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Shen G, Gao M, Cao Q, Li W. The Molecular Basis of FIX Deficiency in Hemophilia B. Int J Mol Sci 2022; 23:2762. [PMID: 35269902 PMCID: PMC8911121 DOI: 10.3390/ijms23052762] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 02/23/2022] [Accepted: 02/27/2022] [Indexed: 12/15/2022] Open
Abstract
Coagulation factor IX (FIX) is a vitamin K dependent protein and its deficiency causes hemophilia B, an X-linked recessive bleeding disorder. More than 1000 mutations in the F9 gene have been identified in hemophilia B patients. Here, we systematically summarize the structural and functional characteristics of FIX and the pathogenic mechanisms of the mutations that have been identified to date. The mechanisms of FIX deficiency are diverse in these mutations. Deletions, insertions, duplications, and indels generally lead to severe hemophilia B. Those in the exon regions generate either frame shift or inframe mutations, and those in the introns usually cause aberrant splicing. Regarding point mutations, the bleeding phenotypes vary from severe to mild in hemophilia B patients. Generally speaking, point mutations in the F9 promoter region result in hemophilia B Leyden, and those in the introns cause aberrant splicing. Point mutations in the coding sequence can be missense, nonsense, or silent mutations. Nonsense mutations generate truncated FIX that usually loses function, causing severe hemophilia B. Silent mutations may lead to aberrant splicing or affect FIX translation. The mechanisms of missense mutation, however, have not been fully understood. They lead to FIX deficiency, often by affecting FIX's translation, protein folding, protein stability, posttranslational modifications, activation to FIXa, or the ability to form functional Xase complex. Understanding the molecular mechanisms of FIX deficiency will provide significant insight for patient diagnosis and treatment.
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Affiliation(s)
- Guomin Shen
- Henan International Joint Laboratory of Thrombosis and Hemostasis, Henan University of Science and Technology, Luoyang 471023, China; (M.G.); (Q.C.)
- School of Basic Medical Science, Henan University of Science and Technology, Luoyang 471023, China
| | - Meng Gao
- Henan International Joint Laboratory of Thrombosis and Hemostasis, Henan University of Science and Technology, Luoyang 471023, China; (M.G.); (Q.C.)
- School of Basic Medical Science, Henan University of Science and Technology, Luoyang 471023, China
| | - Qing Cao
- Henan International Joint Laboratory of Thrombosis and Hemostasis, Henan University of Science and Technology, Luoyang 471023, China; (M.G.); (Q.C.)
- School of Basic Medical Science, Henan University of Science and Technology, Luoyang 471023, China
| | - Weikai Li
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
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Branchini A, Morfini M, Lunghi B, Belvini D, Radossi P, Bury L, Serino ML, Giordano P, Cultrera D, Molinari AC, Napolitano M, Bigagli E, Castaman G, Pinotti M, Bernardi F. F9 missense mutations impairing factor IX activation are associated with pleiotropic plasma phenotypes. J Thromb Haemost 2022; 20:69-81. [PMID: 34626083 PMCID: PMC9298354 DOI: 10.1111/jth.15552] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 10/06/2021] [Accepted: 10/06/2021] [Indexed: 11/30/2022]
Abstract
BACKGROUND Circulating dysfunctional factor IX (FIX) might modulate distribution of infused FIX in hemophilia B (HB) patients. Recurrent substitutions at FIX activation sites (R191-R226, >300 patients) are associated with variable FIX activity and antigen (FIXag) levels. OBJECTIVES To investigate the (1) expression of a complete panel of missense mutations at FIX activation sites and (2) contribution of F9 genotypes on the FIX pharmacokinetics (PK). METHODS We checked FIX activity and antigen and activity assays in plasma and after recombinant expression of FIX variants and performed an analysis of infused FIX PK parameters in patients (n = 30), mostly enrolled in the F9 Genotype and PK HB Italian Study (GePKHIS; EudraCT ID2017-003902-42). RESULTS The variable FIXag amounts and good relation between biosynthesis and activity of multiple R191 variants results in graded moderate-to-mild severity of the R191C>L>P>H substitutions. Recombinant expression may predict the absence in the HB mutation database of the benign R191Q/W/K and R226K substitutions. Equivalent changes at R191/R226 produced higher FIXag levels for R226Q/W/P substitutions, as also observed in p.R226W female carrier plasma. Pharmacokinetics analysis in patients suggested that infused FIX Alpha distribution and Beta elimination phases positively correlated with endogenous FIXag levels. Mean residence time was particularly prolonged (79.4 h, 95% confidence interval 44.3-114.5) in patients (n = 7) with the R191/R226 substitutions, which in regression analysis were independent predictors (β coefficient 0.699, P = .004) of Beta half-life, potentially prolonged by the increasing over time ratio between endogenous and infused FIX. CONCLUSIONS FIX activity and antigen levels and specific features of the dysfunctional R191/R226 variants may exert pleiotropic effects both on HB patients' phenotypes and substitutive treatment.
