Red cell membrane defects

Red cell membrane defects

Hereditary spherocytosis (HS)
The most common of the inherited RBC membrane defects, affecting 1 in 5000 individuals. The disorder characterized by RBC that appear spherical on peripheral blood smear. Autosomal dominant disorder.25% of pts have no family history. HS is a result of alterations in genes that encode for proteins involved in the vertical associations that tie the red cell's inner membrane skeleton to its outer lipid bilayer.

Pathophysiology

The resistance and elastic deformability of red cells are due to a cytoskeleton that underlies the lipid bilayer and to proteins that provide vertical association of the cytoskeleton with the bilayer The abnormal red cells lysis is caused by a defect in cytoskeleton : involves a partial deficiency of spectrin Repeated passages through the splenic cords, a process termed splenic conditioning, promotes membrane lipid loss, leading to a reduction in surface area and a progressively more spheroid red cell The spherical shape has two effects on RBC.  1.they become trapped in the splenic cord. 2.they have shortened life span.The abnormal membrane also demonstrate an increased permeability of sodium

Clinical manifestation

The typical HS pts is relatively asymptomatic with well compensated hemolysis and palpable spleen. The rare pts with severe HS may present early in childhood with life threatening hemolysis. HS has the usual features of chronic hemolysis :*symptoms of anaemia.*splenomegaly. *gall stones. crisis *Aplastic crisis ,hemolytic and megaloblastic#Family members have mild form of the disorder or are carrier.

Diagnosis

*Suggested by a family history of HS and characteristic finding on PBS i.e.* spherocytes. Two studies are used to confirm the diagnosis.1. osmotic fragility test. A positive test shows lysis of the patients red cells at hypotonic saline solution compared to simple swelling in normal cells. 2. Autohemolysis test : Normal autohemolysis is about 1% while HS cells will display Hb release rate of 3% or more 3-flow cytometric tests, detecting binding of eosin-5-maleimide to red cells, are recommended in borderline cases

Diagnosis-cont.

The classic finding is that the osmotic fragility is increased. Autohaemolysis is increased and corrected by glucose. Direct antiglobulin test is negative..


Autohaemolysis test in HS
There is increased haemolysis in the patient in comparison with the control. Glucose has given partial correction.

Treatment

1.Asymptomatic pts with compensated hemolysis should receive supportive treatment with folate supplements 5mg for life.2.Aplastic crisis may require short period of blood transfusion.3.Splenectomy is curative in most pts with HS.

Guide line for performing splenectomy

1. performed only when necessaryi.e moderate to severe hemolysis with complication (pts who required blood transfusion,gall stones)2. should be avoided in pts younger than 6 years of age ,associated risk (fatal pneumonia, sepsis)3. may be performed with cholecystectomy to decrease the amount of hemolysis and the risk of gall stones development.

Red cell enzymopathies

. The Embden-Meyerhof Pathway : for glycolysis provides energy for : a. Na+, K+ and Ca+2 pumps in the cell membrane. b. phosphorylation of membrane components and synthesis of glutathione for protection from oxidative damage c. reduction of NAD to NADH which is important in reducing met-hemoglobin to hemoglobin.
The Pentose-phosphate shunt maintains levels of NADH which is important in the reduction of oxidized glutathione (GSSH) to reduced glutathione (GSH). GSH is important in : a. destroying the oxidant hydrogen peroxide with glutathione peroxidase b. maintaining sulphhydryl group in Hb. and in various enzymes and within the cell membrane

Red cell enzymopathies

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In general, defects in the Pentose - phosphate shunt pathway result in periodic haemolysis precipitated by episodic oxidative stress,whilst those in the Embden–Meyerhof pathway resultin shortened red cell survival and chronic haemolysis.


Oxidant hemolysis (enzymopathy)
1. Glucose – 6- phosphate dehydrogenase (G6PD) deficiency : X-linked disorder is the most common enzymatic disorder of red blood cells in humans, affecting 400 million people worldwideA heterozygous female with 50 percent normal G6PD activity, due to inactivation of one X chromosome in each cell via lyonization, has 50 percent normal red cells and 50 percent G6PD-deficient red cellsDisease variants : The World Health Organization has classified the different G6PD variants according to the magnitude of the enzyme deficiency and the severity of hemolysis

Disease variants

●Class I variants have severe enzyme deficiency (less than 10 percent of normal) and have chronic (nonspherocytic) hemolytic anemia●Class II variants, such as G6PD Mediterranean, also have severe enzyme deficiency, but there are usually only intermittent episodes of acute hemolysis associated with infection, drugs, or chemicals●Class III variants, such as G6PD A-, have moderate enzyme deficiency (10 to 60 percent of normal) with intermittent episodes of acute hemolysis usually associated with infection, drugs, or chemicals●Class IV variants have no enzyme deficiency or hemolysis●Class V variants have increased enzyme activity.

