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shimaa
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i wish to understand genetic basis of hemophilia
« on: /December/ 04, 2005, 03:23:54 PM »

Al salam alaicom wa rahmat Allah

please doctors I can`t find good reasources explaining the genetic basis of hemophilia, faint

would u help me find it ?
 thank u.
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cleo_md
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Re: i wish to understand genetic basis of hemophilia
« Reply #1 on: /December/ 04, 2005, 07:58:50 PM »

Genetics of the hemophilias


INTRODUCTION ? The hemophilias are a group of related bleeding disorders that usually are inherited. Inherited bleeding disorders include abnormalities of coagulation factors as well as platelet function, the most common of which is von Willebrand disease. However, when the term "hemophilia" is used, it usually refers specifically to the following two disorders:

? ?Factor VIII deficiency (hemophilia A) ? Hemophilia A affects 1 in 5000 to 10,000 males; roughly 60 percent have severe disease, with factor VIII activity less than 1 percent of normal.

  Factor IX deficiency (hemophilia B) ? Hemophilia B affects 1 in 25,000 to 30,000 males; approximately one-half have mild to moderate disease, with factor IX activity greater than 1 percent of normal.


Severe factor VIII or factor IX deficiency leads to bleeding because of the role these factors play in the intrinsic pathway X-ase (ten-ase). The X-ase complex consists of activated factor IX (factor IXa) as the protease; activated factor VIII (factor VIIIa), calcium, and phospholipids as the cofactors; and factor X as the substrate (show figure 1) [1].

GENETIC TRANSMISSION ? Hemophilia A and B are X-linked recessive disorders, which explains who is likely to bleed and the modes of genetic transmission [2]. These hemophilias occur almost exclusively in a male having one defective copy of the relevant gene on his X chromosome (ie, he is hemizygous for the defect). Because the affected male will transmit a normal Y chromosome to all his sons and an abnormal X chromosome to all his daughters, his sons will not be affected and all of his daughters will be carriers (ie, they are heterozygous for the defect).

Although female carriers have one normal allele, they may experience bleeding symptoms similar to that seen in a patient with "mild" deficiency. Therefore, their care and symptoms should be carefully evaluated. The female carrier will transmit the disorder to one-half of her sons, and one-half of her daughters will be carriers.

However, some women have more symptomatic hemophilia [3,4]. Possible explanations include mating between an affected male and a female carrier, producing homozygous disease in one-half of their female offspring. Alternatively, loss of part or all of the normal X chromosome, as in Turner syndrome [4] or skewed inactivation of the normal X chromosome [5], may lead to symptomatic disease [4].

Approximately one-third of patients with hemophilia do not have a family history of the disease and appear to represent novel mutational events [6,7]. The large size of the factor VIII gene and the presence of "hot spots" within the gene are thought to predispose the gene to mutation.

FACTOR VIII GENE ? The factor VIII gene is one of the largest genes known, comprising about 0.1 percent of the X chromosome. The gene that encodes factor VIII is divided into 26 exons that span 186,000 base pairs [8-11]. Factor VIII contains several areas of internal homology, consisting of a heavy chain with A1 and A2 domains; a connecting region with a B domain; and a light chain with A3, C1, and C2 domains [10,11].

Some of these domains have specific functions. For example, different epitopes on the C2 domain are responsible for binding to the procoagulant phospholipid phosphatidylserine on activated platelets and endothelial cells, von Willebrand factor (which importantly slows the catabolism of factor VIII), factor Xa, and thrombin. Two domains contribute to the binding of factor IXa (A2 domain and the A1/A3-C1-C2 dimer).

Hemophilia A genes ? Examination of hemophilic genes has not demonstrated a uniform abnormality. Instead, numerous different mutations in the Factor VIII gene have been described:

? ?In one study of 200 affected genes, seven different mutations were demonstrated [8]. Four of them were transpositions of single bases, of which three transformed a codon for arginine into a stop codon, which arrested factor VIII synthesis and resulted in truncated factor VIII and severe hemophilia. The fourth mutation resulted in substitution of a single amino acid and mild hemophilias. The other three mutations involved deletion of several thousand nucleotides and produced severe hemophilia [12].

