Congenital malformations of the central nervous system in spontaneous abortions

Neural tube defects in spontaneous abortions

Nine specimens with neural tube defects (NTDs) were ascertained in a consecutive series of spontaneous abortions in New York City, giving a rate of 10.2 per 1,000 testable embryos and fetuses. All seven successfully karyotyped abortions had a chromosome anomaly. The rate of NTDs in miscarriages in New York is only one-third the rate in miscarriages in London, and the difference is due entirely to a deficit of fetuses with normal chromosomes. Our data, together with data from three other centers, indicate that there is a strongly positive association (r = 0.96) between rates of neural tube defects in early pregnancy and at term. The implications of these findings for genetic counseling and for etiologic studies are discussed.

Significance of cardiac defects in the developing fetus: a study of spontaneous abortuses

We investigated the impact of heart defects on the developing human fetus by examining 412 hearts from consecutive spontaneous abortuses. In each case, the cardiac morphology was correlated with the autopsy findings and the karyotype (unavailable in 115 hearts not successfully cultured). Of the 412 hearts, 10 (2.4%) contained structural defects (six ventricular septal defects, one atrial septal defect with ventricular septal defect, and one each coarctation, atrioventricular septal defect, and tetralogy of Fallot). Only one of 10 had major extracardiac malformations. Of the 277 fetuses with normal karyotype, three (1.1%) had heart defects. Of the 20 fetuses with abnormal karyotype, four (20%) had heart defects. In the remaining three fetuses with heart defects, the karyotype was not obtained. Thus (1) 57% of spontaneous abortuses with congenital heart defects contained major chromosomal abnormalities, (2) the spectrum of heart defects among spontaneous abortuses was similar to that among liveborns, and (3) since the prevalence of heart defects among fetuses without other major abnormalities was similar to that among liveborns, heart defects alone may not jeopardize the survival of a developing fetus.

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 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.

Maternal serum alpha-fetoprotein screening for the detection of neural tube defects

We tested 10,715 low-risk pregnancies in a voluntary maternal serum alpha-fetoprotein screening program for the detection of neural tube defects in California. In all, 5.3 percent of women had one elevated serum level, 3.3 percent were referred for sonography and 1.5 percent for amniocentesis. There were 12 cases of open neural tube defects (1.1 per 1,000); all of the mothers had one elevated serum alphafetoprotein level: nine (75 percent) completed the protocol and the neural tube defects were correctly identified. No normal pregnancies were terminated. The risk of an open neural tube defect occurring was about 1 in 50 after the first abnormal serum level and 1 in 15 at amniocentesis. We found significantly increased risk for fetal death and low birth weight after one elevated serum alpha-fetoprotein level, though the likelihood of a normal pregnancy outcome was about 80 percent. Maternal serum screening was also useful in identifying twin pregnancies and correcting underestimated gestational dates.

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.

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

The parents of 226 of the 360 patients with anencephalus or spinal bifida or both, born in Belfast 1964 to 1968, were visited to document the occurrence of these malformations among other relatives. The proportions of sibs with anencephalus and spina bifida were 10.41% for spina bifida index patients and 6.4% for anencephalus. For patients born after the index patients, the proportions were 12.19% and 6.35%, respectively. The overall incidence of either malformation among sibs was 8.87%. This estimate is higher than the 4 to 5% commonly reported and is probably related to the specific background of the Northern Ireland population, which is known to have the highest incidence of CNS malformations in the United Kingdom. The substantial size of this risk indicates the importance of amniocentesis for monitoring subsequent pregnancies of women who have had one child with a CNS malformation.

Heritability of cranium bifidum and spina bifida in the golden hamster

The heritability (h2) and frequency of the neural tube closure defects, cranium bifidum (CB) and spina bifida (SB), have been estimated for a population of 9-day-old hamster embryos through half-sibling analysis. The average frequency of the total affected embryos per litter is approximately 17% while the pooled estimate forh2based on between sires and between dams within sires components was 4%. This value points to the importance of environmental factors in contributing to the variance in defect frequencies observed within this population.

