questions 4

G6PD Deficiency

Topic updated on 11/10/17 11:02am

  • A 25-year-old man with Mediterranean ancestry presents with jaundice. He also reports being unusually tired and believes this may be due to his recent recovery from  mononucleosis. He was found to be anemic with a hemoglobin of 9 g/dL. His peripheral blood smear revealed bite cells and Heinz bodies.

  • Clinical definition
    • glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked genetic disorder that causes an intrinsic hemolytic anemia
  • Epidemiology
    • prevalence
      • 7.1% worldwide
      • most common enzyme disorder of erythrocytes
    • demographics
      • more severe in males than females
      • common in areas where malaria is endemic
        • sub-Saharan Africa
        • Middle East
        • southeast Asia
        • Mediterranean regions
        • Pacific islands

  • Pathophysiology
    • G6PD affects the pentose phosphate (hexose monophosphate) pathway
      • this pathway generates nicotinamide dinucleotide phosphate (NADPH), which protects red blood cells against oxidative stress
      • in red blood cells (without mitochondria), this pathway is the only source of NADPH
      • acute hemolytic anemia following exposure to oxidative stressors 
        • primaquine
        • dapsone
        • sulfa drugs
        • infections
        • fava bean ingestion
      • oxidative stressors cause
        • rapid depletion of reduced glutathione resulting in
          • precipitation of hemoglobin (manifested as Heinz bodies)
          • erythrocyte membrane damage, both extravascular and intravascular hemolysis  
      • G6PD deficiency is thought to decrease risk of severe malaria
  • Genetics 
    • inheritance pattern
      • X-linked
    • mutations
      • G6PD gene encoding the G6PD enzyme
  • Prognosis
    • natural history of disease
      • typically asymptomatic until exposed to oxidative stressors
  • Symptoms
    • primary symptoms
      • neonatal hyperbilirubinemia on day 2-4
      • acute hemolytic anemia following exposure to precipitants, typically within 24-72 hours after ingestion
        • fatigue
        • jaundice
        • dark urine
        • back pain
  • Physical exam
    • jaundice
  • Labs
    • complete blood count and reticulocyte count
    • peripheral smear 
      • bite cells 
      • Heinz bodies
    • hemolysis labs
      • ↑ indirect bilirubin
      • ↓ haptoglobin
      • ↑ lactate dehydrogenase
    • urine 
      • hemoglobinuria
  • G6PD activity assays
    • indication
      • screening
    • fluorescent spot test
      • most sensitive
    • methemoglobin reduction test
  • Quantitative assays
    • indications 
      • confirmation of diagnosis
        • a normal G6PD level immediately after hemolysis does not rule out G6PD deficiency
    • spectrophotometry analysis
  • Gilbert syndrome
    • jaundice at birth (rather than delayed onset of jaundice)
    • normal G6PD enzyme activity
  • Hereditary spherocytosis
    • spherocytosis seen on peripheral blood smear
  • Conservative
    • avoid oxidative stressors
  • Medical
    • blood transfusion
      • indication
        • if severe
  • Recurrence of acute hemolysis


Qbank (3 Questions)

(M1.HE.27) A 3-month-old African American infant presents to the hospital with 2 days of fever, "coke"-colored urine, and jaundice. The pregnancy was uneventful except the infant was found to have hyperbilirubinemia that was treated with phototherapy. The mother explains that she breastfeeds her child and recently was treated herself for a UTI with trimethoprim-sulfamethoxazole (TMP-SMX). Which of the following diseases is similarly inherited as the disease experienced by the child? Topic Review Topic

1. Marfan syndrome
2. Sickle cell anemia
3. Hemophilia A
4. Beta thalassemia
5. Rett syndrome

(M1.HE.72) A 21-year-old African American male with a history of HIV presents to the clinic with a complaint of cough, shortness of breath, and fever that has seemed to slowly progress over the past week. Upon questioning, he admits to not being able to take his HAART regimen due to recently losing his health insurance. Concerned, the physician pursues a full workup. The patient is found to have a pneumonia caused by a gram-positive, acid fast aerobe, and the physician prescribes the appropriate medication. After 1 day of taking the medication, the patient returns to the physician with complaints of severe weakness and dark colored urine. On exam, the physician notes that the patient is jaundiced and has splenomegaly. Which figure demonstrates the mode of inheritance of this patient's genetic condition? Topic Review Topic
FIGURES: A   B   C   D   E  

1. Figure A
2. Figure B
3. Figure C
4. Figure D
5. Figure E

(M1.HE.86) A 32-year-old Greek male presents with a rash consistent with dermatitis herpetiformis and is treated with a course of oral dapsone. Over the following several days he becomes increasingly fatigued and experiences persistent back pain. Complete blood count reveals a normocytic anemia and urinalysis shows hemoglobinuria. Results from a peripheral blood smear are shown in Figure A. Which of the following is most likely responsible for this patient’s symptoms? Topic Review Topic
FIGURES: A          

1. Glucose-6-phosphate-dehydrogenase deficiency
2. Pyruvate kinase deficiency
3. Paroxysmal nocturnal hemoglobinuria
4. Hereditary spherocytosis
5. Cold immune hemolytic anemia

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