When children are weak,
sometimes the problem is in the motor nerve.
In this lecture, we'll talk about specific
motor nerve disorders that could occur
Let's start with Spinal Muscular
Atrophy or SMA.
often a very debilitating condition.
it's autosomal recessive
in that it may travel in families.
and have unaffective carriers.
The defect is on the survival
motor neuron gene or the SMN gene
It results in a degeneration
of the anterior horn cells
of the spinal cord.
resulting in weakness.
There are three main types of SMA.
I, II and III.
SMA I is very severe.
It usually affects infants and is often
SMA II is more moderate
and SMA III is quite mild.
All of the SMAs, the problem is that small
muscles are not innervated.
The larger ones still have
So, in muscle biopsy it will show a patchy
Much like this.
Patients will present with a
progressive symmetrical proximal weakness.
Remember this is a lower
motor neuron disease.
So, they will be floppy
and may have absent deep tendon reflexes.
You may see muscle fasciculation
And it is often seen easily in the tongue.
But remember, it is just
the motor neurons.
These patients will have normal
So, let's review the three types.
Type one results in severe hypotonia
It generally presents before
six months of age
and death before the age of
two is common.
These children will often die
of respiratory complications.
In Type II disease, they may have the
ability to sit
but often will not have
the ability not walk.
This typically presents a little
around 6-18 months of age.
And it requires nutrition and respiratory
In Type III disease,
patients may lose the ability
to ambulate around 10 years of age.
It often presents after a year
an a half of age
and typically we will involve
Physical therapy and orthopedics
for braces or things like that
so to they can function as long
and as well as possible.
So, the diagnosis of SMA is made
by a genetic test of the SMA I gene.
We'll send it for sequencing and look for
Therapy is really only supportive.
There is no known cure for this condition.
And thoughtful palliative care is needed
especially for SMA I.
There are interventions we can make
who have no tone
but who have an end mortality that
is likely within the first few years of life.
Examples are G-tubes
or breathing machines or
The challeng is that
may cause a different way that that child
maybe spending their life uncomfortably.
This is a very challenging situation
for families who thought
they were having a normal child.
and palliative care
experts can be very very beneficial
in helping to guide therapy.