Thrombophilias Flashcards
Hem A, Hem B, Protein C deficiency, Protein S deficiency, and Factor V Leiden
What lab features are seen in Hemophilia A
normal platelet count
prolonged activated partial thromboplastin time
normal prothrombin time
What lab features are seen in Hemophilia B
normal platelet count
prolonged activated partial thromboplastin time in those w severe/moderate dz; normal or mildly prolonged in pts w mild dz
normal prothrombin time
How is the dx of Hemophilia B established in a male proband? Female?
male w decreased factor 9 clotting activity
Severe: <1% F9 clotting activity
Moderate: 1-5% clotting activity
Mild: 6-40% clotting activity
identification of a hemizygous PV in F9 which can help to predict clinical phenotype
female w bleeding symptoms, decreased F9 clotting activity; and/or identification of a heterozygous PV clotting activity alone cannot identify heterozygous females since only 30% that are heterozygous have clotting levels lower than 40%
What molecular testing should be ordered for Hemophilia B
sequence analysis of F9 followed by del dup if the previous tests are negative
What are the clinical features associated with severe Hemophilia B
Usually dx in the neonatal period or within one yr of life
Hemarthrosis, especially with mild or no antecedent trauma (the most frequent manifestation)
Deep-muscle hematomas (causing pain)
Intracranial bleeding in the absence of major trauma
Neonatal cephalohematoma or intracranial bleeding
Prolonged oozing or renewed bleeding after initial bleeding stops following tooth extractions, mouth injury, or circumcision *
Prolonged or delayed bleeding or poor wound healing following surgery or trauma *
Unexplained gastrointestinal bleeding or hematuria *
Heavy menstrual bleeding, especially with onset at menarche
Prolonged nosebleeds, especially recurrent and bilateral *
Excessive bruising, especially with firm, subcutaneous hematomas
2-5 bleeding episodes per month
leading cause of death related to bleeding is intracranial hemorrhage; major cause of disability is joint pain
What are the clinical features associated with moderate hemophilia B
seldom have spontaneous bleeding, have prolonged or delayed oozing after relatively minor trauma and are usually dx before 5-6yo
bleeding episodes once a month to once a year
What are the clinical features associated with mild hemophilia B
do NOT have spontaneous bleeding
abnormal bleeding w sx, tooth extractions, and major injuries
bleeding episodes a few times a yr to once q10yrs
often not dx until later in life when they undergo sx or tooth excision or experience major trauma
What are the clinical features associated w hemophilia B in females
at risk for bleeding that is comparable to that seen in males with a similar severity of hemophilia
more subtle, abnormal bleeding may occur w baseline factor 9 clotting activity levels between 30-60%
What variants are directly correlated w disease severity in hemophilia B
alloimmune inhibitors occur much less frequently than in hemophilia A; occur with the greatest frequency (40-60%) in individuals w large partial (>50bp) dels, whole gene dels, or early termination variants; missense variants rarely associated
large dels, nonsense variants, and most frameshifts cause severe dz
missense variants can cause severe, moderate, or mild dz dependent on location and specific substitutions involved unlike hem A, severe hem B is often caused by a missense variant
What are the tx recommendations for pts w hemophilia B
Tx should be coordinated through a hemophilia treatment center
IV infusion of plasma-derived or recombinant factor IX to tx acute bleeding or prevent bleeding on a long term basis or prior to/following procedures.
peds issues: males w a FH of hemophilia B should NOT be circumcised unless hemophilia A is excluded or is tx w factor IX; immunizations should be given subcutaneously (not intramuscular if feasible)
for alloimmune tolerance against the first tx, gave use immune tolerance therapy
PT: use of musculoskeletal u/s aids in the eval of bleeding and helps to guide tx
gene therapy also exists and can achieve therapeutic levels in many individuals
PROPHYLACTIC TX IS CONSIDERED THE STANDARD OF CARE; greatest benefit is seen in those who start therapy before 2.5-3yo
How can you test for hemophilia B in pregnancy (in an unconventional way)
assay of factor 9 clotting activity from a cord blood sample obtained by venipuncture of the umbilical vein; factor IX clotting activity in cord blood in a normal term newborn is lower than in adults; therefore, the dx of hemophilia B can be established in those w <1% activity but is not confirmed in those with moderately low activity
women w hemophilia B are NOT protected in pregnancy since factor 9 levels do not rise; they are more likely to need factor 9 infusion support for delivery and/or to tx or prevent postpartum hemorrhage
How is the dx of Hemophilia A established in a male proband? Female?
