ens and hardens the normally flexible erythro-
cytes, pulling them into a sickle or crescent shape.
The rigidity and inflexibility prevents the ery-
throcytes from folding and twisting as they pass
through the small blood vessels, causing them to
create blockages. The blockages cause swelling,
pain, and eventually damage to organs and struc-
tures throughout the body. People who have
sickle cell disease have very high risk for STROKE,
HEART ATTACK, acute chest syndrome (blockages in
the lungs that cause INFECTION), and loss of vision.
The changes also make the erythrocytes more
fragile, and they easily break apart as the flow of
blood jostles them around. Sickled erythrocytes
die after only about 20 days in the blood circula-
tion, whereas normal erythrocytes live for 90 to
120 days. The shortened lifespan further limits the
ability of the blood to transport oxygen, establish-
ing chronic anemia.
ADAPTIVE DEFECT
Researchers believe the gene mutation that
causes sickle cell disease originated in the form
of sickle cell trait as an adaptation to protect
against malaria infection. The sickled erythro-
cytes resist the parasite that causes MALARIA. In
sickle cell trait, the person has some hemoglobin
S and mostly normal hemoglobin—an ideal
blend for simultaneously maintaining health and
thwarting malaria. The adaptation backfires only
when two people with sickle cell trait conceive a
child, at which time the recessive autosomal
inheritance pattern of the mutated hemoglobin
gene becomes a risk for passing on too much of
a good thing to the child.The inheritance pattern for sickle cell disease is
autosomal recessive, which means both parents
must pass the defective hemoglobin gene to their
child. People who are carriers of the mutated
hemoglobin gene have sickle cell trait, with one
mutated and one normal hemoglobin gene. They
have small amounts of hemoglobin S though
mostly have normal hemoglobin and have no
indications of sickle cell disease. However, their
children may end up with sickle cell disease if
they inherit the sickle cell mutation from each
parent. When both parents have sickle cell trait,
there is a 1 in 4 chance for the child to have sickle
cell disease, a 2 in 4 chance the child will also be a
carrier, and a 1 in 4 chance the child will inherit
two normal genes.
Symptoms and Diagnostic Path
Symptoms generally begin to emerge when a child
is about a year old. For the first year of life the
child has an abundant supply of fetal hemoglobin,
which has the ability to prevent polymerization of
hemoglobin S. However, the child’s own hemoglo-
bin gradually replaces the fetal hemoglobin and
this protection disappears, typically between age 6
months and 10 months. Early symptoms of sickle
cell disease in a child are swollen hands and feet
(sometimes called hand and foot syndrome), a
consequence of damaged erythrocytes blocking
the small blood vessels in the hands and feet to
prevent blood from circulating out. Other symp-
toms include- pain from blockages
- FEVER
- fatigue from anemia
- diminished vision from damage to the RETINA
People who have sickle cell disease may also
have- frequent infections resulting from damage to
the SPLEENand LY M P Htissues - jaundice, yellow discoloration of the skin
resulting from excessive bilirubin in the blood
circulation as the components of the dead ery-
throcytes accumulate in the LIVER - delayed growth due to severe anemia
A blood test can detect the presence of hemo-
globin S, which affirms the diagnosis. In the
United States, hospitals routinely run this test on
all newborns. Examination of the erythrocytes
under the microscope also shows the characteristic
sickle shape.
Treatment Options and Outlook
Treatment for sickle cell disease may include ANAL-
GESIC MEDICATIONSfor pain relief, blood transfusions
to replace the damaged erythrocytes with healthy
erythrocytes (which is effective for the life cycle of
the transfused erythrocytes), and the medication
hydroxurea (which can reestablish fetal hemoglo-166 The Blood and Lymph