Spinal dysraphia as an autosomal dominant defect in four families

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.

The paleoepidemiology of Sacral Spina Bifida Occulta in population samples from the Dakhleh Oasis, Egypt

OBJECTIVE

To document sacral spina bifida occulta (SSB0) prevalence in a population sample from the Dakhleh Oasis, Egypt, and address methodological issues in recording and quantifying SSBO variations.

MATERIALS

442 adult sacra from two temporally disjunct samples from the same deme traversing the 3rd intermediate (TIP) and the Roman Periods.

METHODS

Sacra were scored for SSBO, excluding the sacral hiatus. Risk of SSBO was calculated with the common odds ratio and statistical significance by X². Data were compared to other archaeological SSBO data.

RESULTS

SSBO was present in 15.6% of the sample with a slight, but not significant, temporal increase (TIP to Roman Period) in males, and a significant age-correlated increase in both sexes. Most open sacra occurred in young adults.

CONCLUSIONS

Data support that SSBO can be considered as a morphogenetic variant. Dakhleh data fall within the prevalence range for most populations, however inter-population comparisons are complicated by methodological inconsistencies.

SIGNIFICANCE

SSBO can be used in paleogenetic research.

LIMITATIONS

Methodological differences in scoring SSBO prevent effective comparative study.

SUGGESTED FUTURE RESEARCH

Future studies require more rigorous and standardized scoring methods. aDNA may be used to corroborate the morphogenetic value of SSBO and determine its clinical significance.

Missing genetic risk in neural tube defects: can exome sequencing yield an insight?

BACKGROUND

Neural tube defects (NTD) have a strong genetic component, with up to 70% of variance in human prevalence determined by heritable factors. Although the identification of causal DNA variants by sequencing candidate genes from functionally relevant pathways and model organisms has provided some success, alternative approaches are demanded.

METHODS

Next generation sequencing platforms are facilitating the production of massive amounts of sequencing data, primarily from the protein coding regions of the genome, at a faster rate and cheaper cost than has previously been possible. These platforms are permitting the identification of variants (de novo, rare, and common) that are drivers of NYTD etiology, and the cost of the approach allows for the screening of increased numbers of affected and unaffected individuals from NTD families and in simplex cases.

CONCLUSION

The next generation sequencing platforms represent a powerful tool in the armory of the genetics researcher to identify the causal genetic basis of NTDs.

Spina bifida with associated malformations of the central nervous system in Dorper-cross sheep

CASE HISTORY

In 2008, six lambs within a flock of Dorper-cross sheep were born with musculoskeletal and neurological disease. Clinical signs included hindlimb weakness, and urinary incontinence.

CLINICAL FINDINGS

All lambs had focal, inverted areas of alopecic skin over the caudal sacrum, and short, often kinked tails. Four affected lambs were subject to euthanasia, and necropsied. On gross examination, the arches of sacral vertebrae were absent, and spinal nerves and meninges were adherent to the overlying subcutis. Other gross lesions included narrow, elongated skulls, herniation of the occipital lobes into the caudal fossas, hydrocephalus, and syringomyelia. One lamb had coning of the cerebellar vermis, but cerebellar herniation through the foramen magnum was not identified.

DIAGNOSIS

Spina bifida, with associated malformations of the central nervous system.

CLINICAL RELEVANCE

Examination of breeding records suggested either an autosomal recessive or partially penetrant autosomal dominant pattern of inheritance. Because of the associated tail lesions it is proposed that the pathogenesis of this syndrome involves a defect in development of the tail bud (secondary neurulation), that tethering of the spinal cord resulted in the clinical signs, and abnormal pressure of the cerebral spinal fluid resulted in the defects in the skull and brain.

[Degree of genetic homozygosity among patients with spinal dysraphia]

INTRODUCTION

Our study of genetic homozygosity degree includes an analysis of the presence, distribution and individual combination of 15 selected genetically controlled morphophysiological traits in the sample of patients with spinal dysraphia (N=35) and in the control-healthy group (N=50).

OBJECTIVE

Assuming that spinal dysraphia is a genetically controlled disease, we made a hypothesis that an increased homozygosity level, as well as the changed variability among patients, could be a population-genetic parameter for the prediction of the illness.

METHOD

Taking into consideration our experience, as well as the experience of numerous scientists who studied the nature of the inheritance of mono- and oligo-genically controlled qualitative traits, we applied a methodology to estimate the proportion of such homozygously recessive characters (HRC-test,).

RESULTS

This population-genetic study did not only show a statistically significant difference of the mean values of genetic homozygosity (SD 4.8 +/- 0.3; control 3.5 +/- 0.3), but of the differences in the type of distribution too, as well as the differences in the presence of certain individual combinations of such traits.

CONCLUSION

Due to the fact that those genes which control such qualitative recessive traits are distributed in different human chromosomes, being their visible markers, this could indicate that degrees of genetic homozygosity are ostensibly greater in a sample of patients with spinal dysraphia compared to the control group of individuals.

