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Thromb Res. 2001 Nov 15;104(4):257-64.

A new factor X defect (factor X Padua 3): a compound heterozygous between true deficiency (Gly(380)-->Arg) and an abnormality (Ser(334)-->Pro).

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Department of Medical and Surgical Sciences, Second Chair of Medicine, University of Padua, via Ospedale 105, 35100 Padua, Italy.


We report a novel mutation in Factor X (FX) gene which results in a phenotype without any bleeding tendency. The proband has been found to be a compound heterozygote between a novel FX true deficiency (Gly(380)-->Arg) and a previously reported dysfunctional mutation Ser(334)-->Pro (FX Marsiglia). Prothrombin time (PT) and partial thromboplastin time (PTT) were moderately prolonged and were fully corrected by the addition of normal serum. Her FX activity level varied between 8% and 19% of normal according to the method used whereas the FX antigen level was 40% of the normal control value. All the exons and intron/exon junctions of the FX gene were studied using a combined approach of polymerase chain reaction and conformation sensitive gel electrophoresis. A transversion G to A in exon 8 resulting in the replacement of Gly380 by Arg was found in the proband, in the father and in a proband's brother, whereas heterozygous FX Marsiglia was present in the proband's mother and her sister. Gly380 is strictly linked to Ser379, a component of the catalytic triad. The substitution of Gly for Arg causes the introduction of a large charged amino acid which could affect the catalytic function of FX leading to secretion problem, accounting for the cross-reactive material (CRM) negative phenotype.

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