Factor V Leiden Thrombophilia: Exploring Mendelian Genetics & Analysis

This report provides a comprehensive analysis of Factor V Leiden thrombophilia (F-VLT), a genetic disorder resulting in blood clot formation. It delves into the pathophysiology of F-VLT, detailing the clotting mechanism and the impact of the F5 gene mutation, specifically the guanine to adenine substitution at nucleotide 1691. The report explores the Mendelian genetics of F-VLT, including inheritance patterns, pedigree analysis, and gene-level mutations, highlighting its autosomal dominant nature with incomplete penetrance. Furthermore, it discusses the incidence and occurrence of F-VLT, particularly among Caucasian populations. The report also addresses the diagnosis of F-VLT through coagulation screening tests and genetic testing (DNA analysis), emphasizing ethical considerations such as autonomy, informed consent, and privacy. Treatment options, primarily involving anticoagulants like heparin, are discussed, along with the prognosis, which depends on the number of F5 gene mutations and other risk factors. The report concludes by summarizing the key aspects of F-VLT, including its genetic basis, clinical manifestations, diagnostic approaches, ethical considerations, and treatment strategies.

Running head: FACTOR V LEIDEN THROMBOPHILIA
Factor V Leiden Thrombophilia: Analysis of Underlying Mendelian Genetics
Name of the Student
Name of the University
Author Note

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Introduction
Factor V Leiden thrombophilia (F-VLT) is a genetic disorder that results in the
formation of the blood clot mainly in the lower portion of the limbs (deep venous thrombosis
or DVT) or lungs (pulmonary embolism or PE). The gene mutation in the F5 gene, which
plays a significant role in the blood clotting results in the formation of the disease. However,
95% of the population living with this mutation does not develop a clot during their entire
stage of life (National Center for Advancing Translational Sciences, 2019).
The following assignment aims to analyse the underlying pathophysiology of F-VLT
followed by a detailed analysis of the Medelian genetics leading to the gene-level mutation of
F-VLT. At the end, the assignment will discuss diagnosis, ethics, treatment and prognosis of
F-VLT.
Pathophysiology of Factor V Leiden Thrombophilia (F-VLT) 300
The clotting mechanism is broken into 2 stages. First is primary hemostasis (PH) and
secondary hemostatis (SH). In PH vasoconstriction occurs due to vessel injury (damaged
endothelium) mediated by inflammatory mediators and ATP generated by von Willebrand
factor (vWF). This leads to the exposure of endothelial collagen, promoting platelet adhesion
at the site of injury. Plate adhesion occurs by platelet activation followed by platelet
aggregation. Platelet activation is mediated by thrombin. Thrombin directly activates platelets
through proteolytic cleavage. Moreover, thrombin stimulates platelet granule, which activates
platelet activating factor and ADP leading to comprehensive platelet activation. Once platelet
is activated Gp IIb/IIIa receptors adhere to vWF and fibrinogen, forming weak platelet plug.
SH involves clotting factors. Tissue factor (TF) binds to FVII, activating FVII to factor VIIa
(FVIIa), forming TF-FVIIa complex (Garmo & Burns, 2018). This complex activates factor

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X (FX) (extrinsic pathway). TF-FVIIa complex can also activate factor IX (the intrinsic
pathway or alternate pathway). Once Factor X is activated, the cascade continues down the
common pathway of activation of activation of Factor Xa. Factor Xa binds with Factor Va
and calcium to form prothrombinase complex, activating prothrombin (aka Factor II) into
thrombin. Thrombin activates FXIIIa. FXIIIa crosslinks with fibrin forming stabilized clot
(Garmo & Burns, 2018).
Figure: Mechanism of blood Clot
(Source: Garmo & Burns, 2018)
F-VLT causes mutation of Factor V (F5) gene. The mutation in the F-VLT is
characterised by a guanine to adenine substitution at 1691 nucleotide at the exon 10. This
substitution mutation of a nucleotide (at codon 506) leads to a change in the amino-acid
sequence from arginine to glutamine. The mutated gene is known as FV R506 (Leiden) and
leads to resistance towards F-VLT inactivation by protein C. As a result of this, factor V

