Maternal Age in Familial Mongolism

In recent years several writers have attempted to bring the known aetiological effect of maternal age in mongolism into direct relationship with its causation. Brousseau (1928) sifted the available data very carefully, but failed to come to any conclusion as to how maternal age could exert its effect. Benda (1947) considers that advanced age is only a subsidiary factor making maternal illness or endocrine disorder more significant, and a similar view seems to be held by Ingalls (1947). The conclusion is drawn by Geyer (1939) that mongolism is due to an abnormal ovum; if so, the older the mother, presumably the more likely are ova to be abnormal. Conversely, Engler (1949) believes that the foetal dysplasia is caused by faulty embedding of a normal ovum in uterine mucosa which has deteriorated in consequence of age, infection or surgical interference. Jenkins (1933) lays stress on the analogy with certain phenomena seen in animal genetics, for Wright (1926) had shown that the manifestation of hereditary Polydactyly in guinea-pigs was influenced by the age of the dam: young mothers produced more polydactylous offspring than older ones. A similar effect has been found by Holt (1947) in polydactylous mice. There is no experimental evidence as to the nature of the mechanism involved, but it may be supposed to be physical or chemical. The search for a process akin to antigenic incompatibility has also been suggested (Penrose, 1946), immunity developing with greater ease in maturer than in younger maternal tissues. It is not necessary to look for a specifically pathological process, however, since the maternal-foetal reaction might be analogous to that in the aetiology of fraternal twins, which especially occurs at late maternal ages, which centre around 38 years.

Immunological aspects of pre-eclampsia

The first pregnancy preponderance and apparent partner specificity of pre-eclampsia suggest that it might have an immune aetiology. The pathogenesis of pre-eclampsia is undefined although it is clear that it is a placental disorder. The maternal syndrome appears to be mediated by placental ischaemia secondary to spiral artery insufficiency. This leads to a hypothesis that pre-eclampsia is a two-stage disease. The first comprises processes that limit the size of the spiral arteries (poor placentation) or obstruct them (acute atherosis). Either or both may have immunological causes although there is no direct evidence. Factors limiting placentation could involve maternal immune intolerance of the fetal allograft, which in their most extreme expression could lead to immunologically mediated abortion. Thus pre-eclampsia may be part of a wider spectrum of pregnancy loss secondary to poor maternal immune accommodation of her genetically disparate fetus. The second stage involves the consequences of the ensuing placental ischaemia. The syndrome is currently tentatively ascribed to diffuse maternal endothelial dysfunction. There is less reason to invoke immunological mechanisms in the second stage although neutrophil activation could explain generalized endothelial damage. It should be clear that these conclusions are provisional and that the greatest need is for more investigation to eliminate the uncertainty which clouds our concepts.

Pre-eclampsia and trisomy 13: a possible association

Pregnancies of fourteen women who gave birth to babies with trisomy 13 were studied retrospectively for evidence of pre-eclampsia, with twenty-eight controls matched for age and parity. Of the five nulliparous women who subsequently gave birth to a baby with trisomy 13 all had had severe pre-eclampsia, compared with none of the control group. The records of eleven women whose first babies had had trisomy 18 (four) or trisomy 21 (seven) were also studied with appropriate controls and none of these pregnancies had been complicated by pre-eclampsia. Development of pre-eclampsia may be influenced by a gene or genes on fetal chromosome 13.

Genetic control of severe pre-eclampsia

A genetic analysis has been made of published and new data on the familial occurrence of severe pre-eclampsia in primigravid women. This has shown that the condition may be largely a Mendelian recessive one. Bcause the condition occurs only in pregnancy, and because susceptible women cannot otherwise be identified, it is difficult to decide whether the genotype of the parent or of the offspring carried in utero leads to the condition. Data on the incidence of severe pre-eclampsia in the relatives of women who have suffered eclampsia support the maternal genotype hypothesis, while similar data, in which the index cases were women who had had severe pre-eclampsia, are more compatible with the fetal genotype hypothesis. Data on the incidence of the condition in blood relatives of index cases compared to the incidence in their corresponding in-laws are now required. Such a comparison would allow a choice to be made between the two hypotheses if one or the other were correct, or would assess the contribution of each if a genotype X genotype interaction were involved. Recurrent severe pre-eclampsia seems to have the same genetic basis as the more common primigravid type. However, mild, that is non-proteinuric, pre-eclampsia usually seems to be inherited independently of the severe form.

