Spina bifida and anencephalus in greater London

The contribution of de novo coding mutations to meningomyelocele

Meningomyelocele (also known as spina bifida) is considered to be a genetically complex disease resulting from a failure of the neural tube to close. Individuals with meningomyelocele display neuromotor disability and frequent hydrocephalus, requiring ventricular shunting. A few genes have been proposed to contribute to disease susceptibility, but beyond that it remains unexplained1. We postulated that de novo mutations under purifying selection contribute to the risk of developing meningomyelocele2. Here we recruited a cohort of 851 meningomyelocele trios who required shunting at birth and 732 control trios, and found that de novo likely gene disruption or damaging missense mutations occurred in approximately 22.3% of subjects, with 28% of such variants estimated to contribute to disease risk. The 187 genes with damaging de novo mutations collectively define networks including actin cytoskeleton and microtubule-based processes, Netrin-1 signalling and chromatin-modifying enzymes. Gene validation demonstrated partial or complete loss of function, impaired signalling and defective closure of the neural tube in Xenopus embryos. Our results indicate that de novo mutations make key contributions to meningomyelocele risk, and highlight critical pathways required for neural tube closure in human embryogenesis.

Surgical outcomes of myelomeningocele repair: A 20-year experience from a single center in a middle-income country

BACKGROUND AND PURPOSE

Spina bifida is the second major cause of congenital disorders and the most common central nervous system congenital malformation compatible with life primarily. Herein, we describe the short-term outcome of post-natal Myelomeningocele (MMC) surgical management and predictors of its postoperative complications and mortality.

METHODS

This retrospective chart review studies the children who underwent post-natal surgical management for MMC in Namazi hospital, a tertiary referral center, in southern Iran from May 2001 to September 2020.

RESULTS

248 patients were included in this study. The mean age at the operation was 8.47 ± 8.69 days. The most common site of involvement of MMC was Lumbosacral (86%, n = 204). At the evaluation conducted prior to the operation, cerebrospinal fluid leak was observed in 7% (n=16) of the patients. Postoperatively, 5.7% of the patients expired in the 30-day follow-up after the operation (n = 14), while 24% needed readmission (n = 47). The most common complications leading to readmission were wound dehiscence (n = 10, 42%) and wound purulence (n = 6, 25%). Only the site of the lesion (p-value = 0.035) was associated with postoperative complication. After controlling for potential confounders, the site of the lesion (adjusted odds ratio = 0.146, 95% confidence interval = 0.035-0.610, p-value = 0.008) and age at surgery (adjusted odds ratio = 1.048, 95% confidence interval = 1.002-1.096, p-value = 0.041) were significantly associated with mortality CONCLUSIONS: The age of the patients at the surgery and the site of the lesion are the two factors that were associated with mortality. However, further investigations into preoperative interventions and risk factors to mitigate the risk of complications and mortality are highly encouraged.

Influence of social, demographic, and clinical factors in live births with spinal dysraphism in Brazil: an ecological study of 21 years

OBJECTIVES

This study aimed to verify possible associations between sociodemographic and clinical factors in live births with spinal dysraphism.

METHODS

An analytical (descriptive and inferential) and ecological study was carried out based on secondary data of 11,308 live births with spinal dysraphism registered in the Live Birth Information System (SINASC) in Brazil from 1999 to 2019. Demographic factors analyzed were age, education, mothers' marital status and geographic region. The clinical factors analyzed were duration, gestation period, birthweight, and number of prenatal visits performed by women who underwent medical follow-up.

RESULTS

There was an increase in the number of cases of spinal dysraphism in recent years in Brazil with an annual percentage variation of 3.52%. However, the period from 2005 to 2009 showed a reduction in live births with spinal dysraphism. The regions with the highest incidence were the South and Southeast. The risk increased in mothers born after 1980, older than 30 years and with a high level of education. The risk was increased in live births of whites and blacks, born from double pregnancy and with body weight less than 3000 g. The absence of prenatal care was associated with a higher incidence.

CONCLUSION

Sociodemographic and clinical factors have specific characteristics that can predict spinal dysraphism in newborns in Brazil.

Sacral Spina Bifida Occulta: A Frequency Analysis of Secular Change

Substantial relaxation of natural selection beginning around 1900 changed the mutation/selec­tion balance of modern genetic material, producing an increase in variable anatomical structures. While multiple structures have been affected, the temporal increase in variations of the sacrum, specifically, ‘Sa­cral Spina Bifida Occulta,’ have been reliably demonstrated on a localised scale. Calculation of largescale frequency has been hindered by the localised nature of these publications, the morphological variability of this variation, and potential pathological associations, which have produced divergent classifications, and conflicting reported rates of occurrence. A systematic review of the reported literature was conducted to provide an objective analysis of Sacral Spina Bifida Occulta frequency from 2500 BCE to the present. This review was designed to compensate for observed inconsistencies in reporting and to ascertain, for the first time, the temporal trajectory of this secular trend. A systematic review of Sacral Spina Bifida Occulta lit­erature was conducted through the strict use of clinical meta-analysis criteria. Publications were retrieved from four databases: PubMed, Embase, the Adelaide University Library database, and Google Scholar. Data were separated into three historical groups, (1 = <1900, 2 = 1900 to 1980 and 3 = >1980), and frequency outcomes compared, to determine temporal rates of occurrence. A total of 39/409 publications were included in the final analysis, representing data for 16,167 sacra, spanning a period of 4,500 years. Statistically significant results were obtained, with total open S1 frequen­cy increasing from 2.34%, (79 to 1900CE), to 4.80%, (1900 to 1980CE) and to 5.43% (>1980CE). These increases were significant at p<0.0001, with Chi-squared analysis. A clear secular increase in the global frequency of Sacral Spina Bifida Occulta has been demonstrated from 1900 to the present. This research provides a novel and adaptable framework for the future assessment of variation distribution, with impor­tant implications for the fields of biological anthropology and bioarchaeology.

