Heritable Platelet Disorders (BSH 2021)

N.B. There are several useful case studies at the end of BSH guideline

 

Normal Platelet Function

platelets.png

clinical assessment

 

Numerical & functional platelet disorders can co-exist with other bleeding disorders and be indistinguishable from one another.

Symptoms include easy bruising, prolonged bleeding, epistaxis, gum bleeding, GI/GU bleeding, post-procedure bleeding. In children ask about cephalohaematoma, umbilical cord bleeding, heel prick beeding.

(Joint / Muscle / Brain bleeding less common in HPD’s compared to haemophilia)

Can be useful to quantify with a bleeding assessment tool (e.g. ISTH-BAT) but be aware this was validated for VWD not platelet disorders.

Examination should look for phenotypic evidence of recognised syndromes (e.g. TAR) and an assessment for hypermobility (Beighton score)

Diagnosis should be by consensus of a MDT review of the clinical and laboratory features

testing - general considerations

Testing of platelet function highly sensitive to pre-analytical variables

  • Collect sample from a fasted, rested subject

  • Large bore needle with low tourniquet pressure

  • Discard the first 3-5ml and then collect into a 1 in 10 volume of trisodium citrate

  • Keep at room temperature, avoid shaking and test within 4 hours

 

Factors affecting platelet function & test results

  • Drugs - NSAIDS, antibiotics, antidepressants, beta-blockers, anticoagulants

  • Co-morbidities - renal failure, MPN, liver disease

  • Misc - Dextrans, radiographic contrast, expectorants

  • Food – fat, garlic, caffeine, turmeric, alcohol, fenugreek, onion, ginger, ginseng

  • Temperature, pH

  • Platelet count outside the range of 100-600

  • FGN concentration

  • Sample prep and handling

 

investigations

Platelet count:

  • FBC - be aware of method, impedence, light scatter, flow etc

  • Blood film - platelet number / clumping / size / granularity

  • Flow cytometry (using CD41+CD61)

Platelet Volume

  • Derived parameter from FBC

Platelet Aggregometry

  • See below

Platelet Receptor Densities

  • Flow cytometry for Glanzmanns (CD41,CD61), Bernard-Soulier (CD42b,CD42a)

Genetics / Genomics

  • Next Generation Sequencing (NGS) / High Throughput Sequencing (HTS)

  • Multiple genes assessed in one assay (‘Gene panel’)

  • Multiple techniques with varying limitations

Other Tests:

  • Nucleotide release assays - storage pool and release defects

  • Alpha Granule proteins

  • Electron Microscopy - abnormalities of organelles and cytoskeleton

  • Super resolution light microscopy

  • Whole Blood Aggregometry

  • Extended antibody panels - for rare activation disorders (Scott Syn, Stormorken Syn)

  • PFA-100 - no longer recommended in adult practice but see bottom of page for method

Light Transmission Aggregometry (LTA)

 

Method

Light passing through the sample is recorded as agonists are added to platelet-rich plasma and stirred at 37oC.

Confusingly, results may be charted against optical density or light transmission —> produces opposite curves.

Analytical Variables – see above

platelets 4.png

 

A few specific cases

  • Hydroxycarbamide – abnormal ADP and Adrenaline

  • A small percentage of normal population show reduced response to adrenaline

 

Results:

Typical graphs when plotted using light transmission:

plt testing 1.png

 

 

list of heritable Platelet Disorders

 

Glanzmann Thrombasthenia (GT)

 

Autosomal recessive – ITGA2B & ITGB3 gene mutations (& >100 others)

Deficiency or functional deficiency of the GpIIb/IIIa receptor

GpIIb/IIIa mediates the aggregation of activated platelets by VWF, FGN and other proteins

Presentation

  • Usually <5 y.o.

