2. Introduction
• G6PD deficiency is the most common disease
producing enzyme abnormalities in humans,
affecting more than 200 million individuals
worldwide.
• The highest prevalence in the Middle East,
tropical Africa & Asia.
• G6PD Deficiency is caused by 400 different
mutations in gene coding for G6PD, only few of
them causes the clinical symptoms of the disease.
3. What is G6PD?
• G6PD is an metabolic enzyme is involved in
pentose phosphate pathway, especially
important in red blood cell metabolism
• It also protects red blood cells from the effects
of potentially harmful molecules called
REACTIVE OXYGEN SPECIES
4. G6PD Deficiency
• The G6PD gene is located on the telomeric region
of the long arm of X-chromosome (band Xq28).
• Mutation of the X-linked G6PD gene
(approximately 127 have been reported with a
single base substitute leading to amino acid
replacements) results in many variants of protein
with varying enzyme activity that result in
different patterns of clinical manifestations.
5. Male to Female ratio
• Male cases are overrepresented compared with female cases.
• Males are hemizygous for the G6PD gene; therefore the expression
is either normal or deficient.
• In contrast, in females who have two copies of the gene on each
chromosome, the gene expression can be normal or heterozygous.
• Homozygous inheritance in females can occur; whereas,
heterozygous females have genetic mosaicism secondary to X-
chromosome inactivation and can have similar manifestation as
male neonates.
9. What is favism?
• Favism is formally defined as hemolytic response to the
consumption of broad beans
• Favism is disorder characterized by hemolytic reaction to the
consumption of broad beans
• All individual with favism show
G6PD deficiency
• However not all individuals with
G6PD deficiency show favism
10. Decreased amounts of glutathione
due to decreased production of NADPH
• Reduction of amounts of NADPH in RBCs in G6PD deficiency causes
reduction of oxidized glutathione .
Role of reduced glutathione in RBCs:
• Reduced glutathione gets rid of Reactive oxygen species including
hydrogen peroxide.
• Reduced Glutathione helps to keep sulfhydryl groups of
haemoglobin protein in the reduced state.
11. Reduced production of reduced glutathione results in:
1- A decrease in detoxication of peroxides. This causes damage to
RBCs membrane and hemolysis (ending in hemolytic anemia).
2- Hemoglobin protein is denatured forming insoluble masses (Heinz
bodies). Heinz bodies attach to red cell membranes.
Membrane proteins are also oxidized.
Accordingly, red cells become rigid and removed from the
circulation by macrophages in the spleen and liver ending in
anemia
12.
13. Although Deficiency of G6PD occurs in all cells of affected
individual. It is severe in RBCs because the only pathway to form
NADPH in RBCs is pentose phosphate pathway (using G6PD).
Individuals who have inherited one of the many G6PD mutations
do not show clinical manifestation.
Some of patients with G6PD develop hemolytic anemia if they
are exposed or ingest any oxidizing drugs
14. G6PD VARIANTS
• Most G6PD variants are caused by point mutations in the G6PD
gene.
• Some of these point mutations do not disturb the structure of the
enzyme's active site and hence, do not affect enzyme activity.
• Other point mutations may lead to production of mutant enzymes
with one or more of the following:
– altered catalytic activity
– decrease stability
– an alteration of binding affinity for NADP+ or Glucose 6-
phosphate.
15. G6PD variants can be classified into three categories
Class I Mutations
severe deficiency
with no or
minimal detected
enzyme activity
often associated
with chronic non-
spherocytic anemia
(occurs even in
absence of oxidative
stress)
Class II Mutations
(G6PD
Mediterranean)
severe deficiency
with 1% to 10%
residual enzyme
actiity
G6PD enzyme shows
normal stability but,
very low activity in
all RBCs
Class III
(G6PD Group A-)
moderate deficiency
with 10% to 60%
residual enzyme
activity,
RBCs contain
unstable G6PD
enzyme, but normal
activity in younger
RBCs and
reticulocytes
Class IV
Normal enzyme
activity at 60% to
150%
Class V
increased
enzyme activity at
>150%
16. Both G6PD Mediterranean and G6PD A- represent mutant enzymes
that differ from the normal variants by a single amino acid.
This change is due to DNA changes in the form of point mutations or
missense mutations.
Frame shift mutations or large deletions have not been identified
indicating that the complete absence of G6PD is lethal.
Mutation causing non spherocytic hemolytic anemia are clustered
near the carboxyl end of the enzyme, whereas mutations causing
milder forms of the disease tend to be located at the amino end of
the enzyme.
17. Care of G6PD patients
• The most important measure is prevention – avoidance of the drugs
and foods that cause hemolysis.
• Vaccination against some common pathogens (e.g. hepatitis A and
hepatitis B) may prevent infection-induced attacks.
• In the acute phase of hemolysis, blood transfusions might be
necessary, or even dialysis in acute renal failure.
• Blood transfusion is an important symptomatic measure, as the
transfused red cells are generally not G6PD deficient and will live a
normal lifespan in the recipient's circulation.
18. • Some patients may benefit from splenectomy as
this is an important site of red cell destruction.
• Folic acid should be used in any disorder
featuring a high red cell turnover.