Etiology, pathogenesis and prevention of neural tube defects

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.

Human neural tube defects: developmental biology, epidemiology, and genetics

Birth defects (congenital anomalies) are the leading cause of death in babies under 1 year of age. Neural tube defects (NTD), with a birth incidence of approximately 1/1000 in American Caucasians, are the second most common type of birth defect after congenital heart defects. The most common presentations of NTD are spina bifida and anencephaly. The etiologies of NTDs are complex, with both genetic and environmental factors implicated. In this manuscript, we review the evidence for genetic etiology and for environmental influences, and we present current views on the developmental processes involved in human neural tube closure.

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.

Recurrent meningitis in a case of congenital anterior sacral meningocele and agenesis of sacral and coccygeal vertebrae

A rare case of recurrent meningitis due to congenital anterior sacral meningocele and agenesis of the sacral and coccygeal vertebrae is described. An autosomal dominant inheritance is demonstrated for lower cord malformation, and environmental factors (chromic acid or fumes) are discussed.

Absence of linkage between familial neural tube defects and PAX3 gene

Neural tube defects (NTD) are among the most common and disabling birth defects. The aetiology of NTD is unknown and their genetics are complex. The majority of NTD cases are sporadic, isolated, nonsyndromic, and generally considered to be multifactorial in origin. Recently, PAX3 (formerly HuP2, the human homologue of mouse Pax-3), on chromosome 2q35-37, was suggested as a candidate gene for NTD because mutations of Pax-3 cause the mouse mutant Splotch (Sp), an animal model for human NTD. Mutations in PAX3 were also identified in patients with Waardenburg syndrome type 1 (WS1). At least eight patients with both WS1 and NTD have been described suggesting pleiotropy or a contiguous gene syndrome. Seventeen US families and 14 Dutch families with more than one affected person with NTD were collected and 194 people (50 affected) from both data sets were genotyped using the PAX3 polymorphic marker. The data were analysed using affecteds only linkage analysis. The lod scores were -7.30 (US), -3.74 (Dutch), and -11.04 (combined) at theta = 0.0, under the assumption of the autosomal dominant model. For the recessive model, the lod scores were -3.30 (US), -1.46 (Dutch), and -4.76 (combined) at theta = 0.0. Linkage between PAX3 and familial NTD was excluded to 9.9 cM on either side of the gene for the dominant model and to 3.63 cM on either side of the gene for the recessive model in the families studied. No evidence of heterogeneity was detected using the HOMOG program. Our data indicate that PAX3 is not a major gene for NTD.

The Chernobyl accident, congenital anomalies and other reproductive outcomes

Studies of the association between the Chernobyl accident in April 1986 and reproductive outcome, with particular reference to congenital anomalies, are reviewed. All of the studies so far have been based on the detection of a change in frequency over time. An increased frequency of trisomy 21 in the former West Berlin in January 1987, and increases in the frequency of neural tube defects in several small hospital-based series in Turkey, are not confirmed in larger and more representative series in Europe. No clear changes in the prevalence at birth of anomalies which might be associated with the accident are apparent in Byelorussia or the Ukraine, the republics with the highest exposure to fallout. However, these data are difficult to interpret as the methods of acquisition have not been described and they have not yet been reported in full. Thus, there is no consistent evidence of a detrimental physical effect of the Chernobyl accident on congenital anomalies. This is also the case for other measured outcomes of pregnancy. There is evidence of indirect effects--an increase in induced abortions substantial enough to show as a reduction in total births, due to anxieties created. Data are not available on the reproductive outcomes of women pregnant at the time of the accident who were evacuated from the 30 km zone of immediate contamination, of workers in the plant at the time of the accident or of decontamination workers. Moreover, no data are available from several of the other countries closest to the Chernobyl area.

Pentalogy of Cantrell and associated midline anomalies: a possible ventral midline developmental field

Five cases of the Pentalogy of Cantrell (PC), ascertained through the Baltimore-Washington population-based study of infants with congenital cardiovascular malformations, represent a regional prevalence of 5.5/1 million liveborn infants for this disorder. Three of these patients had cleft lip with or without palate. Review of the reported literature of the Pentalogy of Cantrell and various combinations of the anomalies within the spectrum of this pentad suggests that the PC defines a specific midline ventral developmental field. Cleft lip with or without cleft palate and encephalocele tend to specifically associate with ventral midline anomalies within the spectrum of PC. These associations might either illustrate the previously observed tendency of specific occurrence of certain combinations of midline defects or represent defined subunits of the midline developmental field.

Familial dyslexia: use of genetic linkage data to define subtypes

Specific reading disability is an example of a complex behavioral disorder which is clinically heterogeneous. It is probably also heterogeneous at the levels of etiology and process (pathogenesis), but there may not be a 1:1:1 mapping of etiology to process to clinical outcome. Thus, classification of cases by clinical features may not lead to discovery of the underlying processes or etiologies, and it may be profitable to define subgroups by etiology. There is evidence for genetic etiology in some cases, but there is genetic heterogeneity as well. Possible genetic models for specific reading disability include polygenic, oligogenic, and single gene inheritance, and there are several types of genetic analysis that can be used to determine which of these modes of inheritance may be present. Identification of individual genes is possible in single gene and oligogenic disorders. Clinical studies and molecular analysis can then be used to determine gene function.

