polyploidy in protecting against tumor formation, or, conversely, contributing to liver tumorigenesis.

Fetal Pathology of Neural Tube Defects - An Overview of 68 Cases

INTRODUCTION

The prevalence of neural tube defects worldwide is 1 - 2 per 1000 neonates. Neural tube defects result from a disturbance of neurulation in the 3rd or 4th week of development and thus represent the earliest manifestation of organ malformation. Neural tube defects (NTD) are classified into cranial dysraphism leading to anencephaly or meningoencephalocele and spinal dysraphism with or without meningomyelocele. In isolated form they have multifactorial causes, and the empirical risk of recurrence in Central Europe is 2%. As associated malformations they tend to occur sporadically, and in monogenic syndromes they follow Mendelian inheritance patterns with a high risk of recurrence.

PATIENTS

Autopsies were performed on 68 fetuses following a prenatal diagnosis of NTD and induced abortion.

RESULTS

The incidence of NTDs in our autopsied fetuses was 8% and 11% in fetuses with malformations. The percentage of fetuses with anencephaly, encephalocele or spina bifida was 24, 18, and 60%*, respectively. Analysis of the sex distribution showed a female preponderance in cranial dysraphisms but the sex distribution of spina bifida cases was equal. The extent and localization of NTDs varied, with lumbosacral cases clearly predominating. The proportion of isolated, associated and syndromic neural tube defects was 56, 23.5 and 20.6% respectively. In the majority of syndromes, the neural tube defect represented a not previously observed syndromic feature.

CONCLUSION

The high proportion of NTDs with monogenic background underlines the importance of a syndrome oriented fetal pathology. At the very least it requires a thourough photographic and radiographic documentation of the fetal phenotype to enable the genetic counsellor to identify a syndromic disorder. This is necessary to determine the risk of recurrence, arrange confirming mutation analyses and offer targeted prenatal diagnosis in subsequent pregnancies.

Previous miscarriages and GLI2 are associated with anorectal malformations in offspring

STUDY QUESTION

Are anorectal malformations (ARMs) associated with previous miscarriages or single nucleotide polymorphisms (SNPs) in the Bone Morphogenetic Protein 4 (BMP4) and GLI family zinc finger 2 (GLI2) genes?

SUMMARY ANSWER

The SNP rs3738880 in GLI2 and miscarriages were associated with ARM, especially in patients with multiple congenital anomalies (MCA).

WHAT IS KNOWN ALREADY

ARM are one of the most common birth defects of the gastrointestinal tract. The etiology is likely to be multifactorial, involving both environmental and genetic factors. SNPs in BMP4 and GLI2 genes were associated with ARM in non-Caucasian populations. During a patient information day, several mothers of ARM patients reported their concerns about previous miscarriages.

STUDY DESIGN, SIZE, DURATION

A case-control study was performed among 427 ARM patients and 663 population-based controls.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We examined the associations of ARM with SNPs in GLI2 and BMP4 using DNA samples of the children and associations with previous miscarriages using parental questionnaires. In addition, gene-gene and gene-environment interaction analyses were performed.

MAIN RESULTS AND THE ROLE OF CHANCE

The SNP rs3738880 in GLI2 was associated with ARM, especially in patients with MCA (homozygous GG-genotype: odds ratio (OR): 2.1; 95% CI: 1.2, 3.7). We identified previous miscarriages as a new risk factor for ARM, especially when occurring in the pregnancy directly preceding the index pregnancy and in patients with MCA (OR: 2.1; 95% CI: 1.3, 3.5). No association with rs17563 in BMP4, nor gene-gene or gene-environment interactions were found.

LIMITATIONS, REASONS FOR CAUTION

The possibility of recall errors for previous miscarriage, but we expect these errors to be limited, as a miscarriage is a major life event. In addition, potential misclassification regarding miscarriages and stillbirth, but sensitivity analyses showed that this did not influence our results.

WIDER IMPLICATIONS OF THE FINDINGS

This study showed associations of ARM with rs3738880 in GLI2 and with previous miscarriages. Both associations were stronger in patients with MCA, showing the importance of stratifying the analyses by patients with isolated ARM or MCA.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by the Radboudumc. The authors have no conflict of interest to disclose.

Prevention of neural tube defects by the fortification of flour with folic acid: a population-based retrospective study in Brazil

Objective

To determine if the fortification of wheat and maize flours with iron and folic acid – which became mandatory in Brazil from June 2004 – is effective in the prevention of neural tube defects.

Methods

Using data from national information systems on births in central, south-eastern and southern Brazil, we determined the prevalence of neural tube defects among live births and stillbirths in a pre-fortification period – i.e. 2001–2004 – and in a post-fortification period – i.e. 2005–2014. We distinguished between anencephaly, encephalocele, meningocele, myelomeningocele and other forms of spina bifida.

Findings

There were 8554 neural tube defects for 17 925 729 live births notified between 2001 and 2014. For the same period, 2673 neural tube defects were reported for 194 858 stillbirths. The overall prevalence of neural tube defects fell from 0.79 per 1000 pre-fortification to 0.55 per 1000 post-fortification (prevalence ratio, PR: 1.43; 95% confidence interval, CI: 1.38–1.50). For stillbirths, prevalence fell from 17.74 per 1000 stillbirths pre-fortification to 11.70 per 1000 stillbirths post-fortification. The corresponding values among live births were 0.57 and 0.44, respectively.

