Glucose-6-phosphate dehydrogenase deficiency

Introduction to glucose-6-phosphate dehydrogenase deficiency Hemolytic anemia caused by the deficiency of erythrocyte glucose-6-phosphate dehydrogenase (G-6-PD) is a heterogeneous group of diseases, which is the most common type of hemolysis caused by erythrocyte enzyme deficiency. This disease is X-linked incompletely dominant inheritance, and G-6-PD activity measurement is the main means of diagnosis of this disease. There is currently no cure for this disease. basic knowledge The proportion of illness: 0.001% Susceptible people: no special people. Mode of infection: non-infectious Complications: jaundice anemia cholelithiasis

Cause of glucose-6-phosphate dehydrogenase deficiency

G-6-PD and its biochemical variant (30%):

The normal "enzyme" is called G-6-PD B. The G-6-PD deficiency is caused by the abnormality of the G-6-PD structural gene encoding the G-6-PD amino acid sequence, and the detailed biochemistry of the partially purified residual enzyme. Studies suggest that there is heterogeneity between them. These abnormal enzymes are G-6-PD biochemical variants. In 1966, the World Health Organization (WHO) held an international conference in Geneva on the G-6-PD variant. The naming, typing standards and methods are uniformly defined. The G-6-PD is mainly based on electrophoresis rate and enzyme kinetic parameters, such as enzyme activity, electrophoresis rate, glucose-6-phosphate (G6P) and coenzyme II (NADP). The Michaelis constant (KM), the substrate congener (deoxy G6P, galactose, deamination, NADP, coenzyme I) utilization, thermal stability, optimum pH, but at least the following five items are required: 1 enzyme activity 2 electrophoresis speed; 3G-6-PD Michaelis constant; 4 relative deprivation rate of deoxygenated G6P; 5 thermal stability, currently, there are more than 400 G-6-PD variants reported in the world, among which About 300 species are identified according to the standard methods recommended by the WHO, and about 100 variants are identified by other methods, based on these variations. The enzymatic activity and clinical significance are divided into five categories: the first type of variant activity is very low (less than normal 10%) with lifetime hemolytic anemia; the second type of variant, although in vitro activity is very low, but not accompanied Chronic hemolysis, hemolysis occurs only under certain special circumstances, this type is a common type such as G-6-PD Mediterranean type; the third type of variant has a normal enzyme activity of 10% to 60 %, hemolysis occurs only when certain drugs or infections are taken; the fourth type of variation is due to mutations that do not alter the functional activity of the enzyme; the activity of the enzymes of the fifth type of variant is increased, the fourth and Category 5 has no clinical significance. Among the Chinese, 12 species have been found in Hong Kong, Taiwan and overseas Chinese. Du Chuanshu and other found 35 species in Guangdong, Hainan, Guizhou, Sichuan, Guiyang, Yunnan and other provinces, 12 of which are in the world. The new type, the national variant, mainly belongs to the second and third variants.

Incomplete dominant inheritance (35%):

The genetic form of the G-6-PD gene is localized to X q28, and the G-6-PD deficiency is a sexually incomplete dominant inheritance. Therefore, a male with a variant gene will develop the disease, and the abnormal gene will not be passed from father to son. It will only be passed from mother to son. In women, only one of the two X chromosomes is active in each cell. Female G-6-PD lacks heterozygotes and has two red blood cell populations. G-6-PD deficiency The ratio of G-6-PD-deficient cells to normal cells varies greatly between cells and normal cells. Some heterozygous females appear to be completely normal, while others show complete abnormalities. This is significant for G-6-PD heterozygotes. Variability is the result of certain characteristics of the X chromosome inactivation process, because X chromosome inactivation is random, and sometimes more paternal X chromosomes are activated cell clones with proliferative advantages, during X chromosome inactivation and maturation Many generations of cells, even if one clone has a small selective growth advantage over the other, results in a significant difference between normal and missing cell numbers. Thus, G-6-PD depleted red blood cells in the peripheral blood of female heterozygotes. Ratio to normal red blood cells This significant difference can lead to different clinical manifestations.

