Will my child have haemophilia?
Q: What are the chances for a child being haemophilic if the father is infected by haemophilia A factor VIII and the mother is normal? My wife is 45 days pregnant. Is the pregnancy risky for the mother or the child?
A:Blood has a number of proteins (called coagulation factors), which are responsible for clotting. A deficiency of factor-VIII is called haemophilia A and that of factor-IX haemophilia B. One is not infected by haemophilia but inherits it as a defective gene from ones parents. A human male has a sex chromosome make up of xy while a female has xx. Thus, a male always inherits his x-chromosome from the mother while a female gets one x from each parent. The haemophilia gene is carried on the x-chromosome. As a female gets one x-chromosome from each parent, she can be a carrier i.e. carry the defective gene on one x-chromosome while the other x-chromosome has the normal gene. She will not show any signs of the disease as the normal gene on the other x-chromosome ensures adequate factor level but can pass the defective x-chromosome to her children. If a man with haemophilia father's a child, his sons will not have haemophilia (as they get the normal x-chromosome from the mother and the y-chromosome from the father), but all his daughters will be carriers (because the defective x-chromosome is passed from the father while the other x-chromosome from the mother is normal). If a man with haemophilia marries a woman who is a haemophilia carrier, the baby could have haemophilia, even if it is a girl but this is an extremely rare occurrence. Boys born to a carrier mother have a 50:50 chance of getting the defective x-chromosome or a normal x-chromosome from the mother i.e. 50% chance of being a haemophilic. Girls born to such mothers have a 50:50 chance of being a carrier. These odds are the same for each pregnancy. In the instance that you have mentioned, there is no risk during pregnancy. If it is a male child, he will be normal and if it is a girl child she has a 50% chance of being a carrier. DNA analysis can help diagnose the disease while the baby is developing by tests called amniocentesis or chorionic villus sampling. These are invasive tests in which cells are collected from the developing baby. Chorionic villus sampling is done during the first trimester of pregnancy while amniocentesis is done during the second.