Non-Immune Hereditary Red Cell Membrane Disorders (icsh 2015)

Red Cell Membrane Structure 

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Laminated structure composed of two layers with no direct contact

 

Outer layer

  • Outer surface of phospholipid bilayer membrane. A barrier for retention of cat/an-ions

  • Passive outflow of K+, which is then pumped back into cells in exchange for Na+

  • E.g. in Hereditary Stomatocytosis the leak rate exceeds pump rate à pseudohyperkalaemia

 

Inner Layer

  • Cytoplasmic surface of the bilayer is covered by a network of spectrin and actin.

  • Contact points between the membrane and spectrin/actin provided by:

    • Band 3-Ankyrin-Protein 4.1 complex

    • Glycophorin 4.1 complex

 

Quantitative or qualitative deficiencies —> red cell deformity and shortened cell lifespan.

 

 

Diagnostic Tests

 

SDS-PAGE - Sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Gel electrophoresis of red cell membrane proteins

Identifies and quantifies membrane contents

HS --> Reduced a/b spectrin, Ankyrin, Band 3 or Protein 4.1

HE & HPP --> Reduced protein 4.2 (and reduced a-spectrin in HPP)

 

Osmotic Fragility Test

14 concentrations of NaCl.

Patient and normal controls compared for concentration at which the cells lyse.

Simple but non-specific – Any fragile red cells will give a positive result

 

Acid Glycerol Lysis Time

Also positive for other causes of spherocytosis – AIHA, pregnancy, CKD, MDS

 

Osmotic Deformability Test

Plots curves of deformability that can differentiate the membrane disorders

See original guideline for sample graphs.

 

Eosin-5-Maleimide (EMA) Binding Test

Fluorescent test using flow cytometry

Reference ranges need to be established within each laboratory

 

Band 3 is the main binding site for EMA --> HS cells will show reduced binding

 

Results

  • A patient:control ratio of <0.8 consistent with HS & SAO

  • A ratio <0.6 seen in HPP

  • A normal ration is seen in HE

 

Confounding factors

  • Reticulocytes and macrocytes also show reduced binding --> equivocal results or false +

 

Genetic Sequencing

Not usually required where there is a family history to support diagnosis

Poor correlation between mutation and clinical diagnosis

 

Hereditary Spherocytosis (HS)

 

1 in 2000 North Europeans

 

Pathophysiology

75% Autosomal dominant

Defect in the Band 3-Ankyrin-Protein 4.1 complex --> Uncoupling of the cytoskeleton from the cell membrane in localized areas --> formation of spherocytes with reduced flexibility --> destroyed prematurely in spleen.

 

Presentation

Typically anaemia, jaundice, splenomegaly and reticulocytosis with a negative DAT.

Severity usually the same within one family, but highly variable between families.

 

Diagnosis

Newly diagnosed patients with a family history of HS, typical clinical features and typical lab features (spherocytes, raised MCHC and reticulocytosis) do not require further investigation.

If diagnosis is equivocal, screening test with EMA binding or cryohaemolysis is sufficiency for diagnosis.

Gel electrophoresis is the test of choice in atypical cases.

 

Management

Folic acid if mod-severe HS & during pregnancy

Annual Clinic Review

  • USS liver for gallstones every 3-5 years

  • Iron status

Consider Splenectomy if:

  • Severe disease beyond the age of 6

  • Moderate disease that is symptomatic and interfering with lifestyle

  • ?Timing around cholecystectomy

    • If child undergoing splenectomy, cholecystectomy should be performed at the same time for symptomatic stones. Concomitant cholecystectomy for asymptomatic gallstones is controversial.

    • If child undergoing cholecystectomy for symptomatic gallstones, then concomitant splenectomy is controversial. It reduces the risk of bile duct stones, but exposes patient to risk of asplenic sepsis.

  • Remember to give alert card post splenectomy

 

Splenectomy Vaccinations

Men C/Hib                 - 2 weeks before or 2 weeks after.

Men B                         - 2 weeks before or 2 weeks after. Repeat after 1 month

Men ACWY                 - 1 month after Men C

Pneumococcal            - 2 weeks before or 2 weeks after. Repeat every 5 years

Seasonal ‘flu              - Annual

 

Hereditary Elliptocytosis (HE) & Pyropoikilocytosis (HPP)

 

Defect in the Glycophorin 4.1 complex

 

HE

Incidental finding in most patients with a normal Hb or mild compensated anaemia

Elliptocytes vary between 10-100% of cells seen

 

HPP

Rare severe form of HE causing red cell fragmentation, especially in <1 year olds.

May have requirement for transfusion in early years

 

Hereditary Stomatocytosis (HSt)

 

A group of haemolytic conditions resulting from defects in Na/K transfer

 

Overhydrated – moderate to severe haemolytic anaemia

Dehydrated

Cryohydrocytosis

Familial Pseudohyperkalaemia – universally asymptomatic

 

South East Asian Ovalcytosis (SAO)

 

1.5% of SE Asia population

Haemolytic in childhood and then normalizes.