Molecular biology (20%):

In 1986, Persico, Martlni, etc. successfully cloned the human G-6-PD gene by different methods and obtained the cDNA sequence, so that the G-6-PD research can reach the gene level, enabling people to get from the gene level. To investigate the primary structural changes of proteins lacking G-6-PD. In 1991, Ellson et al. determined the full sequence of human G-6-PD genome. The G-6-PD gene is about 18 kb in length and consists of 13 exons and 12 introns. It encodes a G-6-PD protein consisting of 515 amino acids. In recent years, the cloned G-6-PD gene technology has been applied. Or PCR combined with direct sequence analysis has identified more than 120 genetic variants, except for 3 nucleotide deletions, all of which are single or multiple base substitutions, and the G-6-PD gene is a housekeeping gene. (homekeeping gene), therefore may be necessary for survival, mutations (such as deletions or nonsense mutations) that result in complete loss of G-6-PD activity may be lethal, except for exons 1, 3, 13 Mutations, 15 point mutations have been found in Chinese, and existing studies have confirmed that different regions, more than 50% of patients of different nationalities are 1376GT and 1388GA, causing non-spherical cell hemolytic anemia mutations concentrated in the hydroxyl group of the enzyme The terminal, the 362-446 amino acid fragment, and most of the mutations leading to other diseases are concentrated at the amino terminus of the enzyme, the most interesting is the mutation of G-6-PD A-, A- has genetic heterogeneity Sex, it has base substitutions in two parts, one of which is 376AG, the other can Therefore, 202GA, 680GA or 968TC, A- frequency in African Americans is 12%, and another variant commonly found in Africans is G-6-PD A, in African Americans. The frequency is 20%, and the mutation of G-6-PD A is 376AG, which is a certain mutation in G-6-PD A-. Therefore, Beutler et al. think that G-6-PD A- appears from G. -6-PDB (wild type)G-6-PD AG-6-PDA-, the high frequency of natural selection (malaria) A- was preserved.

According to the traditional biochemical classification method, it can be divided into the same G-6-PD biochemical variant. It may be caused by different gene mutations, that is, the gene variants are different in nature. For example, G-6-PD(-) has three types. Gene mutation: 1202GA, 376AG; 2680GT, 376AG; 3968TG, 376AG, previously thought to be some different biochemical variants, the essence of which is caused by the same base mutation, such as G -6-PD biochemical variants Kaiping, Anant, Dhon, Petrieh-like, and Sappoto-like are all 1388GA mutations (463 ArgHis).

(two) pathogenesis

G-6-PD activity decreased exponentially with cell aging. The normal half-life of normal enzyme (G-6-PD B) was 62 days, reticulocytes were twice as active as mixed cell populations, and only half of the aged cells were active. The activity of G-6-PD A- is normal in reticulocytes, but it is rapidly reduced afterwards, with a half-life of only 13 days. The instability of the G-6-PD Mediterranean type is even more pronounced, and the half-life is only a few hours. .

The exact mechanism of G-6-PD deficiency of immature destruction of red blood cells is not fully understood. The mechanism of different hemolysis syndrome may be different. It is thought to be mainly related to the decrease of red blood cell reduced glutathione (GSH) and the peroxidation of red blood cells inside and outside. The product is detoxified by reduction by glutathione peroxidase (GSHPX) and consumes GSH. GSH is oxidized to oxidized glutathione (GSSG) or combined with hemoglobin cysteine to form a mixed disulfide compound (GSS). -Hb), in normal red blood cells, GSSG and GSS-Hb are immediately supplemented by GSH as a supplement to GSH with the participation of reduced coenzyme II (NADPH), G-6-PD lacks GSH of red blood cells After being consumed, sufficient NADPH could not be obtained to restore GSSG and GSS-Hb. GSH could not be replenished, GSH content decreased rapidly, and malignant decrease was formed. As a result, GSSG and GSS-Hb accumulated in red blood cells and denatured to form Heinz bodies. The red blood cells are plasticized and deformed, and when passing through the spleen sinus, the red blood cells are not easily deformed and are blocked and destroyed.

