Novel Compound Heterozygous Factor V Deficiency with Severe Clinical Phenotype.

Congenital factor V (FV) deficiency is a rare clotting disorder associated with mild to severe hemorrhagic symptoms and a prevalence of approximately 1 per million in the general population. Patients with FV deficiency normally show very low or unmeasurable plasma levels of functional and immunoreactive FV and are usually homozygous or compound heterozygous for mutations located in the FV gene. Heterozygous carriers have approximately half-normal levels of FV and are usually asymptomatic.

In this study, a proposita now aged 71 is described, who has less than 3% FV activity and is clinically diagnosed as having severe FV deficiency. Since childhood she has exhibited severe bleeding tendency with surgery/dental extraction or trauma. Other symptoms include frequent nose bleeds, bruising easily and profound menorrhagia that led to eventual hysterectomy in her mid-thirties. Parents were clinically asymptomatic suggesting compound heterozygous FV deficiency for this individual. Her children, a son and a daughter, are also asymptomatic and have FV levels of approximately 50-60%.

DNA was isolated from peripheral blood leucocytes and the FV exon and flanking intron sequences were amplified by PCR, and subjected to automatic DNA sequence analysis. FV levels were assayed in plasma using conventional clotting assays as well as immunoassays using monoclonal and polyclonal antibodies detecting several regions of FV.

DNA sequence analysis revealed two mutations: the first in exon 17 (C > T) changed the codon for Leu-1821 to Ser (L1821S), the second in exon 25 (T > G) changed Gly-2192 to Cys (G2192C). Plasma clotting assays (n=2) showed FV activity levels of 0.5±0.015% for prothrombin time and 2.0±0.10% for activated partial thromboplastin time compared to normal pooled plasma. Western blot analysis using a polyclonal antibody demonstrated the patient FV banding pattern was comparable to normal plasma. Densitometric analysis of the specific bands showed that the patient had 9% of the FV antigen level compared to normal pooled plasma.

Two novel FV mutations have been identified. It has previously been reported in the literature that mutations involving thiols can have deleterious effects on protein folding and secretion. Consequently, the G2192C mutation could alter the FV protein folding and/or secretion which may explain the reduced level of FV antigen detected by immunoassay. In addition, the L1821S mutation is close to a putative activated FV metal ion binding site and may have an important effect on inter subunit reactions and subsequently FV function. Since antigen and activity are discordant, both FV function and secretion appear to be affected by these mutations. Future studies aim to introduce these unique mutations into recombinant FV protein to gain new insight into FV secretion, activity and function.

No relevant conflicts of interest to declare.