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Affiliation(s)
- Alessio Branchini
- Department of Life Sciences and Biotechnology and LTTA CentreUniversity of FerraraFerraraItaly
| | | | - Barbara Lunghi
- Department of Life Sciences and Biotechnology and LTTA CentreUniversity of FerraraFerraraItaly
| | - Donata Belvini
- Transfusion ServiceHaemophilia Centre and HaematologyCastelfranco Veneto HospitalCastelfranco VenetoItaly
| | - Paolo Radossi
- Oncohematology‐Oncologic Institute of VenetoCastelfranco Veneto HospitalCastelfranco VenetoItaly
| | - Loredana Bury
- Department of Medicine and SurgeryUniversity of PerugiaPerugiaItaly
| | - Maria Luisa Serino
- Haemostasis and Thrombosis CentreUniversity Hospital of FerraraFerraraItaly
| | - Paola Giordano
- Paediatric SectionDepartment of Biomedicine and Human OncologyA. Moro” UniversityBariItaly
| | - Dorina Cultrera
- Haemophilia Regional Reference CenterVittorio Emanuele” University HospitalCataniaItaly
| | | | - Mariasanta Napolitano
- Haematology UnitThrombosis and Haemostasis Reference Regional Center and PROMISE DepartmentUniversity of PalermoPalermoItaly
| | - Elisabetta Bigagli
- Department of Neuroscience, PsychologyDrug Research and Child Health (NEUROFARBA)Section of Pharmacology and ToxicologyUniversity of FlorenceFlorenceItaly
| | - Giancarlo Castaman
- Department of Oncology, Center for Bleeding DisordersCareggi University HospitalFirenzeItaly
| | - Mirko Pinotti
- Department of Life Sciences and Biotechnology and LTTA CentreUniversity of FerraraFerraraItaly
| | - Francesco Bernardi
- Department of Life Sciences and Biotechnology and LTTA CentreUniversity of FerraraFerraraItaly
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Doss C GP. In silico profiling of deleterious amino acid substitutions of potential pathological importance in haemophlia A and haemophlia B. J Biomed Sci 2012; 19:30. [PMID: 22423892 PMCID: PMC3361463 DOI: 10.1186/1423-0127-19-30] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 03/16/2012] [Indexed: 01/08/2023] Open
Abstract
Background In this study, instead of current biochemical methods, the effects of deleterious amino acid substitutions in F8 and F9 gene upon protein structure and function were assayed by means of computational methods and information from the databases. Deleterious substitutions of F8 and F9 are responsible for Haemophilia A and Haemophilia B which is the most common genetic disease of coagulation disorders in blood. Yet, distinguishing deleterious variants of F8 and F9 from the massive amount of nonfunctional variants that occur within a single genome is a significant challenge. Methods We performed an in silico analysis of deleterious mutations and their protein structure changes in order to analyze the correlation between mutation and disease. Deleterious nsSNPs were categorized based on empirical based and support vector machine based methods to predict the impact on protein functions. Furthermore, we modeled mutant proteins and compared them with the native protein for analysis of protein structure stability. Results Out of 510 nsSNPs in F8, 378 nsSNPs (74%) were predicted to be 'intolerant' by SIFT, 371 nsSNPs (73%) were predicted to be 'damaging' by PolyPhen and 445 nsSNPs (87%) as 'less stable' by I-Mutant2.0. In F9, 129 nsSNPs (78%) were predicted to be intolerant by SIFT, 131 nsSNPs (79%) were predicted to be damaging by PolyPhen and 150 nsSNPs (90%) as less stable by I-Mutant2.0. Overall, we found that I-Mutant which emphasizes support vector machine based method outperformed SIFT and PolyPhen in prediction of deleterious nsSNPs in both F8 and F9. Conclusions The models built in this work would be appropriate for predicting the deleterious amino acid substitutions and their functions in gene regulation which would be useful for further genotype-phenotype researches as well as the pharmacogenetics studies. These in silico tools, despite being helpful in providing information about the nature of mutations, may also function as a first-pass filter to determine the substitutions worth pursuing for further experimental research in other coagulation disorder causing genes.
