GLUCOSE 6 PHOSPHATE DEHYDROGENASE DEFICIENCY AND HEMOLYTIC ANEMIA

G6PD DEFICIENCY and HEMOLYTIC ANEMIA

G6PD deficiency is a form of inherited disorder (that occurs mostly in males) in which body lacks an enzyme which normally protects RBCs from toxic chemicals.

G6Pd deficiency is commonest enzymopathy of RBCs,

BACK GROUND INFORMATION NECESSARY TO UNDERSTAND THE DISEASE

Applied biochemistry ,red cell enzymes

1.Matured RBCs lack nucleus,mitochondria and ribosomes.

And no tricarboxylic acid cycle and no synthesis of new proteins

2.To maintain integrity –rely on glycolysis

3.Natural decay of enzyme activity  ends the life span of RBC

Energy for RBCs

RBCs require constant energy to maintain biconcave disk form and

hemoglobin in reduced state.

without enrgy RBC lyse,deform

Energy is derived by metabolizing glucose by 2 pathways

1.Aerobic pathway- pentose phosphate shunt

2.via anerobic pathway Embden Myerhof pathway

(Most important is Hexose monophosphate shunt)

Metabolism of glucose

Via hexose monophosphate shunt

By metabolising glucose,ATP is produced

Glucose is metabolized to pyruvate by number of enzymes.(important -Pyruvate kinase)

G6PD-  (Glucose 6 phosphate dehydrogenase ) is the first enzyme which takes part in the above shunt.

The above shunt generates NADPH through the enzyme G6PD

NADPH keeps glutathione(GSSG) in reduced state(GSH)

This GSH protects RBC proteins from oxidative damages;reduced glutathione acts as a scavenger  of free radicles.

In response to oxidant stress normal RBCs produce NADPH

Pathophysiology of Hemolysis

When there is defientG6PD enzyme, NADPH  production is impaired

So,unable to withstand oxidative stress,damage occurs to

 sulph hydryl group of Hemoglobin

and RBC cell membrane causing hemolysis

Note:

·         Oxidative damage occurs due to free radicles  created by conversion of oxy to deoxy HB

and peroxidases created by phagocyting granulocytes

·         Other cells in other tissues have alternative pathways to generate NADPH

·         Enzymes of reticulocytes are very active but as cell ages activity falls.G6PD deficiency worsens as RBCs age .During periods of oxidative stress, hemolysis begins with oldest RBCs and progressively involves younger RBCs depending on severity.As RBCS do not have nuclei, when G6PD degrades,there is no G6PD mRNA to replace it.

BIOCHEMICAL PATHWAY –
THE HEXOSE MONOPHOSPHATE SHUNT

ANEROBIC PATHWAY

PENTOSE PHOSPHATE PATHWAY-Aerobic pathway

Variants of  the enzyme

About 100 variants exist in G6PD  deficiency

Normal type –TypeA and B

Unstable variant found in affected male Africans

 Unstable Variant A called A--

 Reticulocytes in A—have normal activity but declines with age(hemolysis is self limiting)

Variant TypeB—    seen in Mediterraneans ;activity very low,so hemolysis severe.

WHO working group classification

Class I ;  Severely deficient with chronic non spherocytic hemolytic anemia

ClassII;  Severly deficient with acute intermittent hemolysis(G6PD meditteranean)

CLASSIII: Moderately deficient with intermittent hemolysis usually associated with infection or drugs

 ClassIV:   Normal activity(60% -150%)

ClassV:     Increased activity (>150%)   

 TRANSMISSION OF THE DISEASE

Transmission is X linked through a defective G6PD gene located on X chromosome

Mutation of that gene.

Therefore typically affects men

Since this is a X linked gene,prevalence in females –higher but females are usually asymptomatic

Expression of disease occurs in

Hamizygous male and

Homozygous females

(Males possess only one copy of the gene thus they are either normal or G6PD deficient.

