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Haemophilia (Bsh 2010/2011/2012/2013, rcog 2017, UKHCDO)

Deficiency severities for FVIII, IX, X & II

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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.

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

factor 8.png

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.

flip tip.png

 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

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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

haem 5.png

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

 

Start age 1 – 1.5 years old, before the onset of joint bleeds, i.e. Primary Prophylaxis

25-40 iu/kg on alternate days

Aiming for a trough level >0.01 iu/ml

FVIII half-life 8-12 hours, often shorter in younger patients

 

ESPIRIT Trial 2009 – Arthropathy in 30% of treated, 74% of untreated patients

 

Pros

  • Prevent acute, painful bleeds

  • Prevent chronic joint damage

  • Reduce time off school / work

  • Wider range of activities to participate in

 

Cons

  • Venous access / Portacath

  • Inhibitor formation

  • Infection risks

 

Phases of treatment:

  1. Initial introduction in first 3 years of life

  2. Establish regular dosing through childhood

  3. Modify dose for increased activity in teenage years

  4. Modify dose for reduced activity in adulthood

  5. 30% of severe patients can safely stop prophylaxis in adulthood

 

Secondary prophylaxis = starting after the first life-threatening bleed or 2 or more joint bleeds. Also effective in joint healing for older children.

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

 

Enhanced 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

 

emicizumab

Recombinant Bi-specific antibody - bridges activated FIX to FX, replacing the function of the deficient FVIII

Can be given once weekly or fortnightly, compared to 2-3x/week with traditional factor concentrates.

Currently funded by NHS England for use in patients with haemophilia A who have factor VIII inhibitors (as of April 2019). ?Approved indications will be expanded in future

Trials

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

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

 

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:

  1. 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.

  2. Then perform APTT’s on serial dilutions of the patient’s plasma

  3. 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:

  1. Patient plasma + reagent cocktail (IXa, X, thrombin, Calcium, phospholipid)

  2. Incubate at 37 degrees to produce Xa

  3. Add chromogenic substance and incubate

  4. 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

haem 6.png

 

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

 

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

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haem 8.png
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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)