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Biomedical subjects

P M Sheppard

Publications and source records attributed to P M Sheppard.

16 recordsLinked to original sources
PubMed1975

Spina bifida and anencephaly: miscarriage as possible cause.

In two retrospective Liverpool surveys the domestic, family, dietary, and medical environments of the mothers of children affected by anencephaly or spina bifida, or both (ASB) were examined. None seemed to be of more than minor importance and the findings of others were therefore examined to see if they suggested a major factor. The most promising lead came from the hypothesis that ASB is usually due to an interaction between twin fetuses or between a fetus and residual trophoblastic material from the previous normal pregnancy, particularly when this is of the opposite sex to the propositus. The sex finding was not confirmed. It was noted that hydatidiform moles, like children with ASB, were usually female and that moles and choriocarcinomas on the one hand and children with ASB on the other occurred in mothers of similar ages, but were to some extent reciprocal in geographical incidence. This suggested that trophoblastic disease might be a factor common to all three and if so then one would expect the frequency of miscarriages to be higher immediately before than immediately after the birth of an ASB child, since mole and choriocarcinoma seldom follow a normal pregnancy. An analysis of published data confirmed that this was almost certainly so. Hence residual pathological trophoblastic material from either a previous miscarriage or a co-twin may interact unfavourably with another fetus to produce ASB and this may be the primary cause of the condition. The hypothesis is consistent with the observed lack of concordance in twins, the high incidence in females, the maternal age effect, and the greater prevalence in social classes IV and V.

Abortion, Spontaneous↗
PubMed1975

The genetics of the mimetic butterfly Hypolimnas bolina (L.).

Hypolimnas bolina is a Nymphalid butterfly having a west to east distribution from Madagascar to Easter Island, and a north to south one from Japan to Australasia. It is highly migratory in some areas. In much of the western part of its range the female is both monomorphic and a mimic of Euploea. Further east it is frequently polymorphic with the majority of the forms being non-mimetic. The polymorphism is sex-limited to the female and controlled by two unlinked loci, one with two allelomorphs, E and e, determining the extent of the dark pigmentation, the other with three allelomorphs, P, Pn and p, determining the presence and distribution of orange-brown. Only butterflies of the genotypes EEpp and to a lesser extent Eepp are satisfactory Batesian mimics of their Euploea models. The details of the mimetic pattern are under multifactorial control, following those of their local model, as is much of the variation within the non-mimetic forms, particularly with regard to the distribution of white and blue scaling.

Adaptation, Biological↗
PubMed1975

Mechanism of Rh prophylaxis: an experimental study on specificity of immunosuppression.

The mechanism by which Rh immunization is prevented by IgG anti-D was investigated by studying the specificity of immunosuppression. 62 D-negative Kell(K)-negative male volunteers were given two successive stimuli of 1 ml D-positive K-positive red cells. Thirty-one of the volunteers were also given 13-14 mug of IgG anti-K immediately after each stimulus, the others acting as controls. Anti-D developed in 11 of the 31 controls and in one of the 31 volunteers who had received anti-K. This marked suppression of the anti-D response by IgG anti-K was accompanied by the rapid clearance of the injected red cells to the spleen. This shows that the predominant mechanism that must be operating when IgG anti-D prevents Rh immunization is not antigen specific but is one that must involve the whole red cell, probably through destruction within splenic macrophages.

Antibody Formation↗
PubMed1975

Absence of crossing-over in female butterflies (Heliconius).

Absence of recombination between linked markers in female Heliconius is suggested by coupling backcross broods in H. erato, by a repulsion F2 in H. melpomene, and by other crosses with this species. No recombinants have been found in the offspring of doubly heterozygous females in either species. This supports the contention that the absence of chiasmata at oogenesis in these bufferflies prevents genetic crossing-over. Chiasmata are absent in all the female Lepidoptera examined by Suomalainen and others, but Ephestia seems to show the absence of chiasmata but the presence of genetic recombination in the female, and therefore would repay further study.

Animals↗
PubMed1973

Spina bifida and potatoes.

The results of a retrospective survey of the dietetic and other habits of the mothers of 83 children with spina bifida (mostly schoolchildren with meningomyelocele) were compared with 85 carefully matched controls. The survey was particularly concerned with the consumption of or contact with potatoes by the mothers. No significant differences were found in the amount of potatoes eaten as reported by the mothers (mean for spina bifida group 3.60 1b (1630 g), and for controls 3.98 1b (1800 g) per week). Of the seven other comparisons associated with potatoes only one (obtaining them from the chip shop or restaurant) was significant, the mothers of the children with spina bifida being more likely to obtain some of them from this source.When examining other aspects of diet it was found that the mothers of spina bifida children reported a lower consumption of a number of important foods, though the deficiency was not significant in any instance. These mothers were also significantly more likely to have been prescribed drugs other than iron and vitamins early in pregnancy and to have reported a wider variety of illnesses.The results in general do not support the hypothesis that the quantity of potatoes taken is important. They do lend support to the view that poor dietary habits are associated with a higher incidence of spina bifida irrespective of social class. Furthermore, general ill health in the mother may be implicated.

Antidepressive Agents↗
PubMed1970

The magnitude of seasonal changes in larval populations of Aedes aegypti in Bangkok, Thailand.

Weekly surveys of Aedes aegypti larvae were made during 1966-67 in three localities in Bangkok in order to detect and measure any changes in the population which might be correlated with the seasons. The larval habitats were divided into water-jars and miscellaneous containers. Only the data from alternate weekly surveys were analysed. Analysis of variance showed that the changes in the numbers of habitats occupied varied greatly both by month and by locality. It is concluded that there was some reduction in the larval population during the cool and hot seasons and that the magnitude and timing of the fall varied from place to place. The reduction was of the order of 11%-26%. Local environmental changes, as well as climatic changes, greatly influenced the Ae. aegypti population.

Aedes↗
PubMed1969

Replicate surveys of larval habitats of Aedes aegypti in relation to Dengue haemorrhagic fever in Bangkok, Thailand.

Dengue haemorrhagic fever in Bangkok and Thonburi occurs principally during the wet season. The mosquito vector is Aedes aegypti. A study was made of the larval habitats of A. aegypti in 14 localities, at three different times of the year, to determine whether there were fluctuations in the A. aegypti population, as measured by the number of occupied habitats, which could be correlated with the incidence of the infection.The habitats were classified into 6 categories and a single larva was collected for identification from each one that was occupied. The number and percentage of occupied habitats of each category per 100 houses were analysed to determine whether there were differences between localities and between times of the year. Almost all the comparisons between localities were highly significant. There was evidence of slight changes in the number of occupied habitats from time to time, the chief increase being between the cool and the warm seasons and the chief decrease from the wet to the cool season, but it seems unlikely that outbreaks of dengue haemorrhagic fever can be explained by increases in A. aegypti densities during the wet season.

Aedes↗