(ISTH 2024 cut-offs)
Intro
FVIII produced in the liver, spleen, and lymph nodes (+ some endothelial cells, e.g. lung – provides the desmopressin-releasable FVIII pool)
FVIII and FIX form the tenase complex, w/out this there is a failure to produce the thrombin burst
Failure of thrombin burst:
--> only a loose, friable fibrin mesh is produced, which is easily dislodged leading to rebleeding
--> failure to activate thrombin-activatable fibrinolysis inhibitor (TAFI) --> increased fibrinolysis
End result is the failure to consolidate the primary platelet plug, leading to the characteristic delayed bleeding seen in haemophilia.
Why joint bleeds in particular? Theory is low expression of tissue factor in synovial tissue.
Potted History
2nd century Talmudic scripts – “It was taught: If she circumcised her first son and he died, and her second son and he too died, she should not circumcise her third son, so taught Rebbi.”
1904 - Alexei Nikolaevich– haemophiliac – son of Nicholas II of Russia. Taken to Rasputin for treatment
1937 – FVIII identified
1984 – virally inactivated pooled plasma concentrates
1993 – recombinant FVIII licensed
1994 – No. 1 cause of death for haemophiliacs in UK – AIDS, 73 cases
2000’s – B-domain depleted FVIII
2017 - Gene therapy for Haemophilia A
factor viii protein
Triplicated A1, A2, A3 domains which are 30% homologous to one another
B domain connects A2 and A3 and is removed when thrombin activates FVIII
Duplicated C1, C2 domains responsible for phospholipid binding properties
FVIII circulates as light and heavy chains with B domains of varying length
>90% circulates complexed to VWF, prolonging its half-life
genetics
FVIII gene is 187kb in size, found on the long arm of the X chromosome
The 26 exons are separated by multiple large introns
30% of cases are due to sporadic mutations. 5% of cases do not have an identifiable mutation.
Intron 22 Inversion – “Flip-Tip Inversion”
Intron 22 is a large 35 kb intron, responsible for 50% of severe haemophilia A
The X pairs with the Y during meiosis, leaving nothing for the long arm of X to pair with.
Due to similarities between three F8A genes, the tip of X can flip up and bind with itself.
Results in two abnormal A genes both of which fail to produce FVIII when transcribed.
haemophilia a Treatment
factor dosing
Factor concentrates raise factor level by 0.02 iu/ml for every iu/Kg infused
FVIII Expected dose = (% Increment required (i.e. iu/dL) x Weight (Kg)) / 2
Half-life 8-12 hours
Round up to whole vial, do not waste concentrate
Repeat doses at 12 and 24 hour intervals if required
Recombinant Factor Concentrates
1st Generation
No longer in use in UK. Human albumin in concentrate as stabiliser
2nd Generation
Refacto-AF, Kogenate, Helixate NexGen
Contain human albumin in cell culture medium
Refacto-AF is a B-domain deleted FVIII, which requires a specific assay to measure levels
3rd Generation
Advate
No animal products
Desmopressin
SE: Flushing, hypotension, fluid retention, hyponatraemia, aterial occlusion
Safe use:
Fluid restrict to 1L in 24 hours after dose
Monitor Na if <2 y.o.
Avoid use if atherosclerosis
Prophylaxis - principles (BSH 2020)
Primary Prophylaxis - All children with with baseline level of <0.03iu/ml (i.e. all severe, and some moderate). Start before, or immediately after, 1st joint bleed or before 2yrs old. Aim is to preserve normal joint function. Life-long treatment should be the standard of care.
Secondary Prophylaxis - Starts after 2+ joint bleeds but before proven joint disease. Aims to limit consequence of any subclinical joint damage that has already occurred and maximize long-term function.
Tertiary Prophylaxis - Starts after onset of clinical/radiological joint disease and aims to slow down progression of diease and maintain quality of life.
