XLP can be caused by variations in the genetic makeup of a person. Genes are part of our genetic makeup. They provide the instructions our cells need to do their roles within our bodies. XLP can be caused by changes or mutations in one of these genes: SH2D1A or XIAP / BIRC4. When these genes have a defect, the immune system doesn’t work the right way. This can cause the manifestations of XLP to develop.
How is XLP inherited?
XLP1 and XLP2 are both X-linked diseases. This means the genes which cause them are on the X chromosome. Boys have one X chromosome and one Y chromosome. Girls have two X chromosomes. When a boy has an X chromosome that has a mutated, or “bad,” copy of the SH2D1A or XIAP / BIRC4 gene, he develops XLP.
Mothers or sisters of patients with XLP may also have an X chromosome that has a bad copy of the SH2D1A or XIAP / BIRC4 gene. Since females have two X chromosomes, most females will never have any symptoms of the disease. This is because there is a normal copy of the gene on their other X chromosome. Very rarely, female carriers may also develop symptoms of XLP1.
In most cases, patients inherit the X chromosome with the bad copy of the gene from their mother. In some cases, the mutation spontaneously occurs in the child.
I am an XLP carrier. What are the chances my children are affected?
Women who have a bad copy of an XLP gene on one of their X chromosomes are called carriers. For these women, each pregnancy has a 50 percent chance of getting the X chromosome with the bad copy of the gene. Each male child of an XLP carrier has a 50 percent chance of being affected by XLP. Each female child has a 50 percent chance of being a carrier. They will likely never be sick, but their future male children may be affected.