? ?A 1994 hemophilia A database indicated that more than 25 percent of unique nucleotide substitutions were caused by C-to-T transition at CpG dinucleotides [13]. The genetic defects of hemophilia A encompass deletions, insertions, and mutations throughout the gene. Approximately 5 percent have large (greater than 50 nucleotides) deletions in the gene.

? ?Approximately 40 percent of severe hemophilia A is caused by a major inversion of a section of the tip of the long arm of the X chromosome, one break point of which is situated within intron 22 of the gene. A consortium study, involving 22 laboratories from 14 countries, evaluated 2,093 patients with severe hemophilia A [14]. Seven hundred and forty patents (35 percent) had a type 1 (distal) factor VIII inversion, and 140 (7 percent) showed a type 2 (proximal) inversion. In 25 cases, the molecular analysis showed additional abnormal or polymorphic patterns. This observation has had a major impact upon carrier detection.

? ?Approximately 5 percent of patients who have hemophilia A also have normal levels of a dysfunctional factor VIII protein and are termed cross-reacting material (CRM)-positive. The majority of genetic alterations that result in CRM-positive hemophilia A are missense mutations within the A2-domain. The A2 subunit is essential for FVIIIa activity, and in one study, several of these mutants were found to have defective interaction with factor IXa [15].


Inhibitory antibodies that develop in a proportion of patients with hemophilia A and B following replacement therapy are now known to correlate with factor VIII and factor IX mutation type and location [16,17]. This subject is discussed in detail separately. (See "Factor VIII and factor IX inhibitors in patients with hemophilia").

? Deficiency of factors VIII and V ? An uncommon cause of factor VIII deficiency is a mutation in the LMAN1 gene, which causes a rare autosomal recessive disease with combined deficiency of factor VIII and factor V. This gene encodes a protein that may act as a molecular chaperone of these and other secreted proteins from the endoplasmic reticulum to the Golgi apparatus [18-20]. The disease is associated with a moderate bleeding tendency, with plasma levels of 5 to 30 percent of normal for both factors.

In other kindreds, the combined deficiency is associated with mutations in a gene on chromosome 2 called multiple coagulation factor deficiency 2 gene (MCFD2) [20]. MCFD2 encodes a protein that forms a Ca(++)-dependent stoichiometric complex with LMAN1 and acts as a cofactor in the intracellular trafficking of factors V and VIII [20].

FACTOR IX GENE ? The gene encoding factor IX is also located near the terminus of the long arm of the X chromosome. This 34 kb gene contains eight exons and seven introns; its protein product is one of the vitamin K dependent proteins. As such, it is the largest gene of this family and the only one present on the X chromosome. Further, the number of exons and splice junction types are highly conserved in homologous vitamin K dependent proteins.

Hemophilia B genes ? Hemophilia B is a markedly heterogeneous disorder with a wide range of plasma levels of factor IX and a variety of specific gene defects [21]. The original factor IX deficient subject, Mr. Christmas, was a severely deficient patient whose mutation was cysteine206serine [22].

Most affected families show a unique mutation. For example, one study of 70 unrelated patients in the Rhone Alps in France with hemophilia B found 2 complete gene deletions in patients with antifactor IX inhibitor, 6 small insertions/deletions, and 62 point mutations [23]. Two of these nucleotide substitutions were detected in 21 patients (30 percent), suggesting the existence of a local founder effect. Of the mutations, 13 were previously undescribed.

The hemophilia database lists, in an easily accessible form, all known factor IX mutations caused by small changes (base substitutions and short additions and/or deletions of <30 bp) identified in hemophilia B patients [24]. The 9th database includes 1918 patient entries with 689 unique molecular events (www.kcl.ac.uk/ip/petergreen/haemBdatabase.html). Mutations have been detected in all regions of the Factor IX gene except the poly (A) site. Molecular events include 425 different amino substitutions and 143 short deletions and/or additions. Point mutations, the most common defect, can be associated with mild and severe hemophilia B. However, this database may not be completely representative of the disease for the following reasons:

? ?The database over-represents defects leading to severe disease, as these are more likely to be analyzed and reported.

