Thursday, April 23, 2009

Tethered cord release: a long-term study in 114 patients.

Bowman RM, Mohan A, Ito J, Seibly JM, McLone DG. (2009) Tethered cord release: a long-term study in 114 patients. Journal of Neurosurgery Pediatrics. 2009 Mar;3(3):181-7.

Division of Pediatric Neurosurgery, Children's Memorial Hospital, Chicago, USA.

OBJECT: All children born with a myelomeningocele at the authors' institution undergo aggressive treatment to maintain or improve functional outcome. Consequently, when any neurological, orthopedic, and/or urological changes are noted, a search for the cause is initiated. The most common cause of decline in a child born with a myelomeningocele is shunt malfunction. The second most common cause is tethering of the distal spinal cord at the site of the original back closure. In this report, the authors review the indicators of symptomatic spinal cord tethering and discuss the surgical interventions and outcomes in the children with myelomeningocele who underwent treatment at Children's Memorial Hospital from 1975 to 2008.

METHODS: Among the 502 children who underwent original closure at Children's Memorial Hospital, a symptomatic tethered spinal cord developed in 114 (23%). Eighty-one patients (71%) have undergone 1 untethering procedure, and 33 patients (29%) have undergone multiple untetherings, for a total of 163 total surgeries. The indicators of symptomatic spinal cord tethering include scoliosis, decline in lower-extremity (LE) motor strength, LE contractures, LE spasticity, gait change, urinary changes, and pain.

RESULTS: Pain has shown the best response to surgical untethering, with 100% of children experiencing postoperative improvement. The results of long-term follow-up (average 12 years, range 1 month-23.3 years) in this cohort demonstrated scoliosis progression after surgical untethering in 52% of patients, with 28% requiring spinal fusion. On the 3-month postoperative manual muscle test, 70% of patients showed improved LE muscle strength compared to preoperatively. Gait was also similarly improved after untethering as evaluated by an orthopedic surgeon. Spasticity improved in two-thirds of the cohort, and as expected, LE contractures were stable (78%) postoperatively, as assessed by orthopedic and rehabilitation medicine specialists. Urologically, 64% of patients showed improvements on postoperative bladder evaluation.

CONCLUSIONS: Although this is a clinical outcome study with no control group, the authors' experience has been that tethered cord release is beneficial in maintaining neurological, urological, and orthopedic functioning in children born with a myelomeningocele.

PMID: 19338463

Thursday, April 16, 2009

Motor profile and cognitive functioning in children with spina bifida.

Vinck A, Nijhuis-van der Sanden MW, Roeleveld NJ, Mullaart RA, Rotteveel JJ, Maassen BA. Motor profile and cognitive functioning in children with spina bifida.
European Journal of Pediatric Neurology. 2009 Feb 21. [Epub ahead of print]

Department of Medical Psychology, Radboud University Nijmegen Medical Centre, The Netherlands; Department of Paediatric Neurology, Radboud University Nijmegen Medical Centre, The Netherlands.

BACKGROUND: Spina bifida is a complex neuroembryological disorder resulting from incomplete closure of the posterior neural tube. Morbidity in the different fields of motor and cognitive neurodevelopment is variable in nature and severity, and often hard to predict.

AIMS: The current study investigates the relationship between cognitive functioning, fine motor performance and motor quality in children with spina bifida myelomeningocele (SBM) and SB-only, taking into consideration the cerebral malformations.

MATERIAL AND METHODS: Forty-one children were included (22 girls and 19 boys aged between 6 and 14 years, mean age 10;0 years) in the study. A comprehensive assessment was conducted of cognitive functioning and motor profile, including fine motor and visual-motor functioning, and motor quality. The performance outcomes were analyzed for the total group of children and separately for the nonretarded children (FSIQ>/=70, N=30) to eliminate the influence of global intellectual impairment.

RESULTS: Although the children with spina bifida showed increased incidence of cognitive and fine motor impairment, and impaired motor quality, after exclusion of the overall retarded children no associations were found between cognitive functioning and motor profile. In the comparison of SBM to SB-only specific differences were found for performance IQ, visual-motor functioning and motor quality, but not fine motor functioning.

CONCLUSION: Our findings underscore the role of cerebral malformation in spina bifida and its consequences for neuropsychological functioning. The complicated developmental interactions found strengthen the need for an individualized management of children with SB.

PMID: 19237302

Children with cerebral palsy, spina bifida and pragmatic language impairment: Differences and similarities in pragmatic ability.

