A novel factor X mutation Cys81 by Arg and a reported factor VII polymorphism Arg353 replaced by Gln co-occured in a patient

Characterization of a Missense Mutation in the Catalytic Domain and a Splicing Mutation of Coagulation Factor X Compound Heterozygous in a Chinese Pedigree

Background: Congenital coagulation factor X (FX) deficiency is a rare bleeding disorder with an incidence of one in one million caused by mutations in the FX-coding gene(F10), leading to abnormal coagulation activity and a tendency for severe hemorrhage. Therefore, identifying mutations in FX is important for diagnosing congenital FX deficiency. Results: Genetic analysis of the proband identified two single-base substitutions: c.794T > C: p.Ile265Thr and c.865 + 5G > A: IVS7 + 5G > A. His FX activity and antigen levels were < 1% and 49.7%, respectively; aPTT and PT were prolonged to 65.3 and 80.5 s, respectively. Bioinformatics analysis predicted the two novel variants to be pathogenic. In-vitro expression study of the missense mutation c.794T > C: p.Ile265Thr showed normal synthesis and secretion. Activation of FXs by RVV, FVII/TF, and FVIII/FIX all showed no obvious difference between the variant and the reference. However, clotting activity by PT and aPTT assays and activity of thrombin generation in a TGA assay all indicated reduced activity of the mutant FX-Ile265Thr compared to FX-WT. Minigene assay showed a normal splicing mode c.865 + 5G > A: IVS7 + 5G > A, which is inconsistent with clinical phenotype. Conclusions: The heterozygous variants c.794T > C: p.Ile265Thr or c.865 + 5G > A: IVS7 + 5G > A indicate mild FX deficiency, but the compound heterozygous mutation of the two causes severe congenital FX deficiency. Genetic analysis of these two mutations may help characterize the bleeding tendency and confirm congenital FX deficiency. In-vitro expression and functional study showed that the low activity of the mutant FX-Ile265Thr is caused by decrease in its enzyme activity rather than self-activation. The minigene assay help us explore possible mechanisms of the splicing mutation. However, more in-depth mechanism research is needed in the future.

A Compound Heterozygosis of Two Novel Mutations Causes Factor X Deficiency in a Chinese Pedigree

BACKGROUND

Mutations in the F10-coding gene can cause factor X (FX) deficiency, leading to abnormal coagulation activity and severe tendency for hemorrhage. Therefore, identifying mutations in F10 is important for diagnosing congenital FX deficiency.

METHODS

We studied a 63-year-old male patient with FX deficiency and 10 of his family members. Clotting and immunological methods were used to determine activated partial thromboplastin time (aPTT), prothrombin time (PT), thrombin time (TT), fibrinogen levels, FX activity, and FX antigen levels. The platelet count was determined. A mixing study was performed to eliminate the presence of coagulation factor inhibitors and lupus anticoagulant. Mutations were searched using whole-exome sequencing and certified by Sanger sequencing.

RESULTS

Genetic analysis of the proband identified two single-base substitutions: c.1085G>A (p.Ser362Asn) and c.1152C>A (p.Tyr384Ter, termination codon, caused by the DNA sequence TAA). His FX activity and antigen levels were 1.7% and 408.53 pg/mL, respectively; aPTT and PT were 52.3 and 48.0 s, respectively. One brother had the same compound heterozygous mutations, and his FX activity and antigen levels were 1.3% and 465.47 pg/mL, respectively; his aPTT and PT were 65.2 and 54.5 s, respectively. His mother, another brother, and one sister were heterozygous for c.1085G>A (p.Ser362Asn), and his daughter and grandson (6 years old) were heterozygous for c.1152C>A (p.Tyr384Ter).

CONCLUSION

The heterozygous variants p.Ser362Asn or p.Tyr384Ter indicate mild FX deficiency, but the compound heterozygous mutation of the two causes severe congenital FX deficiency and bleeding. Genetic analysis of these two mutations may help characterize the bleeding tendency and confirm congenital FX deficiency.

Rare bleeding disorders and advances in gene therapy

: Rare bleeding disorders usually begin in childhood and manifest as varying degrees of bleeding, which can be life-threatening in severe cases. With the development of gene editing technology, it is expected that hereditary coagulation factor disorders will someday be fundamentally cured by gene therapy. On account of their rarity, comprehension of these diseases is essential for the application of new treatment strategies. We have compiled the features of some newly discovered mutations of prothrombin, factor VII, and factor X in recent years. In addition, this review introduces the advances and obstacles in gene therapy.