male w decreased factor 8 clotting activity and a normal, functional von Willebrand factor level
Severe: <1% F8 clotting activity
Moderate: 1-5% clotting activity
Mild: 6-40% clotting activity
identification of a hemizygous PV in F8 which can help to predict clinical phenotype
female w bleeding symptoms, decreased F8 clotting activity, and a normal functional von Willebrand factor level; and/or identification of a heterozygous PV clotting activity alone cannot identify heterozygous females since only 30% that are heterozygous have clotting levels lower than 40%
What molecular testing should be ordered for Hemophilia A
targeted analysis for intron 22 and intron 1 (45% of PVs in severe type) for those with (1) severe hemophilia, (2) females w a FH of hemophilia, (3) females w a FH of Hemophilia A of unknown severity and a PV is not known
sequence analysis of F8 followed by del dup if the previous tests are negative
What are the clinical features associated with severe Hemophilia A
Usually dx in the neonatal period or within one yr of life
Hemarthrosis, especially with mild or no antecedent trauma (the most frequent manifestation)
Deep-muscle hematomas (causing pain)
Intracranial bleeding in the absence of major trauma
Neonatal cephalohematoma or intracranial bleeding
Prolonged bleeding or renewed bleeding after initial bleeding stops following tooth extractions, mouth injury, or circumcision *
Prolonged or delayed bleeding or poor wound healing following surgery or trauma *
Unexplained gastrointestinal bleeding or hematuria *
Heavy menstrual bleeding, especially with onset at menarche
Prolonged nosebleeds, especially recurrent and bilateral *
Excessive bruising, especially with firm, subcutaneous hematomas
leading cause of death related to bleeding is intracranial hemorrhage; major cause of disability is joint pain
What are the clinical features associated with moderate hemophilia A
seldom have spontaneous bleeding, have prolonged or delayed bleeding after relatively minor trauma and are usually dx before 5-6yo
bleeding episodes once a month to once a year
What are the clinical features associated with mild hemophilia A
do NOT have spontaneous bleeding
abnormal bleeding w sx, tooth extractions, and major injuries
bleeding episodes a few times a yr to once q10yrs
often not dx until later in life when they undergo sx or tooth excision or experience major trauma
What are the clinical features associated w hemophilia A in females
at risk for bleeding that is comparable to that seen in males with a similar severity of hemophilia
25% of females w normal factor 8 clotting activity have a phenotype
What variants are directly correlated w disease severity in hemophilia A
F8 Intron 22 inversions are associated w severe hemophilia A and account for 45% of individuals w severe form
an inversion between 1kb sequence in intron 1 (3%) and an inverted repeat 5- to F8 is also associated w severe form
SNVs leading to stop codons are all associated w severe form, additionally frameshift variants
splice site variants often result in severe dz
missense variants are found in nearly all those w a dx of moderate/mild dz
What are the tx recommendations for pts w hemophilia A
Tx should be coordinated through a hemophilia treatment center
IV infusion of plasma-derived or recombinant factor VIII for bleeding episodes within an hour of noticing symptoms (individuals on emicizumab w bleeding or requiring major sx will need F8 supplementation; emicizumab therapy may be chosen in young children to provide hemostatic protection while avoiding IV infusions)
peds issues: males w a FH of hemophilia A should NOT be circumcised unless hemophilia A is excluded or is tx w factor VIII; immunizations should be given subcutaneously (not intramuscular if feasible)
for those w mild dz, and respond well, can give DDAVP (desmopressin acetate) which often doubles to triples F8 clotting activity
for alloimmune tolerance against the first tx, gave use immune tolerance therapy
PT: use of musculoskeletal u/s aids in the eval of bleeding and helps to guide tx
gene therapy also exists but is not curative, in the mild hemophilia range w tx
PROPHYLACTIC TX IS CONSIDERED THE STANDARD OF CARE; greatest benefit is seen in those who start therapy before 2.5-3yo
How can you test for hemophilia A in pregnancy (in an unconventional way)
assay of factor 8 clotting activity from a cord blood sample obtained by venipuncture of the umbilical vein
women w hemophilia A are protected in pregnancy due to the natural rise of factor 8, but may experience post-partum hemorrhage
What is the de novo rate for hemophilia A? Likelihood mom is a carrier?