Conclusion

The introduction of the mandatory fortification of flour with iron and folic acid in Brazil was followed by a significant reduction in the prevalence of neural tube defects in our study area.

A Study on The Incidence of Neural Tube Defects in A Tertiary Care Hospital Over A Period of Five Years

INTRODUCTION

Several congenital malformations affect developing fetuses, among which Neural tube defect (NTD) is most common. Folic acid supplementation brought decline in the incidence of NTDs. The present study aims at finding the incidence of NTDs in a tertiary care hospital and compares the results with the similar Indian studies published earlier.

MATERIALS AND METHODS

The study was done at Chettinad Hospital & Research Institute (CHRI), Kelambakkam. The total number of deliveries was recorded for a period of five years from 2009 to 2013. Fetuses which were still born with neural defect were collected and observed in detail externally for the sex, type of NTD and other associated anomalies. Indian studies published between 1987 and 2014 reporting the incidence of NTDs among the births occurred were retrieved from the Internet and their various observations were used for comparison.

RESULTS

The number of deliveries conducted between 2009 and 2013 at CHRI was 3220. Of these, babies born with NTDs were nine (5 males and 4 females). The incidence of fetuses with meroanencephaly, holoanencephaly, craniorachischisis, encephalocele and myelocele were 0.62, 0.62, 0.93, 0.31 and 0.31 per 1000 births respectively. Overall incidence of NTDs in the present study was 2.79/1000 births. Fetuses with NTDs also had the following anomalies - Club foot, cleft lip and palate and exomphalos.

CONCLUSION

Comparing the results with the previous studies it is clearly evident that the incidence of NTDs have significantly reduced from 11.42/1000 births to 2.79/1000 births. In most of the previous studies NTDs had a female preponderance whereas present study has a male preponderance.In older studies, spina bifida was the most common NTDs followed by anencephaly. But in the present study anencephaly was the common NTD than spina bifida. Incidence of NTDs has reduced due to various reasons like prenatal screening for fetal anomalies and folic acid supplementation.

Genetic, chromosomal, and syndromic causes of neural tube defects

OBJECTIVE

To ascertain the incidence, and describe the various forms of neural tube defects (NTDs) due to genetic, chromosomal, and syndromic causes.

METHODS

We carried out a retrospective analysis of data retrieved from the medical records of newborn infants admitted to the Neonatal Intensive Care Unit with NTDs and their mothers spanning 14 years (1996-2009) at the Security Forces Hospital, Riyadh, Saudi Arabia. The cases were ascertained by a perinatologist, neonatologist, geneticist, radiologist, and neurologist. The literature was reviewed via a MEDLINE search. Only liveborn babies were included. Permission from the Educational Committee at the Security Forces Hospital was obtained prior to the collection of data.

RESULTS

Out of 103 infants with NTDs admitted during this period, 20 (19.4%) were found to have an underlying genetic syndromic, chromosomal and/or other anomalies. There were 5 cases of Meckel-Gruber syndrome, 2 Joubert syndrome, one Waardenburg syndrome, one Walker-Warburg syndrome, 2 chromosomal disorders, 2 caudal regression, one amniotic band disruption sequence, one associated with omphalocele, one with diaphragmatic hernia, and 4 with multiple congenital anomalies.

CONCLUSION

There is a high rate of underlying genetic syndromic and/or chromosomal causes of NTDs in the Saudi Arabian population due to the high consanguinity rate. Identification of such association can lead to more accurate provisions of genetic counseling to the family including preimplantation genetic diagnosis or early termination of pregnancies associated with lethal conditions.

[Evolution of the frequency of congenital defects in newborn infants and fetuses from terminations of pregnancy after prenatal diagnosis in the period 1982-2009]

BACKGROUND AND OBJECTIVE

The study of congenital defects (CD) must include termination of pregnancy (TOP) for CD and evaluate risk factors that modify their frequency.

PATIENTS AND METHODS

Consecutive series of 517 newborn and 202 TOP with CD among 38,191 childbirths, between 1982-2009 years.

RESULTS

The mean frequency for newborns with CD is 13.54‰ and for newborn and TOP with CD is 18.73‰. Single CD are 61.12% in newborns and 52.17% in TOP. The 18.37% of CD in newborn and 40.58% of TOP are syndromic. Mean gestational age for TOP is 17.92 weeks. Overall frequency of anencephaly is 2.62‰ for newborns and 6.77 for 10,000 for newborns and TOP. Spina bifida is 3.14 for 10,000 newborns and 5.99 for 10,000 newborns and TOP. Overall frequency of Down syndrome (DS) is 10.74 for 10,000 newborns and 22.14 for 10,000 newborns and TOP. The percentage of foreign mothers was 35.9% in 2009 and the mean maternal age significantly increased in this period.