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persists within the circulation leading to development of the mild hyper-coaguable state. The
Leiden mutation accounts for 90 to 95% of APA resistance. Heterozygous carriers of the
mutation have an eight to four-fold high rate of thrombosis. Homozygous individuals for the
mutation have 80 to 100 fold risk of thrombosis. Genetic counselling is recommended for the
homozygous parents (National Centre for Advancing Translational Sciences, 2019).
Genetics of Factor V Leiden Thrombophilia (F-VLT)
Inheritance pattern and pedigree
The chances abnormal blood clot depends on whether an individual has one/two
copies of the factor V Leiden mutation. People who have inherited two copies of the
mutation, one each parent, have a higher risk of developing a clot in comparison to people
who inherit one copy of the mutation (U.S National Library of Medicine, 2019). F-VLT is an
autosomal dominant disorder with but with incomplete penetrance. This signifies that the
people who have one diseased gene located in one allele, the might not have 100% of
penetrance in spite of having autosomal dominant inherence patter. The homozygous
diseased individual with diseased gene in both the alleles shows complete penetrance along
with expresitivity of the diseased trait (U.S National Library of Medicine, 2019).
Parent (RfRn) (heterozygous parent) Parent (RfRn) (heterozygous parent)
RfRf (homozygous diseased) RfRn (heterozygous diseased)
RnRf (heterozygous diseased) RnRn(homozygous normal)
Rn: Normal allele
Rf: Diseased allele
Heterozygous diseased: 50%
Homozygous diseased: 25%

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Homozygous normal: 25%
Parent (RfRf) (homozygous parent) Parent (RfRn) (heterozygous parent)
RfRf (homozygous diseased) RfRn (heterozyhous diseased)
RfRf (homozygous diseased) RfRn (heterozyhous diseased)
Parent (RnRn) (homozygous normal) Parent (RnRf) (heterozygous diseased)
RnRn (homozygous normal) RnRf (heterozygous diseased)
RnRn (homozygous normal) RnRf (heterozygous diseased)
(Source: U.S National Library of Medicine, 2019)
Gene mutation
F-VLT gene is located in chromosome 1 long arm at 24.2 location (1q24.2). F-VLT
gene encodes FV coagulation factor, a 330 kD large plasma glycoprotein that circulates
within blood in an inactive form. Once activated by thrombin, the activated FV protein (FVa)
initiates the formation of clot by forming the cross-linkage of heavy chain and light chain of
calcium ions and simultaneous conversion of prothrombin to thrombin by factor Xa forming
mesh framework of clot. The mutation of the Factor V gene leads to faulty expression of the
factor V protein. This faulty protein is activated even in the absence of thrombin, leading to
the unwanted formation of clot even in the absence of the injury. Alternative opinion suggests
that faulty protein of factor V once activated refuse to get deactivated as there occurs change
in the binding site of the APC (activate Protein C) co-factor leading to the formation of the
enlarged clot. The mapping of the F5 gene in the chromosome 1 is done by Southern
hybridization to the somatic cell hybrid DNA. The in situ-hybridization helped in the

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recognition of 1q21-925 as the main location of the F5 gene within the chromosome. The X-
ray crystallographic structure of factor v protein revealed that it is made of beta barrel
frameworks that provide scaffold for the generation of 3 protruding loops and one of which
adopts different conformations under the 2 different crystal forms. The beta barrel structure
of Factor V protein helps them to entangle within the phsopholipid bilayer of the damaged
tissues leading to clot formation.
Figure: The size, location and the exon count of Factor V Leiden Thrombophilia Gene
Source:
Incidence and occurrence
According to the Royal College of Pathologists of Australia (2019), F-VLT occurs in
only 5% of the Australian population and is mainly in the heterozygous form and has in
increased risk of developing venous thromboembolism. The risk of thrombosis does not
appear to be increased. According to National Human Genome Research Institute (2019),

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Factor V Leiden is the most common inherited form of thrombophilia. At least 3 to 8% of the
Causasian (white) residing in U.S are the main victims. Among the European population, the
majority are heterozygous and only 1 out of the 5000 people are homozygous. The mutation
is less common in other population.
Diagnosis, ethics, treatment and prognosis of Factor V Leiden Thrombophilia (F-VLT)
Diagnosis
The healthcare physicians suspect thrombophilia if there is a family history of
thrombophilia. The diagnosis is done by using a special screening test known as coagulation
screening test or by genetic testing (DNA analysis) of the F5 gene. The genetic testing or the
DNA analysis is done by the help of the PCR. The primers (forward and reverse) are
designed based on the coding region of the F-V gene. The DNA isolated from the blood
stream of the infected person is denatured into single strand and then PCR is conducted with
the help to the primer designed. The PCR product is then run in the agarose gel against the
DNA ladder. The presence of the gene within the DNA indicates the band of the size of the
gene and there indicating the presence of the faulty gene in the DNA. The gel DNA is
extracted and then sequences by Sanger methods for further verification and for reducing the
chances of getting false positive results (MacCallum, Bowles & Keeling, 2014). However,
genetics testing of inherited diseases must be done under controlled supervision of the ethical
guidelines like the principle of autonomy, informed consent while proper maintenance of
privacy and confidentiality.
Ethics
The early detection of F-VTL requires genetic testing. Genetic testing is associated
with several ethical regulations like ethical issue of autonomy. As per these ethical
guidelines, informed consent must be taken from the concerned person before the initiation of