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Affiliation(s)
- George Priya Doss C
- School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu, India.
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Neutrophil Elastase Cleavage of Human Factor IX Generates an Activated Factor IX-Like Product Devoid of Coagulant Function. Blood 1998. [DOI: 10.1182/blood.v92.4.1287.416k29_1287_1296] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In preliminary studies, the generation of thrombin in vivo was found to induce a 92% loss of functional activity of factor IX (F.IX) despite the detection by Western blotting of a product resembling activated F.IX (F.IXa) and a 25% increase in F.IX antigen levels (Hoogendoorn et al, Thromb Haemost 69:1127, 1993 [abstr]). These changes were associated with evidence of increased elastase availability. To study the possibility that these two observations were related, a detailed physical and functional characterization of the hydrolysis of purified human F.IX by human neutrophil elastase (HNE) was performed in vitro. An activated partial thromboplastin time (aPTT) clotting assay demonstrated that, although HNE eliminated the potential of F.IX to be activated, it only marginally reduced the F.IXa activity. Reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that HNE treatment of F.IX generated cleavage products of 30 and 20 kD that could not be distinguished from the respective heavy and light chain peptides that were identified in parallel studies when F.IX was activated by activated bovine F.XI (F.XIa), one of its physiological activators. In addition, nonreducing SDS-PAGE demonstrated that HNE-treated F.IX formed no complexes with antithrombin III (ATIII) in the presence of heparin. Furthermore, HNE-treated F.IX was unable to (1) bind the active site probe p-aminobenzamidine; (2) hydrolyze the synthetic peptide substrate CH3SO2-Leu-Gly-Arg-p-nitroanilide; and (3) activate human factor X (F.X). In contrast to dansyl-Glu-Gly-Arg-chloromethyl ketone (dEGR)-inactivated F.IXa, HNE-treated F.IX (0.01 to 10,000 pmol/L) failed to inhibit the clotting activity of F.IXa (10 pmol/L) in the aPTT. NH2-terminal sequencing indicated that HNE cleaved human F.IX at Thr140, Thr144, Ile164, Thr172, and Val181. The cleavages at Thr140/Thr144 and at Thr172/Val181 are both very close to the normal F.XIa -(Arg145) and β-(Arg180) cleavage sites, respectively. In summary, the results suggest that the activatability of F.IX is eliminated after cleavage by HNE and that the inability of HNE-treated F.IX to support F.IXa-like coagulant function is a consequence of improper active site formation. These in vitro observations support the possibility that increased HNE cleavage of F.IX in vivo may contribute to the disregulation of hemostasis that occurs in conditions such as disseminated intravascular coagulation (DIC).© 1998 by The American Society of Hematology.
