Hereditary angioedema (HAE) is due to mutations in C1 inhibitor (C1-INH) gene causing its deficiency. Two phenotypic variants are known: HAE type I with low antigenic and functional plasma level of C1-INH, and type II with low C1-INH function, but normal or increased antigen due to the presence of a dysfunctional protein. Clinical expression of HAE is unpredictable despite a stable defect. We hypothesize that: i) the type of mutation in C1-INH gene and/or polymorphisms affecting the function of proteins involved in pathogenesis of symptoms could influence HAE expression; ii) the clinical response to treatment with attenuated androgens depends on the upregulation of C1-INH expression in tissues. The experimental approach is based on: i) identification of mutations responsible of HAE, definition of their structural consequences by molecular modeling, functional characterization of expressed mutant C1-INHs. ii) association of polymorphisms of coagulation Factor XII and angiotensin converting enzyme with different clinical phenotypes of HAE; iii) measurement, by real time PCR, of C1-INH mRNA from peripheral blood mononuclear cells of HAE patients on and off treatment with attenuated androgens. Mutation screening will be performed by fluorescence activated mismatch analysis. Preliminary results: 36 different mutations were identified in genomic DNA, 5 of them were present in more than one family. 18 of these mutations have not been previously described. In HAE type I there were 13 different stop codons, 9 different missense mutations, 3 different splicing defects, 4 large deletions and 2 deletions of 1-2 amino acids. In HAE type II all mutations were missense consisting of 4 different substitutions at the reactive site (amino acid 444) and 1 in P10 position (amino acid 436). Compared to normal controls, the amount of C1-INH mRNA was 40% in HAE type I patients (p<0.0001) and 47% in HAE type II (p<0.0001). The difference between HAE type I and type II was not statistically significant. In order to define the frequency of transcribed mutations in HAE we sequenced cDNAs from 44 patients with missense mutations, nonsense mutations and splicing defects: in 34 of them (77%) we detected a transcript originated from the mutated allele. According to the type of mutations the frequency of transcripts was: 28 of 29 in missense mutations, 6 of 11 in nonsense mutations and none in 4 splicing defects. The amount of C1-INH mRNA in transcribed mutations was 1650 (380-6500) representing 46% of normal controls while it was lower, 37% of normal (1350 range 420-3400), in mutations that were not detected in cDNA. In order to analyze patients in whom just wilde-type mRNA was expressed, we considered the 4 large deletions and found that in this type of mutations C1-INH mRNA was 23% compared to controls. In summary: We confirmed that HAE is characterized by a high number of “private” mutations C1-INH mRNA in cytoplasm of PBMC from HAE patients was approximately 50% of that found in normal controls. Amounts of C1-INH mRNA in patients with HAE type I and type II was not significantly different. 70% of the mutations responsible for HAE are transcribed into mRNA. C1-INH mRNA is 25% of controls in mutations that cannot be transcribed. These results suggest that in patients with HAE there is a downregulation of normal C1-INH allele to approximately 50% of its functional efficiency. This fact, in addition to the heterozygous defect, is responsible for plasma levels of normal C1-INH markedly below the expected 50% and eventually exposes to the appearance of angioedema symptoms.

Identification of variables causing different clinical expression of inherited c1-inh deficiency (hereditary angioedema) / E. Pappalardo, S. Caccia, M. Cicardi. ((Intervento presentato al 12. convegno Telethon Scientific Convention tenutosi a Riva del Garda nel 2003.

Identification of variables causing different clinical expression of inherited c1-inh deficiency (hereditary angioedema)

E. Pappalardo
Primo
;
S. Caccia
Secondo
;
M. Cicardi
Ultimo
2003

Abstract

Hereditary angioedema (HAE) is due to mutations in C1 inhibitor (C1-INH) gene causing its deficiency. Two phenotypic variants are known: HAE type I with low antigenic and functional plasma level of C1-INH, and type II with low C1-INH function, but normal or increased antigen due to the presence of a dysfunctional protein. Clinical expression of HAE is unpredictable despite a stable defect. We hypothesize that: i) the type of mutation in C1-INH gene and/or polymorphisms affecting the function of proteins involved in pathogenesis of symptoms could influence HAE expression; ii) the clinical response to treatment with attenuated androgens depends on the upregulation of C1-INH expression in tissues. The experimental approach is based on: i) identification of mutations responsible of HAE, definition of their structural consequences by molecular modeling, functional characterization of expressed mutant C1-INHs. ii) association of polymorphisms of coagulation Factor XII and angiotensin converting enzyme with different clinical phenotypes of HAE; iii) measurement, by real time PCR, of C1-INH mRNA from peripheral blood mononuclear cells of HAE patients on and off treatment with attenuated androgens. Mutation screening will be performed by fluorescence activated mismatch analysis. Preliminary results: 36 different mutations were identified in genomic DNA, 5 of them were present in more than one family. 18 of these mutations have not been previously described. In HAE type I there were 13 different stop codons, 9 different missense mutations, 3 different splicing defects, 4 large deletions and 2 deletions of 1-2 amino acids. In HAE type II all mutations were missense consisting of 4 different substitutions at the reactive site (amino acid 444) and 1 in P10 position (amino acid 436). Compared to normal controls, the amount of C1-INH mRNA was 40% in HAE type I patients (p<0.0001) and 47% in HAE type II (p<0.0001). The difference between HAE type I and type II was not statistically significant. In order to define the frequency of transcribed mutations in HAE we sequenced cDNAs from 44 patients with missense mutations, nonsense mutations and splicing defects: in 34 of them (77%) we detected a transcript originated from the mutated allele. According to the type of mutations the frequency of transcripts was: 28 of 29 in missense mutations, 6 of 11 in nonsense mutations and none in 4 splicing defects. The amount of C1-INH mRNA in transcribed mutations was 1650 (380-6500) representing 46% of normal controls while it was lower, 37% of normal (1350 range 420-3400), in mutations that were not detected in cDNA. In order to analyze patients in whom just wilde-type mRNA was expressed, we considered the 4 large deletions and found that in this type of mutations C1-INH mRNA was 23% compared to controls. In summary: We confirmed that HAE is characterized by a high number of “private” mutations C1-INH mRNA in cytoplasm of PBMC from HAE patients was approximately 50% of that found in normal controls. Amounts of C1-INH mRNA in patients with HAE type I and type II was not significantly different. 70% of the mutations responsible for HAE are transcribed into mRNA. C1-INH mRNA is 25% of controls in mutations that cannot be transcribed. These results suggest that in patients with HAE there is a downregulation of normal C1-INH allele to approximately 50% of its functional efficiency. This fact, in addition to the heterozygous defect, is responsible for plasma levels of normal C1-INH markedly below the expected 50% and eventually exposes to the appearance of angioedema symptoms.
Hereditary Angioedema; C1-Inhibitor ; Serpins ; Conformational Diseases ; Attenuated Androgens
Settore BIO/11 - Biologia Molecolare
Settore MED/09 - Medicina Interna
Telethon Fondazione Onlus
Identification of variables causing different clinical expression of inherited c1-inh deficiency (hereditary angioedema) / E. Pappalardo, S. Caccia, M. Cicardi. ((Intervento presentato al 12. convegno Telethon Scientific Convention tenutosi a Riva del Garda nel 2003.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/163721
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