Causes of Developmental Abnormalities – Weeks 3-8 of Embryogenesis

by John McLachlan, PhD

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    00:01 People have interpreted these in complex and emotive ways in the past. The Romans regarded them as warnings from the Gods. They had effectively, I made this name up I admit, a bureau of two-headed calves. If the number of animals born with abnormalities increased, they interpreted that as a sign of the wrath of the Gods and could actually take political action as a consequence of what they feared was going on.

    00:31 At the same time, continuing too much later, there was the idea that a developmental abnormality was a consequence of some wrongdoing on the part of the parents, of the mother, or indeed, the father that it was a consequence of sin or immorality. Then more recently still, many people may still believe that there are, what I’ve called, proximate emotional causes.

    00:56 So the idea that if you are frightened by a spider, that you might have a spider-shaped birthmark, or in the classic story of the elephant man, it was suggested that his mother had been frightened by an elephant during the course of pregnancy. And somehow, by sympathetic magic that would lead to a defect. So, eating strawberries might give that kind of skin mark called a strawberry nevus. All of these, of course, are completely untrue.

    01:26 In fact, I find animal analogies quite unhelpful in talking about developmental events. So there’s still a tendency to draw parallels between human developmental defects and other forms of animals, and this is irrelevant. There’s no connection between them, whatsoever.

    01:47 So in looking at the causes, we know very little, but what do we know? About 10% of an identifiable major chromosomal defect and about 8% have a single gene cause that we’ve already identified. Environmental factors, which often attract the most attention in people’s minds, we only know of about 7% of cases directly caused by an environmental factor. About 25%, we know to be an interaction. So, it’s between the genes and something in the environment. And the whole 50%, we’re still largely guessing at what’s going on.

    02:26 One thing we do know is that there seems to be an association with poverty, that societies, where people are living in social deprivation, have higher numbers of developmental defects and as a result, we can conclude that there may be in part a political solution to some of these kinds of issues. Very powerful techniques have a reason to identify genes which might be involved, and as our understanding of the genetic control of development increases, so in turn, we begin to understand better what some of the factors influencing developmental abnormalities might be as well. So, human genome project was a huge step forward to identifying all of the genes that are involved in possible developmental abnormalities.

    About the Lecture

    The lecture Causes of Developmental Abnormalities – Weeks 3-8 of Embryogenesis by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Causes of Developmental Abnormalities – Weeks 3-8 of Embryogenesis

     John McLachlan, PhD

    John McLachlan, PhD

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