? ?Founder effects contribute to over-representations at some specific sites.

? ?Double mutations may be underrepresented because of lack of complete gene screening.


Deletions of the gene and some point mutations may be associated with absence of the factor IX antigen, leading to inhibitor formation, with an incidence of approximately 3 percent.

? Leyden phenotype ? In one form, mutations at -20 and -26 in the factor IX promoter region impair transcription by disrupting the binding site for the liver-enriched transcription factor 3333. The -26, but not the -20 mutation, also disrupts an androgen-responsive element, which overlaps the LF-A1/HNF4 site. For this reason, patients with the -20 mutation improve after puberty (The Leyden phenotype); patients with the -26 mutation (Hemophilia B Brandenburg) do not improve [25].

? Dysfunctional protein mutants ? Similar to those families with hemophilia A, some families have antigen-positive (cross-reacting material positive, CRM+) defects, with clinical severity ranging from mild to severe. These patients have antigenic levels of factor IX that are near normal, but they have much lower factor IX activity levels. Approximately one-third of cases fall within this group. Mutations have been described that affect post-translational protein processing, gamma carboxylation and lipid binding, EGF domain function, zymogen activation, and substrate recognition and/or enzymatic activity.

? ?Defects in post-translational processing prevent cleavage of the 18-amino-acid propeptide of factor IX in factor IX Cambridge and factor IX Oxford [26,27].

? ?In factor IX Chapel Hill, the first factor IX mutation characterized at the molecular level, activation of a zymogen is impaired because of the mutation of an arginine preceding a sessile bond [28].

? ?Many of these families display point mutations affecting various regions of the gene, ranging from the Gla region to defects in the 180 to 182 and 390 to 397 trypsin-like (catalytic) domain. In Factor IX Vancouver, for example, the codon for isoleucine 397 (ATA) is changed to a threonine codon (ACA) [29]. Hydrogen bonding between the side chain hydroxyl group of threonine 397 and the carbonyl oxygen of tryptophan 385 reduces the ability of Factor IX Vancouver to bind factor X in a configuration favoring catalysis.

? ?Hemophilia Bm is a variant of hemophilia B that results in a dysfunctional protein, characterized by a prolonged prothrombin time when ox brain but not human brain is used as the source of thromboplastin. The Bm phenotype is associated with mutations at residue 180,181, or 182 near the amino terminus of the heavy chain and at residue 311, 364, 368, 390, 396, or 397 near the beta cleavage site of factor IX [30,31]. Most have clinically severe disease.