In recent years, more and more studies have suggested that G-6-PD deficiency erythrocyte hemolysis is associated with erythrocyte peroxidation damage. Red blood cells in the blood circulation are in a high oxygen environment, and the erythrocyte membrane is always surrounded by intracellular and extracellular peroxides. In erythrocytes, oxyhemoglobin is continuously converted to methemoglobin, which is accompanied by the production of superoxide anion, which protects against various external and intrinsic peroxide damage. Red blood cells have a series of protective mechanisms against oxidation damage, including peroxidation. Hydrogenase (Cat), peroxidase (GSHPX), superoxide dismutase (SOD), GSH, etc., if these natural protective mechanisms are defective or activated, too many harmful oxygen derivatives, hemoglobin and erythrocyte membrane will be affected Peroxidation damage, and can cause irreversible damage, leading to red blood cell destruction, hemolysis, it is now believed that the peroxide formed in the red blood cells of G-6-PD deficiency is easily damaged, the root cause is the insufficient production of NADPH, and This results in low GSH production, functional lack of Cat and GSHPX, antioxidant dysfunction, and increased oxidative vulnerability.

Glucose-6-phosphate dehydrogenase deficiency prevention

In areas with high G-6-PD deficiency, a general survey of G-6-PD deficiency should be performed. Those who are known to be deficient in G-6-PD should avoid eating broad beans and their products, avoid taking oxidative drugs, and strengthen them. Prevention of various infections.

The vast majority of this disease has incentives to induce acute hemolysis, so prevention is extremely important.

Group prevention

In the high-growth areas of G6PD, large-area census or pre-marital antenatal, prenatal, umbilical cord blood screening is a more effective and sensible method to detect G6PD deficiency.

2. Individual prevention

(1) Removal of incentives On the basis of screening, a G6PD-deficient carrying card with banned or prudent use of drugs, food, etc. is issued for medical and personal reference.

(2) Neonatal jaundice: pregnant women with either couple or one of the G6PD deficiency, who take benzobarbital 0.03 to 0.06g per night for 2 to 4 weeks before delivery, can reduce neonatal hyperbilirubinemia or Reduce the incidence rate; take cord blood for routine screening during childbirth to find G6PD deficiency newborn; prenatal and infant refusal to use oxidative drugs or use camphor pills to store clothes, mothers avoid eating broad beans and their products, actively prevent neonatal infection.

3. Treatment

There is no special treatment for erythrocyte G6PD deficiency, no hemolysis is needed without treatment, the cause of hemolysis should be removed, suspicious drugs should be stopped, and broad beans should be stopped to treat infections. The acute hemolysis period of mild patients can be treated with general supportive therapy and rehydration, hemolysis and Those with severe anemia should pay attention to the balance of water and electrolytes, correct acidosis, alkalinize urine, etc. to prevent renal failure; for severe anemia, Hb60g/L, or those with symptoms of heart and brain damage should be timely concentrated red blood cells, and monitored to Hb urine disappears; try to use vitamin E, reduced glutathione and other antioxidant effects, prolong the life of red blood cells; neonatal jaundice is treated according to neonatal hyperbilirubinemia; for CNSHA, blood transfusion is required to maintain splenectomy It may be helpful, if possible, for hematopoietic stem cell transplantation (HSCT).

Glucose-6-phosphate dehydrogenase deficiency complications Complications jaundice anemia cholelithiasis

Common complications of this disease are jaundice, hemoglobinuria, hemolytic crisis, hemolytic, urinary, acid-free, acute renal failure, etc., often complicated by hyperbilirubinemia in the neonatal period. Progressive anemia, cholelithiasis, hepatosplenomegaly, etc.