Holck P, Nettelbladt U, Sandberg AD. Children with cerebral palsy, spina bifida and pragmatic language impairment: Differences and similarities in pragmatic ability.
Research in Developmental Disabilities. 2009 Feb 25.

Pragmatically related abilities were studied in three clinical groups
of children from 5 to 11 years of age; children with cerebral palsy
(CP; n = 10), children with spina bifida and hydrocephalus (SBH;
n = 10) and children with pragmatic language impairment (PLI;
n = 10), in order to explore pragmatic abilities within each group. A
range of pragmatic, linguistic and cognitive assessments were
performed, and comparisons between the groups were made. In
addition, connections between variables were studied. The most
salient result was the many similarities and the lack of clear
boundaries between the groups. The only significant differences
found concerned short-term memory and inference ability, where
all three groups experienced problems but to varying extent.
Different patterns of variance were found in the groups, indicating
that different underlying abilities such as reception of grammar,
inferential comprehension and lexical comprehension seem to
affect pragmatic ability in somewhat different ways. The results
suggest that the children with CP and SBH in this study shared a
number of pragmatically related traits, being more similar than
would be expected according to earlier research. Finally, it is
suggested that pragmatic assessment is further subdivided into a
socially versus a linguistically related assessment.

PMID: 19249190

The scientific basis for eliminating folic acid-preventable spina bifida: a modern miracle from epidemiology.

Oakley GP Jr. The scientific basis for eliminating folic acid-preventable spina bifida: a modern miracle from epidemiology. Annals of Epidemiology. 2009 Apr;19(4):226-30.

Department of Epidemiology, Rollins School of Public Health of Emory University, Atlanta, GA, USA.

One of the most remarkable successes of epidemiology was the demonstration in the late twentieth century that spina bifida and anencephaly-two of the most common and severe birth defects-are caused primarily by folate deficiency. This article reviews the descriptive epidemiological studies that began when we did not have a clue about etiology. The paper tells the success story of the trials that proved that folic acid would prevent folic-acid-preventable spina bifida. Finally, it will tell how difficult it is to get prevention policy implemented, even when the scientific evidence is compelling. It concludes by noting that the inaction or inappropriate actions of food regulatory bodies in so many countries means that only 10% of folic-acid-preventable spina bifida is actually being prevented--a serious failure of public health policy.

PMID: 19344858

Curly tail: a 50-year history of the mouse spina bifida model.

van Straaten HW, Copp AJ. Curly tail: a 50-year history of the mouse spina bifida model. Anatomy and Embryolgy. 2001 Apr;203(4):225-37. Review.

Department of Anatomy and Embryology, Maastricht University, The Netherlands.

This paper reviews 50 years of progress towards understanding the aetiology and pathogenesis of neural tube defects (NTD) in the curly tail (ct) mutant mouse. More than 45 papers have been published on various aspects of curly tail with the result that it is now the best understood mouse model of NTD pathogenesis. The failure of closure of the spinal neural tube, which leads to spina bifida in this mouse, has been traced back to a tissue-specific defect of cell proliferation in the tail bud of the E9.5 embryo. This cell proliferation defect results in a growth imbalance in the caudal region that generates ventral curvature of the body axis. Neurulation movements are opposed, leading to delayed neuropore closure and spina bifida, or tail defects. It is interesting to reflect that these advances have been achieved in the absence of information on the nature of the ct gene product, which remains unidentified. In addition to the principal ct gene, which maps to distal Chromosome 4, the curly tail phenotype is influenced by several modifier genes and by environmental factors. NTD in curly tail are resistant to folic acid, as is thought to be the case in 30% of human NTD, whereas they can be prevented by myo-inositol. These and other features of NTD in this system bear striking similarities to the situation in humans, making curly tail a model for understanding a sub-type folic acid-resistant human NTD.

PMID: 11396850

Mouse models for neural tube closure defects.

Juriloff DM, Harris MJ. Mouse models for neural tube closure defects. Human Molecular Genetics. 2000 Apr 12;9(6):993-1000. Review.

Department of Medical Genetics, University of British Columbia, 6174 University Boulevard, Vancouver, British Columbia, Canada.

