So these varieties will have different effects
depending on the level of which they occur.
So there are also the types of defect as we’ve
just seen in the previous slide, and this
also will influence the outcome which arises
from these conditions. For instance, in severe
cases such as myelomeningocele, or even a
completely open rachischisis, then we may
observe paralysis or loss of function below
the level of the defect and this may include
bowel and bladder function, and of course
in the end, severe cases will lead to death.
So, what causes these neural tube defects?
Well, we know that in a large number, perhaps
60 percent of cases, there is a genetic component.
We know this partly because it seems to be
regionally distributed. So for instance, Scotland
and Ireland were sometimes referred to as
suffering from the Celtic curse because there
are high levels of these neural tube defects
present within them. Ethnic differences can
also be found in California where the Hispanic
population has a higher incidence than the
African American population overall.
Similarly, even within families, if one sibling
has been affected by a neural tube defect,
then other members of the family have a higher
chance of being affected, likewise.
We do know that there’s not a single gene that’s
responsible for this. In fact, there may be
hundreds of genes which are involved in various
ways, and at various times during the course
of development. There’s also an interaction with
genes and the environment so some environmental
factors can increase the incidence. One common
example is sodium valproate, a drug taken
to reduce the instance of epileptic attacks.
Since this is a drug that people may well
be taking over an extended period of time,
it poses a hazard if it was a female who’s
taking the drug and who is planning to become
pregnant during that time period.
However, there are ways of reducing the frequency
of neural tube defects of this kind, even in
populations where there’s a strong predisposition
towards it. One of the most effective ways
is folic acid, which is a B vitamin. Therefore,
we cannot synthesize it and we have to eat
it in our food. It’s present in some foods,
but frankly, it’s hard to eat enough broccoli
in order to get the levels of folic acid that
you need. Strawberries might be more straightforward.
So the guidance is that if women are planning
pregnancy, then they can be given a supplement,
400 micrograms of folic acid per day before
fertilization takes place. It will prevent
nearly 70 percent of neural tube defects from
occurring. This can be taken in the
form of tablets. Since many women do not know that
they were planning to become pregnant, pregnancy
comes as a surprise to them; another alternative
strategy would be to supplement basic food stuffs.
Flour would be a good example, so that the
whole population is exposed to higher
levels of this particular vitamin, folic acid,
in order to prevent this as a possibility.
And both strategies, both taking tablets and
supplementing food stuffs are successful in
reducing the incidence of neural tube defects.
So then, if we summarize what we looked at
in this lecture, we looked first of all at
the basics of formation of the neural tube
from very early stages. We looked at the early
stages of brain development, and we’ll return
to that in a later lecture. And we also looked
at neural tube defects. Thank you very much.