CONCLUSION

We observe a significant decrease of CD in newborns but not in their conception. We have not detected primary prevention for neural tube defects. The decrease in DS in newborns is not statistically relevant but ethnic diversity and maternal aging may be modifying the frequency. The 53% of CD were TOP in the period 2007-2009. It is mandatory a complete study for CD in TOP in order to offer serious reproductive counselling.

Neural tube defects: recent advances, unsolved questions, and controversies

Neural tube defects are severe congenital malformations affecting around one in every 1000 pregnancies. An innovation in clinical management has come from the finding that closure of open spina bifida lesions in utero can diminish neurological dysfunction in children. Primary prevention with folic acid has been enhanced through introduction of mandatory food fortification in some countries, although not yet in the UK. Genetic predisposition accounts for most of the risk of neural tube defects, and genes that regulate folate one-carbon metabolism and planar cell polarity have been strongly implicated. The sequence of human neural tube closure events remains controversial, but studies of mouse models of neural tube defects show that anencephaly, open spina bifida, and craniorachischisis result from failure of primary neurulation, whereas skin-covered spinal dysraphism results from defective secondary neurulation. Other malformations, such as encephalocele, are likely to be postneurulation disorders.

Spinal dysraphism in an early missed abortion: embryofetoscopic diagnosis

Embryofetoscopy is an endoscopic technique that enables direct visualization and morphologic study of embryos during the first trimester and allows a selective tissue sample to be obtained. We describe an early missed abortion in the first trimester, apparently without cause according to findings at ultrasound. Embryofetoscopy revealed a remarkable dorsal cystic formation covered by a blood clot in the thoracolumbar region of the spine, suggestive of meningocele or myelomeningocele. A selective tissue biopsy specimen of the cystic lesion demonstrated meningeal tissue such as a meningocele. Embryofetoscopy in missed abortion could provide information about the causes of severe defects in embryo development so that parents can be effectively advised insofar as future pregnancies.

Zoonotic Ljungan virus associated with central nervous system malformations in terminated pregnancy

BACKGROUND

The Ljungan virus (LV) has been shown to cause central nervous system malformations in laboratory mouse models. The LV has also been associated with intrauterine fetal death in humans. We investigated the presence of LV in a series of human hydrocephaly and anencephaly cases from elective abortions.

METHODS

A series of elective abortions owing to hydrocephaly, anencephaly, and similarly aged trisomy 21 elective abortions as controls were examined for LV by immunohistochemistry and real time RT-PCR. A second experiment involved newborn mice exposed to LV.

RESULTS

LV was diagnosed in 9 of 10 cases with hydrocephalus and in 1 of 18 trisomy 21 controls by immunohistochemistry. Five of nine cases with anencephaly had a positive PCR result, whereas none of the 12 trisomy 21 available for PCR testing had a positive result. The 47 newborn mice exposed to LV all developed encephalitis, with eight having hydrocephalus. None of the 52 control animals had encephalitis or hydrocephalus.

CONCLUSION

The association between LV and both hydrocephaly and anencephaly suggests that LV may be playing an important role in central nervous system malformations in humans.

Association of preterm birth with brain malformations

This study investigates the rate of preterm birth in babies with congenital brain defects. Autopsy case reports of congenital brain anomalies were obtained from the literature. The control cases were from a large registry, a published report from the Metropolitan Atlanta Congenital Defects Program. From 428 publications, 1168 cases were abstracted that had autopsy studies of congenital brain defects and information on the gestational age (GA) at birth. The control data from Atlanta included 7738 infants with significant birth defects of any kind and 264,392 infants without birth defects. In the autopsy cases with brain defects, the mean GA was 36.6 wk, whereas the Atlanta data showed a mean GA of 39.3 wk for infants with no defects and a significantly shorter gestation of 38.1 wk (p < 0.0001) for infants with defects. In the Atlanta data, the rate of preterm birth was 9.3% for those with no defects compared with 21.5% (p < 0.0001) for those with defects. In the autopsy cases with brain defects, the rate of preterm birth was even greater (33.1%, p < 0.0001). In conclusion, these data show an association of brain defects with preterm births.

[Prevalence of neural tube defects in Asturias (Spain): impact of prenatal diagnosis]

OBJECTIVE

To describe the frequency and prevalence trend for neural tube defects (NTD) (anencephaly, spina bifida and encephalocele) in Asturias (Spain), as well as the impact of prenatal diagnosis programs.

METHODS

All cases of NTD in births and induced abortions were studied, using data from the Registry of Congenital Defects of Asturias for 1990-2004. Total and birth prevalence rates were calculated.

RESULTS

The prevalence of NTD for 1990-2004 was 12.2 per 10,000 births (5.9 anencephaly, 5.0 spina bifida and 1.3 encephalocele) and showed a slightly decreasing trend due to a significant decline in spina bifida prevalence. The prevalence of anencephaly and encephalocele remained stable. The percentage of induced abortions after prenatal diagnosis among all NTD was 88% (anencephaly 96.7%, spina bifida 80% and encephalocele 84.6%), leading to a very low birth prevalence (1.4 per 10,000) for the entire period.

