Hemophilia Essay, Research Paper
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In the human body, each cell contains 23 pairs of chromosomes,
one of each pair inherited through the egg from the mother, and the
other inherited through the sperm of the father. Of these
chromosomes, those that determine sex are X and Y. Females have XX
and males have XY. In addition to the information on sex, ‘the X
chromosomes carry determinants for a number of other features of
the body including the levels of factor VIII and factor IX.’1 If
the genetic information determining the factor VIII and IX level is
defective, haemophilia results. When this happens, the protein
factors needed for normal blood clotting are effected. In males,
the single X chromosome that is effected cannot compensate for the
lack, and hence will show the defect. In females, however, only one
of the two chromosomes will be abnormal. (unless she is unlucky
enough to inherit haemophilia from both sides of the family, which
is rare.)2 The other chromosome is likely to be normal and she can
therefore compensate for this defect.
There are two types of haemophilia, haemophilia A and B.
Haemophilia A is a hereditary disorder in which bleeding is due to
deficiency of the coagulation factor VIII (VIII:C)3. In most of the
cases, this coagulant protein is reduced but in a rare amount of
cases, this protein is present by immunoassay but defective.4
Haemophilia A is the most common severe bleeding disorder and
approximately 1 in 10,000 males is effected. The most common types
of bleeding are into the joints and muscles. Haemophilia is severe
if the factor VIII:C levels are less that 1 %, they are moderate if
the levels are 1-5% and they are mild if they levels become 5+%.5
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Those with mild haemophilia bleed only in response to major trauma
or surgery. As for the patients with severe haemophilia, they can
bleed in response to relatively mild trauma and will bleed
spontaneously.
In haemophiliacs, the levels of the factor VIII:C are reduced.
If the plasma from a haemophiliac person mixes with that of a
normal person, the Partial thromboplastin time (PTT) should become
normal. Failure of the PTT to become normal is automatically
diagnostic of the presence of a factor VIII inhibitor. The standard
treatment of the haemophiliacs is primarily the infusion of factor
VIII concentrates, now heat-treated to reduce the chances of
transmission of AIDS.6 In the case of minor bleeding, the factor
VIII:C levels should only be raised to 25% with one infusion. For
moderate bleeding, ‘it is adequate to raise the level initially to
50% and maintain the level at greater that 25% with repeated
infusion for 2-3 days. When major surgery is to be performed, one
raises the factor VIII:C level to 100% and then maintains the
factor level at greater than 50% continuously for 10-14 days.’7
Haemophilia B, the other type of haemophilia, is a result of
the deficiency of the coagulation factor IX – also known as
Christmas disease. This sex-linked disease is caused by the reduced
amount of the factor IX. Unlike haemophilia A, the percentage of
it’s occupance due to an abnormally functioning molecule is larger.
The factor IX deficiency is 1/7 as common as factor VIII deficiency
and it is managed with factor VIII concentrates. Unlike factor VIII
concentrates which have a half-life of 12 hours, the half-life of
factor IX concentrates is 18 hours. In addition, factor IX
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concentrates contain a number of other proteins, including
activated coagulating factors that contribute to a risk of
thrombosis. Therefore, more care is needed in haemophilia B to
decide on how much concentration should be used.
The prognosis of the haemophiliac patients has been
transformed by the availability of factor VIII and factor IX
replacement. The limiting factors that result include disability
from recurrent joint bleeding and viral infections such as
hepatitis B from recurrent transfusion.8
Since most haemophiliacs are male and only their mother can
pass to them the deficient gene, a very important issue for the
families of haemophiliacs now is identifying which females are
carriers. One way to determine this is to estimate the amount of
factor VIII and IX present in the woman. However, while a low level
confirms the carrier status, a normal level does not exclude it. In
addition, the factor VIII and IX blood levels are known to
fluctuate in people and will increase with stress and pregnancy. As
a result, only a prediction of the carrier status can be given with
this method.
Another method to determine the carrier status in a woman is
to look directly at the DNA from a small blood sample of several
members of the family including the haemophiliacs. In Canada,
modern operations include Chorionic Villous Sampling (CVS) and it
helps analyze the DNA for markers of haemophilia at 9-11 weeks of
pregnancy. (Fig. 1)9 A small probe is inserted through the neck of
the mother womb or through the abdomen under local anaesthetics. A
tiny sample from the placenta is removed and sent for DNA analysis.
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Since this process can be done at 9-11 weeks after pregnancy, the
pregnancy is in it’s relatively early stages and a decision by the
mother (and father) to terminate the pregnancy will not be as
physically or emotionally demanding on the mother than if she had
it performed in the late stages of the pregnancy.
Going back to the haemophiliacs, many have become seropositive
for HIV infections transmitted through factor VIII and IX
concentrates and many have developed AIDS. In Canada, the two drugs
currently undergoing clinical testing for treatment of HIV disease
are AZT and DDI. For the use of AZT, the major complication is
suppression of normal bone marrow activity. This results in low red
and white blood cell counts.The former can lead to severe fatigue
and the latter to susceptibility to infections.10 DDI is provided
as a powder, which must be reconstructed with water immediately
prior to use. The most common adverse effect so far is the weakness
in the hands and legs. However, it appears that DDI is free of the
bone marrow.11 AZT and DDI both represent the first generation of
anti-retroviral drug and it is the hope of many people that they
will be followed by less toxic and more effective drugs.
As it can be seen, haemophilia is one of those sex-linked
diseases that must involve the inheritance of both recessive and
deficient chromosomes. It is mostly found in males and since every
male has a Y chromosome, it is a general rule that the male will
not pass it to his male offsprings. Haemophiliacs can have either
inherited the disease or they could have had a mutation. In either
case, these people must try to live a normal life and must avoid
any activities that can result in trauma.
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