Inherited immune disorders are also called primary immune deficiency disorders. These disorders are caused by a mutation (mistake) in a gene that affects the immune system. A gene is an inherited code of instructions that tells the body how to make every cell and substance in the body.
The mutation that causes WAS affects a gene on the X chromosome, which comes from the mother. Disorders inherited on the X chromosome appear only in males. A female with the mutated gene will not have the disease but will be a carrier. This means she may pass the mutated gene on to her children.
In most cases, no one knows what causes the mutation to appear the first time. Once a mutation appears, it can be passed from mother to child through many generations.
In boys with WAS, the gene mutation affects the body’s ability to make certain types of white blood cells that help the immune system fight infection. It also affects the body’s ability to make platelets, blood cells that help control bleeding. Boys with WAS have fewer platelets than normal (thrombocytopenia). The platelets are also smaller than normal.