What Are the Pros and Cons of Gene Therapy for Hemophilia?

Hemophilia is a group of hereditary bleeding disorders with coagulopathy. The common features of hemophilia are the disorder of active thromboplastin production, prolonged coagulation time, and a tendency to bleed after life with minor trauma. Severe patients can also develop "spontaneous" without obvious trauma. "Sexual" bleeding.

Basic Information

English name

hemophilia

Visiting department

Hematology

Common causes

Congenital factor deficiency

Common symptoms

Hemophilia A is prone to bleeding. Hemophilia B may have symptoms similar to those of hemophilia A with less severe symptoms. Hemophilia C, IXa deficiency symptoms are mild

Contagious

no

Hemophilia classification

1. Hemophilia A (hemophilia A), which is a factor procoagulant deficiency (: C) deficiency, also known as AGH deficiency, is a sexually linked recessive genetic disease that is transmitted by women and men.

2. Hemophilia B (hemophilia B), which is a factor deficiency, also known as PTC deficiency and thromboplastin deficiency, is also a sex-linked recessive inheritance, and its incidence is less than that of hemophilia A. Most patients with hemophilia B have milder bleeding symptoms.

3. Hemophilia C (hemophilia C), which is a factor (F) deficiency, also known as PTA deficiency and thromboplastin deficiency. It is an incomplete recessive inheritance of autosomes, and can be affected by both men and women. It is a rare hemophilia.
Among 15 to 20 per 100,000 boys, the incidence is not different among the different races and regions surveyed. The prevalence of hemophilia A is 85%, hemophilia B is 15%, and hemophilia C is rare.

Clinical manifestations of hemophilia

(A) Hemophilia A

Bleeding

Main manifestations of this disease. Lifetime tendency to minor injuries or prolonged bleeding after surgery. The degree of bleeding and the onset of the disease are related to the level of F activity in the patient's plasma. According to the severity of bleeding and the level of coagulation factor activity in plasma, the disease is classified into 4 types:

(1) F activity in heavy plasma <1%, bleeding usually occurs before the age of 2 years, bleeding symptoms occur after the baby begins to crawl, walk away, or even bleeding when the umbilical cord is ligation Patients with multiple and severe bleeding sites, often subcutaneous, muscle and joints and other repeated bleeding, joint hematoma deformities are more common. In addition, it can be seen that renal hemorrhage leads to hematuria, gastrointestinal bleeding, intra-abdominal bleeding, and rare pulmonary, chest, and intracranial hemorrhage.

(2) Intermediate F activity is 1% to 5%. After childhood, onset is mostly subcutaneous and muscle bleeding, and joint bleeding is also present, but the number of repetitions is less and the severity is less severe.

(3) Mild F activity is 5% to 25%, and bleeding is mostly in adolescence. It is found due to more than bleeding after exercise, tooth extraction, or surgery. The bleeding is mild, you can live normally, participate in sports, and occasional joint hematomas.

(4) Subclinical type Bleeding occurs only after major surgery. Laboratory examination can confirm that the disease is present, and F activity is 25% to 40%.
Generally speaking, the earlier the bleeding symptoms appear, the heavier the condition becomes. With the increase of age, the bleeding symptoms may gradually decrease, and sometimes there may be a remission period without bleeding symptoms. Bleeding can occur hours or days after the trauma, or it can bleed more after the trauma or surgery.

2. Compression and complications caused by bleeding

After bleeding to form a hematoma can cause compression symptoms:

(1) The incidence of peripheral nerve involvement is 5% to 15%. The patient has numbness, severe pain, and muscle atrophy.

(2) Upper respiratory tract obstruction Severe bleeding from the bottom of the mouth, throat, tongue, tonsils, posterior pharynx wall or neck is very dangerous and can cause suffocation.

(3) Tissue necrosis can occur when compressing nearby blood vessels .

(B) Hemophilia B

Hemophilia B may also have symptoms similar to those of hemophilia A. The differences are: severe patients with hemophilia B (FB activity less than 2%) are less than hemophilia A, and more mild, so clinical manifestations are lighter than hemophilia A; female passers can also bleed; Anti-F antibodies were rare, accounting for only 1%.