de novo: 30%
mom of a male proband who is a simplex case= 80% chance of being a carrier
if proband has an intron 22 inversion, mom has a 98% chance of being heterozygous, bc most intron 22 inversions occur in spermatogenesis
studies have shown varying frequencies of mosaicism ranging from 13-23% of mothers in apparent simplex cases
What test should NOT be ordered for carrier testing in hemophilia A
factor VIII clotting activity, or its ratio to von Willebrand factor level, is not a reliable test for determining genetic status; it can only be suggestive if low
What is the molecular pathogenesis for hemophilia A
synthesized primarily in the liver, is stabilized by binding to von Willebrand factor
LOF; abnormal gene products vary from deficiency caused by absence of detectable protein to those w normal levels of a dysfunctional protein
What is the prevalence of hemophilia B in relation to hemophilia A
hem B is about 1/5 as prevalent as hemophilia A
expect about the same severity as all other affected males in the family
How is the dx of Factor V Leiden established
pt w a heterozygous OR homozygous c.1691G>A variant in F5 gene w a low APC resistance test result
Known as a risk allele: increases the risk for a condition but is low penetrance
What are the clinical manifestations associated w Factor V Leiden
VTE is the primary clinical manifestation (most common is DVT); pulmonary embolism can also occur but it less common than DVT
homozygotes have an increased risk for thrombosis than heterozygotes (heterozygotes: 3-8 fold increase but overall annual first incidence is only ~0.5% ; homozygotes: 9-12 fold increase)
risk for VTE in pregnancy: normal pregnancy is associated w a 5-10fold increased risk (absolute risk is only 1%; highest risk is at 6wks PP; risk is increased to 17-34 fold in homozygotes (~2-5% absolute risk))
during pregnancy, those w a prior hx of VTE have an increased rr (0-15%); risk is highest in women w a prior unprovoked episode or an estrogen-related VTE
How does Factor V Leiden contribute to pregnancy loss
it is unlikely that Factor V Leiden thrombophilia is a major factor contributing to pregnancy loss and other adverse pregnancy outcomes
What are the tx recommendations for those w Factor V Leiden
first VTE w oral anticoagulant: dabigatran, edoxaban, rivaroxaban, or apixaban over warfarin due to decreased bleeding risk (tx up to 3mo in those w DVT or PE associated w reversible risk factor)
low molecular weight heparin (LMWH) is the preferred antithrombic agent for tx during pregnacy
When is there an increased risk for thrombophilia in those w Factor V Leiden
malignancy, central venous catheter use, travel, oral contraceptives, progesterone contraception, oral HRT, obesity, minor leg injury, sx, age
What is the molecular pathogenesis for Factor V Leiden
F5 functions as a cofactor that accelerates clot formation
genetic changes cause ~10 fold slower rate, leading to less APC cleavage (and a lower APC resistance result)
What is the rule of 5’s in Factor V Leiden
5% of the pop is heterozygous for Factor V Leiden
5% chance of a clot by age 65 in heterozygotes
5% increased risk of DVT relative to the general pop
What is the etiology of Protein C deficiency
rare disorder characterized by reduction in the activity of Protein C, the activated form of which is APC which exerts potent anticoagulant activity
congenital form results from heterozygous PVs in PROC (mild) or biallelic PVs (severe)
What are the clinical features associated with Protein C deficiency
severe: presents in neonates soon after birth w disseminated intravascular coagulation and purpura fulminans (recurrent episodes of which may be triggered by infection, trauma, sx)
moderate: may not present until adolescence and have recurrent VTEs including DVT and PE
mild: can range from asymptomatic to recurrent thrombosis, ischemic arterial stroke, and pregnancy related thrombosis
How is Protein C deficiency dx established
functional assays including clotting assays, ELISA, and chromogenic test to determine protein C activity
can also do mutational analysis of the PROC gene
What is the recommended tx for Protein C deficiency
tx by replacement w protein C concentrate; long term replacement is given prophylactically
anticoagulation txs like high intensity warfarin or low molecular weight heparin can also be used
What is the etiology of Protein S deficiency
mutations in the PROS1 gene (heterozygous or homozygous, mostly point mutations) cause three different forms:
1. quantitative defect w low levels of total protein S and free protein S w reduced protein S activity
2. decreased protein S activity w normal levels of total and free protein S
3. quantitative defect w reduced levels of protein S activity and free protein S but normal total protein S activity
type 1 and 3 most common
What are the clinical features associated with Protein S deficiency
variable penetrance; 50% who are heterozygous will have VTE w annual incidence ~2% w 29yo being the median age of onset (avg age is 40-45); can have VTE in 90% of cases (DVT/PE), some w cerebral, visceral, or axillary vein thrombosis; some women only have loss of fetus as their only clinical sign
homozygous state: neonates w purpura fulminans (small vessel thrombosis w cutaneous and subcutaneous necrosis); often have complications from frequent infusion of plasma like fluid overload which contributes to a high infant death rate
in pts w a FH of VTE, likelihood of protein S deficiency is ~3-5%; in those in the Japanese pop, likelihood goes up to ~13%
How is Protein S deficiency dx established
functional assays, ELISA, to determine levels of protein S activity
mutational analysis of PROS1 via sequencing or amplification and analysis by PCR w gel electrophoresis
What is the recommended tx for Protein S deficiency
in asymptomatic people, can consider prophylactic tx: heparin, vitamin K antagonist, or direct oral anticoagulant
ppl w congenital protein S deficiency, receive anticoagulation tx until coagulation activity has been stabilized for at least 2 consecutive days; need lifelong therapy
