Gary M. Shaw

Neural tube defects and folate: case far from closed.

Neural tube closure takes place during early embryogenesis and requires interactions between genetic and environmental factors. Failure of neural tube closure is a common congenital malformation that results in morbidity and mortality. A major clinical achievement has been the use of periconceptional folic acid supplements, which prevents ∼50–75% of cases of neural tube defects. However, the mechanism underlying the beneficial effects of folic acid is far from clear. Biochemical, genetic and epidemiological observations have led to the development of the methylation hypothesis, which suggests that folic acid prevents neural tube defects by stimulating cellular methylation reactions. Exploring the methylation hypothesis could direct us towards additional strategies to prevent neural tube defects.

Periconceptional vitamin use, dietary folate, and the occurrence of neural tube defects.

With a case-control study, we investigated whether periconceptional intake of supplemental or dietary folate reduced the risk of having a neural tube defect (NTD)-affected pregnancy. Mothers of 549 (88% of eligible) cases and 540 (88%) controls were interviewed in person about vitamin supplements used in either the 3 months before or the 3 months after conception and also about usual diet in the 3 months before conception. Women with any use of a folic acid-containing vitamin in the 3 months before conception had a lower risk of having an NTD-affected pregnancy [odds ratio (OR) = 0.65; 95% confidence interval (CI) = 0.45–0.94]. ORs were similar for 3 levels (< 0.4, 0.4–0.9, and >0.9 mg per day) of average daily intake of folic acid. Any level of use in the first 3 months after conception resulted in a lowered risk as well (OR = 0.60; 95% CI = 0.46–0.79). Reduced risks were less marked for Hispanics and were not observed among women who graduated from college. Modest reduced risks were noted among non-vitamin users whose estimated daily dietary intake of folate was more than 0.227 mg. We observed decreasing risk with increasing folate intake from combined dietary sources and vitamin supplements. A reduction in NTD risk associated with folate intake is consistent with other studies; however, the reduced risk may be particular to subsets of the population, primarily non-Hispanic women and women whose education does not exceed high school.

Maternal corticosteroid use and risk of selected congenital anomalies

Evidence for the teratogenicity of corticosteroids in humans is limited and has resulted in inconsistent recommendations regarding their use during early pregnancy. We examined the association between womens corticosteroid use during the periconceptional period (1 month before to 3 months after conception) and delivering infants with selected congenital anomalies. Data were derived from a population-based case-control study that included cases of orafacial clefts (n = 662), conotruncal heart defects (n = 207), neural tube defects (n = 265), and limb reduction defects (n = 165). Information on medication use was collected via maternal telephone interviews. Corticosteroid use was associated with an increased risk for isolated cleft lip with or without cleft palate (odds ratio 4.3, 95% confidence interval 1.1-17.2) and isolated cleft palate (odds ratio 5.3, 95% confidence interval 1.1-26.5). Increased risks were not observed for the other anomaly groups studied. These data in conjunction with other epidemiologic data suggest a possible causal association between cleft lip and palate and corticosteroid use.

The Continuing Challenge of Understanding, Preventing, and Treating Neural Tube Defects

Background Neural tube defects (NTDs) are debilitating birth defects involving the central nervous system (CNS). Despite recent advances, NTDs represent the second most common group of human birth defects. These defects arise when the complex process of early CNS development goes awry. Normally, the brain and the spinal cord begin to form as a flat sheet of cells that rolls up and closes to form a hollow neural tube. Failure in this rolling and sealing process results in an NTD, such as spina bifida. From animal models, we know of over 200 genes that regulate this process, with many more still likely to be discovered. Environmental factors also can have a profound influence on neural tube closure, as evidenced by the impact of folic acid on NTD prevalence. However, the mechanisms by which environmental factors affect the process of neural tube closure and their critical interaction with genetic factors remain largely a mystery. Successive images showing the progression of neural tube closure in a stylized vertebrate embryo. Initially, the CNS is a flat sheet; paired neural folds elevate along the rostrocaudal axis (rostral = up) and move medially, eventually fusing to enclose the neural tube. Disruption of this process during human embryogenesis results in neural defects, such as spina bifida. Advances Three major advances from three different directions—genetics, epidemiology, and surgery—have advanced understanding, prevention, and treatment of NTDs. The rapidly expanding knowledge of the genetic causes of NTDs in animal models is poised to inform high-throughput whole-genome studies of human patients. Epidemiological studies have led to the identification of folic acid as a primary prevention strategy for NTDs. Recent advances in in utero surgical repair of spinal NTDs have improved the clinical outcome by comparison with postnatal surgery. Outlook Despite the advances, NTDs remain a very common birth defect and, even with surgical intervention, result in enormous clinical, emotional, financial, and societal costs. The implementation of large-scale genomic studies of human NTD patients is expected to move the field beyond its current focus on individual genetic pathways. Experimental animal systems can complement and extend the information that flows from genomic studies, and animal models can also be exploited to understand the mechanisms by which environmental factors alter the risk for NTDs. The technology exists to create patient-derived stem cells, which may hold a key for understanding this very early developmental process in humans and could provide a platform for screening therapeutic agents. Overall, the key challenge will be to understand the developing neural tube, a complex three-dimensional structure that changes rapidly over time and is dependent on the surrounding tissues for developmental signals and biomechanical forces to drive the dynamic and important process of neural tube closure. Prevention or Repair Neural tube defects, such as spina bifida, remain remarkably common, despite widespread efforts to prevent them through supplementing maternal diets with folic acid. Surgery early in development has seen some success, but problems often remain. Wallingford et al. (10.1126/science.1222002) review normal and abnormal neural tube development and suggest that discovering the genetic risk factors for these serious birth defects could provide ways to prevent and treat neural tube defects. Human birth defects are a major public health burden: The Center for Disease Control estimates that 1 of every 33 United States newborns presents with a birth defect, and worldwide the estimate approaches 6% of all births. Among the most common and debilitating of human birth defects are those affecting the formation of the neural tube, the precursor to the central nervous system. Neural tube defects (NTDs) arise from a complex combination of genetic and environmental interactions. Although substantial advances have been made in the prevention and treatment of these malformations, NTDs remain a substantial public health problem, and we are only now beginning to understand their etiology. Here, we review the process of neural tube development and how defects in this process lead to NTDs, both in humans and in the animal models that serve to inform our understanding of these processes. The insights we are gaining will help generate new intervention strategies to tackle the clinical challenges and to alleviate the personal and societal burdens that accompany these defects.