REFERENCES
1.? Brandstetter, H, Bauer, M, Huber, R, et al. X-ray structure of clotting factor IXa: active site and module structure related to Xase activity and hemophilia B. Proc Natl Acad Sci U S A 1995; 92:9796.
2.? Hoyer, LW. Hemophilia A. N Engl J Med 1994; 330:38.
3.? Merskey, C. The occurrence of haemophilia in the human female. Q J Med 1951; 20:299.
4.? Panarello, C, Acquila, M, Caprino, D, et al. Concomitant Turner syndrome and hemophilia A in a female with an idic(X)(p11) heterozygous at locus DXS52. Cytogenet Cell Genet 1992; 59:241.
5.? Valleix, S, Vinciguerra, C, Lavergne, JM, et al. Skewed X-chromosome inactivation in monochorionic diamniotic twin sisters results in severe and mild hemophilia A. Blood 2002; 100:3034.
6.? Lawn, RM. The molecular genetics of hemophilia: blood clotting factors VIII and IX. Cell 1985; 42:405.
7.? Leuer, M, Oldenburg, J, Lavergne, JM, et al. Somatic mosaicism in hemophilia A: a fairly common event. Am J Hum Genet 2001; 69:75.
8.? Gitschier, J, Wood, WI, Goralka, TM, et al. Characterization of the human factor VIII gene. Nature 1984; 312:326.
9.? Wood, WI, Capon, DJ, Simonsen, CC, et al. Expression of active human factor VIII from recombinant DNA clones. Nature 1984; 312:330.
10.? Vehar, GA, Keyt, B, Eaton, D, et al. Structure of human factor VIII. Nature 1984; 312:337.
11.? Toole, JJ, Knopf, Wozney, JM, et al. Molecular cloning of a cDNA encoding human antihaemophilic factor. Nature 1984; 312:342.
12.? Lawn, RM, Vehar, GA. The molecular genetics of hemophilia. Sci Am 1986; 254:48.
13.? Tuddenham, EG, Schwaab, R, Seehafer, J, et al. Haemophilia A: database of nucleotide substitutions, deletions, insertions and rearrangements of the factor VIII gene, second edition [corrected and republished article originally printed in Nucleic Acids Res 1994 Sep;22(17):3511-33]. Nucleic Acids Res 1994; 22:4851.
14.? Antonarakis, SE, Rossiter, JP, Young, M, et al. Factor VIII gene inversions in severe hemophilia A: Results of an international consortium study. Blood 1995; 86:2206.
15.? Amano, K, Sarkar, R, Pemberton, S, et al. The molecular basis for cross-reacting material-positive hemophilia A due to missense mutations within the A2-domain of factor VIII. Blood 1998; 91:538.
16.? Goodeve, AC, Peake, IR. The molecular basis of hemophilia A: genotype-phenotype relationships and inhibitor development. Semin Thromb Hemost 2003; 29:23.
17.? Green, PM. Hemophilia B-- molecular basis. In: Textbook of Hemophilia. Lee, CA, Berntorp, EE, Hoots, WK, eds. Blackwell Publishing, Malden, MA; 2005.
18.? Cunningham, MA, Pipe, SW, Zhang, B, et al. LMAN1 is a molecular chaperone for the secretion of coagulation factor VIII. J Thromb Haemost 2003; 1:2360.
19.? Neerman-Arbez, M, Johnson, KM, Morris, MA, et al. Molecular analysis of the ERGIC-53 gene in 35 families with combined factor V-factor VIII deficiency. Blood 1999; 93:2253.
20.? Zhang, B, Cunningham, MA, Nichols, WC, Bernat, JA. Bleeding due to disruption of a cargo-specific ER-to-Golgi transport complex. Nat Genet 2003; 34:220.
21.? Lillicrap, D. The molecular basis of haemophilia B. Haemophilia 1998; 4:350.
22.? Taylor, SA, Duffin, J, Cameron, C, et al. Characterization of the original Christmas disease mutation (cysteine 206----serine): from clinical recognition to molecular pathogenesis. Thromb Haemost 1992; 67:63.
23.? Attali, O, Vinciguerra, C, Trzeciak, MC, et al. Factor IX gene analysis in 70 unrelated patients with haemophilia B: description of 13 new mutations. Thromb Haemost 1999; 82:1437.
24.? Giannelli, F, Green, PM, Sommer, SS, et al. Haemophilia B: database of point mutations and short additions and deletions--eighth edition. Nucleic Acids Res 1998; 26:265.
25.? Crossley M, Ludwig M, Stowell KM, Recovery from hemophilia B Leyden: an androgen-responsive element in the factor IX promoter. Science 1992; 257:377.
26.? Diuguid, DL, Rabiet, MJ, Furie, BC, et al. Molecular basis of hemophilia B: a defective enzyme due to an unprocessed propeptide is caused by a point mutation in the factor IX precursor. Proc Natl Acad Sci U S A 1986; 83:5803.
27.? Bentley, AK, Rees, DJ, Rizza, C, Brownlee, GG. Defective propeptide processing of blood clotting factor IX caused by mutation of arginine to glutamine at position -4. Cell 1986; 45:343.
28.? Noyes, CM, Griffith, MJ, Roberts, HR, Lundblad, RL. Identification of the molecular defect in factor IX Chapel Hill: Substitution of histidine for arginine at position 145. Proc Natl Acad Sci U S A 1983; 80:4200.
29.? Geddes, VA, Le Bonniec, BF, Louie, GV, et al. A moderate form of hemophilia B is caused by a novel mutation in the protease domain of factor IXVancouver. J Biol Chem 1989; 264:4689.
30.? Taylor, SA, Liddell, MB, Peake, IR, et al. A mutation adjacent to the beta cleavage site of factor IX (valine 182 to leucine) results in mild haemophilia Bm. Br J Haematol 1990; 75:217.
31.? Hamaguchi, N, Roberts, H, Stafford, DW. Mutations in the catalytic domain of factor IX that are related to the subclass hemophilia Bm. Biochemistry 1993; 32:6324.
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cleo_md
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Re: i wish to understand genetic basis of hemophilia
« Reply #2 on: /December/ 04, 2005, 07:59:43 PM »

