II. Epidemiology

  1. Worldwide Prevalence: 400 Million
  2. Caucasians of Mediterranean ancestry (Class II)
    1. Greek patients
    2. Jewish patients
    3. Sardinian patients (from island of Italy)
  3. Black patients or African descent (Class III)
    1. Up to 10% of U.S. african-American Males have G6PD
  4. Asian patients
  5. Filipino patients

III. Pathophysiology

  1. Glucose-6-phosphate dehydrogenase (G6PD)
    1. Catalyzes NADP to NADPH (pentose phosphate path)
    2. Thiol glutathione neutralizes free radicals (superoxide, Hydrogen Peroxide, hydroxyl)
    3. NADPH prevents oxidative damage to cells by regenerating Thiol glutathione after it has been oxidized
    4. RBCs depend on G6PD for sole pathway to NADPH (since RBCs lack mitochondria)
    5. RBCs are most susceptible to insufficient G6PD
  2. Methemoglobin (Fe3+) may form spontaneously
    1. Methemoglobin is typically reduced to normal Hemoglobin (Fe2+) by cellular mechanisms
    2. NADPH is important in combating oxidative stress and converting Hemoglobin back to Fe2+
    3. However in G6PD Deficiency, this fails and Methemoglobinemia is unchecked
  3. Results in acute Hemolytic Anemia
  4. Drug-induced Hemolysis affects older cells
    1. Younger cells have adequate enzyme levels to survive
  5. G6PD mutations occur on distal long arm of C Chromosome
    1. X -Linked Disorder

IV. Grading: Class Severity (WHO)

  1. Abnormal
    1. Class 1: Congenital nonspherocytic Hemolytic Anemia (rare)
      1. Most common in white males of european descent
      2. Hemolysis occurs without oxidative stress exposure
      3. Splenomegaly is present in 40% of patients
    2. Class 2: Severe G6PD (1 to 10% Enzyme Activity)
      1. More common in mediterranean descent
      2. Symptomatic Hemolysis with oxidative stress
    3. Class 3: Mild G6PD (10 to 100% Enzyme Activity, most common)
      1. Hemolytic Anemia occurs only with significant oxidative stress
  2. Normal
    1. Class 4: Nondeficient G6PD Variant (60 to 100% Enzyme Activity)
      1. Common in African Descent
      2. Asymptomatic, even with oxidative stressors
    2. Class 5: Normal activity (>150% normal Enzyme Activity)

V. Causes

  1. See Medications in G6PD Deficiency
    1. Onset within 72 hours of intake
  2. Infection (most common cause)
    1. Salmonella
    2. Eschirichia coli
    3. Beta-hemolytic Streptococcus
    4. Rickettsia
    5. Viral Hepatitis
    6. Influenza A
  3. Fava beans (Italian Broad Beans)
    1. Bell Beans
    2. Broad Beans
    3. English Dwarf Beans
    4. Haba Beans
    5. Horse Beans
    6. Pigeon Beans
    7. Silkworm Beans
    8. Tic Beans

VI. Symptoms and Signs

  1. Usually asymptomatic
  2. See Hemolytic Anemia for acute episodes

VII. Differential Diagnosis

IX. Complications

  1. Increased risk of Sepsis

X. Prevention

  1. Avoid precipitating factors
    1. See Medications in G6PD Deficiency
    2. Keep Immunizations up-to-date
  2. Treat Anemia following Hemolytic Anemia episode
    1. Iron Supplementation
    2. Folic Acid supplementation
  3. Measures that are not recommended (no benefit)
    1. Splenectomy
    2. Vitamin E
    3. Selenium

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Related Studies

Ontology: Favism (C0015702)

Definition (MSH) Hemolytic anemia due to the ingestion of fava beans or after inhalation of pollen from the Vicia fava plant by persons with glucose-6-phosphate dehydrogenase deficient erythrocytes.
Concepts Disease or Syndrome (T047)
MSH D005236
ICD10 D55.0
SnomedCT 154801000, 267558001, 191172001, 76500009
English Favism, Favisms, favism, favism (diagnosis), Favism [Disease/Finding], Favism (disorder), favism; anemia, favism; poisoning, poisoning; favism, anemia; favism
Dutch favisme, anemie; favisme, favisme; anemie, favisme; vergiftiging, vergiftiging; favisme, Favisme
Japanese そらまめ中毒, ソラマメチュウドク
Swedish Favism
Czech favismus, Favismus
Finnish Favismi
Russian ANEMIIA PRIMAKHINOVAIA, FAVIZM, АНЕМИЯ ПРИМАХИНОВАЯ, ФАВИЗМ
Croatian FAVIZAM
Polish Fawizm
Hungarian Favismus
Norwegian Favisme
Spanish favismo (trastorno), favismo, Favismo
French Favisme
German Favismus, Bohnenkrankheit
Italian Favismo
Portuguese Favismo