Temporal and spatial variation of the human microbiota during pregnancy.

Significance The human indigenous microbial communities (microbiota) play critical roles in health and may be especially important for mother and fetus during pregnancy. Using a case-control cohort of 40 women, we characterized weekly variation in the vaginal, gut, and oral microbiota during and after pregnancy. Microbiota membership remained relatively stable at each body site during pregnancy. An altered vaginal microbial community was associated with preterm birth; this finding was corroborated by an analysis of samples from an additional cohort of nine women. We also discovered an abrupt change in the vaginal microbiota at delivery that persisted in some cases for at least 1 y. Our findings suggest that pregnancy outcomes might be predicted by features of the microbiota early in gestation. Despite the critical role of the human microbiota in health, our understanding of microbiota compositional dynamics during and after pregnancy is incomplete. We conducted a case-control study of 49 pregnant women, 15 of whom delivered preterm. From 40 of these women, we analyzed bacterial taxonomic composition of 3,767 specimens collected prospectively and weekly during gestation and monthly after delivery from the vagina, distal gut, saliva, and tooth/gum. Linear mixed-effects modeling, medoid-based clustering, and Markov chain modeling were used to analyze community temporal trends, community structure, and vaginal community state transitions. Microbiota community taxonomic composition and diversity remained remarkably stable at all four body sites during pregnancy (P > 0.05 for trends over time). Prevalence of a Lactobacillus-poor vaginal community state type (CST 4) was inversely correlated with gestational age at delivery (P = 0.0039). Risk for preterm birth was more pronounced for subjects with CST 4 accompanied by elevated Gardnerella or Ureaplasma abundances. This finding was validated with a set of 246 vaginal specimens from nine women (four of whom delivered preterm). Most women experienced a postdelivery disturbance in the vaginal community characterized by a decrease in Lactobacillus species and an increase in diverse anaerobes such as Peptoniphilus, Prevotella, and Anaerococcus species. This disturbance was unrelated to gestational age at delivery and persisted for up to 1 y. These findings have important implications for predicting premature labor, a major global health problem, and for understanding the potential impact of a persistent, altered postpartum microbiota on maternal health, including outcomes of pregnancies following short interpregnancy intervals.

Racial and ethnic variations in the prevalence of orofacial clefts in California, 1983-1992.

To investigate variations in the prevalence of oral cleft anomalies according to parental race and ethnicity and maternal country of birth, the authors analyzed a cohort of 2,221,755 live births and fetal deaths delivered between 1983 and 1992 to residents of California. A total of 2,329 cleft lip with or without cleft palate (CL +/- P) cases and 1,475 cleft palate alone (CP) cases were identified by the California Birth Defects Monitoring Program, a population-based registry. Compared to Whites, the prevalence of CL +/- P was lower among African Americans (prevalence ratio (PR) = 0.56, 95% confidence interval (CI) = 0.45-0.69), higher among Native Americans (PR = 1.81, CI = 1.20-2.69), and the same among the Japanese (PR = 1.07, CI = 0.62-1.82) and Chinese (PR = 0.96, CI = 0.71-1.29). The risk of CL +/- P was slightly lower among the offspring of foreign-born Chinese women relative to U.S.-born Chinese women (PR = 0.71, CI = 0.33-1.57), and slightly higher among foreign-born Filipinos relative to their U.S.-born counterparts (PR = 1.37, CI = 0.57-3.53), although confidence intervals around these risk estimates were wide owing to sparse data. For CP, lower prevalences were observed among African Americans (PR = 0.72, CI = 0.58-0.91) and Hispanics (PR = 0.77, CI = 0.67-0.87) than among Whites. The risk of CP was higher among foreign-born Filipinos compared to U.S.-born Filipinos (PR = 1.52, CI = 0.58-4.33), although the confidence interval around this estimate included unity. These prevalence variations may reflect differences in both environmental and genetic factors affecting clefting risk.