Population-level assessment of atlas occipitalization in artificially modified crania from pre-Hispanic Peru

Atlas occipitalization (AO) is a spinal anomaly, characterized by the fusion of the first cervical vertebra and occipital bone, with a complex etiology that can arise from congenital and environmental causes. AO has been reported in three regions of pre-Hispanic Peru in skeletal remains with artificial cranial modification (ACM), which involves the use of compression devices to permanently alter cranial shape and may have affected the fusion of the atlas and occipital bone. The aims of this study were to gain insights into AO’s etiology by testing correlations between AO and ACM presence/type and geographic region as well as to characterize morphological variation associated with AO. We investigated the geographic distribution of AO and its potential relationship to ACM in a large sample of human crania from eight coastal and highland regions of pre-Hispanic Peru, held at the Smithsonian’s National Museum of Natural History (n = 608, 1300–1500 CE). Eleven cases of AO were observed in three coastal regions—including two previously unreported regions—at an overall frequency of 1.8%. The frequency of AO did not differ significantly between crania with and without ACM, in general or by type, suggesting that ACM is not an etiological factor that influences AO in this sample. AO was observed at a significantly higher rate in the southern coastal region of Arequipa than in any other region. Genetic, dietary, and epidemiological conditions are evaluated as factors possibly shaping the geographic distribution of AO along the central and southern coasts of Peru.

Dominant negative GPR161 rare variants are risk factors of human spina bifida

Spina bifida (SB) is a complex disorder of failed neural tube closure during the first month of human gestation, with a suspected etiology involving multiple gene and environmental interactions. GPR161 is a ciliary G-protein coupled receptor that regulates Sonic Hedgehog (Shh) signaling. Gpr161 null and hypomorphic mutations cause neural tube defects (NTDs) in mouse models. Herein we show that several genes involved in Shh and Wnt signaling were differentially expressed in the Gpr161 null embryos using RNA-seq analysis. To determine whether there exists an association between GPR161 and SB in humans, we performed direct Sanger sequencing on the GPR161 gene in a cohort of 384 SB patients and 190 healthy controls. We identified six rare variants of GPR161 in six SB cases, of which two of the variants were novel and did not exist in any databases. Both of these variants were predicted to be damaging by SIFT and/or PolyPhen analysis. The novel GPR161 rare variants mislocalized to the primary cilia, dysregulated Shh and Wnt signaling and inhibited cell proliferation in vitro. Our results demonstrate that GPR161 mutations cause NTDs via dysregulation of Shh and Wnt signaling in mice, and novel rare variants of GPR161 can be risk factors for SB in humans.

Causes of Congenital Malformations

BACKGROUND

Many different causes of malformations have been established. The surveillance of a consecutive population of births, including stillbirths and elective terminations of pregnancy because of fetal anomalies, can identify each infant with malformations and determine the frequency of the apparent etiologies. This report is a sequel to the first such analysis in the first 10 years of this Active Malformations Surveillance Program (Nelson and Holmes, ).

METHODS

The presence of malformations was determined among 289,365 births over 41 years (1972-2012) at the Brigham and Women's Hospital in Boston. The abnormalities were identified from the review of the examination findings of the pediatricians and consultants and diagnostic testing for the live-born infants and the autopsies of the fetuses in elective terminations and stillbirths.

RESULTS

A total of 7020 (2.4%) infants and fetuses with one or more malformations were identified with these apparent etiologies in 26.6%: Mendelian disorders, including infants with postaxial polydactyly, type B; chromosome abnormalities; vascular disruption; complications of monozygous twinning; and environmental factors. The malformations of unknown etiology were a much larger group.

CONCLUSION

While several causes of malformations have been identified, many remain unexplained. Combining the ascertainment in a future surveillance programs with genome sequencing and chromosome microarray analysis will increase significantly the number of malformations attributed to genetic mechanisms. Birth Defects Research 110:87-91, 2018.© 2018 Wiley Periodicals, Inc.

Genetic epidemiology of neural tube defects

It has been estimated that 60-70% of neural tube defects (NTDs) have a genetic component, but few causative genes have been identified. The lack of information on genes associated with non-syndromic NTDs in humans is especially notable as the "genomic revolution" has led to new tools (e.g., genome-wide genotyping arrays, next-generation sequencing) that are helping to elucidate the full spectrum of genetic variation (from common to rare) contributing to complex traits, including structural birth defects. However, the application of modern genomic approaches to the study of NTDs has lagged behind that of some other common structural birth defects. This may be due to the difficulty of assembling large study cohorts for anencephaly or spina bifida. The purpose of this review is to outline the evolution of genetic studies of NTDs, from studies of familial aggregation to candidate gene and genome-wide association studies, through whole-exome and whole-genome sequencing. Strategies for addressing gaps in NTD genetic research are also explored.

