This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
Genetic risk factor for COPD is 
Select and explain. 
A. a1 Antitrypsin Deficiency, B. Cystic fibrosis, C. Marfan syndrome, D. Severe combined immunodeficiency
A: a1 Antitrypsin Deficiency
Answer: A: a1 Antitrypsin Deficiency 
Explanation: Severe a1 Antitrypsin deficiency is a proven genetic risk factor for COPDAlthough only approximately 1% of COPD patients are found to have severe a1AT deficiency as a contributing cause of COPD, these patients demonstrate that genetic factors can have a profound influence on the susceptibility for developing COPDSpecific treatment in the form of a1AT augmentation therapy is available for severe a1AT deficiency as a weekly IV infusion Patients with cystic fibrosis develop bronchiectasisRef: Harrison 19e pg: 1704