(Three) hemophilia C

Symptoms of factor (F) deficiency are mild, sometimes bleeding only after surgery, tooth extraction, or injury; the transmitter is usually asymptomatic, but bleeding is easier than normal after tooth extraction; F deficiency is often combined with other congenital factor abnormalities , Such as combined FV, dysentery.

Hemophilia test

General item

Normal platelet count, negative beam test, normal bleeding time, normal clot retraction; normal prothrombin time, normal thrombin time, and normal fibrinogen quantification; prolonged clotting time is a characteristic of this disease, but only in F: C Only when the activity is less than 1% to 2%, it will be prolonged, and> 4% can be normal.

2. Preliminary screening test

Prothrombin consumption test (PCT), activated partial thromboplastin time (APTT, when factor , activity is reduced to 30% of normal, can be extended, can detect light patients), simple thromboplastin generation test ( STGT) is helpful for the diagnosis of mild and severe hemophilia A and B.

3. Confirmation test

APTT, STGT, Biggs thromboplastin generation (BiggsTGT) correction tests can be used to identify the type of hemophilia. If the prothrombin consumption and thromboplastin production tests are abnormal, corrective tests can be done. After normal plasma is adsorbed with barium sulfate, it still contains F and F ; normal serum contains F and IXa, so if part of the patient's plasma thromboplastin time is only corrected by normal barium sulfate adsorbed plasma, it is F deficiency; When the normal serum is corrected, it is F deficiency; if both can be corrected, it is F deficiency. The three can be identified.

4.F, F, IXa activity determination

The prothrombin time one-stage method is used to take the plasma of known factors-deficient as matrix plasma, add rabbit brain extract, white clay suspension, calcium chloride and different dilutions of plasma or serum to make relevant factors according to coagulation time. After the activity curve, the test specimens are converted.

5. Determination of FRAg

Patients with hemophilia A have normal or elevated plasma levels.

6. Determination of FCAg

In patients with hemophilia A, plasma : CAg and : C decrease in parallel.

7.Determination of VWFAg

Patients with hemophilia A are normal or elevated.

8. Genetic diagnosis

There is significant genetic heterogeneity at the molecular level of hemophilia. Genetic diagnosis of hemophilia is an effective, accurate and fast method. Currently, PCR is mainly used for gene analysis.

9. Diagnosis and genetic counseling of carriers of hemophilia A and fetus

The level of factor : C in the plasma of most carriers of hemophilia A is only 50% of the average of normal women. In recent years, most people think that the detection of : C and R: Ag is of great significance. The carrier ratio of 70% to 98% is less than normal. From the 8th to 12th gestation weeks of pregnancy, R: Ag and : C can be determined by radioimmunomicrometry using fetal scope amniocentesis or villus sampling. The fetus can be diagnosed for hemophilia before birth in order to consider termination of pregnancy. In recent years, the development of genetic diagnostic technology has been applied to the transmission and prenatal examination.

Differential diagnosis of hemophilia

Vascular pseudohemophilia

Also known as von Willebrand's disease, it is an autosomal dominant inheritance and type III is recessive inheritance, which can be affected by both men and women.

Pedigree surveys also help to distinguish; prolonged bleeding time, positive aspirin tolerance test, decreased platelet adhesion rate, no aggregation response to ristomycin platelets, increased or normal factor : C / R: Ag in plasma, plasma The VW factor is absent or reduced, and all laboratory tests are normal except for hemophilia A, where the ratios of , C and : C / : Ag are reduced.

2. Reduced acquired factor VII

Common in diseases such as hyperthyroidism and disseminated intravascular coagulation. There is no previous history of bleeding or family history, and both sexes can develop. Clinically accompanied by symptoms and signs of primary disease, the reduction of coagulation factors has factors other than factor VII. Insufficient, it is not difficult to identify with hemophilia A.

3. Thrombin complex reduction

The bleeding symptoms and clotting time were similar to those of hemophilia A, but the prothrombin time was prolonged and vitamin K treatment was effective.