Spina bifida

Spina bifida is a birth defect in which the vertebral column is open, often with spinal cord involvement. The most clinically significant subtype is myelomeningocele (open spina bifida), which is a condition characterized by failure of the lumbosacral spinal neural tube to close during embryonic development. The exposed neural tissue degenerates in utero, resulting in neurological deficit that varies with the level of the lesion. Occurring in approximately 1 per 1,000 births worldwide, myelomeningocele is one of the most common congenital malformations, but its cause is largely unknown. The genetic component is estimated at 60-70%, but few causative genes have been identified to date, despite much information from mouse models. Non-genetic maternal risk factors include reduced folate intake, anticonvulsant therapy, diabetes mellitus and obesity. Primary prevention by periconceptional supplementation with folic acid has been demonstrated in clinical trials, leading to food fortification programmes in many countries. Prenatal diagnosis is achieved by ultrasonography, enabling women to seek termination of pregnancy. Individuals who survive to birth have their lesions closed surgically, with subsequent management of associated defects, including the Chiari II brain malformation, hydrocephalus, and urological and orthopaedic sequelae. Fetal surgical repair of myelomeningocele has been associated with improved early neurological outcome compared with postnatal operation. Myelomeningocele affects quality of life during childhood, adolescence and adulthood, posing a challenge for individuals, families and society as a whole. For an illustrated summary of this Primer, visit: http://go.nature.com/fK9XNa.

Spina bifida: a diagnostic dilemma in paleopathology

This article provides information regarding the etiology, pathogenesis, and skeletal manifestation of spina bifida or spinal dysraphisms. On the basis of a review of the medical literature, it addresses discrepancies in documentation and interpretation of spina bifida in paleopathology. Furthermore, it offers suggestions for use of universal terminology and highlights the difficulties in the specific diagnosis of dysraphisms in skeletal remains. In addition, the necessity of examining the entire skeleton for abnormalities to distinguish simple delay/failure of fusion of the posterior neural arches from other occult spinal dysraphisms is emphasized, as it is the need for stratification of the sample by age and sex when reporting frequencies of sacral spina bifida occulta.

Birth defects among maternal first cousins in Irish families with a neural tube defect

BACKGROUND

Maternal first cousins of an individual with a neural tube defect (NTD) are at increased risk for an NTD. It is not known if they are also at risk for other serious birth defects.

METHODS

We carried out an interview study of uncles and aunts and first cousins in Irish NTD families covering their pregnancy histories and the health of family members.

RESULTS

Maternal first cousins were more likely than paternal first cousins to have a birth defect (9.4% vs. 5.5%, p = 0.02; adjusted odds ratio: 1.72, 95% confidence interval: 1.04, 2.84).

CONCLUSIONS

This study shows that two generations of distant relatives (uncles/aunts and first cousins) in NTD families have similar maternal excesses of NTDs and birth defects overall. Inheritance mechanisms favouring matrilineal transmission, currently unknown, may contribute to birth defect occurrence in these families.

Reproductive effects of maternal and pre-weaning undernutrition in rat offspring: age at puberty, onset of female reproductive senescence and intergenerational pup growth and viability

Maternal and/or postnatal undernutrition are widespread in human populations and are components of many experimental developmental and reproductive toxicology bio-assays. This study investigated in utero and/or pre-weaning undernutrition effects on reproductive maturation and senescence in the Sprague-Dawley rat as well as potential intergenerational effects. Pregnant rats were given food ad libitum or at 50% of normal dietary intake throughout pregnancy. Their offspring (control or IUGR) were cross-fostered to control dams with litter sizes of 8 or 16 pups (control and undernourished). Offspring body weights were reduced and onset of male puberty slightly delayed in animals from large postnatal litters. Similar body weight effects were observed in females but there was no difference in the age of vaginal opening. Female reproductive senescence as measured by onset of estrus acyclicity occurred at a younger age in IUGR-8-pup and Control-16-pup groups compared to Control-8-pup or IUGR-16-pup groups. Females were bred to control males and no evidence of adverse reproductive effects was found in any F2 groups. The offspring of the F1 generation did not show an intergenerational effect as documented in humans.

Further evidence for a maternal genetic effect and a sex-influenced effect contributing to risk for human neural tube defects

BACKGROUND

Neural tube defects (NTDs), including spina bifida and anencephaly, are the second most common birth defect with an incidence of 1/1000. Genetic factors are believed to contribute to NTD risk and family-based studies can be useful for identifying such risk factors.

METHODS

We ascertained 1066 NTD families (1467 affected patients), including 307 multiplex NTD families. We performed pedigree analysis to describe the inheritance patterns, pregnancy outcomes, and recurrence risks to relatives of various types.

RESULTS

Myelomeningocele or spina bifida (66.9%) and cranial defects (17.7%) were the most common NTD subtypes observed. The overall male:female ratio for affected individuals was 0.82, and there were even fewer males among individuals with an upper level NTD (0.62). Among twins, 2 of the 5 monozygotic twins and only 3 of 35 dizygotic twins were concordant, while 27% of the same sex twins were concordant, but none of the different sex twins. The estimated 6.3% recurrence risk to siblings (CI 0.04-0.08) is consistent with previous reports. Families with two or more affected individuals show a higher proportion of female transmitters (p = 0.0002). Additionally, the number of affected relatives in maternal compared to paternal lineages was more than double (p = 0.006). There were significantly more miscarriages, infant deaths, and stillborn pregnancies of the maternal aunts and uncles (p < 0.0001) and of first cousins (p = 0.04).

CONCLUSIONS

Our data provide several lines of evidence consistent with a maternal effect, as well as a sex-influenced effect, in the etiology of NTDs.

Pediatric perspective on prenatal counseling for myelomeningocele

BACKGROUND

Over the past 35 years, advances in the prenatal diagnosis of spina bifida using ultrasound and laboratory testing have increased the number of patients seeking prenatal counseling.

