Background: Dissection of genotype-phenotype relationships in haemophilia B (HB) is particularly relevant for challenging (mild HB) or for HB-associated but unclassified factor IX (FIX) missense variants. Here, the identification of a FIX missense variant associated with mild HB, reported but unclassified, prompted a multiple-level approach to contribute elements to interpret unclassified HB-associated FIX missense variants. Methods: Molecular modelling of wild-type (WT) and V92A FIX variants, expression studies in HEK293 cells with evaluation of protein (ELISA, Western blotting) and activity (aPTT-based/chromogenic assays) levels after recombinant expression, and multiple prediction tools. Results: The F9(NM_000133.4):c.275T>C (p.V92A) variant was found in a mild HB patient (antigen, 45.4 U/dl; coagulant activity, 23.6 IU/dl; specific activity, 0.52). Newly generated molecular models showed alterations in Gla/EGF1-EGF2 domain conformation impacting on Ca++ affinity and protein-protein interactions with FXIa. Multi-tool analysis indicated a moderate impact on protein structure/function of the valine-to-alanine substitution, in accordance with patient's and modelling data. Expression studies on the V92A variant showed a specific activity (0.49±0.07; WT, 1.0±0.1) recapitulating that of the natural variant, and pointed toward a moderate activation impairment as the main determinant underlying the p.V92A defect. The validated multi-tool approach, integrated with evidence-based data, was challenged on a panel (n=9) of unclassified FIX missense variants, which resulted in inferred protein (secretion/function) outputs and HB severity. Conclusions: The rational integration of multi-tool and multi-parameter analyses contributed elements to interpret genotype/phenotype relationships of unclassified FIX missense variants, with implications for diagnosis, management and treatment of HB patients, and potentially translatable into other human disorders.
An integrated multi-tool analysis contributes elements to interpreting unclassified factor IX missense variants associated with haemophilia B
Testa, Maria Francesca;Branchini, Alessio
;
2024
Abstract
Background: Dissection of genotype-phenotype relationships in haemophilia B (HB) is particularly relevant for challenging (mild HB) or for HB-associated but unclassified factor IX (FIX) missense variants. Here, the identification of a FIX missense variant associated with mild HB, reported but unclassified, prompted a multiple-level approach to contribute elements to interpret unclassified HB-associated FIX missense variants. Methods: Molecular modelling of wild-type (WT) and V92A FIX variants, expression studies in HEK293 cells with evaluation of protein (ELISA, Western blotting) and activity (aPTT-based/chromogenic assays) levels after recombinant expression, and multiple prediction tools. Results: The F9(NM_000133.4):c.275T>C (p.V92A) variant was found in a mild HB patient (antigen, 45.4 U/dl; coagulant activity, 23.6 IU/dl; specific activity, 0.52). Newly generated molecular models showed alterations in Gla/EGF1-EGF2 domain conformation impacting on Ca++ affinity and protein-protein interactions with FXIa. Multi-tool analysis indicated a moderate impact on protein structure/function of the valine-to-alanine substitution, in accordance with patient's and modelling data. Expression studies on the V92A variant showed a specific activity (0.49±0.07; WT, 1.0±0.1) recapitulating that of the natural variant, and pointed toward a moderate activation impairment as the main determinant underlying the p.V92A defect. The validated multi-tool approach, integrated with evidence-based data, was challenged on a panel (n=9) of unclassified FIX missense variants, which resulted in inferred protein (secretion/function) outputs and HB severity. Conclusions: The rational integration of multi-tool and multi-parameter analyses contributed elements to interpret genotype/phenotype relationships of unclassified FIX missense variants, with implications for diagnosis, management and treatment of HB patients, and potentially translatable into other human disorders.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
