Agammaglobulinemia, x-linked

X-linked agammaglobulinemia (XLA) is an X-linked genetic disorder, meaning that the altered BTK gene is passed from parent to child on the X chromosome. If a woman is a carrier for XLA it means that she carries one altered BTK gene that does not work properly, and one unaltered BTK gene that does work properly. XLA carriers almost never have symptoms of XLA. When a woman who is an XLA carrier has a child, there is a 50% chance for her to pass on the altered copy and a 50% chance for her to pass on the unaltered copy. Her sons who inherit the altered copy will have XLA; her daughters who inherit the altered copy will be carriers like her. Children who inherit the unaltered copy will not have XLA and cannot pass the genetic change onto their children.

Men who have XLA have only one X chromosome that contains an altered copy of the BTK gene. They will pass this X chromosome on to all of their daughters, who will be carriers of XLA. Men pass their Y chromosome onto their sons, so men with XLA cannot pass the disease onto their sons.

Some boys have XLA because of a change in the BTK gene that happened randomly at their conception and was not inherited from their mother. This is called a de novo change. The chance of another child in these families having XLA is very low. If the affected boy eventually has a child, his daughters would be carriers of XLA and his sons would not inherit XLA as described above.