You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Which of the following is the most common form of primary immunodeficiency? and explain in detail?
Selective IgA deficiency (less than 15mcg/ml) is the most common type of primary immunodeficiency. Individuals develop recurrent acute and chronic respiratory infections that may lead to bronchiectasis. These patients are at an increased risk of drug allergies, atopic disorders and autoimmune diseases. Ref: Harrison's Principles of Internal Medicine, 18th edition, chapter 316.