Congenital hypofibrinogenemia is a rare disorder caused by heterozygous mutations in the fibrinogen genes. The aim of this study was to elucidate the molecular defects in two unrelated families with hypofibrinogenemia. The proband from family A was a 19-year-old Chinese boy who was suffering from cervical lymphadenitis. A low plasma fibrinogen concentration (0.63 g/l by Clauss method and 0.77 g/l by immunoturbidimetry) was found in routine clotting tests. Further gene analysis revealed a heterozygous g.5792 G>T mutation in exon 7 of the FGG, leading to a novel Trp208Leu change in the γ D domain. This mutation was also found in other family members with low fibrinogen levels. The proposita from family B was a 37-year-old female who suffered from recurrent shoulder pain for 7 years. Routine clotting studies revealed that her prothrombin time was 15.5 s (normal range: 11.8-14.8 s) and thrombin time was 22.8 s (normal range: 14.0-20.0 s), and the fibrinogen concentration in her plasma was only 0.64 g/l by Clauss method and 0.79 g/l by immunoturbidimetry. A heterozygous A>C transition at nucleotide 5864 of FGG was found in the γ chain, causing a Lys232Thr substitution in the fibrinogen. Further sequencing established that her mother, son, brother and nephew were also heterozygous for the mutation.

Congenital factor XII (FXII) deficiency is a rare autosomal recessive disorder, characterized by a great variability in its clinical manifestations. In this study, we screened for mutations in the F12 gene of 4 unrelated patients with FXII coagulant activity <10% of that of normal human plasma. To investigate the molecular defects in these FXII-deficient patients, we performed FXII mutation screening. By sequencing all coding exons as well as flanking intronic regions of the F12 gene, 6 different mutations, including 3 missense mutations (Gly341Arg, Glu502Lys and Gly542 Ser), 1 insertion (7142insertC) and 2 deletions (5741-5742 delCA and 6753-6755delACA), were identified on the F12 gene. Three of them (Gly341Arg, 5741-5742delCA and 6753-6755delACA) are reported here for the first time. Computer-based algorithms predicted these missense mutations to be deleterious. This study has increased our knowledge of the mutational spectrum underlying FXII deficiency.

Congenital factor V deficiency is a rare bleeding disorder characterized by low coagulant activity, associated with variable phenotypic expression. Among rare inherited coagulopathies, the molecular basis of factor V deficiency is rarely described because of its relatively low prevalence in the general population. Recently, we detected two genetic variations in factor V of a Chinese patient with hereditary factor V deficiency. One was a heterozygous nonsense mutation, C67868T in exon 22, which resulted in Gln2031stop substitution in the C1 domain of factor V. The other was a previously described polymorphism, G1618A in exon10, leading to Arg485Lys substitution. We deduced that the nonsense mutation is responsible for the factor V deficiency, whereas the Arg485Lys polymorphism is expected to compensate for the low plasma factor V levels. Of note, the nonsense mutation has been confirmed to be a novel mutation.

Hypofibrinogenemia is characterized by low plasma fibrinogen concentrations (<1.5 g/l). It is usually caused by heterozygous mutations in one of the three fibrinogen genes. To the best of our knowledge, the vast majority of these mutations have been proven to be inherited from a parent. We studied here a Chinese family in which the proband had low functional and antigen fibrinogen levels, 0.77 and 0.90 g/l, respectively. DNA sequencing revealed a novel Asp316His mutation in the γD domain of fibrinogen. However, both parents were negative for the mutation. Modeling analysis indicated that the Asp316His mutation may destabilize the conformation of the γ314-γ318 loop and lead to hypofibrinogenemia. Haplotype analysis of single-nucleotide polymorphisms excluded the possibility of nonpaternity, indicating it is a de-novo event. Further investigation of her living environment suggested the Asp316His mutation might have been induced by exposure to chromate mutagens.

Congenital coagulation factor VII (FVII) deficiency is a rare disorder caused by mutation in F7 gene. Herein, we reported a patient who had unexplained hematuria and vertigo with consanguineous parents. He has been diagnosed as having FVII deficiency based on the results of reduced FVII activity (2.0%) and antigen (12.8%). The thrombin generation tests verified that the proband has obstacles in producing thrombin. Direct sequencing analysis revealed a novel homozygous missense mutation p.Trp284Gly. Also noteworthy is the fact that the mutational residue belongs to structurally conserved loop 140s, which majorly undergo rearrangement after FVII activation. Model analysis indicated that the substitution disrupts these native hydrophobic interactions, which are of great importance to the conformation in the activation domain of FVIIa.