CONCLUSIONS

The total prevalence of spina bifida has decreased in the last 15 years in Asturias. Secondary prevention through prenatal diagnosis and interruption of affected pregnancies have resulted in a marked decrease in NTD at birth. The recommendation of periconceptional use of folic acid seems not to have achieved the desired effect.

Myelomeningocele: a review of the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals

Although the use of folic acid before conception decreases the chance that a fetus will have an open neural tube defect, this condition still affects 0.5-1.0/1000 pregnancies in the United States. Results of a recent survey suggest that there are gaps in obstetrician-gynecologists' knowledge of risk factors for conception, strategies for prenatal diagnosis, and prognosis for affected individuals. To address these gaps this paper reviews the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals, presents current information, and makes suggestions for expanding obstetrician-gynecologists' knowledge of myelomeningocele.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to state that despite a large amount of professional and public education on the use of folic acid in prevention of open neural tube defects (ONTDs) the incidence still affects 0.5-1.0/1000 pregnancies and recall that a recent survey conducted by the ACOG shows substantial misunderstanding and misinformation on major categories of neural tube birth defects.

Neural tube defects and associated anomalies in a fetal and perinatal autopsy series

Neural tube defects (NTDs) are congenital malformations of the central nervous system (CNS) secondary to abnormal closure of the neural tube during embryonic development. This study provides information on NTD rate, distribution, associated morphologic anomalies and organ weights in a Danish fetal and perinatal autopsy series during a 16 year period. The data were extracted from the autopsy reports of a consecutive series of 1984 fetal and perinatal autopsies from the Copenhagen area performed in the period 1989-2004. Registered parameters included: The location and morphology of the NTD, associated morphological anomalies, and organ weights. Organ weights were evaluated according to new fetal autopsy standards and grouped as low, normal or high. Ninety-seven NTD cases were found (4.9%): Spina bifida (38 cases), cephalocele (17 cases) and anencephaly (42 cases). 63% of NTD cases had associated morphologic anomalies. Among the most common were hydrocephalus, NTD in another region, and anomalies in the urogenital system. 58% of the NTD cases had abnormal weight of one or more organs. Most notable was low adrenal weight not only in anencephalic fetuses but also in cases with cephalocele, suggesting a possible association.

Non-multifactorial neural tube defects

Although most neural tube defects (anencephaly, spina bifida) occur as isolated malformations, a substantial proportion are attributable to chromosome anomalies, known teratogens, or component manifestations of multiple anomaly syndromes. This review describes known chromosome alterations and the candidate genes residing in the altered region, as well as syndromes associated with neural tube defects and causative genes, if known.

Epidemiology of neural tube defects and folic acid

This review article combines four disparate observations about Neural Tube Defects (NTDs). They are the worldwide decline in the birth incidence that began prior to prenatal diagnosis; family recurrence risks; the effect of prenatal diagnosis and termination of affected pregnancies; and the effect of folic acid.

A trisomy 2 fetus with severe neural tube defects and other abnormalities

Examination of an abortus from a 13 week miscarriage revealed a fetus of around 9 weeks developmental age with multiple abnormalities including microcephaly, iniencephaly and encephalocele continuous with cervical and thoracic spina bifida, whose karyotype was subsequently shown to be 47,XY, + 2.

Epidemiology of neural tube defects

Neural tube defects (NTDs)-malformations secondary to abnormal neural tube closure between the third and fourth weeks of gestational age-have a complex and imperfectly understood etiology in which both genetic and environmental factors appear to be involved. A number of specific chromosomal or single-gene disorders, presumably not affected by environmental influences, are associated with the development of NTDs, but such syndromal cases account for a small proportion of NTDs in live-born infants. Analysis of recurrence patterns within families and of twin-concordance data provides evidence of a genetic influence in nonsyndromal cases, but factors such as socioeconomic status and geographic area (independent of race or ethnicity) are also associated with variations in the incidence of NTDs. The prevalence at birth of both anencephaly and spina bifida has decreased, but the advent of antenatal diagnosis and elective termination of affected pregnancies has undermined the reliability of birth prevalence rate as an estimate of incidence. Some occupational and other exposures, including maternal use of antiepileptic drugs (AEDs), are associated with increased risk for NTDs. Among women who have had an NTD-affected pregnancy, recurrence risk is markedly higher than the risk for a first NTD-affected pregnancy in the general population. There is strong evidence, overall, for a protective effect of adequate folate consumption. In some high-risk groups, however, such as women taking AEDs, folate supplementation has not been proven to reduce NTD risk.

Morphology of the 45,X embryo: an embryoscopic study

The morphology of monosomy X in embryos was documented by means of transcervical embryoscopy prior to evacuation in 24 cases of missed abortion. The embryos ranged in size from 13 mm to 26 mm CRL and were all developed beyond the sixth week of development. The embryonic phenotype varied from nearly normal to obviously abnormal with a combination of localized external developmental defects consisting of microcephaly, facial dysplasia, and retarded limb development. A single case of encephalocele was observed. The factors responsible for the wide range of developmental defects observed in monosomy X embryos are currently unknown. Transcervical embryoscopy can serve as a central component for further genetic studies elucidating these mechanisms which are needed for reaching a further understanding of the developmental effects of specific aneuploidy in human morphogenesis.