Pathophysiology

the daily destruction of RBC, Hb is being constantly oxidized to met Hb. but a special protective mechanism that uses the E.M pathway reduces it back to Hb this is important because; Met-hemoglobin dissociates into heme and globin and then precipitates as an insoluble mass (Heinz body) in the RBCs.These red cells with Heinz body are non deformable and have difficulty passing through the spleen. Splenic removal of Heinz bodies damages RBCs membrane, forming spherocytes and causing hemolysis.

Clinical spectrum

●Acute hemolytic anemia●Favism●Congenital nonspherocytic hemolytic anemia●Neonatal hyperbilirubinemiaACUTE HEMOLYTIC ANEMIA :Almost all individuals with the most prevalent G6PD variants, G6PD A- and G6PD Mediterranean, are asymptomatic in the steady state.However, sudden destruction of enzyme deficient erythrocytes can be triggered by certain drugs or chemicals, by selected infections, and rarely by metabolic abnormalities (eg, diabetic ketoacidosis).

At two to four days after drug ingestion, there is the sudden onset of jaundice, pallor, and dark urine, with or without abdominal and back pain. This is associated with an abrupt fall in the hemoglobin concentration of 3 to 4 g/dL, during which time the peripheral blood smear reveals red cell fragments, microspherocytes, and eccentrocytes or "bite" cells). Special stains document the production of Heinz bodies, which are collections of denatured globin chains often attached to the red cell membrane. Hemolysis is both extravascular and intravascular The anemia induces an appropriate stimulation of erythropoiesis, characterized by an increase in reticulocytes that is apparent within five days and is maximal at 7 to 10 days after the onset of hemolysis. Even with continued drug exposure, the acute hemolytic process ends after about one week, with ultimate reversal of the anemia

Clinical course -Favisim

Favism occurs most commonly in children, primarily males, between the ages of 1 and 5. The clinical manifestations begin within 5 to 24 hours after fava bean ingestion and are those of acute intravascular hemolysis . Headache, nausea, back pain, chills, and fever are followed by hemoglobinuria and jaundice. The fall in hemoglobin concentration is acute, often severe, and, in the absence of transfusion, can be fatal. The G6PD variant most commonly implicated in favism is G6PD Mediterranean, the peak seasonal incidence of favism (April and May)

Inciting events

— Patients with class II or III variants develop intermittent hemolysis only after one or more of● Infection●Oxidant drugs ●Chemical agents (eg, moth balls, aniline dyes, henna compounds)●Diabetic ketoacidosis●Ingestion of fava beans ( fava beans and bitter melon' )

Diagnosis

(G6PD) deficiency should be suspected in any subject with an episode of non-immune hemolytic anemia, especially if occurring after drug ingestion, exposure to fava beans, or associated with an infection 1. red cell enzyme levels measured by electrophoresis show very low activities in severe disease and low to normal activity in mild disease depending on when the test is performed. measurement should not be taken at the time of hemolysis and reticulocytosis 2.The presence of bite (blister) cells on the peripheral smear and Heinz bodies on supravital staining suggest the present of oxidant sensitivity

Diagnosis

Heinz bodies
The blood film shows irregularly contracted cells [deep red arrows] and sometimes hemighosts [deep blue arrow] in which all the haemoglobin appears to have retracted to one side of the erythrocyte

Treatment

●Treatment of hemolytic episodes•Episodes of hemolysis in patients with G6PD deficiency are usually self-limited. Transfusion with packed red cells may be necessary in cases of severe hemolysis and symptomatic anemia.•There is no specific treatment for subjects with Class I variants who have chronic hemolysis. Avoidance of oxidant agents is the most prudentAdministration of folic acid in a dose of 1 mg/day may prevent worsening of anemia due to folate depletion in this group of patients●Prevention of future hemolytic episodes – Subjects with G6PD deficiency should avoid drugs and chemicals with oxidant potential

Pyruvate kinase(PK) deficiency

*Congenital non-spherocytic hemolytic anaemia(CNSHA). *Autosomal recessive.*Characterized by decreased generation of ATP.*Impairement of glycolysis lead to increased 2,3 DPG level.

Clinical manifestation

1.-chronic hemolytic syndrome of variable severity.2.severe deficient may be apparent in neonatal stage.3.-may be a symptomatic.4.-manifestation (reticulocytosis, marrow hyperplasia, splenomegaly, jaundice, gall stone).



Diagnosis
*measuring PK enzyme level in red cells Treatment :  1.depend on severity of anaemia.folate supplements,2.Splenectomy