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Missense changes in the catalytic domain of coagulation factor X account for minimal function preventing a perinatal lethal condition
Author(s) -
Ferrarese Mattia,
Baroni Marcello,
Della Valle Patrizia,
Spiga Ivana,
Poloniato Antonella,
D'Angelo Armando,
Pinotti Mirko,
Bernardi Francesco,
Branchini Alessio
Publication year - 2019
Publication title -
haemophilia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.213
H-Index - 92
eISSN - 1365-2516
pISSN - 1351-8216
DOI - 10.1111/hae.13761
Subject(s) - missense mutation , null allele , loss function , nonsense mutation , medicine , genetics , nonsense , mutation , biology , gene , allele , phenotype
Inherited deficiencies in the coagulation pathway provide diversified models to investigate the molecular bases of perinatal lethality associated with null‐like variants. Differently from X‐linked haemophilias, homozygous/doubly heterozygous null variants in the rare autosomally inherited deficiency of factor X (FX) might be incompatible with perinatal survival. Aim To provide experimental evidence about the null/close‐to‐null FX function. Methods The residual secreted (ELISA) and functional (thrombin generation assays) protein levels associated with the novel nonsense (c.1382G>A; p.Trp461Ter) and missense (c.752T>C; p.Leu251Pro) variants, found in the proposita with life‐threatening symptoms at birth, were characterized through recombinant (r)FX expression. Results The rFX‐461Ter showed very low secretion and undetectable function. Expression and function of the predicted readthrough‐deriving missense variants (rFX‐461Tyr, rFX‐461Gln) were also severely impaired. These unfavourable features, due to nucleotide and protein sequence constraints, precluded functional readthrough over the 461 stop codon. Differently, the poorly secreted rFX‐251Pro variant displayed residual function that was characterized by anti‐TFPI aptamer‐based amplification or selective inhibition of activated FX function by fondaparinux in plasma and found to be reduced by approximately three orders of magnitude. Similarly to the rFX‐251Pro, a group of catalytic domain missense variants cause poorly secreted molecules with modest function in FX‐deficient patients with life‐threatening symptoms. Conclusions Our data, contributing to the knowledge of the very severe FX deficiency forms, support life‐saving requirement of trace FX function, clearly exemplified by the dysfunctional but not completely inactive rFX‐251Pro variant that, albeit with severely reduced function, is compatible with a residual activity ensuring minimal haemostasis and permitting perinatal survival.