Ontology: Glucosephosphate Dehydrogenase (C0017757)

Definition (NCI) Glucose-6-phosphate 1-dehydrogenase (515 aa, ~59 kDa) is encoded by the human G6PD gene. This protein plays a role in pentose metabolism to produce NADPH.
Concepts Amino Acid, Peptide, or Protein (T116) , Enzyme (T126)
MSH D005954
SnomedCT 259705000, 9024005
CPT 1011452
LNC LP15601-5, MTHU027273, LP182422-8
English Dehydrogenase, Glucose-6-Phosphate, Dehydrogenase, Glucosephosphate, Glucose 6 Phosphate Dehydrogenase, Glucose-6-Phosphate Dehydrogenase, Glucosephosphate Dehydrogenase, glucose 6 phosphate dehydrogenase, D-Glucose-6-phosphate:NADP+ 1-oxidoreductase, Glucose-6-phosphate dehydrog, GLUCOSE PHOSPHATE DEHYDROGENASE 06, GPD, G6PD - Gluc-6-ph dehydrogenase, G6P - Gluc-6-phos dehydrogen, Glucosephosphate Dehydrogenase [Chemical/Ingredient], glucose-6-phosphate dehydrogenase (G6PD), g-6pd, g6pd, glucosephosphate dehydrogenase, Glucose-6-Phosphate 1-Dehydrogenase, Glucose-6-Phosphate dehydrogenase, Glucose-6-phosphate dehydrogenase (G6PD), G-6PD, Glucose-6-phosphate dehydrogenase, G6PD - Glucose-6-phosphate dehydrogenase, G6P - Glucose-6-phosphate dehydrogenase, Glucose-6-phosphate dehydrogenase (substance), G6PD, EC 1.1.1.49
Swedish Glukosfosfatdehydrogenas
Czech glukosafosfátdehydrogenasa
Finnish Glukoosifosfaattidehydrogenaasi
Italian Glucosio-6-fosfato deidrogenasi, Glucosiofosfato deidrogenasi
Russian GLIUKOZO-6-FOSFAT-DEGIDROGENAZA, GLIUKOZOFOSFAT-DEGIDROGENAZA, ГЛЮКОЗО-6-ФОСФАТ-ДЕГИДРОГЕНАЗА, ГЛЮКОЗОФОСФАТ-ДЕГИДРОГЕНАЗА
German GLUCOSE PHOSPHAT DEHYDROGENASE 06, Glucose-6-Phosphat-Dehydrogenase, Glucosephosphat-Dehydrogenase, Glukosephosphat-Dehydrogenase
Croatian GLUKOZAFOSFAT DEHIDROGENAZA
Polish Dehydrogenaza glukozofosforanowa
Japanese グルコースリン酸デヒドロゲナーゼ, グルコース-6-リン酸-1-デヒドロゲナーゼ, グルコース-6-りん酸デヒドロゲナーゼ, グルコースりん酸デヒドロゲナーゼ, グルコース-6-リン酸デヒドロゲナーゼ, グルコース燐酸デヒドロゲナーゼ
Spanish Glucofosfato Deshidrogenasa, Glucosa-Fosfato Deshidrogenasa, Glucosa Fosfato Deshidrogenasa, G-6-FD, G6FD, G-6-PD, G6PD, G - 6PD, glucosa - 6 - fosfato deshidrogenasa (sustancia), glucosa - 6 - fosfato deshidrogenasa, Glucosa-6-Fosfato Deshidrogenasa, Glucosafosfato Deshidrogenasa
Portuguese G6FD, Glucose-Fosfato Desidrogenase, G6PD, G-6-PD, Glucofosfato Desidrogenase, Glucose Fosfato Desidrogenase, G-6-FD, Glucose-6-Fosfato Desidrogenase, Glucosefosfato Desidrogenase
French Glucose 6-phosphate dehydrogenase