Neural tube closure defects (NTDs), in particular anencephaly and spina bifida, are common human birth defects (1 in 1000), their genetics is complex and their risk is reduced by periconceptional maternal folic acid supplementation. There are > 60 mouse mutants and strains with NTDs, many reported within the past 2 years. Not only are NTD mutations at loci widely heterogeneous in function, but also most of the mutants demonstrate variable low penetrance and some show complex inheritance patterns (e.g. SELH/Bc, Abl / Arg, Mena / Profilin1 ). In most of these mouse models, the NTDs are exencephaly (equivalent to anencephaly) or spina bifida or both, reflecting failure of neural fold elevation in well defined, mechanistically distinct elevation zones. NTD risk is reduced in various models by different maternal nutrient supplements, including folic acid ( Pax3, Cart1, Cd mutants), inositol ( ct ) and methionine ( Axd ). Lack of de novo methylation in embryos ( Dnmt3b -null) leads to NTD risk, and we suggest a potential link between methylation and the observed female excess among cranial NTDs in several models. Some surprising NTD mutants ( Gadd45a, Terc, Trp53 ) suggest that genes with a basic mitotic function also have a function specific to neural fold elevation. The genes mutated in several mouse NTD models involve actin regulation ( Abl/Arg, Macs, Mena/Profilin1, Mlp, Shrm, Vcl ), support the postulated key role of actin in neural fold elevation, and may be a good candidate pathway to search for human NTD genes.

PMID: 10767323

Investigations into the etiology of neural tube defects.

Cabrera RM, Hill DS, Etheredge AJ, Finnell RH. Investigations into the etiology of neural tube defects. Birth Defects Research. Part C, Embryo Today 2004 Dec;72(4):330-44. Review.

Center for Environmental and Genetic Medicine, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030, USA.

Neural tube defects (NTDs) are serious malformations affecting approximately 1 per 1000 births, yet the mechanisms by which they arise are unknown. There have been consistent efforts in many fields of research to elucidate the etiology of this multifactorial condition. While no single gene has been identified as a major independent risk factor for NTDs, candidate genes have been proposed that may modify the effects of maternal and/or embryonic exposures. Folate supplementation effectively reduces the occurrence of NTDs and, consequently, has focused much research on metabolism of folate-related pathways during pregnancy and development. Further understanding of normal development and how teratogens can perturb these orchestrated processes also remains at the fore of modern scientific endeavors. The composite of these factors remains fragmented; the aim of this review is to provide the reader with a summary of sentinel and current works in the body of literature addressing NTD disease etiology. 2005 Wiley-Liss, Inc.

PMID: 15662706

Pathobiology and genetics of neural tube defects.

Finnell RH, Gould A, Spiegelstein O. Pathobiology and genetics of neural tube defects. Epilepsia. 2003;44 Suppl 3:14-23. Review.

Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston 77030-3303, USA.

PURPOSE: Neural tube defects (NTDs), including spina bifida and anencephaly, are common congenital malformations that occur when the neural tube fails to achieve proper closure during early embryogenesis. Based on epidemiological and clinical data obtained over the last few decades, it is apparent that these multifactorial defects have a significant genetic component to their etiology that interacts with specific environmental risk factors. The purpose of this review article is to synthesize the existing literature on the genetic factors contributing to NTD risk.

RESULTS: To date, there is evidence that closure of the mammalian neural tube initiates and fuses intermittently at four discrete locations. Disruption of this process at any of these four sites may lead to an NTD, possibly arising through closure site-specific genetic mechanisms. Candidate genes involved in neural tube closure include genes of the folate metabolic pathway, as well as those involved in folate transport.

CONCLUSIONS: Although extensive efforts have focused on elucidating the genetic risk factors contributing to the etiology of NTDs, the population burden for these malformations remains unknown. One group at high risk for having children with NTDs is epileptic women receiving antiepileptic medications during pregnancy. Efforts to better understand the genetic factors that may contribute to their heightened risk, as well as the pathogenesis of neural tube closure defects, are reviewed herein.

PMID: 12790882

Mouse models of neural tube defects: investigating preventive mechanisms.

Greene ND, Copp AJ. Mouse models of neural tube defects: investigating preventive mechanisms. American Journal of Medical Genetics. Part C, Seminars in Medical Genetics. 2005 May 15;135C(1):31-41. Review.

Neural Development Unit, Institute of Child Health, University College London, UK.