Glucose-6-phosphate dehydrogenase deficiency symptoms Common symptoms Dizziness, oliguria, fatigue, jaundice, hypoxemia, splenomegaly, abdominal pain, hemolytic anemia, back pain, no urine

1. Certain drugs, such as chloramphenicol, can induce mild hemolysis in patients with severe Mediterranean-type G-6-PD deficiency, but hemolysis does not occur in patients with mild A- or Canton-type deficiency. In addition, different individuals of the same G-6-PD variant respond differently to the same drug. For example, thiazosulfone may cause hemolysis in some patients with G-6-PD deficiency, while other patients with the same type are normal. Primary quinacridol-type drug-induced hemolytic anemia is acute hemolysis caused by taking certain drugs with oxidative properties, including: antimalarials (primaquine, quinine, etc.), analgesic antipyretics (aspirin, antipyrine, etc.) nitrofuran, sulfonamides, sulfones, naphthylaniline, large doses of vitamin K, probenecid, Chuanlian, plum plum, etc., often appear 1-3 days after taking the drug Acute vascular congestion, dizziness, anorexia, nausea, vomiting, fatigue and other symptoms, followed by jaundice, hemoglobinuria, severe hemolysis can occur oliguria, no urine, acidosis and acute renal failure, hemolysis process is self-limiting An important feature of the disease, mild hemolysis 1-2 days or 1 week clinical symptoms gradually improved and self-healing.

2. Infectious hemolysis: infection-induced hemolytic anemia may be more common than drug-induced hemolytic anemia, and anemia can occur within a few days after a febrile infection in patients with G-6-PD deficiency. Hemolysis infection in patients with PD deficiency, more definitely reported typhoid fever, lobar pneumonia, hepatitis, etc., in addition to influenza, infectious mononucleosis, leptospirosis, chickenpox, mumps, necrotic enteritis In addition, Salmonella, Escherichia coli, -hemolytic streptococcus, Mycobacterium tuberculosis and Rickettsia infection have also been reported, anemia is generally relatively light, jaundice is generally not obvious, but in patients with viral hepatitis, jaundice is obvious, red blood cells Accelerated destruction increases the bilirubin load on the already damaged liver, leading to a sharp increase in serum bilirubin levels. In addition, there have been reports of acute renal failure secondary to massive intravascular hemolysis, infection-induced hemolysis. In addition to the destruction of G-6-PD red blood cells caused by leukocyte phagocytosis during infection, some viruses such as influenza A can initiate hemolysis, and infection can also be Temporary hair erythropoiesis stagnation, so in addition to shorten the life span of red blood cells, but may also be present simultaneously aplastic crisis.

3. Broad bean disease: The disease of acute hemolytic anemia occurs after eating broad bean in the broad bean disease. Most of the cases are caused by eating fresh broad beans. Therefore, in the high season of harvesting the broad beans in April and May, eating dried broad beans can also cause Hemolysis, the mother can eat the baby through the mother's milk after the consumption of broad beans, the milk of the goats who eat the dried broad beans can also occur, despite the reported influx of broad bean pollen caused by faba bean disease, but the incidence of faba bean disease during the flowering period of the broad bean (March) No increase, faba bean disease is common in children aged 1 to 5 years old, mainly male patients, the ratio of male to female patients is 7:1, acute intravascular hemolysis occurs after 5 to 24 hours after eating broad beans, headache, nausea, back Pain, chills and fever, followed by hemoglobinuria, anemia and jaundice, hemoglobin concentration drops sharply and severely, 80% of patients are below 60g/L, 30% of patients are below 40/L, if not transfused for anemia The mortality rate is about 8%, and it recovers slowly after 3 to 4 days.

4. Chronic non-spherical erythrocyte hemolytic anemia: a common feature of the chronic nonspherocytic hemolytic anemia (CNSHA) G-6-PD variant is low or significant instability in vivo.

Anemia and jaundice often appear in the neonatal period for the first time. Hyperbilirubinemia may require blood transfusion therapy. Generally, hemolysis does not have obvious starting factors. After infancy, the symptoms and signs of hemolytic disease are mild and variability, and pale complexion is rare. Intermittent yellow staining of the sclera, rarely splenomegaly, can cause acute hemolytic crisis due to infection, medication and other inducements.

Examination of glucose-6-phosphate dehydrogenase deficiency

General laboratory tests for G-6-PD deficiency are non-specific compared to other hemolytic anemias. The diagnosis depends on the determination of erythrocyte G-6-PD enzyme activity, screening experiments and enzymes for G-6-PD deficiency. There are several methods for quantitative determination of activity.