Trihalomethane exposures from municipal water supplies and selected congenital malformations

BACKGROUND

Concerns about potential health effects of trihalomethanes (THMs) have prompted investigations on whether infants whose mothers were periconceptionally exposed to drinking water containing THMs are at greater risk of congenital malformations.

METHODS

We used two large case-control maternal interview studies that were conducted among California deliveries from 1987 through 1991. One study comprised 538 infants/fetuses with neural tube defects (NTDs) and 539 nonmalformed control infants. The second study included an additional 265 infants with NTDs, 207 infants with conotruncal heart defects, 409 infants with orofacial clefts, and 481 control infants. Expert personnel from municipal water companies estimated THM levels for a particular residence and specific periconceptional time period using quarterly monitoring measurements. Estimates were also made for four individual THM levels and for the total THM level.

RESULTS

NTD risk in the first study was inversely associated with total THM exposure. Although the second study did not show the same inverse relationship for NTDs, there were no positive associations of NTDs or the other malformations with total THM as estimated from continuous models. Elevated risks were observed for the lowest category of exposure (1-24 ppb), but risks were either not substantially elevated or were imprecise for higher exposure levels. Thus no evidence was observed for an exposure-response relation.

CONCLUSIONS

Our results do not provide a clear pattern of association between THM exposure and risks of specific congenital malformations. Imprecise exposure measures coupled with a lack of information about other possible sources of THM exposure may have caused associations to be underestimated.

Neural tube defects in missed abortions: embryoscopic and cytogenetic findings

Transcervical embryoscopy, a new technique for direct visualization of the first trimester conceptus was carried out in 116 cases of missed abortion. Embryonic neural tube defects and other localized developmental defects, were diagnosed in 10 out of 99 cases in which a complete embryoscopic evaluation was possible. All eight successfully karyotyped cases had a numerical chromosomal abnormality. A ninth unkaryotyped embryo with open spina bifida showed, on embryoscopy, a malformation pattern highly suggestive of triploidy. Our embryoscopic and cytogenetic findings provide valuable information for genetic counseling in future pregnancies.

Awareness of folic acid for neural tube defect prevention among Israeli women

The failure of neural tube closure during early embryogenesis results in a range of neural tube defects (NTD), the most common of which is spina bifida. The role of folic acid in reducing the rate of NTD has been well-established. Three recent cases of infants with NTD inspired this investigative study into the level of awareness and knowledge of folic acid and its function in the prevention of NTD among Israeli women. Of 920 women interviewed, only 51 (5.5%) had heard of folic acid, and 27 (2.8%) were reported to have taken it. The source of information and the motivation for self-medication were also explored with regard to socioeconomic and health profile. Awareness of folic acid was significant among women aged 17-29 years (P = 0.005) and those aged 30-39 years (P = 0.009), and among semireligious and nonreligious women (P = 0.008 and 0.01, respectively). Among women who were aware of folic acid, only nonreligious women tended to take it. No correlation was found between folic acid intake and age, religiosity, nationality, number of pregnancies, and health status among women who were aware of folic acid intake. The poor level of awareness, evident in our study, demands that the medical community broadcast the benefit of folic acid. Furthermore, government health initiatives, such as the addition of folic acid to flour preparations, may effectively ensure its appropriate daily intake. These improved education and prevention programs may forcibly reduce the rate of NTD-affected pregnancies.

Central nervous system malformations in a perinatal/neonatal autopsy series

Congenital malformations of the central nervous system (CNS) are among the most common anomalies, but data on the incidence of CNS malformations in autopsy populations are scant. We examined 4122 autopsies between the years 1958 and 1995. There were 363 cases (8.8%) with CNS malformations; 235 were neonates and 128 stillborns. The overall gender ratio was 1:1, although more male neonates and more female stillborns had malformations. The body weights ranged from 24 to 6440 g. Neural tube defects were the most common types of malformations (45.5%) and included anencephaly, meningoencephalocele, meningocele/meningomyelocele, craniospinal rachischisis, and spina bifida occulta. The incidences of other malformations were: congenital hydrocephalus (12.4%), neuronal/glial proliferation disorders such as micro- and macrocephaly (8.8%), neuronal migration disorders (8.8%), prosencephalon growth disorders such as holoprosencephaly and arhinencephaly (8.5%), abnormalities of the midline structures such as agenesis of corpus callosum (4.1%), developmental cysts (3.3%), cerebellar malformations (3%), and vascular malformations (2%). Miscellaneous malformations (3%) consisted of acephalia in four cases with twin reversed arterial perfusion (TRAP), two cases of hydranencephaly, and four cases of rare degenerative and metabolic encephalopathies.

Folates and the fetus

It is proven that folic acid supplied in the periconceptional period can lower the recurrence and occurrence rate of neural tube defects (NTDs). Our research team on prevention of birth defects could demonstrate that folic acid preventable NTDs are partly based on hyperhomocystinemia and a genetic predisposition (mutation of the methylenetetrahydrofolate-reductase gene (MTHF-R)). Reduced activity of the folate methylation cycle seems to be an attractive working hypothesis in the aetiology of NTDs. This genetic metabolic defect can be overcome by treatment with folic acid and/or vitamin B12.