Pros
Prevent acute, painful bleeds
Prevent chronic joint damage
Reduce frequency of intracranial haemorrhage (in severe haemophilia w/out inhibitors)
Reduce time off school / work
Wider range of activities to participate in
Cons
Venous access / Portacath
Inhibitor formation
Infection risks
How to Start
20-40 iu/kg on alternate days
Aiming for a trough level >0.01 iu/ml
FVIII half-life 8-12 hours, dosing schedule can be tailored to individual’s pharmacokinetics (see guideline)
Psychosocial needs of child and family need to be addressed and supported
Route of administration (periph / portacath / external CVAD) should be agreed with parent / guardian
Phases of treatment:
Initial introduction in first 3 years of life
Establish regular dosing through childhood
Modify dose for increased activity in teenage years
Modify dose for reduced activity in adulthood
30% of severe patients can safely stop prophylaxis in adulthood
Example Evidence for Use of Prophylaxis
ESPIRIT Trial 2009 – Arthropathy in 30% of treated, 74% of untreated patients
SPINART Trial 2013 - RCT comparing tertiary prophlyaxis vs on-demand treatment —> prophylaxis reduced bleeding (by 94%) and chronic pain (by 54%).
Joint Bleeds
Definitions
Early bleed: fullness, stiffness, tingling in joint with no trauma. Full range of motion.
Moderate: Pain with some swelling and restriction of movement
Severe: Severe pain with an immobilized joint
-Re-bleed: worsening symptoms whilst on treatment or within 72 hours of stopping
Initial Treatment
Aim for peak level of 0.5-0.6 in moderate bleeds, 0.6-0.8 in severe bleeds
FVIII Approx 25-30 IU/kg
FIX Approx 40-60 IU/Kg
Doses may need to be repeated in response to ongoing symptoms
Treatment for bleeds in inhibitor patients
Patient knows best, differing preferences for FEIBA or rFVIIa
FEIBA approx. 50-100 IU/Kg every 12 to 24 hours (Max 200 IU/kg in 24 hours)
rVIIa approx.. 270 microg/Kg as single dose (instead of prev 90 x3)
Additional measures
Protection, Rest, Ice, Compression, Elevation
Analgesia
TXA – prev concern over prothrombotic in combo with concentrate not substantiated
Target Joints and Synovitis
Chronic synovitis results from recurrent bleeding into joints à chronic painless swelling.
Target joint = 3 or more bleeds into a single joint in a 6 month period
Treatment:
Radioactive synovectomy
Selective angiographic embolization
Intra-articular steroid injection
Surgery
Dental Procedures
For mild and moderate haemophilia most non-surgical dental work can be done with TXA.
Severe haemophilia
Screen for inhibitors before any invasive procedures
Local infiltration of gum – 30% rise
Inferior nerve block – 50-80% rise, then 50% the following day
Dental extraction – 50-80% rise, then 50% the following day
Extended Half-Life (EHL) Products
Engineered to prolong half-life of the factor concentrate in vivo. The native clotting factor glycoprotein can be modified in one of three ways:
Addition of polyethylene glycol (PEG), e.g. Bax855, Bay 94-9027, N8-GP / N9-GP
Fusion to recombinant human albumin, e.g. rFIX-FP
Fusion to Fc-region of human IgG, e.g. rFVIIIFc / rFIXFc
How/When to start?
Consider switch to EHL in severe haemophilia pts after first 50 doses of standard product
To avoid the highest risk period for inhibitor development
Test for inhibitor prior to start, after 10 doses, after 3 months and then 6 monthly
Perform a pharmacokinetic study to individualise the dosing.
E.g. for FVIII, levels pre-dose, 15 min, 6/24/48 & 72 hours post dose
Prophylaxis strategies
Less frequent infusions (e.g. twice weekly for FVIII) to reduce no. of venepunctures
Infusions at traditional frequencies (e.g. alt days FVIII) to increase trough level
Hybrid regimens improve troughs and reduce frequencies
Dosing EHL’s
EHL-FVIII half-life increased 1.5-fold (EHL-FIX 3-5 fold) compared to standard products
This is an average for adults and adolescents, with wide variability.
Therefore dosing schedules must be individualized
Variability even greater in children, and not been studied in pts with a history of inhibitors
Monitoring EHL’s
FVIII – Chromogenic assay
FIX – One stage assay
APTT assays give variable results and careful choice of reagent required
Treating bleeds on EHL’s
Treatment dose should be based on time since last dose, & patient’s known incremental recovery (IR).
A single infusion should be effective for most bleeds
Newer EHL Products
FVIII + Antibody fragment + VWF fragment. The VWF fragment protects the FVIII extending the half-life
Efanesoctocog alfa - recombinant FVIII modified to be less reliant on endogenous VWF (NEJM 2023)
emicizumab
Recombinant Bi-specific antibody - bridges activated FIX to FX, replacing the function of the deficient aFVIII
Dosing - 3 loading doses, followed by fortnightly administration (monthly dosing being investigated (2022)).