Ontology: Glucose-6-phosphate dehydrogenase deficiency anemia (C0237987)

Concepts Disease or Syndrome (T047)
ICD10 D55.0
SnomedCT 62403005, 191171008
English ANAEMIA HAEMOLYTIC G6PD, ANEMIA HEMOLYTIC G6PD, Anaemia due to glucose-6-phosphate dehydrogenase [G6PD] deficiency, Anemia due to glucose-6-phosphate dehydrogenase [G6PD] deficiency, Anemia hemolytic G6P, Glucose-6-phosphate deficiency anemia, NOS, Glucose-6-phosphate dehydrogenase deficiency anemia, Hemolytic anemia glucose-6-phosphate dehydrogenase defici, Hemolytic anemia glucose-6-phosphate dehydrogenase deficienc, Hemolytic anemia glucose-6-phos dehydrogenase deficiency, Anaemia haemolytic G6P, Anaemia haemolytic G6PD, Anemia hemolytic G6PD deficiency, Hemolytic anemia G6PD deficiency, Anemia hemolytic G6PD, Anemia due to glucose-6-phosphate dehydrogenase deficiency, G6PD deficiency, anemia due to G6PD deficiency, G6PD deficiency anemia (diagnosis), Haemolytic anaemia G6PD deficiency, Haemolytic anaemia glucose-6-phos dehydrogenase deficiency, Anaemia haemolytic G6PD deficiency, G-6-PD deficiency anaemia, G-6-PD deficiency anemia, Glucose-6-phosphate dehydrogenase deficiency anaemia, G6PD deficiency anaemia, G6PD deficiency anemia, Glucose-6-phosphate dehydrogenase deficiency anemia (disorder), deficiency; anemia, G-6-PD, deficiency; anemia, enzyme, glucose-6-phosphate dehydrogenase (G-6-PD), deficiency; anemia, glucose-6-phosphate dehydrogenase (G-6-PD), deficiency; glucose-6-phosphate dehydrogenase anemia, glucose-6-phosphate dehydrogenase deficiency; anemia, glucose-6-phosphate dehydrogenase; deficiency with anemia, hemolytic; anemia, nonspherocytic, congenital or hereditary, glucose-6-phosphate dehydrogenase deficiency, anemia; deficiency, G-6-PD, anemia; deficiency, enzyme, glucose-6-phosphate dehydrogenase (G-6-PD), anemia; deficiency, glucose-6-phosphate dehydrogenase (G-6-PD), anemia; glucose-6-phosphate dehydrogenase deficiency, anemia; hemolytic, nonspherocytic, congenital or hereditary, glucose-6-phosphate dehydrogenase deficiency, G-6-PD deficiency anemia, NOS, Glucose-6-phosphate dehydrogenase deficiency anemia, NOS, Glucose-6-phosphate dehydrogenase deficiency anemia [dup] (disorder)
Dutch hemolytische anemie G6PD, hemolytische anemie glucose-6-fosfaatdehydrogenasedeficiëntie, hemolytische anemie G6PD-deficiëntie, hemolytische anemie G6PD deficiëntie, hemolytische anemie G6P, G-6 PD-deficiëntie hemolytische anemie, anemie hemolytisch G6PD, hemolytische anemie glucose-6-fosfaat-dehydrogenase deficiëntie, anemie; deficiëntie, G-6-PD, anemie; deficiëntie, enzym, glucose-6-fosfaatdehydrogenase (G-6-PD), anemie; deficiëntie, glucose-6-fosfaatdehydrogenase (G-6-PD), anemie; glucose-6-fosfaatdehydrogenasedeficiëntie, anemie; hemolytisch, niet-sferocytair, congenitaal of hereditair, glucose-6-fosfaatdehydrogenasedeficiëntie, deficiëntie; anemie, G-6-PD, deficiëntie; anemie, enzym, glucose-6-fosfaatdehydrogenase (G-6-PD), deficiëntie; anemie, glucose-6-fosfaatdehydrogenase (G-6-PD), deficiëntie; glucose-6-fosfaatdehydrogenase met anemie, glucose-6-fosfaatdehydrogenase; deficiëntie met anemie, glucose-6-fosfaatdehydrogenasedeficiëntie; anemie, hemolytisch; anemie, niet-sferocytair, congenitaal of hereditair, glucose-6-fosfaatdehydrogenasedeficiëntie, Anemie door deficiëntie van glucose-6-fosfaatdehydrogenase [G-6-PD]