METHODS

Traditionally, this counseling has been provided by practitioners with little direct experience in the care of individuals with spina bifida across their life span.

RESULTS

Physicians experienced in the care of children with spina bifida are able to provide information that is not available from other sources.

CONCLUSIONS

This review provides a broad overview of many of the issues encountered during prenatal counseling sessions and emphasizes the additional value of the pediatric perspective during the process of informed decision making or preparation for an the birth of an affected child.

Adverse reproductive outcomes among pregnancies of aunts and (spouses of) uncles in Irish families with neural tube defects

Adverse pregnancy outcomes may be more frequent among sibs of individuals with neural tube defects (NTDs), and transmission of risk in families with an NTD may be more frequent among maternal relatives. In a study designed to evaluate matrilineal risk for NTDs, we compared adverse pregnancy outcomes among maternal and paternal first cousin pregnancies. Pregnancy histories were obtained by interview with 288 uncles and aunts (parents of the first cousin pregnancies) in 48 Irish NTD families. We analyzed pregnancy outcomes (preterm deliveries, stillbirths, and miscarriages) among 1,033 singleton first cousin pregnancies and compared risk among maternal versus paternal relatives. Maternal first cousin pregnancies were more likely to end adversely when compared to paternal first cousin pregnancies (17.4% vs. 11.7%, P = 0.01). In a logistic regression analysis of pregnancies unaffected by birth defects, maternal line remained independently associated with adverse outcomes (odds ratio (OR) = 1.55, 95% confidence interval (CI) 1.06, 2.27) after controlling for NTD type, maternal age, maternal smoking during pregnancy, first cousin pregnancy's year of birth. The excess risk with maternal line related mainly to spina bifida occulta families (OR = 42.4; CI 2.64, 681; P = 0.008); risk in open spina bifida families was 1.24 (CI 0.82, 1.87; P = 0.3). These results support the hypothesis of excess risk for adverse pregnancy outcomes among maternal relatives in NTD families. Further work is needed, epidemiological as well as clinical and molecular, not only to confirm these findings, but also to define the underlying biological mechanisms linking adverse reproductive outcomes, excess maternal risk and occurrence of NTDs.

An intervention study to increase knowledge and use of folic acid among relatives in neural tube defect-affected families in Washington, D.C

BACKGROUND

Little is known about the level of knowledge and use of folic acid among near relatives in U.S. families of a child with spina bifida. We hypothesized that relatives would be more knowledgeable than the general population and more likely to take folic acid. Further, we hypothesized that relatives would be more motivated by an intervention to increase their use of folic acid.

METHODS

We conducted an intervention study among females in families attending a hospital spina bifida clinic in Washington, DC.

RESULTS

The 231 subjects consisted of the affected individuals, mothers, sisters, and aunts. The average age was 34 years. At baseline, most (87.4%) reported that they had heard of folic acid; 37.6% were currently taking multivitamins with folic acid and 6.9% were taking folic acid tablets. The intervention significantly increased both knowledge (to 99%) and intake of folic acid from 41.9 to 48.5%. Folic acid intake increased significantly among African-American women and women with less education, women who were older, married, with children, and nonsmokers.

CONCLUSIONS

This intervention was successful in increasing folic acid intake among female relatives in spina bifida-affected families. By the end of the study, almost all women had heard of folic acid and folic acid use had increased by 16%. Among these women at higher than expected risk for having an affected child, this rate of intake, while more than the general population, still falls short of optimum. Fortification of food with folic acid may be the only way to ensure increased folic acid intake.

Epidemiology of neural tube defects

The epidemiological investigation of the common open neural tube defects (NTDs), anencephaly, and spina bifida, has a long history. The most significant finding from these past studies of NTDs was the identification of the protective effect of maternal, periconceptional supplementation with folic acid. Fortuitously, the association between folic acid and NTDs became widely accepted in the early 1990s, at a time when genetic association studies of complex traits were becoming increasingly feasible. The confluence of these events has had a major impact on the direction of epidemiological, NTD research. Association studies to evaluate genes that may influence the risk of NTDs through their role in folate-related processes, or through other metabolic or developmental pathways are now commonplace. Moreover, the study of genetic as well as non-genetic, factors that may influence NTD risk through effects on the nutrient status of the mother or embryo has emerged as a major research focus. Research efforts over the past decade indicate that gene-gene, gene-environment, and higher-order interactions, as well as maternal genetic effects influence NTD risk, highlighting the complexity of the factors that underlie these conditions. The challenge for the future is to design studies that address these complexities, and are adequately powered to detect the factors or combination of factors that influence the development of NTDs.

Spina bifida

Spina bifida results from failure of fusion of the caudal neural tube, and is one of the most common malformations of human structure. The causes of this disorder are heterogeneous and include chromosome abnormalities, single gene disorders, and teratogenic exposures. However, the cause is not known in most cases. Up to 70% of spina bifida cases can be prevented by maternal, periconceptional folic acid supplementation. The mechanism underlying this protective effect is unknown, but it is likely to include genes that regulate folate transport and metabolism. Individuals with spina bifida need both surgical and medical management. Although surgical closure of the malformation is generally done in the neonatal period, a randomised clinical trial to assess in utero closure of spina bifida has been initiated in the USA. Medical management is a lifelong necessity for individuals with spina bifida, and should be provided by a multidisciplinary team.

Parental employment status and neural-tube defects and folic acid/multivitamin supplementation in Hungary

OBJECTIVE

To study the role of parental employment status as indicator of socio-economic status (SES) in the origin of neural-tube defect (NTD) and in the use of periconceptional folic acid/multivitamin supplementation.

