Dear Doctor;Two of my older sister recently developed asthma despite the family not having a history of the disease. I worry might also get it. Is asthma hereditary? What causes it and can it be prevented? Ndayisaba, 17, Butare.Dear Ndayisaba, Asthma in most of the cases is hereditary. The immediate family may not be having this problem but  if it existed in somebody 2 or 3 generations before or even in far flung blood relatives, one may get it. This is due to the fact that people related by birth  share common genetic pool from one generation to all subsequent generations existing. Now which gene shall manifest in which person remains unpredictable. There is no need  to fear for development of asthma. Firstly it is not necessary that you shall have asthma. Even if you develop it, it can be very well controlled with avoidance of risk factors and inhalers of medicines. There are specific breathing exercises in yoga which help in controlling asthma and reducing number of attacks.