Benefits - Reduces bleeds, Improves Quality of Life, Bypasses Inhibitors
Testing FVIII levels on treatment - Use chromogenic assay with bovine reagents (human reagents provide a substrate for the drug —> erroneous results)
Treating bleeds in inhibitor patients on emicizumab - Use NovoSeven. High doses of aPCC’s should be avoided due to association with inducing thrombosis and MAHA.
SE - reported cases of MAHA when co-administered with activated promthrombin complex concentrate (aPCC, e.g. FEIBA)
Currently (2022) available in UK for:
As prophylaxis for all severe haemophila A
As prophylaxis in any severity of haemophilia A where inhibitors are present
Trials
NEJM 2018 - Use as prophylaxis in patients without inhibitors
HAVEN 1 2017 - Use as prophylaxis in patients aged 12-75 with FVIII inhibitors
HAVEN 2 Interim Analysis 2017 - Use as prophylaxis in patients, children and adults, with FVIII inhibitors
Gene Therapy
Current process (2022)
Given as a single IV infusion, usually AAV vector, followed by close monitoring for transaminitis.
Intent is to increase the expression of FVIII or FIX in order to change the bleeding phenotpye.
Does not alter the genetic defect or inheritance.
For more, see EMJ Congres 2022 of gene therapy
AAV5-Factor Gene Transfer in severe haemophilia A – S. Rangarajan – NEJM 2017
9 men with severe haemophilia A
1 low dose, 1 intermediate dose, 7 high dose
After one year, High dose group = FVIII:C >0.05iu/ml in all patients, >0.50 iu/ml in 6 of them
Annualised bleeding rate fell, all patients stopped using concentrate by week 22
SE: Transient ALT rise
‘re-balancing’
Fitusiran - AT3 siRNA targeting antithrombin
Aims to restore thrombin generation by suppressing antithrombin —> ‘Re-balancing’ levels
SE: Two thrombotic events so far, one death (Sept 2019)
tissue factor pathway inhibitors
Concizumab - Early days. Some efficacy data at ISTH 2019
Some trial products withdrawn due to thrombotic side effects.
Comprehensive Care Centre (CCC) Annual Review
Review of treatment episodes – product, dose, venous access, ?prophylaxis indicated
Orthopaedic issues – Review joints, perform joint score, physiotherapist review, offer referral to surgeon / rheumatologist is needed
Health promotion - smoking, alcohol, diet, exercise, blood pressure, bone health, cancer screening
Vaccinations – Hep B titre >100
Social – school occupation, time missed from either, sports, living allowance, travel arrnagements
Review HaemTrack record – online / paper / App
Bloods – FBC, U&E, LFT, Inhibitor screen, Anti-Hbs titre, Trough factor level, Viral screening
Radiology – directed by symptoms
Factor VIII Assays
Reminder: APTT – Plasma + surface activator + phospholipid + Calcium
One Stage Factor Assay
Principle:
Perform APTT’s on serial dilutions of standard reference plasma (diluted using factor deficient plasma) and plot the results to create a best fit line.
Then perform APTT’s on serial dilutions of the patient’s plasma
This should produce a best fit line parallel to the reference best fit, from which the patient’s factor level can be read.
Causes of Non-Parallel lines
You made a mistake in plotting the lines
An inhibitor is present, with increasing dilutions the inhibitor is diluted out
You cannot dilute nothing – if the factor level is <1% the clotting times will be grossly prolonged and not change with dilution.
Interference with the 1 stage Assay
Antiphospholipid antibodies, recombinant FVIII and pre-activation of FVIII
Chromogenic 2-Stage Assay
Principle:
Patient plasma + reagent cocktail (IXa, X, thrombin, Calcium, phospholipid)
Incubate at 37 degrees to produce Xa
Add chromogenic substance and incubate
Chromogenic substance changes colour when cleaved by Xa —> Calculate Xa concentration, with the FVIII concentration having been the rate limiting step.