Good luck dr shimaa...let me know if you need more help


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musheera
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Re: i wish to understand genetic basis of hemophilia
« Reply #3 on: /December/ 05, 2005, 12:13:48 AM »

Nuha as always your posts are so informative
THANKS!!
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cleo_md
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Re: i wish to understand genetic basis of hemophilia
« Reply #4 on: /December/ 07, 2005, 07:53:23 PM »

You are most welcome Musheera....I'm glad you find it beneficial Smiley

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shimaa
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Re: i wish to understand genetic basis of hemophilia
« Reply #5 on: /December/ 18, 2005, 04:21:47 PM »

thank you dr cleo
I`m really happy to join the forum & the article is very useful. I searched alot but didn`t find such a good material like this. Smiley
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Re: i wish to understand genetic basis of hemophilia
« Reply #6 on: /December/ 19, 2005, 04:48:56 PM »

you're most welcome Dr Shimaa . I'm glad it was helpful Smiley Welcome to the forum!!
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shaimaa
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Re: i wish to understand genetic basis of hemophilia
« Reply #7 on: /December/ 20, 2005, 12:18:16 PM »

alsslamu alikum my friend shaimaa i hope you enjoy here between us

thanks dr nuha about this great explanation thanks iam also benefit so much thanks again

i want to know the genatics of thalassimia  Smiley
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Re: i wish to understand genetic basis of hemophilia
« Reply #8 on: /December/ 20, 2005, 09:30:03 PM »

Do we have 2 Dr Shiamaa's here ? Smiley? Here you go!? taa

The thalassemias are profoundly heterogeneous from a genetic standpoint ; however, certain clinical terms are available to describe the phenotypic expression of this disorder:

Beta (0) thalassemia ? Beta (0) thalassemia refers to the more than 40 different genetic mutations of the beta globin locus which result in the absence of production of beta globin. Patients homozygous or doubly heterozygous for beta (0) thalassemic genes cannot make normal beta chains and thus are unable to make any hemoglobin A.

Beta (+) thalassemia
? Beta (+) thalassemia refers to the more than 30 different genetic mutations which result in decreased production of beta globin. Patients homozygous for beta (+) thalassemic genes are able to make some hemoglobin A, and are generally less severely affected than those homozygous for beta (0) genes.

Beta thalassemia major ? Beta thalassemia major is the term applied to patients who have either no effective production (as in homozygous beta (0) thalassemia) or severely limited production of beta globin. These are the patients originally described by Cooley (Cooley's anemia). Starting during the first year of life, they have profound and life-long transfusion-dependent anemia, hepatosplenomegaly, and skeletal deformities due to bone marrow expansion; they are prone to infection and skeletal fractures and unless, appropriately treated, die during adolescence of iron overload syndromes.

Beta thalassemia minor ? Beta thalassemia minor, also called beta thalassemia trait, is the term applied to heterozygotes who have inherited a single gene leading to reduced beta globin production. Such patients are asymptomatic, may be only mildly anemic, and are usually discovered when a blood count has been obtained for other reasons.