Hemophilia Treatment

Local hemostatic treatment

For small wounds, apply local pressure for more than 5min; for large wounds, apply gauze or cotton balls to normal human plasma or thrombin, epinephrine, etc., and apply pressure to the wound. Some foreign countries have prepared hemostatic agents containing 5ml of cold precipitation, 750mg of aminocaproic acid, and 50U of thrombin in physiological saline. When the mouth, skin, and foreskin lesions bleed, topical hemostasis can be used, and the effect is better. When the joint cavity is bleeding, the activity should be reduced, and a local cold compress should be applied. When the swelling is no longer aggravated, change to a hot compress.

2. Alternative therapy

It is an effective method for treating hemophilia, and the purpose is to increase the patient's plasma factor level to the hemostatic level. When the F: C level reaches 3% to 5% of normal people, patients generally do not have spontaneous bleeding, and bleeding occurs only after trauma or surgery; however, severe patients with frequent bleeding require alternative treatment.

(1) Plasma transfusion is the preferred treatment for mild hemophilia A and B. However, its application is limited due to excessive blood volume.

(2) Cryoprecipitate In frozen (-20 ° C) cryoprecipitate preparations, the average activity of factor in each bag is 100U, which can increase the plasma concentration of factor in the body to more than 50% of normal. It has the advantages of high efficiency and small capacity. After being left at room temperature for 1 hour, the activity is lost by 50%. Freeze-drying can be stored for more than 25 days when stored below -20 ° C. Suitable for light and medium patients.

(3) Factor IX and IX concentrates are freeze-dried products, and the activity of each factor IX and IX is equivalent to the average activity of fresh human plasma in 1ml. Each bottle contains 200U. Injecting 1U of factor per kilogram of body weight can increase the activity of factor in the body by 2%, but injecting each factor of 1U only increases the activity by 0.5% to 1%. Factors and have a short half-life in the circulation and must be replenished every 12 hours to maintain high factor levels and control bleeding.

(4) 200U per bottle of prothrombin complex (PPSB) , which is equivalent to factor in 200ml of plasma, which is suitable for hemophilia B.

(5) The advantage of alternative treatment of recombinant F is that it is not contaminated by viruses. Pharmacokinetic tests show that it is very similar to the biological half-life of plasma F. Since 1987, it has been used in clinical trials. Obvious side effects.

3.DDAVP (1-desamino-8-d-d-arginine vasopressin)

An artificial anti-diuretic hormone derivative, which has the effects of anti-diuresis and increasing plasma factor levels, and can increase : C and R: Ag by 2 to 3 times after intravenous injection. For mild hemophilia and hemophilia transmitters.

4. Adverse effects of substitution therapy

(1) Hepatitis is seen in 40% to 50% of those who regularly use blood products. Transaminases are continuously elevated, and liver function abnormalities account for more than 50%, especially in children. The current treatment of hepatitis C with interferon gamma 3 million U, 3 / Week for 6 months.

(2) Hemolytic F concentrate is prepared in a large amount of mixed plasma, and IgM and IgG anti-A, anti-B allolectins exist to varying degrees. A large number of patients treated with F concentrates often have hemolytic reactions, the degree is related to the dose ; Patients with hemophilia have multiple blood transfusions, and serum globin is reduced, which is related to chronic subclinical hemolysis in the patient.

(3) Acquired immunodeficiency disease (AIDS, AIDS) is a serious complication that has received widespread attention in recent years, with a return mortality rate of 40% and a long-term mortality rate of 100%. Heat treatment of plasma products can kill the HIV virus and reduce AIDS caused by plasma transfusion.

5. Surgical problems in hemophilia patients

Even minor operations such as tooth extraction should be avoided as much as possible. With the application of preparations such as factor , such as adequate preparation for surgical procedures, the risk has been greatly reduced. The degree of coagulation factor deficiency should be fully estimated before surgery, and the concentration needed to stop bleeding during surgery should be maintained, and replacement therapy must be maintained until the wound is completely healed.

6. Gene therapy

Research is underway, with initial success in animal experiments.