Neural Tube Defects – Week 2 of Embryogenesis

by John McLachlan, PhD

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    00:00 So, these are the defects that can arise; neural tube defects and these are actually quite common as abnormalities go. Perhaps, 0.3% of all pregnancies, three babies per thousand that may show an identifiable neural tube defect. How many babies are actually born alive with a neural tube defect? It depends upon local laws. It’s relatively easy to detect on ultrasound scans, you can see that a part of the neural tube that’s not closed properly.

    00:35 That then presents parents with a dilemma, as whether they wish to attempt the termination of the pregnancy or to allow the pregnancy to continue, as we’ll see, there are significant problems that can arise from a neural tube defect of that kind.

    00:52 Variety of different versions of it. It may be an open or a closed neural tube defect.

    00:57 And of course, it may be at different levels. So it may be at the head-end, more commonly, turned towards the lower back. If the defect is at the head end, this condition is called anencephaly.

    01:12 That means that the fore-brain has not closed properly. Therefore, much of the neural structures of the brain cannot develop.

    01:21 We will see that it’s largely the brain that drives the formation of the skull.

    01:26 That might be surprising. You tend to think of the skull as being very solid, very well-determined structure, and the brain is being something which is relatively soft and pliable.

    01:36 It’s actually the other way around. There’s the development of the brain that induces and drives the development of the skull. Therefore, if the fore-brain does not close properly, if there’s a neural tube defect, anencephalic defect at the head end and so what that means is that the bony plates of the skull will not form either and there’ll be a massive opening at the anterior end.

    02:03 And this will be a massive opening at the back of the baby's head as a result.

    02:08 As a result of this skull and brain failing to develop properly, then this condition will invariably be fatal after birth. It’s just not something that the baby can survive, but the baby will survive during its time in the uterus. As a result, what can sometimes happen is that if a baby is born with this condition, one possibility is that that baby might be used as an organ donor for other babies or adults who are lacking some important structure, kidneys, for instance, or heart. But there’s a very difficult ethical dilemma of allowing an anencephalic pregnancy to continue to full term because of course that in turn will pose some risks for the mother. A closed defect of the spine will still have the membranes covering the spinal cord intact, and therefore, the damage is less severe as a result.

    03:07 If it’s open, then there will be an interruption of the function of the spinal cord. That can mean in time that when the baby is born, there may well be severe nerve problems resulting from that. So, for instance, you could have paralysis and loss of function, and that loss of function is very likely to affect the bladder and bowels, and of course in the extreme, such a condition will lead to death. So again, it can be fatal.

    03:39 At the very minor end, you can have what’s called spina bifida occulta. That means that everything has happened fairly normally, but the vertebrae at the lower part of the spine have failed to fuse over. So there’s a kind of opening in the spine itself. A little bit of the spinal cord is perhaps a little more exposed than it would be normally. But essentially, you may not even be aware of that. One odd consequence is that in spina bifida occulta, you sometimes get a little patch of hair to the base of the spine. So that’s something that you can check for. But spina bifida occulta is not a defect. It’s merely a variation, and the chances are, that there will not be of any clinical significance during the course of your development if you have this condition. So the incidence of neural tube defects can be significantly reduced, perhaps, by up to 70% by giving folic acid beforehand.

    04:41 Folic acid is a vitamin that is found in some food, but it’s really hard to eat the amount of these particular kinds of foods, broccoli, for instance, to get the amount of folic acid that you would need. So it’s common to advice women who are thinking of becoming pregnant to supplement their diet with folic acid tablets beforehand. Even if you haven’t been taking it beforehand, there may be the benefit as soon as you realize that you’re pregnant and stepping up your folic acid. But absolutely, the best thing is to take it before you actually become pregnant.

    About the Lecture

    The lecture Neural Tube Defects – Week 2 of Embryogenesis by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Neural Tube Defects – Week 2 of Embryogenesis

     John McLachlan, PhD

    John McLachlan, PhD

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