Family history is a risk factor for asthma, with many different genes being implicated.  If one identical twin is affected, the probability of the other having the disease is approximately 25%.  By the end of 2005, 25 genes had been associated with asthma in six or more separate populations, including GSTM1 , IL10 , CTLA-4 , SPINK5 , LTC4S , IL4R and ADAM33 , among others.  Many of these genes are related to the immune system or modulating inflammation. Even among this list of genes supported by highly replicated studies, results have not been consistent among all populations tested.  In 2006 over 100 genes were associated with asthma in one genetic association study alone;  more continue to be found. 
Asthma is a disease of the airways which causes difficulty in breathing. It is caused by inflammation of the air passages that make them narrow. Symptoms of narrowing airways include whistling noise with breathing, shortness of breath, chest tightness and coughing. There can be several triggers or factors that can aggravate the symptoms of asthma. Common factors include dust, mites, pollen, smoke, pollution , weather changes, cold & cough and respiratory infections . Asthma can be broadly categorised into two categories – specific and non-specific. Specific asthma is caused by breathing in allergens or irritants while non-specific asthma is caused by exercise, weather or genetic predisposition. The exact cause of asthma is not known but it is seen in families having a history of asthma. Asthma cannot be cured, but it can be managed well with a number of treatment options aimed at relieving the symptoms and preventing the occurrence of severe asthma attacks. Here's what Dr Navneet Sood, Consultant, Pulmonary & Critical Care Medicine, Jaypee Hospital, Noida has to say about causes, symptoms, and treatment of asthma.