Death before birth: clues from gene knockouts and mutations

A survey of mouse gene knockouts, transgene insertions and spontaneous mutations that are lethal prenatally reveals that surprisingly few developmental disturbances lead to death of the embryo and early foetus. These disturbances include failure to establish and maintain a vascular circulation, and failure to make the transition from yolk-sac-based to liver-based haematopoiesis. The embryo must also establish gestation-dependent routes of nutritional interaction with the mother, including implantation, formation of a yolk-sac vascular circulation, and formation of a chorioallantoic placenta. A number of embryonic organ and body systems, including the central nervous system, gut, lungs, urogenital system and musculoskeletal system, appear to have little or no survival value in utero.

Maternal zinc deficiency, but not copper deficiency or diabetes, results in increased embryonic cell death in the rat: implications for mechanisms underlying abnormal development

The mechanisms underlying the teratogenicity of maternal copper deficiency, zinc deficiency, and diabetes are largely unknown. Here we investigated whether these insults are associated with altered patterns of cell death in gestation day (GD) 11.0 rat embryos. Four weeks prior to mating, rats in the copper-deficient group (CuD) were fed a copper-deficient diet supplemented with the chelator, triethylenetetramine, to facilitate the depletion of tissue copper stores. Rats in this group were switched to a triethylenetetramine-free copper-deficient diet 1 week prior to mating. Dams in the diabetic and control groups were fed a control (8 micrograms copper, 25 micrograms zinc/g) diet throughout the study. On GD 3.0, one subset of the control dams was assigned to the zinc-deficient group (ZnD) and fed a zinc-deficient diet. A second subset of control dams was assigned to a restricted fed group and fed the control diet in quantities consumed by the zinc-deficient dams. Litters were taken by cesarean section on GD 11.0. Embryos were examined for gross morphology and assessed for patterns of cell death using Nile blue sulfate. Embryos from the CuD dams were characterized by edematous hindbrain. Embryos from the diabetic group were characterized by delayed development. Altered patterns of cell death were only detected in embryos from the ZnD dams. Within the ZnD group, embryos were either characterized by small size, edematous head region, and control patterns of cell death, or normal size, normal morphology, and increased cell death. These different patterns of morphology and cell death in the embryos of ZnD dams were associated with different patterns of maternal food intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Human adverse reproductive outcomes and electromagnetic field exposures: review of epidemiologic studies

Concerns have been raised regarding a relation between residential and occupational electromagnetic (EM) field exposures and adverse reproductive effects. This paper reviews the epidemiologic evidence for this possible relation, including some pertinent methodologic issues, notes relevant findings from the experimental literature, and discusses areas for future research. Evidence is lacking for a strong association between a woman's use of a video display terminal (VDT) during pregnancy and spontaneous abortion. The evidence for a strong association between a women's use of a VDT and other adverse reproductive endpoints is also lacking, with some suggestive findings for congenital malformations and too few data to reach a conclusion about other endpoints. With respect to low-level EM field exposures other than VDTs, the paucity of data prevents one from determining whether there are reproductive health risks associated with such exposures. Therefore, this is an area that needs further investigation. Given that altered growth may be an underlying biologic effect of EM field exposures, endpoints that might be pursued in future studies include congenital malformations not associated with chromosomal anomalies, intrauterine growth retardation, and chromosomally normal spontaneous abortions.

Prevalence of neural tube defects in South Australia, 1966-91: effectiveness and impact of prenatal diagnosis

OBJECTIVE

To determine trends in total prevalence of neural tube defects in South Australia during 1966-91, the impact of prenatal diagnosis on birth prevalence, and the effectiveness of prenatal screening for neural tube defects in 1986-91.

DESIGN

All births and terminations of pregnancy affected by neural tube defects and information on prenatal screening were ascertained from multiple sources including the South Australian perinatal and abortion statistics collections, birth defects register, and state maternal serum alpha fetoprotein screening programme.

SETTING

Southern Australia.

SUBJECTS

All 1058 births and terminations of pregnancy affected by neural tube defects in 1966-91.

MAIN OUTCOME MEASURES

Total prevalence and birth prevalence of individual and all neural tube defects. The proportion of screened cases detected prenatally.

RESULTS

Total prevalence of neural tube defects during 1966-91 was 2.01/1000 births with no upward or downward trend. However, birth prevalence fell significantly (by 5.1% a year), with an 84% reduction from 2.29/1000 births in 1966 to 0.35/1000 in 1991 (relative risk = 0.16, 95% confidence interval 0.07 to 0.34). The fall was 96% for anencephaly and 82% for spina bifida. 85% of defects, both open and closed, were detected before 28 weeks' gestation in women screened by serum alpha fetoprotein or mid-trimester ultrasonography, or both, in 1986-91 (99.0% for anencephaly and 75.7% for spina bifida).

CONCLUSIONS

While the total prevalence of neural tube defects in South Australia remained stable, prenatal diagnosis and termination of pregnancy resulted in an 84% fall in birth prevalence during 1966-91. Screening detected over four fifths of cases in 1986-91.

