Now we will cover sickle cell anemia.
Sickle cell anemia is an inherited form of anemia which is a
condition in which the aren't enough healthy red blood cells
to carry the oxygen throughout the body.
Normally your red blood cells are flexible and
round and they move easily through the blood vessels.
In sickle cell anemia, the red blood
cells become malformed, sticky and rigid
and they're shaped like
crescent moons or sickles.
These irregularly shaped cells can get stuck in the blood
vessels and this is going to cause the blood flow to slow
and decreased oxygen
delivery to parts of the body.
There is no cure for most
patients with sickle cell anemia
but treatments can relieve pain and help
prevent problems associated with the disease.
Sickle cell anemia is also known as sickle
cell disease, hemoglobin S, SS disease
or sickling disorder due to hemoglobin S.
Sickle cell anemia is an autosomal recessive
disorder due to a genetic homozygous defect
that is caused by the presence of
hemoglobin S instead of hemoglobin A.
Hemoglobin A is the normal type of hemoglobin.
Because it's recessive, both the mother and the
father must pass on this defective form of the gene
for the child to be affected.
If only one parent passes on
the sickle cell gene to their child,
that child will have sickle cell
trait and this is a carrier state.
These patients do not have sickle cell disease.
A carrier has only one defective hemoglobin
gene and they also have one normal hemoglobin gene
so they're gonna make
both normal and sickled cells.
These patients are usually asymptomatic but they
can pass this defective gene on to their children.
In this pedigree chart, both parents are carriers
because they each have one defective hemoglobin gene.
They do not have the disease because
remember that requires two defective genes.
You can see the probability that each of their offspring
will have sickle cell anemia which is the disease,
be a carrier which is sickle
cell trait, or be unaffected.
Now it's possible that this family
will have children with the disease,
children as carriers, or children who are
unaffected, maybe they'll have a mixture of all three
because the probability and the
risk resets with each pregnancy.
There's a 25% chance that their child will have sickle
cell disease because they would inherit both diseased genes.
There's a 50% chance that their
children will have the sickle cell carrier gene
or have the trait by inheriting
only one diseased gene.
And there's a 25% chance that their children
will have normal hemoglobin and be unaffected.
In the United States, most people have
sickle cell disease are of African ancestry
but the condition is also common in
people from Mediterranean countries
as well as patients from India,
Saudi Arabia and Hispanic countries.
Because the disease runs in families, couples
planning to have children can have genetic testing.
Sickle cell anemia is caused by mutation in the gene
that tells your body to make the red iron-rich compound
that gives blood its color,
this is the hemoglobin.
Hemoglobin allows red blood cells to carry
oxygen from your lungs to all parts of your body.
In sickle cell anemia, the abnormal hemoglobin causes the
red blood cells to become rigid, sticky and misshapen.
Sickle cells in the circulation increase the
viscosity of blood, the blood becomes thicker.
this is gonna slow the circulation thereby
increasing the time of exposure to a hypoxic injury
particularly in the small
vasculature of the spleen.
This repeated sickling of the red blood
cells ultimately damages the membrane.
These cells cannot squeeze freely through the capillaries
and they can block the blood vessel in the microvascular tree.
There are two major features of sickle
cell anemia, the first is chronic hemolysis.
The sickled cells cannot change shaped easily
so they tend to become damaged or burst apart.
A normal healthy red blood cell lives about 120 days
but a sickled cell survives for only 10 to 20 days.
The body is not able to reproduce
new red blood cells fast enough
to keep up with this rapid
destruction of the sickled cells.
This results in a chronic hemolysis and anemia.
The second is the acute episodic vaso-occlusive
crisis that can result in organ failure
and this is when the sickled-shaped cells
stick to the vessel wall and create a blockage
that's gonna slow or stop the blood flow.
When the blood supply is blocked, the
oxygen can't reach the nearby tissues
and this lack of oxygen causes a crisis
which is an acute sudden severe pain.
There are two components to the
pathology associated with sickle cell anemia.
First the person has to have the genetic
mutation to make the abnormal hemoglobin
and then that hemoglobin
needs to be triggered.
Once it's triggered, the abnormal proteins transform within
the red blood cells and they're gonna alter the shape.