Factor V Deficiency

Pattern of Inheritance

Factor V deficiency is inherited in an autosomal recessive pattern. Patients may be heterozygous, compound heterozygous, or homozygous for mutations. The North American Rare Bleeding Disorders Registry classified all patients with FV levels less than 0.2 U mL–1 (<20%) as homozygotes and those with levels greater than or equal to 0.2 U mL–1 (≥20%) as heterozygotes, although this classification was not corroborated with genetic analysis. Therefore, individuals in this registry will hereafter be referred to as those with <20% activity versus those with >20%.

Genetic Testing Options

Almost all FV mutations identified to date are private mutations specific to each family. Hence, the entire gene must be screened for the molecular diagnosis of FV deficiency to be made. Currently, FV sequencing is not available as a clinical test. However, sequencing may be available in specific research laboratories. See the Research section for list of laboratories that are doing research on FV. 

Prenatal Diagnosis

Prenatally obtained FV levels need to be interpreted with caution, as FV levels appear to be developmentally regulated. At 19-23 weeks’ gestation, the mean FV level is 32.1%, whereas it is 48.9% at 30-38 weeks and 89.9% at term.{Reverdiau-Moalic, 1996 #513} However, prenatal molecular diagnosis is in theory possible if the mutations in both parents are known and facilities are available for fetal DNA sequencing.

Available Genetic Databases

Human Genome Mutation Database www.hgmd.org

Rare Bleeding Disorders Database http://www.rbdd.org