As a
final wrap up to this Sickle Cell Series, I will explore what kind of
problems people with Sickle Cell Disease face.
In my first post, I described how genes are passed from parent to child
to demonstrate the probability of a child inheriting a good hemoglobin gene or
a bad hemoglobin gene. In the second post,
I clearly defined the difference between a good hemoglobin gene (which leads to a
healthy hemoglobin protein and healthy red blood cells) and a bad
hemoglobin gene that yields improperly behaving hemoglobin protein that
distorts the red blood cells to a long, sickled shape.
This
leaves us asking the question: What do sickled red blood cells do to the body?
If you
remember from the Sickle Cell Introduction post, I said each person has one of three
combinations of hemoglobin genes: two bad genes, two healthy genes, or one of
each. We know how patients with two
healthy genes are – happy and healthy!
What about the other two?
Two unhealthy hemoglobin
genes, the patient has Sickle Cell Disease:
Hemoglobin’s role is to carry
oxygen from the lungs to the far reaches of the body. Cells require oxygen for their health and
function (see
Carbon Monoxide post). Hemoglobin is
carried in cells called red blood cells.
Healthy red blood cells are circular and flexible. Blood (of which red blood cells are a key
component) travels through veins and arteries (also known as blood vessels) in
the body. In some places, these vessels
become very narrow. Healthy red blood
cells can squeeze through and continue moving along with relative ease. Unfortunately, sickled red blood cells are
sticky and have lost their flexibility.
These cells get stuck in narrow areas.
This difference is nicely illustrated in Figure
53.1, which comes from the National Heart Lung and Blood Institute
webpage covering Sickle Cell Disease.
What kind of problems does this lead
to?
Pain. Red blood cells are piling up and trying to
pass through areas of narrow vessels, which include the chest, abdomen and
joints. Doctors refer to these times as crises. The pain can last a few hours or a few
weeks. These crises can happen as often
as a dozen times a year and may require hospitalization. Small blood vessels are also present in the
eye so when sickled cells block them, patients may develop vision problems due
to retina damage.
Anemia. The sickled red
blood cells are weak. Healthy red blood
cells live for about 120 days, but the sickled ones only last 10 – 20 days. The
body is constantly short of red blood cells, which means it's short on
hemoglobin and cells are short on oxygen.
This is why Sickle Cells Disease is sometimes referred to as Sickle Cell
Anemia.
Spleen damage. The spleen is
important for healthy red blood cell function and the body’s ability to deal
with infection (quite frankly, just looking up what the spleen does makes me want to write
a post on it. I had no idea!). Sickled red blood cells can damage the spleen
which results in a patient having frequent infections.
Other problems. Delayed
growth, swollen hands and feet. Children
with sickle cell disease typically start to show symptoms around 4 months of
age.
In my research for this post, I
found a blog written by a girl suffering from sickle cell disease. Beginning in 2007, the blogger used this
platform to discuss her trials. As she
states in her first post “My illness does not define me ---I define my
illness. This is my story.” Reading unfiltered first-hand accounts, which
is one of the most useful and unique things about blogs, from someone suffering
with this disease is both poignant and fascinating. In 2010, she moved on to writing on the
Sickle Cell Warriors website. Check them
out!
On healthy and one
unhealthy hemoglobin gene, patient has Sickle Cell Trait
Since
sickled cells are less common in these patients, their symptoms are usually
mild and sometimes unnoticeable. Rare
complications do exist so don’t think that they don’t have any adverse effects,
but in general it is seen as a mild problem.
It should also be noted that at low oxygen pressures, cells tend to
sickle, especially when coupled with extreme exercise. This is why Ryan Clark was dissuaded from
playing football in Denver; the mile high city has lower air pressure and therefore
lower oxygen pressures.
What is
most interesting about sickle cell trait is its resistance to malaria
infection. Without getting into the
specifics of malaria infection (because it’s a bit complicated), just know that
malaria is caused by a parasite that infects the red blood cells. Scientists found that red blood cells from
sickle cell trait patients sickled in response to parasite infection. As described above, sickled red blood cells
live a much shorter time than healthy red blood cells. This means that infected, sickled cells will
be destroyed quickly by the body. Less red
blood cells with the parasite means less infection and it is more likely that
the patient will survive malaria.
Fascinating! This is why in incidence of malaria and sickle
cell disease tend to be found in the same regions. Such a detrimental defect in hemoglobin
should have been weeded out by natural selection a long time ago (in that those with
two unhealthy hemoglobin genes would die before they ever had children either
due to Sickle Cells Disease or malaria infection and the gene would not have
been passed on), however it persisted.
Those with just one unhealthy hemoglobin gene were more like to survive
malaria so the gene hung around in these populations.
Much
more exists on the malaria/sickle cell trait topic as well as everything else
discussed in this series. I tried to
give you as many resources as possible at the end of my posts. Don’t take my word for it or as the last word
on these subjects – there is so much more to learn!
REFERENCES
Symptoms of sickle
cell disease: http://www.nhlbi.nih.gov/health/health-topics/topics/sca/
Symptoms of sickle
cells disease: http://www.mayoclinic.com/health/sickle-cell-anemia/DS00324/DSECTION=symptoms
Sickle Cell Blog:
http://sicklecellblog.blogspot.com/2010_05_01_archive.html
Sickle Cell Warriors:
http://sicklecellwarriors.com/
Malaria and Sickle
Cell Trait: http://sickle.bwh.harvard.edu/malaria_sickle.html
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