French Anémie hémolytique due à un déficit en G6PD, Anémie hémolytique due à un déficit en glucose-6-phos déshydrogénase, Anémie hémolytique due à un déficit en glucose-6- phosphate déshydrogénase, Anémie hémolytique par carence en G6PD, Anémie hémolytique par carence en glucose-6-phosphate déshydrogénase, Anémie hémolytique G-6 P, ANEMIE HEMOLYTIQUE G6PD, Anémie hémolytique due à une carence en G6PD
German haemolytische Anaemie durch G6PD-Mangel, Anaemie, haemolytisch G6PD, haemolytische Anaemie durch Glukose-6-phosphat-Dehydrogenase-Mangel, Anaemie, haemolytisch G6P, Anaemie, haemolytisch G6PD-Mangel, haemolytische Anaemie durch G-6-PDH-Mangel, ANAEMIE HAEMOLYTISCH G6PD, Anaemie durch Glukose-6-Phosphat-Dehydrogenase[G6PD]-Mangel
Italian Anemia emolitica da deficit di glucoso-6-fosfato deidrogenasi, Anemia emolitica da deficit di G6 fosfato deidrogenasi, Anemia emolitica, G6 fosfato deidrogenasi, Anemia emolitica da deficit di glucosio-6-fosfato deidrogenasi, Anemia emolitica con deficit di glucosio-6-fosfatasi, Anemia emolitica da deficit di glucosio-6-fosfato-deidrogenasi, Anemia emolitica, glucoso-6-fosfato deidrogenasi
Portuguese Anemia hemolítica por carência de G6PD, Anemia hemolítica por carência de glucose-6-fosfato desidrogenase, Anemia hemolítica G6P, ANEMIA HEMOLITICA AUTOIMUNE G6PD
Spanish Anemia hemolítica por deficiencia de G6P, Anemia hemolítica G6PD, Anemia hemolítica por deficiencia de glucosa-6-fosdeshidrogenasa, Anemia hemolítica por déficit de G6P, Anemia hemolítica por deficiencia de G6DP, Anemia hemolítica por déficit de G6PD, Anemia hemolítica por déficit de glucosa-6-fosfato deshidrogenasa, Anemia hemolítica por deficiencia de G6PD, ANEMIA HEMOLITICA G6PD, anemia por deficiencia de glucosa-6-fosfato deshidrogenasa [dup] (trastorno), anemia por deficiencia de glucosa-6-fosfato deshidrogenasa [dup], anemia por deficiencia de G - 6 - PD, anemia por deficiencia de glucosa - 6 - fosfato deshidrogenasa (trastorno), anemia por deficiencia de glucosa - 6 - fosfato deshidrogenasa
Japanese 溶血性貧血G6PD, グルコース−6−リン酸脱水素酵素欠乏性溶血性貧血, 溶血性貧血G6P, ヨウケツセイヒンケツG6P, グルコース6リンサンダッスイソコウソケツボウセイヨウケツセイヒンケツ, ヨウケツセイヒンケツG6PD
Czech Hemolytická anémie při deficitu glukózo-6-fosfátdehydrogenázy, Anémie hemolytická při deficitu G-6-P, Hemolytická anémie při deficitu G-6-PD, Anémie hemolytická při deficitu G-6-PD
Korean 포도당6인 산탈수소효소[G6PD] 결핍증에 의한 빈혈
Hungarian Haemolytikus G6P anaemia, Hemolítikus G6PD-hiányos anaemia, Haemolytikus G6PD anaemia, Haemolytikus G6PD hiányos anaemia, Haemolytikus glucose-6-phosphatase dehydrogenase-hiányos anaemia, Haemolyticus glucose-6-phosphat dehydrogenase hiányos vérszegénység, Haemolyticus glucose-6-phosphat dehydrogenase deficiens anaemia, Haemolyticus G6PD-hiányos vérszegénység, Haemolyticus G6PD-anaemia, Haemolytikus G6PD-hiányos anaemia, Haemolyticus glucose-6-phosphatase dehydrogenase hiányos anaemia

