X-SCID and its causes

X-SCID is a form of severe combined immunodeficiency (SCID) that is inherited as an X-linked disorder. This means that only males can be affected and that females can be carriers. There may be a history of SCID in other males in the family (maternal uncles, male cousins on the mother’s side), but often it occurs as a ‘new mutation’ that has developed ‘out of the blue’ or sporadically, in which case there is no previous family history. More information about X-linked inheritance can be found in the leaflet 'Genetic aspects of primary immunodeficiency'.

X-SCID is caused by a mistake (mutation) in a gene on the X chromosome. The affected gene codes for a protein known as the ‘common gamma chain’ (γc). γc is very important for normal development and functioning of a number of cells that are vital for a healthy immune system. These include T cells, natural killer (NK) cells and B cells. In X-SCID, γc is either absent or not working, and this results in a severely abnormal immune system.

Reviewed October 2017