Maternal obesity, gestational diabetes, and central nervous system birth defects.

Background: Maternal obesity and diabetes are both associated with increased risk of congenital central nervous system (CNS) malformations in the offspring and may share a common underlying mechanism. Our objective was to evaluate whether gestational diabetes influenced the association of prepregnancy maternal obesity and risks for CNS birth defects. Methods: This Texas population-based case-control study evaluated births occurring January 1997 through June 2001. Data came from structured telephone interviews. Cases (n = 477) were mothers of offspring with anencephaly (n = 120), spina bifida (n = 184), holoprosencephaly (n = 49), or isolated hydrocephaly (n = 124). Controls (n = 497) were mothers of live infants without abnormalities randomly selected from the same hospitals as cases. Response rates were approximately 60% for both cases and controls. We evaluated maternal obesity (body mass index ≥30.0 kg/m2) and risks for CNS birth defects, as well as whether gestational diabetes influenced the risks. Results: After adjusting for maternal ethnicity, age, education, smoking, alcohol use, and periconceptional vitamin use, obese women had substantially increased risks of delivering offspring with anencephaly (odds ratio = 2.3; 95% confidence interval = 1.2–4.3), spina bifida (2.8; 1.7–4.5), or isolated hydrocephaly (2.7; 1.5–5.0), but not holoprosencephaly (1.4; 0.5–3.8). Odds ratios were higher for the joint effects of maternal obesity and gestational diabetes, with evidence for interaction on a multiplicative scale. Conclusions: Maternal obesity and gestational diabetes may increase the risk of CNS birth defects through shared causal mechanisms.

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.

Holoprosencephaly: Epidemiologic and clinical characteristics of a California population

Holoprosencephaly is a brain defect resulting from incomplete cleavage of the embryonic forebrain. It involves forebrain and facial malformations that can range from mild to severe. The epidemiology of holoprosencephaly is largely unknown. Published prevalence estimates have been derived from clinic-based case series, and suggested risk factors for holoprosencephaly have been identified in case reports, without confirmation from systematically conducted population-based studies. Using data from a population-based birth defects registry in California, we describe the epidemiologic and clinical characteristics of cytogenetically and phenotypically distinct types of holoprosencephaly. A total of 121 cases was identified among a cohort of 1,035,386 live births and fetal deaths. The prevalence of holoprosencephaly was 1.2 per 10,000 births (95% confidence interval 1.0-1.4 per 10,000). Of all cases, 41% (50/121) had a chromosomal abnormality, most commonly Trisomy 13. Among the 71 cytogenetically apparently normal cases, 18 had recognizable syndromes and the remaining 53 were of unknown cause. Among the cytogenetically abnormal cases, females had a greater risk than males (odds ratio = 2.3,95% confidence interval [1.2, 4.4]). Among the cytogenetically normal cases, increased risks were observed among Hispanic whites (OR = 1.8 [0.9, 3.6]) and cases whose mother was born in Mexico (OR = 2.2 [1.0, 4.5]). Approximately 46% of all cases had alobar holoprosencephaly, the most severe form of the forebrain malformation. The facial phenotype did not strongly predict the severity of the brain defect; however, severity was inversely correlated with length of survival. This study is the first to present findings based on such a large population-based series of infants/fetuses affected by holoprosencephaly, and demonstrates the importance of investigating the component subgroups of this rare phenotype.

Maternal residential proximity to hazardous waste sites and risk for selected congenital malformations.

Using data from two population‐based case‐control studies, we investigated whether maternal residential proximity to hazardous waste sites increased the risk for neural tube defects, conotruncal heart defects, and oral cleft defects in California. We obtained a residential history by interview for mothers of 507 neural tube defect cases (82.7% of eligible) and their 517 controls (84.6%); and 201 heart cases (84.4%), 439 cleft cases (82.2%), and their 455 controls (72.1%). We identified the locations of 764 inactive hazardous waste sites and systematically collected information on site‐related contamination for the subset of 105 National Priority List sites. After controlling for several potential confounders, we found little or no increased risk for maternal residence in a census tract containing a site [odds ratio (OR) = 0.9, 95% confidence interval (CI) = 0.7–1.3 for neural tube defects; OR = 1.3, 95% CI = 0.8–2.1 for heart cases; OR = 1.2, 95% CI = 0.8–1.8 for clefts], but elevated risks for neural tube defects (OR = 2.1, 95% CI = 0.6–7.6) and heart defects (OR = 4.2, 95% CI = 0.7–26.5) for maternal residence within 1/4 mile of a National Priority List site. Furthermore, we observed elevated ORs (≥2.0) for neural tube defects and heart defects in association with maternal residence within 1 mile of National Priority List sites containing selected chemical contaminants. Among controls, only 0.6% and 4.4% lived within 1/4 mile and 1 mile of a National Priority List site, respectively, resulting in imprecision in risk estimation.