Neural tube defects (NTD), including anencephaly and spina bifida, are a group of severe congenital abnormalities in which the future brain and/or spinal cord fail to close. In mice, NTD may result from genetic mutations or knockouts, or from exposure to teratogenic agents, several of which are known risk factors in humans. Among the many mouse NTD models that have been identified to date, a number have been tested for possible primary prevention of NTD by exogenous agents, such as folic acid. In genetic NTD models such as Cart1, splotch, Cited2, and crooked tail, and NTD induced by teratogens including valproic acid and fumonisins, the incidence of defects is reduced by maternal folic acid supplementation. These folate-responsive models provide an opportunity to investigate the possible mechanisms underlying prevention of NTD by folic acid in humans. In another group of mouse models, that includes curly tail, axial defects, and the Ephrin-A5 knockout, NTD are not preventable by folic acid, reflecting the situation in humans in which a subset of NTD appear resistant to folic acid therapy. In this group of mutants alternative preventive agents, including inositol and methionine, have been shown to be effective. Overall, the data from mouse models suggests that a broad-based in utero therapy may offer scope for prevention of a greater proportion of NTD than is currently possible. Copyright 2005 Wiley-Liss, Inc

PMID: 15800852

Pathophysiology, prevention, and potential treatment of neural tube defects

Manning SM, Jennings R, Madsen JR. Pathophysiology, prevention, and potential treatment of neural tube defects. Mental Retardation and Developmental Disabilities Research Reviews. 2000;6(1):6-14. Review.

Division of Newborn Medicine, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.

Neural tube defects (NTD) remain a major cause of morbidity in spite of the reduction in liveborn incidence with periconceptional folic acid. However, the etiology remains unknown. This article reviews studies that address causation and potential treatment of NTD in humans and in animal models that resemble aspects of the common human NTD. Studies of nutritional markers of vitamin B12 and folic acid support a defect in homocysteine metabolism; a thermolabile variant of methylene tetrahydrofolate reductase, an enzyme that remethylates homocysteine to methionine, correlates with a risk of NTD in some human populations. Numerous mouse mutant models of NTD exist, attesting to the ease of disruption of neurulation, and a genetic basis for this malformation. Of these models, the curly tail mouse mutant most closely resembles the common human NTD. Folic acid does not prevent NTD in this model; however inositol supplementation does result in a significant reduction in incidence. Recent advances in fetal surgery, and evidence from mechanically created myelomeningocele in large animals amenable to surgical intervention suggest that the handicaps associated with myelomeningocele and associated Chiari Type II malformation may be prevented by in utero NTD closure. Success will depend on preservation of neurological tissue until such intervention is possible. Further research in animal models at the genetic and cellular levels, together with technological surgical advances, provide hope that prevention of more NTD and the associated handicaps may be possible. MRDD Research Reviews 6:6-14, 2000. Copyright 2000 Wiley-Liss, Inc.

PMID: 10899792

Epidemiology of neural tube defects.

Frey L, Hauser WA. Epidemiology of neural tube defects. Epilepsia. 2003;44 Suppl 3:4-13. Review.

Department of Neurology, G. H. Sergievsky Center, College of Physicians & Surgeons, Columbia University, New York, New York 10032, USA.

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.

PMID: 12790881

Spina bifida and other neural tube defects

Northrup H, Volcik KA. Spina bifida and other neural tube defects. Current Problems in Pediatrics. 2000 Nov-Dec;30(10):313-32. Review.

Department of Pediatrics, Division of Medical Genetics, University of Texas Medical School, Houston, Texas, USA.

NTDs, resulting from failure of the neural tube to close during the fourth week of embryogenesis, are the most common severely disabling birth defects in the United States, with a frequency of approximately 1 of every 2000 births. Neural tube malformations involving the spinal cord and vertebral arches are referred to as spina bifida, with severe types of spina bifida involving protrusion of the spinal cord and/or meninges through a defect in the vertebral arch. Depending on the level of the lesion, interruption of the spinal cord at the site of the spina bifida defect causes paralysis of the legs, incontinence of urine and feces, anesthesia of the skin, and abnormalities of the hips, knees, and feet. Two additional abnormalities often seen in children with spina bifida include hydrocephalus and the Arnold-Chiari type II malformation. Despite the physical and particular learning disabilities children with spina bifida must cope with, participation in individualized educational programs can allow these children to develop skills necessary for autonomy in adulthood. Advances in research to uncover the molecular basis of NTDs is enhanced by knowledge of the link between both the environmental and genetic factors involved in the etiology of NTDs. The most recent development in NTD research for disease-causing genes is the discovery of a genetic link to the most well-known environmental cause of neural tube malformation, folate deficiency in pregnant women. Nearly a decade ago, periconceptional folic acid supplementation was proven to decrease both the recurrence and occurrence of NTDs. The study of folate and its association with NTDs is an ongoing endeavor that has led to numerous studies of different genes involved in the folate metabolism pathway, including the most commonly studied thermolabile mutation (C677T) in the MTHFR gene. An additional focus for NTD research involves mouse models that exhibit both naturally occurring NTDs, as well as those created by experimental design. We hope the search for genes involved in the risk and/or development of NTDs will lead to the development of strategies for prevention and treatment. The most recent achievement in treatment of NTDs involves the repair of meningomyelocele through advancements in fetal surgery. Convincing experimental evidence exists that in utero repair preserves neurologic function, as well as resolving the hydrocephalus and Arnold-Chiari malformation that often accompany meningomyelocele defects. However, follow-up is needed to completely evaluate long-term neurologic function and overall improved quality of life. And in the words of Olutoye and Adzick, "until the benefits of fetal [meningomyelocele] repair are carefully elucidated, weighed against maternal and fetal risks, and compared to conventional postnatal therapy, this procedure should be restricted to a few centers that are committed (clinically and experimentally) to investigating these issues."

