Dear User, Thanks for using health care magic. Ig A deficiency is relatively mild genetic immunodeficiency. Individual with this deficiency lack one particular type of immunoglobulin which is mostly involved in mucosal membrane defense. Because of the deficiency there is impaired immune defense at mucous membranes lining the mouth, airways, and digestive tract. To conclude it is genetic disorder and no cause is known behind this deficiency. My advise in care of your grand daughter involves prompt medical attention if there are any sign or symptoms of infection. Hope I have answered your query. If you have any further questions I will be happy to help . Thanks