• Although vitamin E and selenium have
antioxidant properties, their use does not
decrease the severity of G6PD deficiency.
19. Hemolytic Anemia
• G6PD deficiency cause impraired red blood cells’
transport of oxygen effectively throughout the
body resulting in stress conditions and hence
leading to hemolysis.
• There are other conditions that also caused by
G6PD deficiency- neonatal jaundice, abdominal
back pain, dizziness, headache, irregular breathing,
and palpitations.
21. Neonatal hyperbilirubinemia in G6PD
• Newborns with G6PD deficiency have a 9% incidence of
hyperbilirubinemias.
• Estimated at 3.4% incidence, the condition ranges by
infant race/ethnicity (12.2% in African American male
infants to nearly 0% in white female infants).
• Oxidant stressors, sepsis, and delay in bilirubin
elimination (such as co-inheritance with Gilbert’s
disease or persistent enterohepatic recirculation) add
to total plasma or serum bilirubin (TSB) rise, need for
phototherapy, and risk for exchange transfusion.
Vinod K. Bhutani, MD,jaundice due to glucose-6-phosphate dehydrogenase deifciency, NeoReviews Vol.13
No.3 March 2012
22. Clinical patterns of hyperbilirubinemia in G6PD
deficient neonates
• Early-onset hyperbilirubinemia (ie, TSB >75th percentile and
increased bilirubin production)
• Pre-discharge TSB <75th percentile track exacerbated by starvation,
unrecognized sepsis or late prematurity;
• Slow postnatal rise with natural decline
• Slow postnatal rise with persistent prolonged unconjugated
hyperbilirubinemia, >2 weeks age
• Complicated by acute-onset, dramatic hyperbilirubinemia with TSB
rise >1 mg/dL per hour (“favism”).
Vinod K. Bhutani, MD,jaundice due to glucose-6-phosphate dehydrogenase deifciency, NeoReviews Vol.13
No.3 March 2012
23.
24. Elevation of COHb in G6PD deficient neonates
• Within the reticuloendothelial system, hemoglobin releases
globin and heme, which in turn undergo further degradation
to release equimolar amounts of bilirubin and CO.
• The CO released then binds strongly to hemoglobin, forming
carboxyhemoglobin (COHb).
Cathy Hammerman, MD and Michael Kaplan, MB, ChB; Recent Developments in the
Management of Neonatal Hyperbilirubinemia.
25. • Because endogenous CO production in the newborn occurs
almost exclusively by this pathway, hemolysis can be
quantitated by determining blood COHb levels.
• Elevated COHb levels have been correlated with increased
hemolysis in fetuses and neonates suffering from immune
hemolytic disease and even with kernicterus and death in
G6PD-deficient infants.
Cathy Hammerman, MD and Michael Kaplan, MB, ChB; Recent Developments in the
Management of Neonatal Hyperbilirubinemia.
26. Risk of Sepsis
• Increased risk of sepsis has also been reported
among preterm infants with G6PD deficiency.
• The prevalence of G6PD deficiency among 170
infants with birthweight <2.0 kg admitted to a
neonatal intensive care nursery was 5.3%.
• Stage 2 necrotizing enterocolitis was 6.9-fold
higher (95% CI: 2–23.5) compared with matched
cohort.
Schutzman DL, Porat R. Glucose-6-phosphate dehydrogenase deficiency: another risk factor for necrotizing
enterocolitis? J Pediatr. 2007;151(4):435–437
27. Neonatal screening for G6PD deficiency
• Newborn screening relies on the accurate (phenotypic)
identification of deficient enzyme activity.
• However, variations due to partial genotypic manifestations,
postnatal age, and population of younger, high enzyme
activity RBCs are significant confounding factors.
Vinod K. Bhutani, MD,jaundice due to glucose-6-phosphate dehydrogenase deifciency, NeoReviews Vol.13
No.3 March 2012
28. • The definitive biochemical test is the spectrophotometric
quantitative enzyme assay based on rate of NADPH
formation (mmoles/min/gHb) with absorbance at 340 nm
wavelength and expressed as IU/ gHb.
• A useful semi-quantitative screening test, Fluorescent spot
test (FST) relies on the ability of NADPH to fluoresce
intensely with exposure to long wave ultraviolet light.
• It lacks the sensitivity to diagnose infants with partial
enzyme activity (20%–60%) including female heterozygotes.
29.
30. • Other tests that detect NADPH such as
methylene blue reduction, cresyl blue dye
decolorization, cytochemical staining are also
available.
• Identification of specific mutations by
DNA/polymerase chain reaction (PCR) screening,
ideal for identification of female heterozygotes, is
limited by the diversity of known mutations,
time-intensive process and occasional mismatch
with phenotype expression of enzyme activity.
31. • In patients with acute hemolysis, testing for G6PD
deficiency may be falsely negative because older
erythrocytes with a higher enzyme deficiency
have been hemolyzed.
• Female heterozygotes may be hard to diagnose
because of X-chromosome mosaicism leading to
a partial deficiency that will not be detected
reliably with screening tests.
32. • Thus, a two-step approach to measure
enzyme functional assay with concomitant
DNA verification seems to be the most
accurate and practical approach to screen,
monitor and diagnose neonatal G6PD
deficiency.