Neural tube defects: a review of human and animal studies on the etiology of neural tube defects

Although neural tube defects are a common congenital anomaly, their etiology is not known. Human studies have emphasized the pathology and epidemiology of the defects and suggest that in the majority of cases the etiology is multifactorial. Factors which appear possibly to be important are genetic predisposition, maternal illness, and fetal drug exposure. Animal studies have utilized naturally occurring neural tube defects and teratologically induced lesions. No animal model has been convincingly established as the equivalent of human neural tube defects. However, animal models have allowed investigation of the mechanisms of suggested human teratogens and determination of the pathogenesis of naturally occurring animal defects. Their most important contribution has been in furthering the understanding of the normal mechanisms of neural tube closure. It may be through this understanding that the etiology of human neural tube defects will be determined.

Neural tube defects: heterogeneity and homogeneity

Detailed investigations were made on 150 fetuses with neural tube defects (NTD). After eliminating those with recognised causes, the rest were found to consist of fetuses with both isolated NTD and NTD with other developmental abnormalities. On evaluation of reproductive history, type and frequencies of NTD in pregnancies before conception, and sex of the fetuses involved, no demonstrable difference between these two types of NTD was found. Secondly, in those with additional developmental abnormalities, a significant clustering of developmental defects rather than a uniform distribution throughout abnormalities were found predominantly in cases of total craniorachischisis and upper thoracic spina bifida, less often in anencephaly and thoraco-lumbar spina bifida, and never in lumbo-sacral spina bifida. Thus it appears that there is not a random concurrence of other developmental abnormalities with NTD but a definite pattern. We suggest that this implies a connection between the developmental abnormality and the NTD and that the additional abnormalities arise due to mechanical induction by the particular specific disturbance of the neural tube and its surrounding tissues. The most important difference between isolated NTD and those with other associated abnormalities is that the disruption in development at neurulation is more far reaching in the latter than in the former.

Possible causal heterogeneity in spina bifida cystica

A study was performed to determine whether causal heterogeneity can be demonstrated among the nonsyndromal spina bifida cysticas based on the vertebral level of the defect. Two groups were compared, probands with defects at or above T 11, likely representing defects of neuralization, and probands with defects at or below T 12, likely defects of canalization. Differences between the two groups were found with respect to reproductive history and occurrence of other malformations. A high degree of concordance for the type of defect among affected sib pairs was also observed. These findings indicate that there is probably heterogeneity within the spina bifida cysticas based on the level of the defect.

Maternal serum alpha-fetoprotein screening for neural tube defects. Report of a combined study in Germany and short overview on screening in populations with low birth prevalence of neural tube defects

The basis of maternal serum alpha-fetoprotein (AFP)-screening for neural tube defects is discussed. A report is given of a large scale screening study in the Federal Republic of Germany combining the experiences in Giessen and Hannover on over 50,000 pregnant women, about evenly distributed among both centers. Published and known forthcoming data from other low incidence populations, particularly of European countries, are reviewed briefly. The conclusion is reached that general screening could effectively be instituted and in the final result should also be cost-beneficial.

Epidemiology and genetics of neural tube defects: an application of the Utah Genealogical Data Base

The distribution and prevalence of births with neural tube defects in Utah from 1940 to 1979 are analyzed with regard to prevalence rates, secondary sex ratios, seasonality, yearly rates, and time-space clustering. The overall prevalence rate of 1.00 per thousand live births is comparable to that of other populations in the western United States. Analysis of sex ratios indicates a substantially higher proportion of females than males. No significant secular trends or time-space clustering are observed. No seasonality is seen for spina bifida; however, the anencephaly cases are delivered more frequently in the early spring and fall months. Following linkage of the neural tube defect cases to the Utah Genealogical Data Base, application of the genealogical index method shows substantial familial clustering of the disease. The average inbreeding coefficient of the neural tube defect cases is not elevated over that of matched controls. The empirical recurrence risk for the disease is calculated to be 3%, and the heritability estimate is 70%. Likelihood analysis of pedigrees containing spina bifida occulta and spina bifida cystica indicates that they may segregate as an autosomal dominant trait with a penetrance of 75%.

Occurrence of neural tube defects among first-, second-, and third-degree relatives of probands: results of a United States study

Data on the occurrence of neural tube defects in first-, second-, and third-degree relatives of probands were collected in a United States study. The proportions of affected individuals were 3.2%, 0.5%, and 0.17% respectively. These findings are compared to those from other recent North American studies, and differences are discussed. It is pointed out that accurate recurrence risk figures may not be available, and that caution should be used when counseling families with relatives who are affected with NTD.