Ontology: Deficiency of glucose-6-phosphate dehydrogenase (C2939465)

Definition (MSH) A disease-producing enzyme deficiency subject to many variants, some of which cause a deficiency of GLUCOSE-6-PHOSPHATE DEHYDROGENASE activity in erythrocytes, leading to hemolytic anemia.
Definition (MEDLINEPLUS)

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a genetic disorder that is most common in males. About 1 in 10 African American males in the United States has it. G6PD deficiency mainly affects red blood cells, which carry oxygen from the lungs to tissues throughout the body. The most common medical problem it can cause is hemolytic anemia. That happens when red blood cells are destroyed faster than the body can replace them.

If you have G6PD deficiency, you may not have symptoms. Symptoms happen if your red blood cells are exposed to certain chemicals in food or medicine, certain bacterial or viral infections, or stress. They may include

  • Paleness
  • Jaundice
  • Dark urine
  • Fatigue
  • Shortness of breath
  • Enlarged spleen
  • Rapid heart rate

A blood test can tell if you have it. Treatments include medicines to treat infection, avoiding substances that cause the problem with red blood cells, and sometimes transfusions.

NIH: National Library of Medicine

Definition (NCI) An X-linked recessive inherited disorder caused by mutations in the G6PD gene. It is characterized by the absence or presence of very low levels of glucose-6-phosphate dehydrogenase. Patients develop hemolytic anemia usually in response to infection or exposure to drugs.
Definition (CSP) common hereditary enzyme deficiency causing varying degrees of hemolytic anemia; can cause favism, some drug induced hemolytic anemias, and chronic nonspherocytic hemolytic anemia.
Concepts Disease or Syndrome (T047)
MSH D005955
SnomedCT 267498002, 154738008, 124134002, 62403005
LNC LA12540-3
English Deficiencies, Glucosephosphate Dehydrogenase, Deficiencies, GPD, Deficiency, Glucosephosphate Dehydrogenase, Deficiency, GPD, Dehydrogenase Deficiencies, Glucosephosphate, Dehydrogenase Deficiency, Glucosephosphate, Glucosephosphate Dehydrogenase Deficiencies, Glucosephosphate Dehydrogenase Deficiency, GPD Deficiencies, GPD Deficiency, G6PD - Gluc-6-phos dehydr defi, Glucose-6-phosph dehydrog defi, glucose 6 phosphate dehydrogenase deficiency, DEFIC GLUCOSEPHOSPHATE DEHYDROGENASE, GLUCOSEPHOSPHATE DEHYDROGENASE DEFIC, DEFIC GPD, GPD DEFIC, glucose-6-phosphate dehydrogenase deficiency, Glucose-6-phosphate dehydrogenase deficienc, G-6 PD deficiency, Glucosephosphate Dehydrogenase Deficiency [Disease/Finding], G6PD Deficiency, Glucose-6-Phosphate Dehydrogenase Deficiencies, Deficiency, G6PD, G6PD Deficiencies, Deficiencies, Glucose-6-Phosphate Dehydrogenase, Deficiency, Glucose-6-Phosphate Dehydrogenase, Dehydrogenase Deficiencies, Glucose-6-Phosphate, Dehydrogenase Deficiency, Glucose-6-Phosphate, Deficiencies, G6PD, Glucose-6-Phosphate Dehydrogenase Deficiency, Glucose 6 Phosphate Dehydrogenase Deficiency, Deficiency of glucose-6-phosphate dehydrogenase, deficiency g 6 pd, g-6pd deficiency, deficiency g6pd, Deficiency;G6PD, anemia