May spina bifida result from an X-linked defect in a selective abortion mechanism?

It is suggested that the major genetic factor in determining the birth of children with neural tube defects may be a single X-linked gene. It acts as an X-linked dominant, not by producing neural tube defects, but by enabling the affected fetus to survive selective spontaneous abortion. This mechanism, mediated at the deciduoplacental junction, may be under the control of both maternal and fetal genes. With more mutant alleles, survival would become more likely, reaching a maximum in the homozygous affected female fetus of a homozygous affected mother. The female excess in anancephaly is greater than that in spina bifida because of its prenatal severity, thus requiring relatively more mutant alleles for survival.

Comparison of central nervous system malformations in spontaneous absortions in Northern Ireland and south-east England

A study of 1140 pregnancies ending in spontaneous abortion disclosed a central nervous system (CNS) malformation in 4.9% of all complete conceptuses. Life-table analysis suggested that the incidence of CNS malformations is 16/1000 at the beginning of the eighth week of gestation. It was also estimated that only one-fifth of these infants are born alive, 41% being aborted spontaneously and 38% stillborn. A hypothesis that differences in the incidence of CNS malformations result from area differences in the mortality rate of malformed embryos and fetuses was examined by comparing the findings in Northern Ireland, an area of high incidence, with those in south-east England, an area of low incidence. In Northern Ireland 4.6% of complete conceptuses had a CNS malformation compared with 3.0% in south-east England, but the difference was not statistically significant. There is no evidence that in Northern Ireland a lower mortality rate among malformed fetuses and embryos is responsible for the high incidence of malformation at birth. The geographical variation of CNS malformations in the United Kingdom still awaits explanation.

Neural-tube defects: importance of a history of abortion in aetiology

The overall incidence of anencephaly and spina bifida (ASB) in 69,056 pregnancies was 4.7/1000 births. ASB was more common (8.4/1000 births) among children of mothers who had had two or more abortions, but the increased risk was confined to spina bifida. A history of abortion was more common in older women and women of higher parity, but this was not matched by a similar increase in the incidence of ASB. The incidence of ASB was related to social class, but the prevalence of previous abortions was similar in all classes. The results suggest that expectant mothers with a history of two or more abortions have an increased risk of producing a child with spina bifida. The abortions are considered to be a manifestation of previous abnormal conceptions rather than the primary cause.

Neural tube malformations: complex segregation analysis and calculation of recurrence risks

Familial data on neural tube malformations in Great Britain were submitted to segregation analysis under the mixed model. Maternal and fetal factors cannot be discriminated in the absence of substantial bodies of data on spina bifida survivors who reproduce or on half-sibs. Early abortion studies would allow differential mortality in utero to be taken into account. After fitting the mixed and generalised single locus models, it is concluded that the multifactorial model can provisionally be used for calculation of recurrence risks. Pathogenic hypotheses implicating twinning seem to rest on little evidence.

Etiology of neural tube defect in man--Do teratogens play any part? Evidence from sex ratios

Neural tube defect (NTD) is more common among spontaneously aborted fetuses than in infants born in the third trimester, but there is no direct evidence that NTD-affected conceptuses, presenting at these two different gestational ages, are components of a single disease process. Evidence for homology is here presented in an analysis of the sex ratios of spontaneously and therapeutically aborted NTD-affected fetuses, and of sex ratios differing with variations in prevalence of NTD-affected infants. If it could be shown conclusively that NTD is a single disease process, with an inverse relationship between components expressed early and late in gestation, there would be implications for the ascertainment of families at risk for NTD, and for the search for environmental factors potentially involved in the causation of NTD.

Meckel syndrome and the prenatal diagnosis of neural tube defects

Two fetuses, terminated after prenatal diagnosis of aneural tube defect, had Meckel syndrome. There have now been three fetuses with this syndrome in a series of 35 terminated because of open lesions of the neural tube. It is suggested that such therapeutically aborted fetuses represent a highly selected group, among which a rare condition like Meckel syndrome will be concentrated. The need for a detailed examination of all terminated fetuses is emphasised, for the identification of such an autosomal recessive condition alters the genetic counselling for a future pregnancy.

