These disorders may be caused by mutations, sometimes in a specific gene. If the mutated gene is on the X (sex) chromosome, the resulting disorder is called an X-linked disorder (see Inheritance Patterns : X-Linked Inheritance). X-linked disorders occur more often in boys. About 60% of people with primary immunodeficiency disorders are male.
Some PIDs are of more complex polygenic origin. All forms of PIDs are rare and have an overall prevalence of approximately 1:10,000 live births with the exception of IgA deficiency. However, a much higher rate is observed among populations with high consanguinity or among genetically isolated populations.
PIDDs are sometimes difficult to detect. Diagnosing PIDD requires the expertise of a physician with specialized knowledge and experience. Since PIDDs are caused by genetic changes, these may be inherited. Sometimes, symptoms of PIDD do not arise until adulthood, and knowing the family medical history may indicate that your child should be tested, even if symptoms are not apparent.