1. Methmoglobin reduction test: The speed is significantly slower than that of normal people. This method is one of the commonly used tests for screening G-6-PD activity in China. The micro-histochemical elution method is suitable for heterozygotes. The reliability of the test is 75%. The disadvantage of this method is that if there is HbH, unstable hemoglobin, hyperlipidemia, macroglobulinemia and the like all cause false positive results.

2. Ascorbate-cyanide test If G-6-PD is deficient, H202 destroys hemoglobin and forms a brown spot.

3. Nitrotetrazolium blue test: This test can be used to detect the amount of NADPH produced.

4. Fluorescent spot test: This test is the simplest, most reliable and most sensitive screening test.

5. G-6-PD activity assay The amount of NADPH produced per unit time reflects the activity of erythrocyte G-6-PD. The commonly used methods are the Zink Jam method recommended by the World Health Organization (WHO) and the International Hematology Standardization Committee (ICSH). The recommended Glock and Mclean methods should be used to detect the clinical status of the patient during the test. In the hemolysis period, the aging, enzyme-deficient red blood cells are selectively removed from the peripheral blood, young. Red blood cells are protected by high enzyme levels. The analysis of these cells can not truly reflect the G-6-PD activity of red blood cells. In order to solve this problem, it can be reviewed after acute hemolysis for 2 to 4 months, or Centrifugal sedimentation technique removes young red blood cells and then detects red blood cell G-6-PD activity. However, the use of precipitated red blood cells in the test system is not standard. If red blood cell infusion is received during the hemolysis episode, the G-6-PD activity measurement result will also be affected. .

Chronic non-spherical erythrocyte hemolytic anemia, no specific hematological changes, hemoglobin is generally 80 ~ 100g / L, reticulocyte count increased to 4% ~ 35%, due to the increase in the proportion of reticulocytes, the average red blood cell volume increased, The half-life of red blood cells is significantly shortened, generally 2 to 17 days, and the spleen of the defect-free cells is detained, so the spleen is generally ineffective, and the self-hemolytic test has no diagnostic value. In some patients with severe G-6-PD deficiency, due to white blood cell G- 6-PD deficiency can cause leukocyte function defects, mainly due to the reduced phagocytic activity, and thus the clinical manifestation is repeated infection of peroxidase-positive bacteria.

In neonates with jaundice, the serum total bilirubin concentration in most cases exceeds 273.6 mol/L, and even as high as 684-8557 mol/L. Due to the severity of jaundice, a considerable proportion of children may develop bilirubin encephalopathy. The incidence rate is 10.5% to 15.4%.

Broad bean disease patients are divided according to the amount of hemoglobin:

(1) Heavy: hemoglobin is below 30g/L; hemoglobin is at 31-40g/L, and urinary occult blood is above +++ or without urine; or with serious complications such as pneumonia, heart failure, acidosis, mental disorders, Hemiplegia or binocular deviation in the same direction.

(2) medium: hemoglobin in 31 ~ 40g / L, urinary occult blood below ++; or hemoglobin 41 ~ 50g / L; or hemoglobin 51g / L or more, urinary occult blood ++++.

(3) Light type: hemoglobin 51g/L or more, urinary occult blood +++ or less.

(4) Concealed type: The number of hemoglobin and red blood cells is normal or slightly decreased. The Heinz body can be found in the peripheral blood. The patient will develop the disease after eating the broad bean. The same - the individual reacts to the broad bean at different times, obviously, except In addition to enzyme deficiency, there are other factors related to the disease. For example, Turrin et al found that there is macromolecular agglutination and protein cross-linking in the erythrocyte membrane during the hemolytic crisis induced by broad bean; membrane damage may be 10 times higher than that of red blood cells. It is related to the decrease of calcium-ATP activity. It is known that the two glycocalyx (fabaris and nucleus) in the broad bean are toxic components of broad bean. De Flora et al found that these two substances quickly inhibited the GSH production ability of defective red blood cells. , leading to metabolic disorders.