The prevalence of anencephalus and spina bifida in New Zealand

Despite the plethora of epidemiological research conducted on anencephalus and spina bifida, few of the studies have used multiple source case ascertainment and controlled for the effect of possible confounding factors. This paper reports the results from a study of the relationships between various risk factors and the prevalence of anencephalus and spina bifida in New Zealand during 1978-82, using case data obtained from multiple sources and a national cohort of births as the denominator. The rates of anencephalus and spina bifida in New Zealand were 0.78/1000 and 0.94/1000 total births, respectively. The rate of a neural tube defect (NTD) birth for Maori parents was less than for their non-Maori counterparts. Paternal ethnic origin and maternal ethnic origin made similar contributions to the model of anencephalus rates, but the results suggest that paternal ethnic origin is a less important risk factor in the prevalence of spina bifida. The rate of both NTD was high among female infants and low among births to women born in countries other than the British Isles and New Zealand. The rate of anencephalus showed a distinct north-south gradient, but there was no evidence of effects for maternal or paternal age, parity, urban-rural place of residence, nuptiality, social class or season of birth in the prevalence of either NTD in New Zealand.

Neural tube defects after infertility treatment: a review

OBJECTIVE

To investigate whether an association exists between ovulation induction and neural tube defects (NTDs).

MATERIALS AND METHODS

Risk estimations in the medical literature were identified through Medline, and validity and power were assessed. Large in vitro fertilization-embryo transfer (IVF-ET) registries represent another source of information. The total number of NTDs and the total number of fetuses were computed from five registries. These data were expressed as proportions and compared with data from the general population.

RESULTS

Only one study could be identified as both valid and powerful, through literature review. This case-control study concluded there was no association between ovulation induction and NTDs. The pool of IVF-ET registry data represents another powerful epidemiologic tool. Analysis of the registry data confirms the findings of the case-control study.

CONCLUSIONS

Ovulation induction does not seem to represent a risk factor for NTDs in the offspring.

Anencephaly in the United States, 1968-1987: the declining incidence among white infants

The ethical issues concerning the use of fetal tissue as a source for organ transplantation has focused interest on anencephaly. For reasons that are not entirely clear, the incidence of anencephaly has been declining. As anencephaly is easily recognized and invariably fatal, mortality figures provide an excellent reflection of incidence. In the United States, between 1968 and 1987, infant mortality rates per 100,000 live births due to anencephaly declined from 22.4 to 12.1 (46.0%) for male infants and from 32.7 to 16.6 (49.2%) for female infants. However, when separated by race, the mortality rate declined for white male infants from 25.0 to 13.3 (46.8%) but only decreased from 9.0 to 7.7 (14.4%) for nonwhite male infants. The mortality rate declined for white female infants from 36.7 to 17.6 (52.0%) and actually increased slightly from 12.8 to 13.2 (3.1%) for nonwhite female infants. Thus, the declining incidence of anencephaly reflects a declining incidence of affected white infants but not of affected nonwhite infants.

Prevalence of neural tube defects in 20 regions of Europe and the impact of prenatal diagnosis, 1980-1986. EUROCAT Working Group

STUDY OBJECTIVE

The aims were (1) to determine whether in Europe, 1980-86, geographical differences in total prevalence of neural tube defects persist; (2) to examine the stability of total prevalence rates over time; (3) to evaluate the impact of prenatal diagnosis in terms of frequency and timing of termination of pregnancy.

DESIGN

Prevalence rates of neural tube defects were determined from case registration data in 20 EUROCAT regional registers of congenital anomalies, 1980-86. The chi 2 test for homogeneity in proportions was used to test whether differences in total prevalence rates were significant between regions or over time.

SETTING

Geographically defined populations were used in the Republic of Ireland, United Kingdom, Belgium, The Netherlands, Luxemburg, Denmark, France, Italy, Yugoslavia, and Malta.

PATIENTS

The patients were 3113 cases of anencephaly, spina bifida, encephalocele, and iniencephaly. Total cases (livebirths, stillbirths and induced abortions following prenatal diagnosis) were registered in 14 regions. Induced abortions were excluded from registration in six regions.

MEASUREMENTS AND MAIN RESULTS

Total prevalence rates (including livebirths, stillbirths and induced abortions) were 24 to 38 per 10,000 in six areas of Ireland and United Kingdom. Average total prevalence rate in eight continental European areas was 11.5 per 10,000. There was a secular decline in total prevalence in Dublin (Republic of Ireland) and Northern Ireland (United Kingdom) and a fluctuation in Glasgow, Liverpool, and South Glamorgan (United Kingdom). Total prevalence in continental Europe was stable over time. There was no significant geographical or secular variation in the spina bifida to anencephaly ratio (1.3). The ratio of encephalocele to other neural tube defects was lower in the British Isles (0.09) than in continental Europe (0.18). The impact of prenatal diagnosis and termination of pregnancy is increasing over time. Terminations were performed 1984-86 in at least 80% of total cases of anencephaly in 6/11 centres registering induced abortions, and in at least 40% of total cases of spina bifida in four centres. Serum alpha fetoprotein screening in British centres was associated with earlier prenatal diagnosis of spina bifida than ultrasound screening in other centres.