PMID: 11147289

Etiology, pathogenesis and prevention of neural tube defects.

Padmanabhan R. Etiology, pathogenesis and prevention of neural tube defects.
Congenit Anom (Kyoto). 2006 Jun;46(2):55-67. Review.

Department of Anatomy, Faculty of Medicine and Health Sciences, UAE University, Al Ain, United Arab Emirates.

Spina bifida, anencephaly, and encephalocele are commonly grouped together and termed neural tube defects (NTD). Failure of closure of the neural tube during development results in anencephaly or spina bifida aperta but encephaloceles are possibly post-closure defects. NTD are associated with a number of other central nervous system (CNS) and non-neural malformations. Racial, geographic and seasonal variations seem to affect their incidence. Etiology of NTD is unknown. Most of the non-syndromic NTD are of multifactorial origin. Recent in vitro and in vivo studies have highlighted the molecular mechanisms of neurulation in vertebrates but the morphologic development of human neural tube is poorly understood. A multisite closure theory, extrapolated directly from mouse experiments highlighted the clinical relevance of closure mechanisms to human NTD. Animal models, such as circle tail, curly tail, loop tail, shrm and numerous knockouts provide some insight into the mechanisms of NTD. Also available in the literature are a plethora of chemically induced preclosure and a few post-closure models of NTD, which highlight the fact that CNS malformations are of hetergeneitic nature. No Mendelian pattern of inheritance has been reported. Association with single gene defects, enhanced recurrence risk among siblings, and a higher frequency in twins than in singletons indicate the presence of a strong genetic contribution to the etiology of NTD. Non-availability of families with a significant number of NTD cases makes research into genetic causation of NTD difficult. Case reports and epidemiologic studies have implicated a number of chemicals, widely differing therapeutic drugs, environmental contaminants, pollutants, infectious agents, and solvents. Maternal hyperthermia, use of valproate by epileptic women during pregnancy, deficiency and excess of certain nutrients and chronic maternal diseases (e.g. diabetes mellitus) are reported to cause a manifold increase in the incidence of NTD. A host of suspected teratogens are also available in the literature. The UK and Hungarian studies showed that periconceptional supplementation of women with folate (FA) reduces significantly both the first occurrence and recurrence of NTD in the offspring. This led to mandatory periconceptional FA supplementation in a number of countries. Encouraged by the results of clinical studies, numerous laboratory investigations focused on the genes involved in the FA, vitamin B12 and homocysteine metabolism during neural tube development. As of today no clinical or experimental study has provided unequivocal evidence for a definitive role for any of these genes in the causation of NTD suggesting that a multitude of genes, growth factors and receptors interact in controlling neural tube development by yet unknown mechanisms. Future studies must address issues of gene-gene, gene-nutrient and gene-environment interactions in the pathogenesis of NTD.

PMID: 16732763

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

Byrne J, Carolan S. Adverse reproductive outcomes among pregnancies of aunts and (spouses of) uncles in Irish families with neural tube defects. American journal of medical genetics. Part A. 2006 Jan 1;140(1):52-61.

Boyne Research Institute, 5 Potato Market Square East, Drogheda, Ireland.

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.

PMID: 16333827

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

Deak KL, Siegel DG, George TM, Gregory S, Ashley-Koch A, Speer MC; NTD Collaborative Group. (2008) Further evidence for a maternal genetic effect and a sex-influenced effect contributing to risk for human neural tube defects. Birth defects research. Part A, Clinical and molecular teratology. 2008 Oct;82(10):662-9.

Center for Human Genetics, Duke University Medical Center, Durham, North Carolina, USA.

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.

PMID: 18937341