Myeloschisis in a six weeks embryo of a leukemic woman treated by busulfan

A case of myeloschisis in a six weeks old human embryo is reported. The 39-year-old mother was treated by busulfan before and during the early stages of gestation for chronic lymphatic leukemia. Additional histological findings consisted in a decrease of mesenchymal elements together with a somitic disorganisation in the affected area of the embryo. In spite of the well known experience that this drug is well tolerated by leukemic pregnant women, a possible interference of busulfan with the oocyte differentiation in this elderly primipara is proposed.

Spontaneous abortion rates, gravidity and neural tube defects

Kline and her co-workers [20, 21] suggest that spontaneous abortions show no overall gravidity effect. However, spontaneous abortions seem to show a negative gravidity effect in some sibships (those containing an infant affected by anencephaly or spina bifida) [22]. It is inferred that there is a heterogeneity among spontaneous abortion sibships, and that there are other sibships in which spontaneous abortions show a positive gravidity effect (perhaps as a result of e.g. iso-immunization).

Central nervous system abnormalities--contrasting patterns in early and late pregnancy

A total of 509 specimens of spontaneous abortion were studied. Of 364 complete specimens, 15 (4.1%) had central nervous system (CNS) abnormalities. The defects which were seen were anencephaly, spina bifida, iniencephaly, encephalocele and anencephaly combined with complete rachischisis. A high proportion (five out of 15) had the more unusual defects of iniencephaly and encephalocele. All except one had ceased development at less than 12 weeks of gestation. Sex chromatin studies showed that males outnumbered females amount CNS defective fetuses. When the month of conception was calculated for these abnormal pregnancies, summer and winter peaks were detected. Only one of the 15 patients had a family history of neural tube defect (NTD). Histological examination of all small fetuses aborted spontaneously revealed two additional facts. First, in fetuses with a localised external CNS defect, the internal abnormality was more extensive. Second, the CNS was also abnormal in some fetuses with no visible external defect. The proportion of abnormality is much higher than at birth and is also higher than in other surveys of spontaneous abortion. We suggest that screening for serum alphafetoprotein should be undertaken and amniocentesis considered in pregnancies subsequent to an abortion of this type.

Birth ranks of spontaneous abortions in sibships of children affected by anencephaly or spina bifida

Data on the birth ranks of miscarriages within sibships in which a case of anencephaly or spina bifida (ASB) had occurred were analysed by the Haldane-Smith statistical test. This showed that miscarriages in ASB sibships tend to have a negative birth order effect--that is, they occur in earlier rather than later pregnancies within the sibship. The strongest source of bias in this analysis--the fact that mothers tend to forget early spontaneous abortions--worked against this finding, so the negative birth order effect is probably genuine. Because ASB itself shows a negative birth order effect and because spontaneous abortions in normal sibships do not show such an effect, the additional spontaneous abortions in ASB sibships are probably of fetuses affected by ASB.

Encephaloceles in Nigerian Igbos

A survey of surgical specimens submitted to a central laboratory suggests that the Igbos of Nigeria are a further ethnic group in whom the anterior encephalocele is comparatively common.

A cytogenetic study of human spontaneous abortions using banding techniques

The karyotypes of 941 singleton and 42 twin abortuses and 4 cystic placentae were determined. 30.5% of the singletons were chromosomally abnormal; 49.8% of these were trisomic, 23.7% X-monosomics and 17.4% polyploid. 143 trisomies were identified by banding; over a third had an extra chromosome 16, more than 10% an extra 21 or 22 and about 5% an extra 2, 18 or 15. Examples of trisomy 3, 4, 8, 9, 10, 13, 14 and 20 were also encountered. Using the data from two other published studies, the prevalence of different trisomies was estimated and an attempt was made to relate the karyotype of the conceptus to its subsequent development.