A family study of spina bifida and anencephalus in Belfast, Northern Ireland (1964 to 1968)

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.

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.

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.

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.

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.

Sibs of probands with neural tube defects--a study in the Federal Republic of Germany

Data for the risk of neural tube defects in sibs of affected children are needed for genetic counselling, for decision on prenatal studies, and for planning of preventive measures. Data have been reported from various populations but were lacking for Germany. This study presents data on the siblings of 240 index patients in the Western part of the Federal Republic of Germany. The prevalence among sibs of affected individuals was found to be 2.6%. This figure agrees well with reports from other countries in Continental Europe and the United States, and fits the expectation of lower recurrence risks in low incidence populations.

Recurrence risk after neural tube defects in a genetic counselling clinic

The recurrence of isolated neural tube defects in a population of women from a genetic counselling clinic was found to be 3.4%. After one baby with a neural tube defect the recurrence was 2.3%. Of the 15 pregnancies of women who had two previous babies with neural tube defects, there were three further recurrences. These findings show that the Hungarian recurrence risk of isolated neural tube defects has not changed with a declining birth prevalence, and that the rate in genetic counselling clinic patients is the same as in a previous population based epidemiological study.

Epidemiology of neural tube defects in Germany

A survey is made of the epidemiologic studies of neural tube defects (NTD) in Germany. A temporary increase is noted in the prevalence of NTD at birth for the time during and shortly after the Second World War, followed by a downward trend thereafter. Thus an earlier observation of Lenz (1965) could be confirmed. Falling rates of NTD were also reported from various other countries in recent years. No convincing etiological explanation is available so far. The current prevalence of NTD at birth can be estimated for Germany to be about 1.0-1.5 per thousand newborns with about an even distribution to anencephalus and spina bifida.

Recurrence risk of neural tube defects following a miscarriage

Data from 280 sibships in three published series were used to see if the increased risk of neural tube defect (NTD) associated with having had a miscarriage in the immediately preceding pregnancy was also found in women with a previous affected pregnancy. A statistically significant relative risk of 4.0 (2-tail P = 0.0111, Fisher exact test) was found among such women, and this could not be accounted for by the effect of parity or of a history of miscarriage in general. The finding may be useful when counselling patients.

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.

Etiologic heterogeneity of neural tube defects. II. Clues from family studies

We previously reported that among neural tube defects (NTDs) with no known causes the ones that occur alone (singles) have different epidemiologic characteristics from those that occur in combination with other defects (multiples), suggesting an underlying causal heterogeneity. In this study, we compared family histories of 223 single NTD cases and 66 multiple cases ascertained through the Metropolitan Atlanta Congenital Defects Program (MACDP) between 1970 and 1979. Compared with siblings of multiples, siblings of singles had a higher precurrence rate for NTDs (2.0% vs. 0.0%) and for birth defects in general (10.9% vs. 3.0%). Furthermore, siblings of singles that were born within 2 years before the birth of the index case had a higher precurrence rate for NTDs (8.0% vs. 1.1%) and for major birth defects (20.0% vs. 2.9%) than had those born earlier. These results further suggest that NTDs are etiologically heterogeneous, depending on the presence of associated defects, and point to important environmental influences in the increased risk for birth defects among siblings of singles. Larger studies are needed to confirm these data and show that single and multiple NTDs have different recurrence rates, not only for NTDs but also for other birth defects.

Recurrence rates for neural tube defects and vitamin supplementation

An attempt is made to assess the result of Smithells et al¹ in the light of published data on recurrence rates for neural tube defects.

Recurrence risks for neural tube defects in a genetic counseling clinic population

The recurrence of neural tube defects (NTD) in the sib following the index case of all patients who consulted the South-East Thames Regional Health Authority Genetics Centre in the period 1972 to mid-1979 was calculated. A total of 1037 consecutive patients was studied, of whom 958 (93%) were traced. The overall recurrence was 3.44% (1 in 29). However, if the index case was the first affected child in the family, the recurrence in the next sib was 3.15% (1 in 32), and if it was the second affected child, the recurrence was 11.76% (1 in 9). These figures give an indication of the actual recurrence among the 'selected' population who consult a genetic advice centre, and are somewhat, but not significantly, different from figures for the general NTD population, which have been derived from studies of whole families.

Influence of social class on the risk of recurrence of anencephalus and spina bifida

This study suggests that social class has an effect on the incidence of anencephalus and spina bifida, the malformations being more frequent in the lower socio-economic groups. A family study of 226 patients with a CNS malformation suggests that social class also may be important in determining the recurrence risk of such malformations: there are higher risks in social classes III, IV and V than in social classes I and II.