MATERIALS AND METHODS

One thousand two hundred and two cases with neural-tube defects, 38,151 population controls without any defects and 22,475 patient controls with other defects were compared in the population-based data set of the Hungarian case-control surveillance of congenital abnormalities, 1980-1996.

RESULTS

The proportion of professionals was lower, while the proportion of semi- and unskilled workers was higher in the neural-tube defect group compared with the population control group. However, the comparison of neural-tube defect and patient control groups showed a lower socio-economic status in the patient control group. In addition, the socio-economic status of fathers in the neural-tube defect group seemed to be better than in the population and patient control groups. The higher periconceptional folic acid supplementation and the higher use of multivitamins during pregnancy occurred in the professional and managerial categories in all the three study groups.

CONCLUSION

The occurrence of neural-tube defect shows a slight socio-economic dependence in the mothers at the comparison with population control group, however, patient control group had the lowest socio-economic status. The higher maternal education goes together with a higher proportion of periconceptional folic acid supplementation.

Neural tube defects

Defects of development of the neural tube can result in a number of seemingly different malformations. Understanding the abnormal embryology helps one understand the malformations and their surgical treatments. The clinical presentations and the follow-up of these patients require attention to various end organs besides the nervous system. For most of these conditions, long-term follow-up is necessary regardless of initial treatment. A decline in function is not a part of the natural history of these malformations and requires prompt evaluation and treatment.

Identification of a growth arrest specific (gas 5) gene by differential display as a candidate gene for determining susceptibility to hyperthermia-induced exencephaly in mice

Neural tube defects (NTDs) are among the most common congenital malformations, affecting approximately 1 per 1,000 liveborn infants in the United States [Nakano, 1973; Richards et al., 1972]. Maternal exposure to hyperthermia, either through recreational sources or due to an infectious agent, is thought to account for approximately 10% of observed NTD cases. The specific genes conferring susceptibility or resistance to hyperthermia-induced NTDs have not been identified. This study used differential display-polymerase chain reaction (DD-PCR) to characterize alterations in gene expression in the anterior embryonic neural tube of two highly inbred murine strains (SWV/Fnn, LM/Bc/Fnn) known to differ in their genetically determined susceptibility to heat-induced NTDs. Herein, we report the neural tube-specific differential expression of the growth arrest specific (gas 5) gene in the highly susceptible SWV/Fnn strain during neural tube closure (NTC). Although the expression of gas 5 did not appear to be altered by the teratogenic heat treatment, its spatial and strain-specific pattern of expression makes it an excellent candidate gene responsible for the observed genetic differences in NTD susceptibility between these two inbred murine strains.

Socioeconomic status, neighborhood social conditions, and neural tube defects

OBJECTIVES

This study evaluated the contributions of lower socioeconomic status (SES) and neighborhood socioeconomic characteristics to neural tube defect etiology. The influence of additional factors, including periconceptional multivitamin use and race/ethnicity, was also explored.

METHODS

Data derived from a case-control study of California pregnancies from 1989 to 1991. Mothers of 538 (87.8% of eligible) case infants/fetuses with neural tube defects and mothers of 539 (88.2%) nonmalformed infants were interviewed about their SES. Reported addresses were linked to 1990 US census information to characterize neighborhoods.

RESULTS

Twofold elevated risks were observed for several SES indicators. Risks were somewhat confounded by vitamin use, race/ethnicity, age, body mass index, and fever but remained elevated after adjustment. A risk gradient was seen with increasing number of lower SES indicators. Women with 1 to 3 and 4 to 6 lower SES indicators had adjusted odds ratios of 1.6 (1.1-2.2) and 3.2 (1.9-5.4), respectively, compared with women with no lower SES indicators.

CONCLUSIONS

Both lower SES and residence in a SES-lower neighborhood increased the risk of an neural tube defect-affected pregnancy, with risks increasing across a gradient of SES indicators.

Neural tube defect among Palestinians: a hospital-based study

A preliminary study was undertaken to estimate the incidence of neural tube defect (NTD) among Palestinians living in East Jerusalem and the southern part of the West Bank (600,000 inhabitants). Between 1 January 1986 and 31 December 1993, all NTD in fetuses weighing more than 500 g or of more than 22 weeks gestation, whether the product of abortion, therapeutic termination, stillborn or liveborn, were included. Mothers' data recorded included age, parity, residential area, gestational age, obstetrical history and consanguinity. The study included 26,934 consecutive newborns registered at Makassed Hospital in the study period. There were 148 cases of NTD, an incidence of 5.49 per 1000 births. The female to male ratio was 1.5:1. The incidences of spina bifida, encephalocele and anencephaly were 2.23, 0.44 and 2.41 per 1000, respectively. The incidence of NTD increased with maternal age. This preliminary report reveals a high incidence of NTD in the Palestinian community and further monitoring is necessary to confirm these findings and implement suitable policies for the detection and prevention of NTD.