Causes of 1-Stage / 2-Stage Discrepancy
Normal 1-stage FVIII seen in 10% of mild haemophilia patients —> check chromogenic
Low 1-stage but normal chromogenic due to a F8 mutation that does not cause bleeding
Inhibitors
25-30% of severe patients develop inhibitor, but many low level and transient
Most likely to occur in first 25 doses
Inhibitor may have specificity against the exogenous factor or patient’s own factor
Risks for developing inhibitors
Mutation: Large deletions or stop codons in the light chain, Intron 22 inversion
African / Hispanic
Age <6
HIV negative
Large doses e.g. following severe bleed
Adminstering at the same time as an inflammatory stimulus, e.g. surgery
Inhibitor Properties:
Immediate acting or Time-dependent (2-4 hours)
Type 1 kinetics (linear FVIII inactivation)
Low responder antibody – remain at a low level (5-10 BU) after FVIII exposure
High responder antibody – sharp anamnestic rise after 5-8 days (100 – 1000’s BU)
1 Bethesda Unit (BU) = amount of antibody required to reduce FVIII activity in pooled normal plasma by 50% after two hours incubation
When to screen:
After every 3rd exposure until 20 exposures
Then every 3-6 months
Initial screen with trough level. If trough <0.01 iu/ml at 48 hours —> APTT Screen
APTT Inhibitor Screen
Bypassing Agents
Factor Eight Inhibitor Bypassing Agent (FEIBA)
Plasma product containing Prothrombin and Factor Xa (and other factors)
Peak thrombin generation at 15-30minutes. Returns to baseline at 8-12 hours.
Recombinant FVIIa (NovoSeven)
Recombinant. M.O.A thought to be binding to surface of activated platelets at site of injury and promote FXa formation at that site
Example dosing:
Joint bleeding in Haem A with inhibitors: 3 doses of 90ug/kg every 3 hours, or single dose 270ug/kg
FVIII Immune Tolerance Induction (ITI)
Administration of FVIII at 50 iu/kg on alt days, increasing to 200 if required
No evidence for which is better dose
Continued for minimum 12 months
May combine with: Rituximab, steroids, alkylating agents, IVIg, plasmapheresis
Success Criteria:
FVIII half-life >7 hours and BU negative
Or a measurable 48 hour trough whilst on 50 IU/kg on alternate days
70% overall success rate
Factors in favour of a good success are:
Age <7, peak BU <200, starting treatment after BU has fallen <5
UKHCDO iti Protocol for children 2017
Start ITI as soon as inhibitor identified, regardless of the titre
CVC insertion if needed to allow uninterrupted infusions
First line ITI should be conducted with patient’s usual product
If <5 BU:
Start at 50 IU/kg on alternate days
If bleeds, first increase to daily, then increase dose in 50IU/kg increments
If titre rises >40 BU, immediately increase dose to 100 IU/Kg daily
If titre rises >200 BU, immediately increase dose to 200 IU/Kg daily
If 5-199 BU:
Start at 100 IU/kg daily
If bleeds, first increase to daily, then increase dose in 50IU/kg increments
If titre rises >200 BU, immediately increase dose to 200 IU/Kg daily
If >200 BU:
Start at 200 IU/kg daily
Measure inhibitor titre (BU) weekly during start of ITI to define the peak titre
Once peak is defined, check BU monthly
Continue ITI for as long as there is an ongoing downward trend in the titre
If there is an upward trend, or the titre fails to fall by 20% over 6 months, change treatment:
If dose <200 IU/kg/day, increase the dose
If dose already 200 IU/Kg/day, change to 2nd line therapy (pFVIII +/- Ritux)
Female Haemophilia A
Symptomatic Carriers:
Random process of X chromosome inactivation allows one FVIII allele to function in each cell
On average this will result in carriers having 50% of normal FVIII levels
But random process, so some will have normal levels, others develop mild haemophilia
Causes of True Female Haemophilia A
1. Homozygous haemophilia A (often consanguineous)
2. Compound heterozygosity
3. Turner Syndrome (XO)
4. Translocation through the FVIII locus on the normal X chromosome
5. Complete Androgen Insensitivity – Phenotypically female but genetically XY
6. Extreme lyonisation
- As a result of mutation in Xist gene (controls methylation of X chromo)
Haemophilia B
Rarer – 1 in 30,000 live male births
Usually missense or nonsense mutations in FIX gene
Essentially the same clinical features, possible slightly less severe
Longer half-life of FIX (18 hours) so less frequent concentrate administration
Inhibitors much less common (2-3%), present with anaphylaxis to concentrate, not time dependent, ITI far less likely to be successful
FIX Expected dose = % Increment required (i.e. iu/dL) x Weight (Kg)
BeneFIX currently the only recombinant concentrate available (as of 2016)
Haemophilia B Leyden
2% of cases. Initially moderate or severe FIX deficiency —> postpuberty normalization
Normalisation thought due to androgens increasing F9 gene expression
F9 mutation causing extreme sensitivity to warfarin
Normal FIX levels, not a haemophilia disorder
But mutation affects the gamma-carboxylation of FIX
In the presence of warfarin —> FIX level <1% and bleeding complications
Haemophilia A/B Pregnancy Plan
Haemostatic Changes in Pregnancy
Increases: Fibrinogen, VWF, FVIII, FVII, FX
Stable: FIX, FII, FV, Prot C (but acquired APCr occurs due to high FVIII)
Decreases: FXIII, Protein S, (AT falls to low normal but remains within the reference range)
Causes of Consumptive Coagulopathy in Pregnancy
Placental abruption
Intrauterine fetal death
Pre-Eclampsia
Acute fatty liver of pregnancy
Amniotic fluid embolus
Amniotic fluid embolus triggers tissue factor --> a particularly aggressive consumptive coagulopathy which is further aggravated by dilutional effects of resuscitation.
