Among the many genetic diseases, some are sex-linked genetic diseases. The genetic rule is: a mother who carries a disease-causing gene but does not have the disease herself will only pass the disease on to a boy, while a girl is healthy (but can carry the disease-causing gene like her mother). Such women often have men (such as brothers and uncles) in the family who are sick, while women (such as sisters and aunts) are healthy. Hemophilia is a disease that only affects boys. With this disease, the blood does not clot easily due to the lack of a coagulation substance. Therefore, minor injuries will cause bleeding, and even without injuries, there will be subcutaneous and intra-articular bleeding. Once cerebral hemorrhage occurs, there is a fatal risk. expert