Pre-eclampsia/eclampsia in twin pregnancies

A study of 1045 twin gestations with regard to known or likely zygosity and the incidence of pre-eclampsia/eclampsia failed to reveal differences between known dizygous twins and like-sex 'presumed' and 'estimated' monozygous twins except in the 'estimated' data for multigravidae. There was a threefold increase in the incidence for twins as opposed to singleton pregnancies. These results are discussed in relation to increased conceptus-mother antigenic differences. It is suggested that the risk of gestosis in twin pregnancy involves more than a summation of that operating in two singleton pregnancies.

Observation on the familial appearance of diseases associated with metabolic disorders of the mother

The familial appearnace of diseases in which a metabolic disorder of the mother causes foetal damage is examined and illustrated with typical pedigrees. The expected frequencies with which relatives of the probands are at risk are tabulated, and the effect of reduced maternal fertility is discussed. The familial appearance of disease is compared with that produced by maternal--foetal antigenic imcompatibility.

Case and kindred in mental deficiency

The analysis of family data in the hope of detecting a recognizable pattern in the distribution of disease may be of value in respect of cause and of prevention. The recognition of classical Mendelian ratios, for instance, is both a partial explanation and an opportunity for genetic counselling which may lead relatives to take eugenic measures. In mentally subnormal populations, however, the occurrence of disease in families often shows more complicated distributions. From knowledge of the relationship between cause and distribution models may be constructed with which empirical data may be compared, for instance, in maternal-foetal incompatibility in respect of some antigen, or in polygenically determined diseases showing threshold effects in liability to disease.

Genetics of obstetrical variables. A study from the collaborative perinatal project

Several obstetric variables were examined for genetic correlation in data from more than 8200 women (roughly 60 % black and 40 % white) linked into about 3200 family groups by birth or marriage and registered in the Collaborative Perinatal Project. Sister‐in‐law pairs yielded estimates of non‐genetic and spurious correlations which were generally absent or low. Pairs of sisters, mothers and daughters, half sisters, first cousins, and aunts and nieces were compared; such relatives were also compared in certain combinations of three. Familial correlation was present for age at menarche and durations of stages 1 and 3 of labor. None was found for gestation time of livebirths or for stage 2 of labor. A significant sister correlation for diagonal conjugate (size of pelvic inlet) was apparent in the white, but not the black, sample.

No families had two or more occurrences of the infrequent conditions: thrombosis, infertility diagnosis, incompetent cervix, leiomyoma, hyperemesis gravidarum, hydramnios, placenta praevia, or prolapsed cord. Familial correlation was significant for fetal death risk, but not for bleeding during pregnancy, abnormal presentation of the fetus, abruptio placentae, breast abnormalities and hypertension. Familial associations for anemia, postpartum hemorrhage, varicose veins and albuminuria were significant in the black data, but not in the smaller white sample. There was a positive, but non‐significant, association of toxemia in sisters.

Contribution of fetal/maternal incompatibility to aetiology of pre-eclamptic toxaemia

Data are presented on an association between toxaemia of pregnancy and consanguinity of patients, seen at a Turkish hospital, and their husbands. Women with toxaemia were less frequently related to their husbands than those with no signs of pre-eclampsia. The relationship between toxaemia in twin pregnancies and the sexes of the twin pairs from four sources are examined. In all four pre-eclampsia seems to be more common in unlike-sex than in like-sex twin pregnancies, and, by extension, to be more common in dizygous than in monozygous twin pregnancies.

Sex ratio of newborns: preponderance of males in toxemia of pregnancy

The ratio of males to females in 1061 babies born to mothers with toxemia of pregnancy is 1.24. The ratio increases as the severity of the disease increases, being 1.71 in cases in which the urinary output of protein is equal to or greater than 3 grams per 24 hours. Histoincompatibility of the fetus and mother, including incompatibility due to an antigen (or antigens) dependent on the Y chromosome, is suggested to function in the pathogenesis of pregnancy toxemia.

Mongolism in both of monozygotic twins

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