Multigeneration maternal transmission in Italian families with neural tube defects

Periconceptional vitamin supplementation with folate prevents about three-quarters of expected cases of neural tube defects (NTDs) in clinical trials. However, vitamin action may be regulated at the level of the gene, and individual susceptibility to environmental agents, including dietary components, also may be under genetic control. We investigated the presence of familial factors in a retrospective case control study of neural tube defects in Genoa, Italy. Cases included all patients treated at a single pediatric neurosurgical service. Controls matched on age and sex came from the same hospital. We found strong evidence for the contribution of genetic factors in this study. There was an excess risk of 14 for the occurrence of NTDs in first-degree relatives compared to controls (P < .0005). There was no difference in sex ratio in any group of relatives, but maternal grandparents of children with a high spinal lesion had 14% fewer off-spring than paternal grandparents (P < .005), possibly because of excess miscarriages. Our study is the first to show complex patterns of inheritance in spina bifida families affecting three generation in one clinical subgroup and preferentially on the mother's side. These results support a role for genomic imprinting and highlight the value of multidisciplinary epidemiologic and clinical studies that include multiple generations. New studies incorporating dietary and genetic approaches will help clarify and extend these findings.

Spontaneous abortion--high risk factor for neural tube defects in subsequent pregnancy

An increased spontaneous abortion rate has been observed in pregnancies preceding that of fetuses or newborn infants with neural tube defects (NTDs). There are 2 suggested explanations for this observation. One is that a trophoblastic cell rest, remaining from a previous aborted pregnancy, interferes with normal embryogenesis. The second is that the previous lost fetus was affected with NTD. We studied the obstetric history of mothers of newborn infants with NTDs compared to those with other birth defects, in low and high risk groups for NTD (Jew and Bedouins). A significantly higher spontaneous abortion rate (48%) in the preceding pregnancy was found in the NTD group compared to the group with other birth defects (20%). This was especially remarkable for spina bifida cases in the Jewish study population. A significantly higher rate of preceding spontaneous abortion was also found in congenital heart defects (CHD) when compared to other congenital malformations. A hypothesis based on the multifactorial threshold model is put forward to explain these findings. Based on the realization that spontaneous abortion constitutes a high risk factor for NTD and possibly also CHD, we recommend a delay of subsequent pregnancy and periconceptional treatment with folic acid following spontaneous abortion.

Genetic study of indirect inguinal hernia

We performed a genetic analysis of 280 families with congenital indirect inguinal hernia ascertained in Shandong province. The multifactorial threshold model and segregation analysis were applied to these families to investigate the mode of inheritance of congenital indirect inguinal hernia. Our results indicate that congenital indirect inguinal hernia is not compatible with a multifactorial threshold model, and the frequent vertical transmission and high segregation ratio suggest autosomal dominant inheritance with incomplete penetrance and sex influence. Through further pedigree analysis of the multiple case families with at least two closely related affected members, we noted preferential paternal transmission of the disease gene, which might suggest the role of genomic imprinting in the aetiology of this condition.

Techniques in current use in prenatal diagnosis

Prenatal diagnosis is now offered to the majority of pregnant women in Europe and the United States. Advances in obstetric and laboratory techniques mean that increasing numbers of conditions can be diagnosed prenatally; indeed, gene carriers can be identified before pregnancy in some cases. Current obstetric and laboratory techniques for prenatal screening and diagnosis of genetic disorders are discussed.

Genetic-epidemiologic study of omphalocele and gastroschisis: evidence for heterogeneity

On the basis of clinical manifestations, epidemiologic characteristics, and the presence of additional malformations, omphalocele (OM) and gastroschisis (GA) are considered casually and pathogenetically distinct abdominal wall defects. More than 50% of infants with OM have additional defects, but only about 15% of those with GA do. To evaluate whether there is heterogeneity between isolated and multiply affected cases of OM and GA, we analyzed epidemiologic characteristics and familial risks of major defects for 82 OM and 81 GA cases drawn from a population-based study in the Maryland-Washington, DC-Northern Virginia area and born from 1980 through June 1987. We examined year of birth, sex, race, and maternal age distributions after stratifying the infants into isolated and multiple defect groups. We found significant differences in maternal age between cases with isolated OM and GA, but not between cases with GA or OM who had other defects. Using regressive logistic models, we analyzed familial aggregation of birth defects among relatives of infants with OM and GA. An autosomal recessive model of inheritance was found to be the most parsimonious explanation for the families of infants with isolated OM or GA. However, for families of infants with multiple defects, a sporadic or nongenetic model fit best. These findings are not only useful for estimating familial risk of major birth defects, but they also suggest further heterogeneity of infants with OM and GA according to the presence of other malformations.

Parental sex effect in spina bifida: a role for genomic imprinting?

Fifty families (491 individuals in 137 sibships) with more than one living case of isolated, nonsyndromic spina bifida (SB) were analyzed genetically. There were twice as many gene-carrier females (56) as gene-carrier males (28) (P < 0.005). This was not an artifact of ascertainment bias because the sex ratio of gene-carriers was the same whether the pedigree was obtained through the proband's father or mother. Also, this effect was not observed in other disorders analyzed by the same method. Neither was the effect due to differential fertility because the number and sex of affected and unaffected children per gene-carrier parent were not different for male or female gene-carrier parents. There was no evidence that the missing male gene-carriers were lost by selective spontaneous abortion. There was no deficit of male-to-male or male-to-female transmission, excluding simple X-linked or simple mitochondrial inheritance. If genomic imprinting plays a role in the unequal female and male carrier frequencies in SB, penetrance should differ with parental sex. Penetrance was higher for offspring of female parents than of male parents, but the difference was not statistically significant. In addition, both male and female gene-carriers were frequently found in the same pedigree. Thus, the present data suggest a possible role for imprinting in SB.

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.

