Download A Sickle-cell Crisis

Sickle-cell Anaemia
Sickle-cell anaemia (also known as sickle-cell disease) is a hereditary, noncontagious genetic disease in which the normally disk shaped red blood cells,
due to a mutation in the haemoglobin gene, mutate into an irregular or sicklelike shape. The mutated sickle shaped red blood cells can cause many
problems due to their reduced flexibility and smaller surface area which affects
their ability to carry oxygen.
A Sickle-cell Crisis
A ‘sickle-cell crisis’ is a term used to describe the complications the disease
causes. These include;
 A Vaso-occlusive crisis: During a Vaso-occlusive crisis the rigid sickle
shaped blood cells block the smallest blood vessels, known as capillaries,
causing acute pain and reducing oxygen and energy delivery to various
tissues.
 A Splenic sequestration crisis: During a Splenic sequestration crisis
the spleen or parts of the spleen die or become un-functional and can
cause infection. This is caused by the spleen over-working to clear blood
vessels blocked by sickle shaped cells.
 An Aplastic crisis: During an Aplastic crisis the individual becomes
infected with the Parvovirus B19 virus which virtually stops the
production of red blood cells for approximately 4-7 days. This would
cause no threat to someone not suffering from anaemia but for
someone suffering from anaemia this can cause serious problems as the
body’s tissues do not receive sufficient oxygen.
 Haemolytic crisis: During a Haemolytic crisis, although not caused by
sickle-cell disease, the body is unable to produce enough haemoglobin
and becomes starved of oxygen
Sickle-cell anaemia can cause many other complications. These include stroke
and brain damage, internal ulcers and miscarriages.
Sickle-cell anaemia and malaria
Sickle-cell anaemia is most common in Sub-Saharan Africa, where one in three
people carry the gene and account for three quarters of the world’s sicklecelled population, and other countries affected by malaria. This is because it is
thought that carrying even one of the two sickle-cell causing genes can reduce
the severity of the malaria infection and lower the individual’s likelihood of
dying from it. This means that there are more malaria survivors with the sickle
cell causing gene to pass onto their descendants.
Sickle-cell anaemia and hereditary
Sickle-cell anaemia is inherited in the autosomal recessive pattern (see Fig.1.1).
If one parent has sickle-cell anaemia (both sickle-cell causing genes) and one
parent has the sickle-cell trait (one of the sickle cell causing genes) there is a
50% chance that their decadences will have either sickle-cell anaemia or the
sickle-cell trait. When both parents have the sickle-cell trait there is a 25% of
each of their children having sickle-cell anaemia (see Fig.1.1). In Fig.1.1 blue
figures have neither sickle-cell anaemia nor the sickle cell trait, purple figures
have the sickle-cell trait and red figures have sickle-cell anaemia.
A picture showing healthy, disk
shaped red blood cells and sickle
shaped red blood cells.
Fig.1.1