 |
ADD DRUGS-WEB.COM AS FAVORITE - SITE MAP |
 |
HAEMOPHILIA CAUSES |
||
|
Hemophilia A and B are both caused by a
genetic defect present on the X chromosome. (Hemophilia C is
inherited in a different fashion.) About 70% of all people with
hemophilia A or B inherited the disease. The other thirty percent
have hemophilia because of a spontaneous genetic mutation. The following concepts are important to understanding the inheritance of these diseases. All humans have two chromosomes which determine their gender: females have XX, males have XY. Because the trait is carried only on the X chromosome, it is called "sex-linked." The chromosome's flawed unit is referred to as the gene. Since both factors VIII and IX are produced by a genetic defect of the X chromosome, hemophilia A and B are both sex-linked diseases. Because a female child always receives two X chromosomes, she nearly always will receive at least one normal X chromosome. Therefore, even if she receives one flawed X chromosome, she will still be capable of producing a sufficient quantity of factors VIII and IX to avoid the symptoms of hemophilia. Such a person who has one flawed chromosome, but does not actually suffer from the disease, is called a carrier. She carries the flaw which causes hemophilia and can pass it on to her offspring. If, however, she has a son who receives her flawed X chromosome, he will be unable to produce the right quantity of factors VIII or IX, and he will suffer some degree of hemophilia. (Males inherit one X and one Y chromosome, and therefore have only one X chromosome.) In rare cases, a hemophiliac father and a carrier mother can pass on the right combination of parental chromosomes to result in a hemophiliac female child. This situation, however, is extraordinarily rare. The vast majority of people with either hemophilia A or B are male. About 30% of all people with hemophilia A or B are the first member of their family to ever have the disease. These individuals have had the unfortunate occurrence of a spontaneous mutation; meaning that in their early development, some random genetic accident befell their X chromosome, resulting in the defect causing hemophilia A or B. Once such a spontaneous genetic mutation takes place, offspring of the affected person can inherit the newly-created, flawed chromosome. |
||
|
||
| HAEMOPHILIA RELATED ITEMS | ||