CONCLUSIONS

Geographical and secular variation in total prevalence of neural tube defects persists in Europe 1980-86, independent of the practice of prenatal diagnosis. There is considerable regional variation in the impact of prenatal diagnosis in terms of frequency and timing of diagnosis and pregnancy termination linked to different policies and practices of prenatal screening.

Fallacies of international and national comparisons of disease occurrence in the epidemiology of neural tube defects

Despite extensive research, little progress has been made in elucidating the etiologies of anencephalus and spina bifida. International and national distributions of disease occurrence have often been used as a basis for generating etiological hypotheses (e.g., potato blight, tea consumption, and zinc deficiency hypotheses). However, few of the epidemiological studies of neural tube defects (NTDs) have been conducted with scientific rigor in design, and most are of dubious validity, often with low precision in the estimates. This paper shows that the accepted geographic patterns of NTDs may be attributable to variations in the validity of studies used to describe these patterns. The nonuniformity in the duration and diligence of case ascertainment, the lack of a standardized nomenclature and classification, and the definition of the denominator remain principal problems in evaluating the epidemiology of NTDs. For example, the distinction between incidence and prevalence is not always made, and there is no consistency in the placement of the gestational boundary between late fetal deaths and spontaneous abortions. Findings are compared from studies conducted at different times, without due regard to the effect of secular trends, and using studies that have varying levels of case ascertainment. In etiological research, it is important to perform studies that are accurate and precise, but the literature used to define the spatial distribution of NTDs has often been accepted without due regard to the effect of these factors.

Ullrich-Turner syndrome with agenesis of the corpus callosum

We report on a 19-year-old woman with 45,X Ullrich-Turner syndrome who was severely mentally retarded and had hypotonia. Computer tomography (CT) scan showed agenesis of the corpus callosum. There have been few reports of gross developmental central nervous system (CNS) abnormalities in Ullrich-Turner syndrome. Only one case of Ullrich-Turner syndrome with agenesis of the corpus callosum has been reported. The high prenatal lethality of Ullrich-Turner syndrome may mask a CNS abnormality.

Triamcinolone acetonide-induced meningocele and meningoencephalocele in rhesus monkeys

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Maternal fertility, reproductive loss, and defective human embryos

It is possible that many abnormal conceptuses are lost at an early stage without the mother's knowledge. To investigate this further the reproductive history of the mothers of defective embryos (neural tube defects, holoprosencephaly, cleft lip, polydactyly, and early embryonic resorption) was compared with that of the mothers of normal embryos. The frequency of prior miscarriages was higher in the case mothers than in normal controls matched for maternal age and gravidity, the difference being significant for all the anomalies except for polydactyly. The case mothers had fewer prior recognised pregnancies than control mothers matched for maternal age. There were more primigravid mothers in abnormal groups, and the difference from controls was significant for neural tube defects. It was assumed that the gravidity of the case mothers may be underestimated, possibly due to increased early abortions which are not recognised clinically. Thus, it seems that both recognised and unrecognised abortions occur more often in the mothers of defective embryos. Since many spontaneous abortuses are morphologically and/or cytogenetically abnormal, some women appear to conceive abnormal embryos repeatedly. Most of these embryos, however, may be screened out prenatally and escape clinical detection. Information on prior reproductive history of the woman should be examined carefully in genetic counselling.

Survey of neural tube defects in spontaneously aborted embryos

Although variations in the incidence and types of central nervous system abnormalities have been demonstrated between early and late pregnancy, the reason for this finding has not yet been determined. Among 569 spontaneously aborted embryos, we describe 38 central nervous system lesions, many of which are different from those observed at birth. The importance of correlating morphology and cytogenetic studies in the understanding of pathogenesis of embryonic neural tube defects is emphasized.

Central nervous system malformations induced by triamcinolone acetonide in nonhuman primates: pathogenesis

The pathogenetic sequence for TAC-induced encephalocele is in agreement with hypotheses proposing that neural tube closure is followed by protrusion of the mesencephalon, with subsequent growth and development resulting in herniation of the cerebrum and cerebellum. This model could serve to clarify the pathogenesis of encephalocele and to stimulate further study in comparing this defect to other dysraphic states. Triamcinolone acetonide (TAC) was administered intramuscularly (10 mg/kg) to 16 pregnant rhesus monkeys (Macaca mulatta) for 5 alternate days of pregnancy, beginning on gestational day (GD) 23. Conceptuses were removed by hysterotomy at GD 35, 42, 50, or 70 and examined grossly and histologically. Length, area, and perimeter of the tectum and aqueduct area and perimeter were measured with an image analyzer. Changes in treated specimens were suggestive of forces within or ventral to the tectum resulting in dorsal protrusion, rostral-posterior stretching, and attenuation. The angle of the cephalic, pontine, and cervical flexures was also measured. The more acute angle of the cephalic flexure and less acute cervical flexure of treated specimens could represent altered orientation secondary to a mesenchymal deficiency. However, the less acute angle of the pontine flexure in treated specimens suggests an intrinsic alteration in the neural tube. This suggests that encephalocele may result from a combination of mesenchymal and neural tube abnormalities.