00:01
So let's think a little bit more
about these dystrophinopathies.
00:04
And we're going to start with the
x-linked dystrophinopathies.
00:08
And then we'll move
to other inherited causes
of muscular dystrophy,
particularly
limb-girdle muscular dystrophy.
00:14
There are two x-linked
inherited muscular dystrophies
and they are Becker's and
Duchenne's muscular dystrophy.
00:21
We see these in young boys,
who present with proximal weakness,
and a prominently elevated CK.
00:28
And those three findings
should really point us
in the direction of thinking of
Duchenne's and Becker's
muscular dystrophy.
00:35
What's the distribution?
We can see here in this schematic
that this is a proximal predominant
muscular dystrophy.
00:41
So, patients present
with
prominent leg
and arm proximal weakness,
difficulty with
walking and running,
and walking upstairs
or running upstairs,
getting up out of a chair,
reaching up to
high counters or cabinets,
or those sorts of things
to pull themselves up.
00:57
And in the severe cases,
we can see Gowers's sign,
where patients use their arms
to walk themselves up
from a seated position
because of prominent proximal
lower extremity weakness.
01:09
This distribution is
really key to understand
and to evaluate on exam.
01:16
What about the etiology?
Let's start with
Duchenne's Muscular Dystrophy
and think a little bit more
about the typical features there.
01:22
This is an
X-linked recessive disorder
that results from nonexistent
or absent dystrophin.
01:29
And we'll think a little bit more
about dystrophin
the pathophysiology of
Duchenne's Muscular Dystrophy
and the subsequent slide.
01:36
This affects boys.
01:37
It is an
X-linked muscular dystrophy,
and though moms and women
can be slightly affected,
prominent presentations
are in young boys.
01:48
So one of the typical manifestations
of Duchenne's Muscular Dystrophy,
we typically see weakness
that begins,
usually in the ages of
two to three years
is when the symptoms begin.
01:59
Patients present with
early proximal muscle weakness,
difficulty with jumping,
and running, and walking,
and getting up out of chairs.
02:07
And then calf pseudohypertrophy.
02:10
And this results from replacement
of muscle with fibrosis,
that increases the
total volume of the muscle.
02:16
Even though the muscles are weak
because of loss of muscle function.
02:20
the calf are hypertrophied.
And this is a prominent finding.
02:23
It's something
that's easily seen on exam
to the astute eye,
and points us in the direction
of Duchenne's or Becker's
muscular dystrophy.
02:31
What about the workup?
What do we do to evaluate
these young boys
that present with
proximal muscle weakness,
and calf pseudohypertrophy?
Well, the most important
test is the CK.
02:41
And whenever we're evaluating
any muscle disorder,
we know that a CK
is an important test
and points us towards
inflammation in the muscle.
02:49
And the CK is prominently elevated
more than 10,000 times
the upper limit of normal
in most patients with
Duchenne's muscular dystrophy.
02:58
Genetic testing is the next step.
And this confirms the diagnosis.
03:01
This is a genetic or inherited cause
of muscle weakness
and muscular dystrophy.
03:07
What about the typical course?
We use prednisone
to treat these patients.
03:11
The inflammation
in and around the muscle
is the earliest,
earliest finding
and is treated with prednisone
or anti inflammatory.
03:19
That early inflammation leads
to subsequent degeneration
and necrosis of the muscle.
03:24
And so in late stages,
prednisone is not helpful.
03:26
And this is a treatment
that we really begin
early in the course of therapy
to prevent
prominent respiratory weakness,
early in the course of the disease.
03:36
Patients do ultimately die
of this disease frequently,
and that's often from
respiratory muscle weakness,
and typically pneumonia.
03:43
What's the prognosis?
Men have a shortened lifespan.
03:47
They often live into
the third or fourth decades of life.
03:51
And there are new treatments
that are being explored.
03:53
And we'll discuss those
in some of the next slide.
03:55
I think importantly,
sometimes
we diagnose a young boy
with this condition
and find that mom also has symptoms
that have gone unrecognized.
04:03
And this may present
with mild weakness
or cardiac conduction
abnormalities,
that can be a tip off to this
inherited predisposition.
04:13
So what are some of the treatments?
What are some of
the other treatments
that we would consider
for Duchenne's Muscular Dystrophy?
Well, there's really three
that I want you to know.
04:20
The first is prednisone.
This is a tried and true treatment.
04:24
This is something that
we've been utilizing for decades
for these patients.
04:27
And it's best when initiated early.
04:29
It's been used the longest.
04:31
It reduces muscle inflammation,
which is seen early in the condition
and results in that elevation of CK.
04:38
And it's effective early.
04:39
And so it's really a treatment
that we begin early
when evaluating and
diagnosing these patients.
04:44
The second and a
more recent treatment
to come onto the market
is deflazacort.
04:49
It is a similar medication and
acts very similar to prednisone.
04:53
It's a glucocorticoid and so it
has a similar mechanism of action.
04:57
Its potency is around
70% to 80% that of prednisone.
05:01
But it costs a lot of money
around 80,000 per year.
05:05
And so in clinical practice,
we often see prednisone
being favored over deflazacort,
except in those patients
who may not respond to prednisone.
05:13
And then the last treatment
that I'd like for you to know,
and perhaps the most interesting
these days is Exondys 51.
05:21
This acts very differently to
prednisone and deflazacort.
05:24
It is an antisense oligonucleotide,
and it really works
as an exon skipping agent,
which we'll talk about
in the next slide.
05:33
It works as a bridging piece
of DNA or RNA
so that the dystrophin protein
can be made.
05:41
It only works for specific
Duchenne's Muscular
Dystrophy mutations,
and we'll talk about some of those.
05:48
And the thing to remember
with this medication is
it is an exon skipping therapy,
really unique mechanism of action.
05:55
So how does it work?
What's happening with Exondys 51?
Well, here we see
what happens in the
healthy adult or healthy child.
06:04
Duchenne's muscular dystrophy,
pre-mRNA
is composed of a number of exons,
and that's exon
48 to 49, 50, 51, 52.
06:14
In order to make a normal
healthy dystrophin protein,
those exons are spliced
into a messenger RNA,
and you can see
the messenger RNA here
contains exon 48, 49, 50, 51 52.
That's really important.
06:29
And ultimately,
that messenger RNA is translated
into the
functioning dystrophin protein.
06:34
And that's what happens
in the healthy individual.
06:38
In Duchenne's muscular dystrophy,
we see that a mutation
results in an early stop code on
and there is incomplete
transcription and translation
of that dystrophin protein.
06:50
So we see a fewer number of exon's.
06:52
Here exon 48 to 51, and 52
as a result of mutation
in exon 49, or 50.
06:59
Results in a truncated or early
premature stopped messenger RNA,
and a lack of
any dystrophin protein.
07:08
So what does Exondys 51 do?
This is a antisense oligonucleotide
that skips the coding of exon 51.
07:17
So instead of transcribing exon 51,
we skip that and we see we
are resulted with a messenger RNA
containing exon 48 and 52.
07:27
And this is sufficient
to generate a shortened
but functional dystrophin protein.
07:32
Doesn't have all of the normal
functions of dystrophin,
but substantially improves
the situation within
the muscle and symptoms
in these Duchenne's Muscular
Dystrophy patients.
07:43
and exon skipping therapy.