X-Linked Lymphoproliferative Disease 2 (XLP2) / XIAP Deficiency

XLP2 is a type of X-linked lymphoproliferative disease. XLP2 typically affects boys. It can also occasionally affect girls. The condition was first described in 2006. Only about 100 boys have been diagnosed with it so far.


XLP2 is caused by a change in the XIAP gene. This is sometimes called the BIRC4 gene.

The XIAP gene codes for the XIAP protein that the body needs to regulate the immune system. People with this genetic change either have problems with the XIAP protein, or they do not have the protein. Another name for this condition is XIAP deficiency. This is a unique disorder. The term we use is “XIAP deficiency.”

XIAP deficiency is an “X-linked” disease. This means that the genes that cause it are on the X chromosome. Boys have one X chromosome and one Y chromosome. Girls have two X chromosomes. If a boy has a changed XIAP gene on his X chromosome, he will develop XIAP deficiency.

For a girl to develop XIAP deficiency, she would need to have genetic changes on both X chromosomes. Another way she could develop XIAP deficiency would be by a “skewing” of X-chromosome inactivation. This causes many cells to be deficient in XIAP. Most girls with a genetic change are just carriers. They do not develop symptoms of XIAP / XLP2.

Girls that are affected by XIAP deficiency most commonly develop inflammatory bowel disease. But they can also develop other problems caused by XIAP deficiency. Girls who are affected or who are carriers can pass the disease on to their sons. The chance of this happening is 50%. They can also pass carrier status or, more rarely, the disease to their daughters.