  • Purpura, epistaxis, gum bleeding (but major neonatal complications are rare)

  • May present later in adolescence as severe menorrhagia

  • Associated with angiodysplasia and GI bleeding

Natural history

  • Severity of bleeding diminishes with age

  • Except severe risk of bleeding in labour remains

Investigation

  • Normal platelet count & size

  • PFA-100 non-closure

  • LTA – no response except for partial aggregation with ristocetin

  • Flow cytometry for GpIIb and GpIIIa receptor density

 

Bernard-Soulier Syndrome (BSS)

 

Autosomal recessive (GP9, GP1BA, GP1BB) and dominant (GP1BA, GP1BB)

Deficiency or absence of GpIb/IX/V complex

GpIb/IX/V complex is a receptor for VWF —> deficiency results in defective plt adhesion

Presentation

  • Usually presents in childhood

  • Epistaxis, easy bruising, gum bleeding

  • Sometimes 1st diagnosed in pregnancy, or confused with ITP

Investigation

  • Macrothrombocytopenia (count anywhere from 30 to normal)

  • PFA-100 non-closure

  • LTA – no response to ristocetin

  • Flow cytometry for GpIb-alpha receptor density

 

Grey Platelet Syndrome

 

<100 cases worldwide

Storage pool disorder - Absence of alpha granules

Associated with myelofibrosis

Investigations

  • Macrothrombocytopenia of typical grey appearances

  • PFA-100 normal

  • Absence of alpha-granules on electron microcopy

 

Chediak-Higashi

 

Autosomal recessive – CHS gene mutation

Platelet granule abnormality

Clinical Features:

  • Associated with albinism

  • Infection + lymphoproliferative disease often results in death in 1st decade of life

Investigation

  • Normal platelet count

  • Peroxidase-positive cytoplasmic granules in neutrophils

Hermansky-Pudlak

 

Puerto Rican ethnicity (1 in 1800, compared to 0.5 per million worldwide)

Delta granule deficiency

Multiple genetic mutations identified, inc. HPS1, HPS4, AP3B1.

Clinical Features:

  • Oculocutaneous Albinsim, pulmonary fibrosis, granulomatous colitis

  • Early death due to fibrosis

  • Pattern of presenting syndrome maps to different causative gene mutation

Investigation

  • Normal platelet count

  • Absent 2o wave on LTA

  • Electron microscopy

 

myh-9 related disorders

e.g. May-Hegglin Anomaly (see photo on morphology page)

Clinical Features:

  • Sensorineural hearing loss, presenile cataracts, glomerulonephritis, abnormal LFTs

Wiskott-Aldrich Syndrome

 

X-linked, WAS mutation —> WASP protein deficiency

Clinical Features:

  • Severe immunodeficiency, eczema

 

CATCH-22 Syndrome

 

Deletion on chromosome —> deletes 30-50 genes, including the Gp1b gene

Multi-system disorder, CATCH only some of the features

  • Cleft lip

  • Abnormal facies

  • Thymus

  • Cardiac abnormalities

  • Hypocalcaemia

Even rarer syndromes

Scott Syndrome - Impaired annexin V binding.

Stormoken Syndrome - STIM1 gene. Enhanced annexin V binding. Myopathy, Hyposplenism, Hypocalcaemia

Sitosterolaemia - ABCG5, ABCG8 genes. Inability to excrete plant sterols. Atheroscelorosis, Xanthomas

Quebec Platelet Disorder - Duplication of PLAU gene. Platelet granule disorder

 

Management of Congenital Platelet Disorders

 

General Guidance

 

Manage at a specialist haemophilia centre with 24-hour access to care

Lifestyle

  • Avoid contact sports

  • Avoid aspirin / NSAIDs

Vaccinate for Hepatitis A & B, and monitor LFTs

Often iron deficient, replace as required

Manage pregnancy with a pre-written plan and MDT consultation.

 

Specifics to consider

 

Tranexamic Acid

Desmopressin – for plt storage pool disorders

Platelet transfusion

rFVIIa – licensed for use in Glanzmanns

Stem cell transplant

 

summary

platelets 6.png

Platelet Function Analyser (PFA-100)

No longer routinely used in adult practice

 

A measure of global platelet function

Used at the screening stage alongside PT, APTT, VWF, FVIII

A normal result may avoid the need for more difficult, time consuming tests

Method:

platelets 2.png

Results:

High negative predictive value

If PFA-100 if normal then primary haemostasis very likely to be intact

(Exceptions: Storage pool disorders, Primary secretion defects, mild type 1 VWD)

‘Non-Closure’ is typical of Glanzmann, Bernard-Soulier and Platelet-Type VWD

platelets 3.png