Neural tube defect etiology: new evidence concerning maternal hyperthermia, health and diet

The authors conducted a retrospective case-control study to determine risk factors for neural tube defects (NTD). 88 Louisiana women (44 matched pairs) were interviewed. Previous evidence suggested that maternal health and/or nutrition may be involved in the etiology of NTD. The findings substantiate the importance of maternal risk factors, including the apparent elevation of body temperature from taking hot baths during the first gestational month. Maternal health, as measured by reported illness and use of medications during pregnancy, was also significant. Several dietary factors, including intake of foods high in beta carotene, appeared to confer a protective effect. These findings suggest that some risk factors, particularly those involving maternal nutrition, may be population-specific.

Further genetic studies of the cause of exencephaly in SELH mice

We have developed an inbred stock of mice called SELH that has a high frequency of the neural tube defect exencephaly at birth. A previous genetic study indicated that the exencephaly is due to two to three additive loci differing between SELH and a closely related normal strain, ICR/Bc, but this analysis was not designed to detect genetic maternal effects. Recently, we demonstrated that there is genetic polymorphism among normal mouse strains leading to differences in site of initiation of closure of the cranial neural tube. In the present study, an inbred substrain of SELH mice, with 24% exencephaly among embryos, was crossed with an unrelated normal strain, SWV/Bc, and the frequency of exencephaly in subsequent generations used to extend our understanding of the genetic cause of exencephaly in SELH mice. The purposes of the genetic studies reported here were twofold. First, based on the influence of genetic maternal effects on other genetically complex birth defects in mice, we hypothesized that the exencephaly of SELH mice would exhibit strong genetic maternal effects. This hypothesis was tested by comparisons among the four possible reciprocal backcrosses to SELH. The result was an overall frequency of 2.3% exencephaly in first backcross embryos with no difference among the four crosses and no evidence of genetic maternal effects. Second, the frequency of exencephaly recovered in the backcross and F1 embryos was compared with the previous genetic study and with various genetic models. The frequencies were similar to those obtained from the cross to ICR/Bc mice and were compatible with a hypothesis of additive gene action at a few loci.(ABSTRACT TRUNCATED AT 250 WORDS)

Birth defects in twins: study in a Spanish population

The risk for specific defects among twins compared to singletons was studied using data collected by the Spanish Collaborative Study of Congenital Malformations (ECEMC). A total of 136 twins had a major and/or minor congenital defect. The overall rate of congenital defects in twins (2.37%) did not deviate significantly from the rate in singletons (2.21%). Like-sex (LS) and male-male (MM) twin pairs had a slightly higher rate of birth defects than unlike-sex (US) and female-female (FF) pairs, respectively. Defects of the central nervous system, cardiovascular system and genitourinary system were significantly more frequent in LS twins than in singletons, with relative risks of 2.8, 2.5 and 1.6, respectively. No significantly increased risk was found among US twins. Among defects of the central nervous system, the rates of anencephaly, encephalocele and hydrocephaly were significantly higher in total and LS twins; however, no significantly increased risk for spina bifida was observed when compared to singletons. MM twins were also 1.9 times more likely to have hypospadias, but the risk among males of male-female (FM) pairs was decreased.

Effect of race and gender on neurological level in myelomeningocele

The association of race and gender with different neurological levels of myelomeningocele was studied in 251 patients. Over-all, the white to black ratio was 3.6 and the male to female ratio was 0.86. However, the proportions of whites and females were significantly increased in thoracic-level patients (white to black ratio 13.6, male to female ratio 0.43), whereas the lumbar-level patients had sex and white to black ratios equivalent to the area population. This supports the concept that thoracic-level myelomeningocele has a different pathogenesis from lumbar-level.

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.

Expression of a new mutation (Axd) causing axial defects in mice correlates with maternal phenotype and age

A new autosomal mutation, Axd (axial defects), is described. Axd segregates in a simple Mendelian fashion, and it is dominant with incomplete penetrance and variable expressivity. The phenotype of Axd heterozygotes ranges from a variety of tail anomalies to visibly normal tails. Approximately 12% of neonates from curly-tail (CT) F1 (Axd/+) x F1 (Axd/+) matings exhibit open neural tube defects (NTD) in the lumbosacral region and 16% have curly tails. Mean litter sizes and resorption rates comparable to wild type indicate that homozygosity for Axd is not obligately lethal. Genetic background plays a major role in Axd expression. Strains such as BALB/cByJ allow the highest penetrance of the mutation in single dose (46%), whereas, in CF-1 mice Axd is recessive. The tail phenotype of heterozygous Axd/+ dams, in part reflective of their genetic background, correlates with the incidence of NTD in F2 offspring: CT mothers produce significantly more neonates with frank NTD than normal tail mothers. At the one embryonic period examined for this study (D13/D14 post-coitus), an 85% higher incidence of total axial defects is observed than among the F2 at birth. Unchanging litter size and the relative increase in phenotypically normal offspring by birth suggest that Axd acts by delaying posterior neural tube closure. One of the most significant findings in this study is that maternal age influences the survival of Axd embryos in utero. Axd/+ dams older than 8 months yield fewer mean implants, higher resorption rates, and fewer viable embryos with axial defects than do Axd/+ dams younger than 8 months. Axd is not allelic to nor linked to the Sp (splotch) gene which also affects neurulation.

Evidence for a major gene in familial anencephaly

A 21-year-old white woman sought counseling after the birth of two consecutive anencephalic male fetuses with complete rachischisis and discordant renal dysplasia. The presence of parental consanguinity prompted reconsideration of recessive inheritance. The segregation ratio from 23 additional consanguineous cases was compared with that observed in 294 presumably nonconsanguineous families previously reported. Using classical segregation analysis, the segregation ratios in the non-sporadic cases were consistent with a major autosomal recessive locus in both populations.

