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Hemophilia

Clinical types

Hemophilia A - deficiency of factor 8 in the hemostasis (blood clotting) mechanism.

Hemophilia B - deficiency of factor 9 in the hemostasis mechanism

Other deficiencies in the hemostasis system imitating hemophilia.

The different types of hemophilia can be differentiated by clinical and laboratory findings after examination by a hematologist and/or geneticist.

Clinical signs

The severity of the condition depends on the degree of deficiency of the hemostasis factor. In severely affected patients, the activity of the factor is less than 7% of normal. Half of all hemophiliacs belong to this category. Due to the inability to form blood clots there is a tendency for hemorrhages, mainly internal ones.

These patients typically tend to bleed into joints after any slight trauma.

Sometimes hemorrhage occurs into other internal organs, the most ominous being into the brain.

To correct this condition, the patients need repeated transfusions of the missing factor.

Today, there is available a synthetically manufactured hemostasis factor, which appears to be free of side effects.

This means that treatment today is effective, despite therapeutic discipline being required.

The diagnosis can be ascertained with accuracy using laboratory tests. The factor that rectifies blood clotting is established - this is the missing factor in the patient. In carrier women, the deficiency of the factor can be demonstrated in only 50% of cases. This means that a normal level of the factor does not rule out carrier status in a woman who has an affected relative.

Inheritance pattern

X-linked.

Penetrance

In males, the disease is fully expressed.

Females carrying the gene can express a partial deficiency in the hemostasis factor in specific situations where bleeding occurs, such as after birth or during an operation. In such situations they also need a transfusion of the hemostasis factor they are deficient in.

Associated features that can be demonstrated by imagery

Usually there are no defects that can be identified by ultrasound examination during pregnancy.

What is the risk of recurrence in a subsequent pregnancy?

It is necessary to consult a genetic counselor in order to determine the carrier status of the mother based on the family pedigree.

If there is only one patient in the family

The mother need not necessarily be a carrier. If the couple has only one child with hemophilia A or B, and he is the only known affected individual in the family, there is a 66% chance that his mother is a carrier. Therefore in each subsequent pregnancy with a male fetus, the couple has a 33% chance of having another affected son. In these cases, the risk that a sister or maternal aunt of the patient will be a carrier is half that of the mother.

In cases where there are many affected individuals in the family

Women who have given birth to more than one affected son are considered to be carriers, with a 50% risk in every subsequent pregnancy that a male fetus will be affected and a female fetus will be a carrier.

Molecular genetic information

The genes for the disease

Hemophilia A: F8C

Hemophilia B: F9C

Genetic testing

Diagnostic testing (identification of the genetic mutation and confirmation of the disease)

Regarding diagnosis by non-genetic methods, see above under laboratory tests. Regarding direct genetic testing to identify the mutation in the gene: the gene for hemophilia is long and can be examined, but this test is not necessary for an exact diagnosis of patients and is therefore not routinely performed. See: Screening test for identifying defects (mutations) using various methods such as SSCP - X-linked diseases.

Carrier testing

50% of carriers have a reduced blood factor level (see above under laboratory tests).

Genetic carrier tests are divided in accordance with the family type:

In cases where there are many affected individuals in the family, the defect (mutation) must be identified in the patients. Testing for carriers in the family starts with the first-rank relatives of the affected individuals, and initially, the daughters, sisters and mothers of the patients are examined. Based on the results, the carrier tests can then be extended to other women who are related to the patients and to the carriers detected in the first round of tests. Each carrier identified can be offered prenatal diagnosis in pregnancy - during this the sex of the fetus will be determined, and in the case of a male fetus, whether or not he is affected. All these tests must be carried out through a genetic institute - see Screening test for identifying defects (mutations) using various methods such as SSCP - X-linked diseases.

If the mutation cannot be identified easily, an indirect test (linkage analysis) can be performed, but not before it is established with certainty that the mother, and any other woman in the family wishing to test her status, is a carrier. This is based on analysis of the pedigree and must be discussed with the geneticist. Hemostatic testing (see above) can also be carried out. Only then is it possible to use the indirect tests for prenatal diagnosis. See: testing for genetic markers in a family that has one or more patients - when there is only one gene that can cause the disease - X-linked diseases.

In cases where the affected individual is the only one in the family, his mother is not necessarily a carrier, and other women in the family are certainly not obligate carriers. The mutation must first be identified in the patient and looked for in his mother. If it is not found in the mother, then this is a new mutation that has occurred in the patient. Only his daughters (all his daughters) must be carriers, and they and their offspring can be offered testing for the disease and for carrier status.

If the defect (mutation) found in the patient is also present in his mother, then she is a carrier. Testing for carriers in the family starts with the first-rank relatives of the affected individual, and initially, the daughters, sisters and mothers of the patient are examined. Based on the results, the carrier tests can then be extended to other women who are related to the carriers detected in the first round of tests. Each carrier identified can be offered prenatal diagnosis in pregnancy - during this the sex of the fetus will be determined, and in the case of a male fetus, whether or not he is affected. All these tests must be carried out through a genetic institute.

If the mutation cannot be identified easily, an indirect test (linkage analysis) can be performed, but not before it is established with certainty that the mother, and any other woman in the family wishing to test her status, is a carrier. This is based on analysis of the pedigree and must be discussed with the geneticist. Hemostatic testing (see above) can also be carried out. Only then is it possible to use the indirect tests for prenatal diagnosis. See: testing for genetic markers in a family that has one or more patients - when there is only one gene that can cause the disease - X-linked diseases.

Fetal testing

After it has been established that the woman (mother, sister, or a more distant relative of a patient) is a carrier, genetic tests can be used for prenatal testing. In the case of a male, it is possible to determine whether he has received the mutation identified in the patients in the family. See: Screening test for identifying defects (mutations) using various methods such as SSCP - X-linked diseases.

If the defect is not identified, indirect tests may be employed, once again on basis that the mother is a carrier, because if she is not, the next fetus may be healthy even if he has received the same allele as the affected child, because the affected child may have a new mutation which occurred only in the ovum that created him - see: testing for genetic markers in a family that has one or more patients - when there is only one gene that can cause the disease - X-linked diseases.

The level of the hemostatic factor can also be measured in the fetus-s blood. These tests were common in the past, but nowadays genetic tests usually give a reliable diagnosis in all families, and are replacing the necessity for testing the fetus-s blood.

Hemophilia Health Byte


 
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