PI is an umbrella term for more than 400 disorders in which genetic or congenital defects in the immune system cause an increased susceptibility to infections. PI can affect anyone, regardless of age or gender. Although some types of PI are diagnosed at birth or soon after, other types are often not recognized and diagnosed until later in life. US population prevalence per 100,000 people: despite having similar prevalence to better-known genetic disorders, PI often goes unrecognized. Diagnosis often leads to 34 cystic fibrosis, 83 primary immunodeficiency and 125 systemic lupus erythematosus.