Duchenne Muscular Dystrophy, or DMD for short,
is one of the most common genetic conditions worldwide,
affecting approximately 1 in every 3500 male births.
Let's start by breaking down the name.
Duchenne was the name of the neurologist
who first described the disease in the 1860s.
Muscular tells us that it's a disease
affecting the muscles and Dystrophy essentially means degeneration.
So we can conclude that DMD is a genetic
disease in which your muscles are gradually degenerating.
DMD is, in fact, characterized by weakness
and wasting of the muscles of the pelvis, shoulders, trunk, arms and more.
The disease is progressive in nature,
meaning it gets more extensive throughout one's lifetime.
Most affected individuals require a wheelchair by their teenage years
and the average life expectancy is approximately 30 years.
So that's just a little bit about DMD.
But what we're really interested in today
is what's actually going on on a genetic level.
What causes DMD?
How is it screened and diagnosed?
What therapies exist?
These are the three main questions you'll be able to answer by the end of the video.
Let's backtrack a little.
We told you DMD is a genetic disease,
but let's figure out what that actually means.
Zooming into our bodies,
we see that we are made up of cells and within these cells is our DNA.
Our DNA has these sections called genes,
which can be thought of as a series of letters that are read by the cell
and used to create proteins that form our unique features.
Quite frequently,
there's a change to the gene which could mean that letters are cut out,
additional letters are put in, or letters are exchanged with other letters.
And this is what we call a mutation.
In most cases, this does not actually
affect how the cell reads the gene and the protein is made as planned.
However, genetic disorders happen when a change to a gene prevents the cell
from reading the gene properly and as a result, the cell produces
a nonfunctioning protein, leading to a problem.
Let's now take a look at what this specifically looks like in DMD.
DMD arises when some letters of the DMD
gene, which, fun fact, is the largest known human gene, are removed.
The cell reads a normal DMD gene as
a signal to produce dystrophin, a protein that is essential for our muscles.
Dystrophin essentially strengthens muscle
fibers and protects them from injury as the muscle contracts.
However, when the DMD gene is missing some
letters, the cell cannot produce dystrophin properly,
and without this protein, muscles get weak and injured and can no longer perform.
You may be surprised to know that DMD
mostly affects males and almost never affects females.
But why?
Well, the DMD gene is found on the X
chromosome and a chromosome is just a molecule of DNA.
As you may know, females have two copies
of the X chromosome, while males have one X chromosome and one Y chromosome.
For this reason, if a female had the mutated DMD gene on only one X chromosome,
the other one would still be able to be
read properly by the cell to produce dystrophin as normal.
This would explain why females do not seem to be as frequently affected. For males
since they only carry one copy of the DMD gene on their one X chromosome,
if this gene is altered, then dystrophin cannot be produced
and they are going to face the consequences of DMD.
So that was a very simple explanation of what we call X-linked genetic disorders.
And if you want to learn more about these genetic diseases, then you can check out
the link that we've provided in the description.
So now that we know a little more about
what DMD looks like, how can it then be diagnosed?
We'll only look at two examples today, but just know that there are many more
that can be used and are used to diagnose DMD.
First is genetic screening.
In this test, cells are first taken from the patient.
So for example, some cells can be scraped off from the inside of one's cheek.
The DNA can then be separated
from the rest of the cellular material and then be read using very fancy
machinery to check for mutations in the DMD gene.
We should realize however,
that not every mutation in this gene will lead to DMD and that DMD only arises if
a very specific part of the gene is cut out.
We can also look at the actual muscle through a muscle biopsy.
This involves removing a small piece of muscle through a cut in the skin using
a very hollow needle and the muscle is then examined in the lab to check
for the amount of dystrophin protein that is present. In DMD,
this protein is absent, which makes it then possible to diagnose the patient.
Finally, what therapies exist to treat DMD?
Most genetic diseases do not have a cure
because they result from gene changes that are present in the DNA that is
in almost all cells of the body, making it very difficult to target.
In most cases, the gold standard of care
is really just managing the symptoms and slowing the progression of the disease.
DMD is no different.
There currently exists no cure
and the standard of care is prescribing corticosteroids,
a drug that aims to reduce inflammation and therefore the symptoms of the disease.
However, many new therapies are up and coming for genetic diseases and DMD
in specific. One popular one currently being vector-mediated gene therapy.
At the end of 2020, Health Canada actually
approved the first targeted gene therapy treatment for DMD.
Let's take a closer look at what this actually is and what this means.
Vector-mediated gene therapy is when
a virus is modified to carry normal good dystrophin genes.
The way this works is that the modified
virus is injected into the body and then when the virus tries to infect the cell,
it actually releases a smaller dystrophin gene into the cell.
The cell can then make functional dystrophin protein out of this,
instead of the nonfunctional protein that the mutation caused.
There are still many clinical trials ongoing to test this therapy in DMD
patients, most of which are actually still in the beginning phases of testing human
safety rather than the actual effectiveness of the therapy.
For example, one study in the United States is
currently injecting DMD patients aged 4 to 12 with this therapy to measure
safety, dystrophin production, muscle strength, and muscle quality.
And with that, we've reached the end of this video.
Today we learned about DMD (Duchenne Muscular Dystrophy).
We talked about what causes DMD,
how it is screened and diagnosed, and finally a therapy known as gene therapy.
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