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the genetic testings process. During the process of genetic screening, privacy and
confidentiality of the individuals and their family must be secured. Thus storing of the gene
samples must be done through proper allocation of the numbers or codes and the name or
other identification information must be kept withheld (Andrews et al., 1994).
Treatment
Management of individuals with factor V Leiden depends on the impending clinical
circumstance. People with F-VLT who have DVT or PE are treated with the help of blood
thinners or administration of anti-coagulants. Anticoagulants like heparin are administered
under varied dilution and in different interval depending of the individual condition. Lifelong
administration of heparin or other anti-coagulants are not recommended unless additional risk
factors apart from DVT and PE is present (MacCallum, Bowles & Keeling, 2014). The
presence of Factor V Laiden increases the risk of developing DVT during pregnancy by 7
folds. Regular follow-up and medications help to overcome this situation (National Human
Genome Research Institute, 2019).
Prognosis
The expression of the diseased trait is no directly proportional to the presence of the
gene mutation. The expression of the faulty trait depends on the number of the FV or F5 gene
mutations, which the person have inherited and the presence of other gene alterations
associated with blood clotting (like haemophilia another genetic disorder, X-linked recessive
inheritance) and other circumstantial risk factors like surgery, oral contraceptives and
pregnancy. The appearance of the first symptoms of F-VLT occurs at the age of 30 or by the
age of 50 (Stevens et al. 2016).

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Conclusion
Thus from the above discussion it can be concluded that F-VLT is an autosomal
dominant disorder with incomplete penetrence. It occurs as a result of the mutation in the F5
gene presence in the chromosome 1 responsible for the formation of the factor 5 protein, an
important factor in blood coagulation process. The diseases person is found of have un-
necessary clots within the blood stream resulting in the formation of DVT and PE. The
appearance of symptoms occurs after the age of 30 years in some cases 50 years and mainly
prevalent among Caucasians. The disease prognosis is poor is there is no recovery and the
main medicines used for relief is use of anticoagulant like heparin. The use of PCR/DNA
testing is employed for the identification of the disease under strict ethical consideration of
autonomy, privacy, confidentiality and informed consent.

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References
Andrews, L., Fullarton, J., Holtzman, N., & Motulsky, A. (1994). Social, legal, and ethical
implications of genetic testing. In Assessing Genetic Risks: Implications for health
and social policy. National Academy Press, Washington, DC.
Garmo, C., & Burns, B. (2018). Physiology, Clotting Mechanism. Access date: 8th Feb 2019.
Retrieved from: https://www.ncbi.nlm.nih.gov/books/NBK507795/
MacCallum, P., Bowles, L., & Keeling, D. (2014). Diagnosis and management of heritable
thrombophilias. bmj, 349, g4387.
National Center for Advancing Translational Sciences. (2019). Genetic and Rare Diseases
Information Center: Factor V Leiden Thrombophilia. Access date: 8th Feb 2019.
Retrieved from: https://rarediseases.info.nih.gov/diseases/6403/factor-v-leiden-
thrombophilia
National Human Genome Research Institute. (2019). Learning About Factor V Leiden
Thrombophilia. Access date: 8th Feb 2019. Retrieved from:
https://www.genome.gov/15015167/learning-about-factor-v-leiden-thrombophilia/
NCBI. (2019). F5 coagulation factor V [ Homo sapiens (human) . Access date: 13th Feb
2019. Retrieved from: https://www.ncbi.nlm.nih.gov/gene?
Db=gene&Cmd=DetailsSearch&Term=2153
Royal College of Pathologists of Australia (2019). Molecular Genetics - Genetic Disorders.
Access date: 8th Feb 2019. Retrieved from: https://www.rcpa.edu.au/Manuals/RCPA-
Manual/Pathology-Tests/M/Molecular-genetics-genetic-disorders

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Stevens, S. M., Woller, S. C., Bauer, K. A., Kasthuri, R., Cushman, M., Streiff, M., ... &
Douketis, J. D. (2016). Guidance for the evaluation and treatment of hereditary and
acquired thrombophilia. Journal of thrombosis and thrombolysis, 41(1), 154-164.
U.S National Library of Medicine. (2019). Factor V Leiden thrombophilia. Access date: 8th
Feb 2019. Retrieved from: https://ghr.nlm.nih.gov/condition/factor-v-leiden-
thrombophilia#inheritance