(1) In The Human Body, Each Cell Contains 23 Pairs Of Chromosomes, One Essay

(1) 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 thesechromosomes, those that determine sex are X and Y. Females have XXand males have XY. In addition to the information on sex, ‘the Xchromosomes carry determinants for a number of other features ofthe body including the levels of factor VIII and factor IX.’1 Ifthe genetic information determining the factor VIII and IX level is defective, haemophilia results. When this happens, the proteinfactors needed for normal blood clotting are effected. In males,the single X chromosome that is effected cannot compensate for thelack, and hence will show the defect. In females, however, only one of the two chromosomes will be abnormal. (unless she is unluckyenough to inherit haemophilia from both sides of the family, whichis rare.)2 The other chromosome is likely to be normal and she cantherefore 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 todeficiency of the coagulation factor VIII (VIII:C)3. In most of the cases, this coagulant protein is reduced but in a rare amount ofcases, this protein is present by immunoassay but defective.4Haemophilia A is the most common severe bleeding disorder andapproximately 1 in 10,000 males is effected. The most common typesof bleeding are into the joints and muscles. Haemophilia is severeif 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(2) Those with mild haemophilia bleed only in response to major traumaor surgery. As for the patients with severe haemophilia, they canbleed in response to relatively mild trauma and will bleedspontaneously. In haemophiliacs, the levels of the factor VIII:C are reduced. If the plasma from a haemophiliac person mixes with that of anormal person, the Partial thromboplastin time (PTT) should becomenormal. Failure of the PTT to become normal is automaticallydiagnostic of the presence of a factor VIII inhibitor. The standard treatment of the haemophiliacs is primarily the infusion of factorVIII concentrates, now heat-treated to reduce the chances oftransmission of AIDS.6 In the case of minor bleeding, the factorVIII:C levels should only be raised to 25% with one infusion. Formoderate bleeding, ‘it is adequate to raise the level initially to50% and maintain the level at greater that 25% with repeatedinfusion for 2-3 days. When major surgery is to be performed, oneraises the factor VIII:C level to 100% and then maintains thefactor level at greater than 50% continuously for 10-14 days.’7 Haemophilia B, the other type of haemophilia, is a result ofthe deficiency of the coagulation factor IX – also known asChristmas disease. This sex-linked disease is caused by the reduced amount of the factor IX. Unlike haemophilia A, the percentage ofit’s occupance due to an abnormally functioning molecule is larger. The factor IX deficiency is 1/7 as common as factor VIII deficiencyand it is managed with factor VIII concentrates. Unlike factor VIII concentrates which have a half-life of 12 hours, the half-life offactor IX concentrates is 18 hours. In addition, factor IX(3) concentrates contain a number of other proteins, includingactivated coagulating factors that contribute to a risk ofthrombosis. Therefore, more care is needed in haemophilia B todecide on how much concentration should be used. The prognosis of the haemophiliac patients has beentransformed by the availability of factor VIII and factor IXreplacement. The limiting factors that result include disabilityfrom recurrent joint bleeding and viral infections such ashepatitis B from recurrent transfusion.8 Since most haemophiliacs are male and only their mother canpass to them the deficient gene, a very important issue for thefamilies of haemophiliacs now is identifying which females arecarriers. One way to determine this is to estimate the amount offactor 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 tofluctuate 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 isto look directly at the DNA from a small blood sample of severalmembers of the family including the haemophiliacs. In Canada,modern operations include Chorionic Villous Sampling (CVS) and ithelps analyze the DNA for markers of haemophilia at 9-11 weeks ofpregnancy. (Fig. 1)9 A small probe is inserted through the neck ofthe mother womb or through the abdomen under local anaesthetics. Atiny sample from the placenta is removed and sent for DNA analysis. (4) Since this process can be done at 9-11 weeks after pregnancy, thepregnancy is in it’s relatively early stages and a decision by themother (and father) to terminate the pregnancy will not be asphysically or emotionally demanding on the mother than if she hadit 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 IXconcentrates and many have developed AIDS. In Canada, the two drugs currently undergoing clinical testing for treatment of HIV diseaseare AZT and DDI. For the use of AZT, the major complication issuppression of normal bone marrow activity. This results in low red and white blood cell counts.The former can lead to severe fatigueand the latter to susceptibility to infections.10 DDI is providedas a powder, which must be reconstructed with water immediatelyprior 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 thebone marrow.11 AZT and DDI both represent the first generation ofanti-retroviral drug and it is the hope of many people that theywill be followed by less toxic and more effective drugs. As it can be seen, haemophilia is one of those sex-linkeddiseases that must involve the inheritance of both recessive anddeficient chromosomes. It is mostly found in males and since everymale has a Y chromosome

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