Acquired Haemophilia A
Intro
EACH2 Registry – European Acquired Haemophilia Registry reported 482 patients in Blood 2012
Typically elderly patients affected
Associated with other autoimmune disorders
Commonly GI, urogenital, muscle and retroperitoneal bleeding (Haemarthosis is uncommon)
Delayed diagnosis is a significant problem
Rarity of presentation, usually to a general clinician unfamiliar with the diagnosis
Associated with anticoagulant use à further delay as bleeding blamed on the AC
10-20% relapse rate
Diagnostic Investigations
See inhibitor notes above
Treatment
1. Avoid Iatrogenic bleeding
Manual blood pressure measurements
Limit venesection, do not place cannula useless plan to use
Falls prevent measures
2. Bypassing Agent if Bleeding
NovoSeven (rFVIIa) 90 mcg/kg every 2 hours
FEIBA (FII, FXa) 50-100 iu/kg every 6-12 hours
3.6% thrombotic events in all treated patients. 2.9% rFVIIa, 5.8% aPCC (EACH-2)
+/- Tranexamic acid
Alternatives to bypassing agents - Desmopressin, IVIg, Human FVIII + Immunoabsoprtion
3. Eradicate the Inhibitor
Start at same time as treating the bleed
Options:
Steroids
Steroids + Oral Cyclophosphamide
Rituximab
Calcineurin inhbitors, IVIg, Immune tolerance induction
Pregnancy-Associated Acquired Haemophilia A
1 in 350 million pregnancies
Presents in the 3 months postpartum
Longer time to remission
Consider side effects/breast feeding/ time commitments when selecting treatments.
questions
Question1: Give a differential diagnosis for a FVIII:C of 0.15 iu/ml
Mild haemophilia A
Haemophilia A on factor concentrate prophylaxis
Von Willebrand Disease
Type 1 or 2
Combined FV + FVIII deficiency
Discrepant 1-stage / 2-stage assays
Question 2a: A pregnant woman tells you she has a family history of ‘haemophilia’. How would you proceed?
Explore pedigree
Who is the index case and are they still alive / contactable?
Patient’s bleeding history (Score >7 significant in women)
Bloods
Check VIII, IX, XI, VWF & others based on ethnicity
Genetic sequencing – only takes 2 weeks
Question 2b: You find nothing from the above, what possibilities remain?
Rare coag disorder
Platelet function disorder
3-5% of Haemophilia A families do not have a detectable mutation
Question 3a: In an asymptomatic woman, whose father has severe haemophila A and mother is normal, what is the risk that her daughter is a carrier of severe haemophilia A?
Superficially the daughter will be an obligate carrier, having taken X from father
But the quoted non-paternity rate in the UK is 1%
Question 3b: The daughter is a carrier (FVIII 0.68 iu/ml). She goes on to have two twin girls of her own. One twin has a FVIII of 0.69 iu/ml. What would you predict the levels to be in the other twin?
Could be the same
Or could be very low due to mirror image lyonisation between the twins
Question 4: In which situations can you be sure someone is an obligate carrier?
If they are a daughter of an affected mother
If they are the mother of two affected children
(not if they are the daughter of an affected father for reasons of non-paternity)