1. Screening test for erythrocyte G-6-PD deficiency: 3 methods are commonly used:

(1) methemoglobin reduction experiment: the normal reduction rate is >0.75, the intermediate type is 0.74-0.31, and the significant deficiency is <0.30. This test is simple, the sensitivity is high, but the specificity is slightly poor, and false positives may occur.

(2) Fluorescence spot test: Fluorescence occurs within 10 minutes of normal, fluorescence occurs in 10-30 minutes in the middle type, and fluorescence does not appear in 30 minutes after severe deficiency. The sensitivity and specificity of this test are high.

(3) Nitrotetrazolium blue (NBT) paper method: the normal filter paper is purple-blue, the middle type is light blue, and the significantly lacking is red.

2, red blood cell G-6-PD activity determination: This is a specific direct diagnosis method, the normal quality varies with the measurement method:

(1) The Zinkham method recommended by the World Health Organization (WHO) is 12.1±2.09 IU/gHb.

(2) The Clock and Mclean methods recommended by the International Hematology Standardization Committee (SICSH) are 8.34 ± 1.59 IU/gHb.

(3) The NBT quantitative method is 13.1-30. OBNT units.

(4) G-6-PD/6-PGD ratio determination: The heterozygous detection rate can be further improved, the normal adult value is 1.0-1.67, and the cord blood is 1.1-2.3, which is lower than the G6PD deficiency.

3, denatured globin small body production test: positive cells in hemolysis > 0.05, hemolysis stopped negative, patients with unstable hemoglobin disease can also be positive.

Regular chest X-ray, ECG and B-ultrasound, pay attention to the presence or absence of lung infection, can find gallstones, hepatosplenomegaly and so on.

Diagnosis and differential diagnosis of glucose-6-phosphate dehydrogenase deficiency

diagnosis

(1) History and symptoms

(1) Medical history questions: Note:

1 Have a family history.

2 The cause of anemia: whether it is related to the consumption of broad beans, primaquine and other oxidative drugs or infections.

3 Whether there is a history of jaundice and hemoglobinuria.

(2) Clinical symptoms: dizziness, headache, palpitations, difficulty breathing, abdominal pain, low back pain, severe hemoglobinuria can lead to renal failure.

(2) Physical examination found

Anemia appearance, skin, sclera yellow staining, mild swelling or normal liver and spleen.

(3) Auxiliary inspection

1. Blood: Hemoglobin is reduced, positive cells are positively pigmented anemia; reticulocytes are increased; see bite red blood cells and vesicular cells, young red blood cells can be seen; Heinz bodies, white blood cells, and platelet counts are seen in red blood cells.

2. Bone marrow: hyperplasia is active or significantly active, erythroid, granulocyte hyperplasia.

3. Blood indirect erythropoietin increased, serum haptoglobin decreased or disappeared, plasma free hemoglobin increased, and urinary hemosiderin was positive.

4. Hemoglobin reduction test: reduction rate <75%; fluorescence spot test: fluorescence time > 10 min; nitrotetrazolium basket paper method: filter paper is pale purple blue or still red.

5. Conditionally perform quantitative determination of G-6-PD activity.

Differential diagnosis

1. G-6-PD lacks drug-induced hemolytic anemia. Its clinical features and certain experimental features are similar to hemolytic anemia induced by unstable hemoglobin-related drugs, such as glutathione synthetase deficiency and its clinical manifestations. The G-6-PD lacks similarity and should be identified.

2. Other enzyme defects in the hexose phosphate bypass should be noted for identification.

3. Exclusion of hemoglobin disease by heat instability test and hemoglobin electrophoresis, G-6-PD deficiency These two tests are normal, and some screening tests such as ascorbic acid (vitamin C) cyanide test hemoglobin can also be positive. However, the G-6-PD activity assay or the fluorescence spot assay is only positive for G-6-PD deficiency and can be identified accordingly.

It is also differentiated from paroxysmal nocturnal hemoglobinuria, paroxysmal cold hemoglobinuria and other hemolytic anemia.

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