Beta thalassemia intermedia ? Beta thalassemia intermedia is the term applied to patients with disease of intermediate severity, such as those who are compound heterozygotes of two thalassemic variants. Such patients may have the skeletal abnormalities and hepatosplenomegaly seen in thalassemia major. However, their hemoglobin concentrations usually range from 5 to 10 gm/dL and they usually require transfusions only when they have an intercurrent event, such as an infection, which impairs erythropoiesis. Their clinical symptoms may not be apparent until well after the first year of life.

___________________________________________________________________________________________________________________________________________

Alpha (0) thalassemia ? Alpha (0) thalassemia refers to the more than 20 different genetic mutations of the alpha globin locus which result in the deletion of both alpha chain loci (show figure 1) on one chromosome 16. Patients who carry alpha (0) gene mutations on both chromosomes cannot make alpha chains and are therefore unable to make any hemoglobin A, F, or A2. This condition is incompatible with extrauterine life (see "Hydrops fetalis and hemoglobin Bart's" below).

Alpha (+) thalassemia ? Alpha (+) thalassemia refers to the more than 15 different genetic mutations which result in decreased production of alpha globin, usually due to deletion of one of the two alpha chain loci in the affected chromosome. As a result, there are three general forms of alpha (+) thalassemia based upon the number of inherited alpha genes:

? ?Inheritance of three normal alpha genes (aa/a-) has been termed alpha thalassemia minima, silent carrier of alpha thalassemia, alpha thalassemia-2 trait, or heterozygosity for alpha (+) thalassemia. Affected subjects are clinically normal and may also be hematologically normal; the diagnosis can be reliably made only via DNA analysis.

? ?Inheritance of two normal alpha genes has been termed alpha thalassemia minor or alpha thalassemia-1 trait, and is due either to heterozygosity for alpha (0) thalassemia (aa/--) or homozygosity for alpha (+) thalassemia (a-/a-). These subjects are clinically normal but may have minimal anemia along with reductions in mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH)

? ?Inheritance of one normal alpha gene (a-/--) is termed hemoglobin H (HbH) disease, because of the formation of HbH, which is composed of tetramers of the resulting excess beta chains. These patients have moderate to severe degrees of lifelong hemolytic anemia, very modest degrees of ineffective erythropoiesis, splenomegaly, and variable bony changes .

? ?As mentioned above, inheritance of no alpha genes (--/--) is incompatible with extrauterine life, since the affected fetus will be unable to make any of the hemoglobins normally produced after birth (eg, hemoglobins A, F, and A2), all of which require the ability to produce alpha globin chains.


These definitions are useful as a starting point but the classification of the alpha thalassemias can become extremely complex. For example, two general forms of HbH disease have been recognized, the deletional and non-deletional forms. In the former, the patient has inherited only a single alpha globin gene (ie, a-/--). In the non-deletional form, the patient has inherited two alpha globin genes from one parent, but one of these carries a non-deletional defect, such as a point mutation (ie, aa*/--, where a* represents the mutated alpha chain). HbH disease tends to be more severe in patients with the non-deletional form [3], due, at least in part, to interference with transcription of the normal alpha chain gene by the abnormal one [4].

As another example of the potential complexity of these disorders, individual patients may have combinations of alpha and beta globin gene mutations of varying nature and severity (eg, combinations or variants of alpha (0) from one parent and alpha (+) from the other with one or more beta chain abnormalities).





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cleo_md
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Re: i wish to understand genetic basis of hemophilia
« Reply #9 on: /December/ 20, 2005, 09:30:45 PM »

Fig

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Oliver
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Re: i wish to understand genetic basis of hemophilia
« Reply #10 on: /June/ 13, 2009, 06:42:25 AM »

Hey Doctors!  can anyone tell me that how to prevent our next generation to inherit this genetic disease and
the measures that we should use to prevent the  hemophilia patient from adverse situations? Thnx in Advance for your help.

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chandler
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Re: i wish to understand genetic basis of hemophilia
« Reply #11 on: /October/ 09, 2009, 04:46:17 PM »

cleo_md, thanks for posting all those helpful resources.  i also have been wondering about oliver's question.  is there any ongoing researching that's looking into preventing the passing on of hemophilia to our children (short of forced sterilization of course)?
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