Heterozygous females withG6PDD have 2RBC populations;one normal,one withenzyme deficiency)

Affected people are intolerant to oxidative stress ,result is hemolysis

X chromosome and the position of G6PD gene atXq28 locus

.Epidemiology:

About 400 million people affected world wide

Highest prevelance in :

people of African, meditteranian  and Asian heritage

G6PD deficiency confers a relative resistance against plasmodium falciparum

CLINICAL FEATURES   

·         Usually asymptomatic                    

·          In all patients  severity varies

·         Varies from intermittent hemolysis to chronic hemolysis

or sudden life threatening intra vascular hemolysis with loin pain and hemoglobinurea

TYPES OF PRESENTATION

 !. Acute Hemolysis

2. Intermittent hemolysis

#. Chronic mild hemolysis

4. Drug induced hemolysis

5.Favism

6. Neonatal jaundice

7. Congenital non spherocytic hemolytic anemia

1. ACUTE HEMOLYTIC ANEMIA

After remaining asymptomatic

Sudden hemolysis 2-3 days after precipitating factor

Abrupt fall in Hemoglobin to 4 gms /dlrange

In 5-7 days reticulocytes increase and reverse anemia

even without removal of the drug

In Meditteranean type –severe form- hemolysis continues  even after withdrawl of drug.

2. DRUG INDUCED HEMOLYTIC ANEMIA

Occurs with all types

severe in medetteranean and oriental types

In African type –less severe self limiting

Drugs causing hemolysis

Antimalarials-         primaquin,qunine,chloroquine

Anti bacterials-       Sulpha,nalidixic acid,nitrofurantoin chloromycetin,+pyridium

Anti tuberculous-   Para aminosalicylic acid

Anti lepromatous-  Dapsone

Analgesics-            Aspirin,phenacetin

Vitamin K

Methelene blue--- Antitode for meth hemoglobinemia

Certain Chinese medicines

Food s triggering

Fava beans,fava bean products

 Other triggers causing hemolysis

House hold products- Moth balls

Naphthalene containing products

Metabolic precipitant-Diabetic keto acidosis

Severe Hemolysis and acute renal failure and death may occur.

3. FAVISM

Severe hemolysis followed by ingesting  fava beans

Even inhalation of fava pollens

Occurs in Mediterranean group

fava beans

4.INTERMITTENT HEMOLYTIC EPISODES

Provoked by 

Pneumonia.

Hepatitis ,Diabetic ketoacidosis

5.CHRONIC MILD HEMOLYSIS –occurs with some varients

6.NEONATAL JAUNDICE-

Common in meditteranean and oriental group.

Provoked by Vit K

D.D-Rhesus hemolytic disease of new born

7.Congenital  non spherocytic hemolytic anemia

ClassI variant

Defect very severe;normal stress   in circulation cannot be withstood.

New born period itself-anemia &jaundice develop.

Severe cases-neutrophilic defect also associated

NOTE:

In all patients severity varies from clinically inapparent to dramatic life threatening event.

Physical exam during hemolysis shows jaundice and spleenomegaly.

Tests for G6PD  deficiency

1 .Many variants exist in G6PD deficiency (about 100)

2. Old cells hemolyse more thanyoung RBC,since they contain more enzymes

5. G6PD assay Just after hemolysis can be misleading since new normal cell are released into circulation

6. In young cells G6PdD >6PGD.So,G6Pd/6pgd ratio will give correct picture in acute hemolysis.

7 .G6PD/6PGD  ratio help to detect heterozygotes

   Screening tests for G6PD deficiency are available

After initial screening ,select patients for further investigations

Best technique Spectro photometer assay  

If equivocal reassay after few weeks if clinical suspicion exists

More sensitive is Electrophoretic technique.

DIFFERENTIAL DIAGNOSIS for G6PD deficiency

Hemolytic anemia

Sickle cell anemia

Heriditary sphrocytosis

INVESTIGATIONS      

CBC

Reticulocyte count

Urine analysis

LDH/Hepatoglobin

Serum haptoglobin level will reduce in hemolysis ;is an index of hemolysis

Fractionated bilirubin

Blood smear with stains for Heinz bodies They are denatured hemoglobin.within RBCS

G6PD fluroscent Spot test

This test looks for fluorecense of NADPH

In this disease when NADPH is absent ,fluorescence is absent

G6PD spectrophotometry

Genetic test variant

Imaging studies

Abdominal USG shows splenomegaly and gall stones

TREATMENT

Avoid offending drugs and any other precipitating agents

Supportive care(oxygen,bed rest)

In neonatal jaundice phototherapy or  exchange transfusion

Adequate hydration to avoid renal failure

Transfusion

Folic acid

Vitamin E as antioxidant (Efficiecy?)

Splenectomy

 One Significant Complication

Myoglobinuria or hemoglobinuria  from hemolysis can cause Acute Tubular Necrosis
Microscopic exam of urine shows granular casts;

Urine is reddish brown .

Pathogenesis

Heme pigment casts obstruct the tubles,volume depletion and ischemia

FeNa less than  one percent as against typical ATN

This shows that there is tubular obstruction rather than ischemia.

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