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Neutrophil Elastase Cleavage of Human Factor IX Generates an Activated Factor IX-Like Product Devoid of Coagulant Function. Blood 1998. [DOI: 10.1182/blood.v92.4.1287] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AbstractIn preliminary studies, the generation of thrombin in vivo was found to induce a 92% loss of functional activity of factor IX (F.IX) despite the detection by Western blotting of a product resembling activated F.IX (F.IXa) and a 25% increase in F.IX antigen levels (Hoogendoorn et al, Thromb Haemost 69:1127, 1993 [abstr]). These changes were associated with evidence of increased elastase availability. To study the possibility that these two observations were related, a detailed physical and functional characterization of the hydrolysis of purified human F.IX by human neutrophil elastase (HNE) was performed in vitro. An activated partial thromboplastin time (aPTT) clotting assay demonstrated that, although HNE eliminated the potential of F.IX to be activated, it only marginally reduced the F.IXa activity. Reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that HNE treatment of F.IX generated cleavage products of 30 and 20 kD that could not be distinguished from the respective heavy and light chain peptides that were identified in parallel studies when F.IX was activated by activated bovine F.XI (F.XIa), one of its physiological activators. In addition, nonreducing SDS-PAGE demonstrated that HNE-treated F.IX formed no complexes with antithrombin III (ATIII) in the presence of heparin. Furthermore, HNE-treated F.IX was unable to (1) bind the active site probe p-aminobenzamidine; (2) hydrolyze the synthetic peptide substrate CH3SO2-Leu-Gly-Arg-p-nitroanilide; and (3) activate human factor X (F.X). In contrast to dansyl-Glu-Gly-Arg-chloromethyl ketone (dEGR)-inactivated F.IXa, HNE-treated F.IX (0.01 to 10,000 pmol/L) failed to inhibit the clotting activity of F.IXa (10 pmol/L) in the aPTT. NH2-terminal sequencing indicated that HNE cleaved human F.IX at Thr140, Thr144, Ile164, Thr172, and Val181. The cleavages at Thr140/Thr144 and at Thr172/Val181 are both very close to the normal F.XIa -(Arg145) and β-(Arg180) cleavage sites, respectively. In summary, the results suggest that the activatability of F.IX is eliminated after cleavage by HNE and that the inability of HNE-treated F.IX to support F.IXa-like coagulant function is a consequence of improper active site formation. These in vitro observations support the possibility that increased HNE cleavage of F.IX in vivo may contribute to the disregulation of hemostasis that occurs in conditions such as disseminated intravascular coagulation (DIC).© 1998 by The American Society of Hematology.
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Giannelli F, Green PM, Sommer SS, Poon MC, Ludwig M, Schwaab R, Reitsma PH, Goossens M, Yoshioka A, Brownlee GG. Haemophilia B (sixth edition): a database of point mutations and short additions and deletions. Nucleic Acids Res 1996; 24:103-18. [PMID: 8594556 PMCID: PMC145614 DOI: 10.1093/nar/24.1.103] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The sixth edition of the haemophilia B database lists in easily accessible form all known factor IX mutations due to small changes (base substitutions and short additions and/or deletions of <30 bp) identified in haemophilia B patients. The 1380 patient entries are ordered by the nucleotide number of their mutation. Where known, details are given on factor IX activity, factor IX antigen in circulation and origin of mutation. References to published mutations are given and the laboratories generating the data are indicated.
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7
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Giannelli F, Green PM, Sommer SS, Lillicrap DP, Ludwig M, Schwaab R, Reitsma PH, Goossens M, Yoshioka A, Brownlee GG. Haemophilia B: database of point mutations and short additions and deletions, fifth edition, 1994. Nucleic Acids Res 1994; 22:3534-46. [PMID: 7937052 PMCID: PMC308314 DOI: 10.1093/nar/22.17.3534] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The fifth edition of the haemophilia B database lists in easily accessible form all known factor IX mutations due to small changes (base substitutions and short additions and/or deletions of < 30bp) identified in haemophilia B patients. The 1,142 patient entries are ordered by the nucleotide number of their mutation. Where known, details are given on: factor IX activity, factor IX antigen in circulation, and origin of mutation. References to published mutations are given and the laboratories generating the data are indicated.
