Is Haemophilia a genetic disease?
Q: I am 33 years old, married recently and have haemophilia A. On my blood test, Factor VIII was detected 4.4%. The doctors diagnosed my problem as moderate Haemophilia A. If in future we have a boy child, then will he also suffer from haemophilia A?
A:Clotting factor defects are genetic i.e. inherited with a baby receiving half of its genetic information from its mother (through her egg) and half from its father (through his sperm). If the mother or father has the haemophilia gene, it may be passed to the baby through the egg or sperm. A male has 2 sex chromosomes x & y while a woman’s sex chromosomes are two x chromosomes x & x. Thus, a son always receives his father’s y chromosome and the x is always from the mother while a girl receives one X chromosome from each parent. The haemophilia defect is carried on the X chromosome. A haemophiliac father can never pass the disease to his son because the son will get only the y chromosome but the daughter will always be a carrier (called an obligate carrier because she will always inherit the abnormal x from the father). Carriers are normal individuals not manifesting any symptom of the disease but capable of transmitting it to their offspring. The daughter of a haemophiliac male is normal because only one of the X chromosome (paternal) is defective while the maternal X chromosome is normal (and capable of producing enough factor-VIII not to manifest the disease). Son's born to an obligate carrier mother have a 50-50 chance of having haemophilia while daughters have a 50-50 chance of being carriers and the odds are same in each pregnancy. This is so as there is equal chance of inheriting the abnormal or the normal X chromosome from the mother. If a haemophiliac man marries a carrier woman, the baby could have haemophilia, even if it is a girl though this is a rare occurrence. Sometimes haemophilia is caused by a spontaneous mutation i.e. there is no family history of the disease. Studies suggest that this may be seen in upto 30% of all children born with haemophilia. But the mutant gene can be passed on to their children. A fetus can tested to see if it has haemophilia by tests called amniocentesis and chorionic villus sampling in which cells are collected from the fetus. Chorionic villus sampling is done during the first trimester of pregnancy and amniocentesis during the second.