g6pd hemolytic, anemia g-6-pd deficiency, g6pd deficiency, Hemolytic Anemia Due to G6PD Deficiency, Deficiency of Glucose 6 Phosphate Dehydrogenase, Deficiency of Glucose-6-Phosphate Dehydrogenase, Glucose-6-phosph.dehydr.defic., Glucose-6-phosphate Dehydrogenase Deficiency, G-6-PD Variant Enzyme Deficiency Anemia, G6PD, G6PD deficiency, g6pd deficiency (diagnosis), G6PD - Glucose-6-phosphate dehydrogenase deficiency, Glucose-6-phosphate dehydrogenase deficiency, Deficiency of G-6PD, Deficiency of glucose-6-phosphate dehydrogenase (disorder)
Italian Deficit di glucosio-6-fosfato deidrogenasi, Deficit di glucoso-6-fosfato-deidrogenasi, Carenze di glucosio fosfato deidrogenasi, Carenza GPD, Carenza di glucosio fosfato deidrogenasi
Dutch G-6 PD-deficiëntie, glucose-6-fosfaatdehydrogenasedeficiëntie, Deficiëntie, glucose-6-fosfaatdehydrogenase, Glucose-6-fosfaatdehydrogenasedeficiëntie
French Déficit en glucose-6-phosphate déshydrogénase, Déficit en G-6 PD, Déficit en G6PD, Déficit en glucose-6-phosphate-déshydrogénase
German G-6 PD-Mangel, Glukose-6-phosphat-Dehydrogenase-Mangel, Glucose-6-Phosphat Dehydrogenase-Mangel, Glukosephosphat-Dehydrogenasemangel
Portuguese Carência de G6PD, Deficiência de Glucosefosfato Desidrogenase, Deficiência da G6FD, Deficiência de G6PD, Deficiência da G-6-PD, Deficiência de Glucose Fosfato Desidrogenase, Deficiência da G6PD, Deficiência de G-6-PD, Deficiência da G-6-FD, Deficiência de G6FD, Deficiência de Glucofosfato Desidrogenase, Deficiência de Glucose-6-Fosfato Desidrogenase, Deficiência de Glucose-Fosfato Desidrogenase, Deficiência de G-6-FD, Carência de glucose-6-fosfato desidrogenase
Spanish Déficit de G6PD, Deficiencia de Glucosafosfato Deshidrogenasa, Deficiencia de Glucosa-6-Fosfato Deshidrogenasa, Deficiencia de Glucosa Fosfato Deshidrogenasa, Deficiencia de la G-6-FD, Deficiencia de la G6FD, Deficiencia de Glucosa-Fosfato Deshidrogenasa, Deficiencia de la G-6-PD, Deficiencia de la G6PD, Deficiencia de Glucofosfato Deshidrogenasa, deficiencia de G - 6PD, deficiencia de glucosa - 6 - fosfato deshidrogenasa (trastorno), deficiencia de glucosa - 6 - fosfato deshidrogenasa, Déficit de glucosa-6-fosfato deshidrogenasa
Swedish Glukosfosfatdehydrogenasbrist
Czech glukosafosfátdehydrogenasa - nedostatek, Deficit G-6-PD, Deficit glukózo-6-fosfátdehydrogenázy
Finnish Glukoosifosfaattidehydrogenaasin puutos
Russian GLIUKOZOFOSFAT-DEGIDROGENAZY NEDOSTATOCHNOST', ГЛЮКОЗОФОСФАТ-ДЕГИДРОГЕНАЗЫ НЕДОСТАТОЧНОСТЬ
Japanese G6PDケッソンショウ, グルコース6リンサンダッスイソコウソケッソンショウ, グルコース−6−リン酸脱水素酵素欠損症, G−6−PD欠損症, グルコースリン酸脱水素酵素欠損症, グルコースリン酸デヒドロゲナーゼ欠損症, グルコースりん酸デヒドロゲナーゼ欠乏症, グルコースりん酸脱水素酵素欠乏症, グルコース燐酸脱水素酵素欠乏症, プリマキン過敏症, 葡萄糖六燐酸脱水素酵素欠損症, グルコース-6-リン酸デヒドロゲナーゼ欠損症, グルコースリン酸脱水素酵素欠乏症, グルコース燐酸デヒドロゲナーゼ欠乏症, ブドウ糖六リン酸脱水素酵素欠損症
Croatian GLUKOZAFOSFAT DEHIDROGENAZA, NEDOSTATAK
Polish Niedobór dehydrogenazy glukozo-6-fosforanowej
Hungarian G6PD-hiány, Glucose-6-phosphat dehydrogenase deficiencia, Glucose-6-phosphat dehydrogenase hiány
Norwegian Mangel på glukose-6-fosfatdehydrogenase, Glukose-6-fosfatdehydrogenase-mangel, Mangel på glukosefosfatdehydrogenase, Hemolytisk anemi av g6-pd-mangel