Now, before we move on, I’m going to cover some of the X-linked recessive disorders that you should
understand for your exams. We don’t need to know all of them by a long shot. You don’t need to know
all of the details of each of these. But you should definitely be familiar with the idea that these are
X-linked recessive disorders and be able to recognize them as such. First of all, we’ve already covered
Duchenne muscular dystrophy. Then we have Lesch-Nyhan syndrome which is most commonly known
as juvenile gout. We have overabundance of uric acid in the tissues. Usually, this happens
in older individuals but this will show up in early childhood. Now HGPRT, I’m not even going to say it.
That’s one of those tongue twister chemicals. You don’t need to be able to say the whole word.
But HGPRT deficiency, basically we’re missing an enzyme that helps in the clearance of uric acid.
Another condition is metabolic disorder of glucose-6-phosphate dehydrogenase. You may recall
glucose-6-phosphate, probably one of those that you should recall. Where does that come up?
Well as we know, it comes up in glucose metabolism. In this disorder, it’s affecting red blood cells primarily.
So, red blood cells will lyse or break up early. So, we see essentially the effects of anemia because of
glucose-6-phosphate dehydrogenase deficiency. Now, we also know hemophilia A and hemophilia B.
We’re familiar with color blindness. Red-green color blindness is an X-linked trait. Another one to consider
is Menkes disease. Menkes disease is a copper malabsorption disease so that copper cannot be
transported into cells where it’s particularly necessary. Some of those are the brain cells.
Of course, that has a large effect. It’s a neurodegenerative disease. It also has some phenotypic
manifestations in very interesting hair texture and color. It has also been known as steely hair disease,
so Menkes disease, steely hair disease. It’s had a lot of different names but that’s the one
that I’ll use to remember it by. Another thing is ornithine transcarbamylase deficiency,
transcarb amino amylase, meaning we’re having a build-up of ammonia because proteins
aren’t being digested properly. That results in toxicity, again affecting the nervous system.
Then finally, a big one to keep in mind is X-SCID which is severe combined immunodeficiency that’s X-linked.
This has to do with problems with T cells and natural killer cells. Without those, the B cells don’t function
properly so it’s a disorder of immunoglobulins. That’s one to keep in mind. Again, it’s not so important
for you to know all of the details of these. I give you some characteristics so that you have some way
to remember them. What I recommend right now is that you pause the video and write down
as many of these as you can remember because truthfully, it sort of comes down to some memorization.
For me, I don’t know about you, memorization is the hardest part. Take a moment, pause, write them down.
Then we’ll move on.