Comparison of the incidence of 5-azacytidine-induced exencephaly between MT/HokIdr and Slc:ICR mice

The incidence of 5-azacytidine-induced exencephaly was compared between MT/HokIdr strain (MT) and Slc:ICR strain (ICR) mice. MT mice have a genetic predisposition for exencephaly, but ICR mice do not. Pregnant mice were given 5-azacytidine (1 mg/kg to 100 micrograms/kg) injected intraperitoneally on Day 7.5 of gestation (vaginal plug day = Day 0.5), and fetuses were observed for external malformations on Day 18.5 of gestation. One hundred micrograms/kg 5-azacytidine induced exencephaly in MT mice but not in ICR mice, and 1 mg/kg 5-azacytidine resulted in resorptions in MT mice but caused exencephaly in ICR mice. These results indicated that MT mice had 10-fold more sensitivity to 5-azacytidine than ICR mice. It seems likely that less than effective doses of teratogens for animals without genetic predispositions are still effective in inducing malformations in animals with a genetic predisposition for malformations. When 4-somite-stage embryos of both MT and ICR mice were cultured in rat serum supplemented with 5-azacytidine, 0.02 micrograms/ml 5-azacytidine induced the failure of closure of cephalic neural tube in MT embryos but not in ICR embryos, and 0.2 micrograms/ml 5-azacytidine induced severe growth retardation in MT embryos but in ICR embryos it only induced embryos with smaller heads and fewer somites than in control. These results indicated that MT mouse embryos in culture also had a 10-fold-increased sensitivity to 5-azacytidine compared with ICR mouse embryos, suggesting maternal effects play no significant role in their increased sensitivity to 5-azacytidine.

Severe neural tube defect syndrome from the Early Archaic of Florida

The Early Archaic Windover site is on the east coast of mid-peninsular Florida. A subadult skeleton (about 15 years old at time of death) was recovered with multiple pathologies related to spina bifida aperta of the neural arch at the L3-S2 level of the spine. Other evidence indicates s.b. cystica, although the degree of severity of the dysraphic neural tube syndrome cannot be directly determined. In addition to spina bifida, the lumbar region is scoliotic from malformation of zygapophyses. The defect is accompanied by severe infection of the right tibia and fibula, and disuse atrophy of long bones. It is hypothesized the NTD (neural tube defect) led to progressive sensory deprivation, which in turn led to increased loss of mobility, ulceration, and risk of serious infections. Other "minor" anomalies such as cone-shaped epiphyses, enlarged nutrient foramina, and vental vertebral cavitation are also discussed. The chronic nature of these defects provide insight on the high level of long-term care and attention provided a severely handicapped individual 7,500 years ago.

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.

A study of the value of measuring maternal serum alpha-fetoprotein for the antenatal diagnosis of neural tube defects

Two neighbouring centres, both located in an area where the prevalence of neural tube defects (NTDs) is low, were compared to determine if there was any advantage in their differing policies as regards the antenatal detection of NTDs. At both centres routine ultrasound examinations were performed at 16-18 weeks gestation but at Hospital A serum alpha-fetoprotein (AFP) was measured at 16 weeks gestation. The prevalence of NTDs was 1.3 per 1,000 births at Hospital A and 1.7 per 1,000 births at Hospital B. The detection of anencephaly at both hospitals was 100%, however, only 43% of spina bifidas were detected at Hospital A compared with 60% at Hospital B. These results, the loss of two fetuses following amniocentesis at Hospital A and the lower detection rate for NTDs at the hospital employing AFP measurement are discussed.

Common hierarchies of susceptibility to the induction of neural tube defects in mouse embryos by valproic acid and its 4-propyl-4-pentenoic acid metabolite

The teratogenic effects of valproic acid and its 4-propyl-4-pentenoic acid (4-en) metabolite were investigated in three inbred mouse strains that were known to possess differing sensitivity to heat-induced neural tube defects. In the heat-resistant DBA/2J strain, administration of either valproic acid or the metabolite during the critical period of neural tube development failed to produce any abnormal offspring. Similar treatment in the moderately heat-sensitive LM/Bc strain resulted in up to 19.8% exencephalic fetuses. The highly heat-sensitive SWV strain was also very susceptible to the induction of neural tube defects by either valproic acid or its 4-en metabolite. When administered on gestational day 8 plus 12 hours, the parent compound produced 35% exencephalic fetuses, while the metabolite had a response frequency of 32.4%. Thus, the hierarchy of susceptibility for the induction of neural tube defects in these inbred mouse strains was exactly the same whether the teratogen was a physical agent such as hyperthermia or a chemical compound such as valproic acid. If such diverse agents as these should interact to produce malformations, then it is possible that a wide variety of other agents might interact in a similar manner to produce neural tube defects.

The epidemiology and service implications of congenital and constitutional anomalies in ethnic minorities in the United Kingdom

The literature on the incidence in the UK of congenital and constitutional anomalies in populations deriving from Africa, the Caribbean, the Far East, the Indian subcontinent and the Mediterranean is reviewed. These groups represent an increasing proportion of the whole child population. Comparison with the white population and between groups reveals that the burden of impairment varies with country of origin. Some of the reasons implicated include different gene frequencies and mating patterns, age/parity distribution and uptake of preventive services. Comparisons with prevalence at birth in the countries of origin are made where possible. In general, populations with high rates in their country of origin retain their high rates (e.g. central nervous system anomalies among births to parents deriving from the Indian subcontinent). There is a general lack of data on the prevalence of handicapping conditions such as cerebral palsy, as well as the associated health needs and service utilisation amongst ethnic minorities.