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8
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Giannelli F, Green PM, High KA, Sommer S, Poon MC, Ludwig M, Schwaab R, Reitsma PH, Goossens M, Yoshioka A. Haemophilia B: database of point mutations and short additions and deletions--fourth edition, 1993. Nucleic Acids Res 1993; 21:3075-87. [PMID: 8392713 PMCID: PMC309734 DOI: 10.1093/nar/21.13.3075] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
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9
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Giannelli F, Green PM, High KA, Sommer S, Lillicrap DP, Ludwig M, Olek K, Reitsma PH, Goossens M, Yoshioka A. Haemophilia B: database of point mutations and short additions and deletions--third edition, 1992. Nucleic Acids Res 1992; 20 Suppl:2027-63. [PMID: 1598234 PMCID: PMC333981 DOI: 10.1093/nar/20.suppl.2027] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
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10
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Aly AM, Arai M, Hoyer LW. Cysteamine enhances the procoagulant activity of Factor VIII-East Hartford, a dysfunctional protein due to a light chain thrombin cleavage site mutation (arginine-1689 to cysteine). J Clin Invest 1992; 89:1375-81. [PMID: 1569180 PMCID: PMC443005 DOI: 10.1172/jci115725] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
We have recently identified the molecular defect responsible for cross-reacting material-positive hemophilia A in two unrelated patients in which the substitution of cysteine for arginine-1689 (Factor VIII-East Hartford[FVIII-EH]) abolishes a critical Factor VIII light chain thrombin cleavage site. As other mutant proteins with a cysteine for arginine substitution have been modified in the presence of cysteamine, we have determined the effect of this and other reducing agents on FVIII-EH function. Cysteamine concentrations between 0.1 and 10 mM caused dose- and time-dependent increases in FVIII-EH VIII:C activity, as much as 14-fold (to 35 and 62 U/dl for the two patients tested). Comparable data were obtained in a standard one-stage VIII:C coagulation assay and in a chromogenic substrate assay measuring Factor Xa generation. Thrombin cleavage of the FVIII-EH light chain in the presence of cysteamine was documented by immunoadsorption and analysis. Cystamine and cysteamine-S-phosphate, similar compounds that do not possess a free thiol group, had no effect. Cysteamine augmentation of FVIII-EH VIII:C was abolished by the simultaneous addition of N-ethyl maleimide or iodoacetamide, but these sulfhydryl blocking agents did not prevent the VIII:C increase and light chain cleavage by thrombin if the plasma samples were dialyzed to remove the inhibitors before adding the cysteamine. However, incubation with DTT before iodoacetamide prevented the cysteamine effect after dialysis. These data suggest that when isolated from patient plasma, FVIII-EH cysteine-1689 is present in a disulfide bond. This bond is cleaved by cysteamine to form a new mixed disulfide, a pseudolysine that restores a thrombin cleavage site that is essential for procoagulant function.
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Affiliation(s)
- A M Aly
- Holland Laboratory, American Red Cross Blood Services, Rockville, Maryland 20855
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11
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Giannelli F, Green PM, High KA, Sommer S, Lillicrap DP, Ludwig M, Olek K, Reitsma PH, Goossens M, Yoshioka A. Haemophilia B: database of point mutations and short additions and deletions--second edition. Nucleic Acids Res 1991; 19 Suppl:2193-219. [PMID: 2041805 PMCID: PMC331353 DOI: 10.1093/nar/19.suppl.2193] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Affiliation(s)
- F Giannelli
- Paediatric Research Unit, Guy's Tower, London, UK
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12
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Suehiro K, Miyata T, Takeya H, Takamatsu J, Saito H, Murakawa M, Okamura T, Niho Y, Iwanaga S. Blood clotting factor IX Nagoya 3: the molecular defect of zymogen activation caused by an arginine-145 to histidine substitution. Thromb Res 1990; 60:311-20. [PMID: 2087690 DOI: 10.1016/0049-3848(90)90109-p] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Factor IX Nagoya 3 (IX Nagoya 3) is a natural mutant of factor IX recognized in a patient with moderately severe hemophilia B. The patient had 0.60 units/ml of factor IX antigen and 2-5% of clotting activity. IX Nagoya 3 was purified from the patient's plasma by immunoaffinity chromatography with an anti-factor IX monoclonal antibody column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the treatment of IX Nagoya 3 with factor XIa/calcium ions resulted in cleavage only at the Arg180-Val181 bond. The amino acid sequence analysis of one of the lysyl endopeptidase peptides derived from IX Nagoya 3 revealed that Arg-145 is replaced by His. This substitution impairs the cleavage between the light chain and the activation peptide by factor XIa/calcium ions.
