Red Blood Cell Enzyme Defects

G6PD deficiency

Pyruvate Kinase deficiency

Methemoglobin Reductase deficiency

Hereditary Enzyme Defects

red blood cells only

Hereditary enzyme defects apply to

G6PD deficiency

most encountered anemia caused by enzyme deficiency

inherited: sex linked

Body doesn't have enough G6PD enzyme which is the enzyme involved in hexose monophosphate pathway to make GSH (needed to protect hemoglobin from oxidative denaturation)

GdB and GdA

Normal G6PD activity

GdB

Normal G6PD activity

most common in Caucasian pops (99%)

GdA

Normal G6PD activity

found in Black pop (20%)

Gd Mediterranean

Gd A(-)

Gd Canton

Abnormal G6PD activity

Gd Mediterranean

Abnormal G6PD activity

reduced activity of G6PD

found in Caucasian pop

GdA(-)

Abnormal G6PD activity

reduced stability of G6PD

found in Black pop

Gd Canton

Abnormal G6PD activity

defect unknown

found in Asian pop

increased hemolysis

People with G6PD defects can live a normal life until their RBCs are challenge, which results in

exposures/stressors of G6PD deficiency

Infection

Favism (sensitive to Fava Bean)

Mothball poisoning (Naphthalene)

Drugs (Antimalaria, Sulfonamides, Some analgesics)

clinical features of G6PD deficiency

Hemoglobinuria

Jaundice

Hemoglobinemia

Anemia

**vary depending on severity of hemolytic episode

lab features of G6PD deficiency

increased retic count

Polychromasia and poikilocytosis

Heinz bodies, bite cells, spherocytes

quantitative and qualitative deficiencies in G6PD activity

Dye Reduction Test

G6PD Qualitative Lab Test

based on principle that G6PD deficient RBCs fail to generate NADPH

rx: Glu 6-PO4 + NADP -- G6PD --> 6-phosphoglyconate + NADH

NADH + blue dye -- PMS --> NADP + colorless complex

resutls:

Normo: blue to rust color

Abnorm: stays blue (don't have G6PD, so rxn can't take place

Fluorescent spot test for G6PD

screening test for G6PD deficiency

normal G6PD activity will convert NADP to NADPH and show fluorescence

Abnormal rxn: no fluorescence

Ascorbate Cyanide Test for G6PD

screening test for G6PD deficiency

G6PD deficient RBCs fail to reduce hydrogen peroxide when added to sodium ascorbate, sodium cyanide, and glucose

- causes hgb in G6PD deficient RBCs to become oxidize and form methemoglobin

Normo: blood stays red

Abnormo: solution turns dark brown

treatment of G6PD

avoidance of causative agent

denatured hgb

What precipitates to form Heniz bodies?

supravital stain

What blue stain is used to see Heinz bodies?

Pyruvate Kinase

utilized in Embden-Meyerhof pathway to turn PEP into pyruvate that can be used to make ATP

Pyruvate kinase deficiency

fail to generate enough ATP to maintain normal red cell membrane function

results in decreased ATP and short RBC life cycle

clinical features of PK deficiency

may develop during infancy / early childhood

splenomegaly

jaundice

anemia

lab features of PK deficiency

polychromasia, poikilocytosis, Howell-Jolly bodies, and NRBCs

Burr cells (echinocyte)

Increased retic count

osmotic fragility test

screening test for PK deficiency

incubated OF abnormal

- normal at first but increased after incubating for 24-hours due to decrease in energy

Fluorescent spot test for PK deficiency

qualitative assay for PK deficiency that detects NADH (fluorescence) --> NAD (no fluorescence)

Normal: no fluorescence after hour incubation

Abnormal: fluorescence after hour

treatment for PK deficiency

Treatment: splenectomy

Methemoglobin Reductase

enzyme responsible for conversion of methemoglobin (deoxyhemoglobin) back to oxyhemoglobin

deficiency results in increased levels of methemoglobin leading to methemoglobinemia (RBCs cannot carry oxygen)

Blood cholate-brown in color

clinical features of Methgb Reductase deficiency

Cyanosis (no O2 in tissues leads to bluing of skin)

Mehgb can not carry O2 so pts exhibit symptoms like anemia (left shift RDW)

lab features of Methgb Reductase deficiency

increased Methgb levels

decresed Methgb Reductase

normal Hgb electrophoresis pattern (compared to HgbM)

benign

course of disorder with methemoglobinemia

patients are fine (typically treated only for cosmetic reasons)

IV methylene blue

treatment for MetHgb

used to activate the NADPH-methgb reductase system