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Affiliation(s)
- K Suehiro
- First Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan
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Giannelli F, Green PM, High KA, Lozier JN, Lillicrap DP, Ludwig M, Olek K, Reitsma PH, Goossens M, Yoshioka A. Haemophilia B: database of point mutations and short additions and deletions. Nucleic Acids Res 1990; 18:4053-9. [PMID: 2377450 PMCID: PMC331159 DOI: 10.1093/nar/18.14.4053] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- F Giannelli
- Paediatric Research Unit, Guy's Tower, London Bridge, London, UK
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Taylor SA, Liddell MB, Peake IR, Bloom AL, Lillicrap DP. A mutation adjacent to the beta cleavage site of factor IX (valine 182 to leucine) results in mild haemophilia Bm. Br J Haematol 1990; 75:217-21. [PMID: 2372509 DOI: 10.1111/j.1365-2141.1990.tb02652.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The genetic basis of a mild form of haemophilia Bm has been investigated. The patient under investigation has a mild bleeding disorder and has never experienced spontaneous bleeds. Factor IX coagulant activity (FIX:C) was 0.15 units/ml and factor IX antigen (FIX:Ag) 1.32 units/ml. The prothrombin time performed with an ox brain thromboplastin was 65 s (normal plasma 31 s). Studies of the abnormal factor IX protein in this patient showed a normal molecular weight and normal calcium binding properties. Activation of the mutant factor IX with factor XIa showed normal proteolytic cleavage. DNA sequence from the eight factor IX exons and flanking introns was amplified from this patient using the polymerase chain reaction. The amplified material was subjected to direct chain termination nucleotide sequencing. The only nucleotide sequence alteration found was a G----C transversion at nucleotide 20,524, changing the amino acid encoded at residue 182 from valine to leucine. This residue is one amino acid removed from the beta cleavage site of factor IX. This residue is highly conserved in other vitamin K dependent serine proteases and we propose that its alteration in this patient is responsible for his mild haemophilic phenotype, and for the abnormal interaction of this factor IX protein with the extrinsic system of coagulation.
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Affiliation(s)
- S A Taylor
- Department of Pathology, Queen's University, Kingston, Ontario, Canada
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Abstract
The polymerase chain reaction (PCR) is a technique that allows a million-fold, or greater, amplification of defined regions of DNA or RNA. It is potentially capable of detecting a single copy of a gene, present only once in 105 eukaryotic cells. This remarkable level of sensitivity has allowed the development of many diagnostic assays for human pathogens and disease states. These include: the detection of viral, bacterial and protozoal agents; diagnosis and genetic analysis of inherited diseases such as β-thalassaemia, sickle cell disease, haemophilia, Tay-Sachs disease and many others; diagnosis and analysis of neoplastic disorders such as, chronic myelogenous leukaemia (CML), acute lymphocytic lymphoma (ALL), follicular lymphomas and various other cancers, including the detection of activated oncogenes; prenatal and pre-implantation diagnosis; and the development of genetic risk prediction. The PCR can greatly simplify diagnostic processes that were previously difficult to perform, particularly where the initial amounts of biological material were very limited. In other cases, PCR provides the only method available for detection and diagnosis. However, although simple in theory, the PCR technique remains, for routine clinical diagnostic purposes, currently in the domain of the specialist laboratory. This is because of its sensitivity to nucleic acid contamination from other sources that can cause misleading results. Procedures and precautions are being developed to minimize this problem and there is little doubt that, in many instances, the PCR will be the diagnostic method of choice within the next few years.
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