Severe combined immunodeficiency
Severe combined immunodeficiency (SCID) is a very rare and serious condition that affects the immune system, your body's defence against infections. X-linked SCID, the most common type, usually affects only boys. Without treatment, even a common cold could be life threatening for a child with SCID. So until they can be treated, children diagnosed with SCID need to be looked after in a sterile environment, or 'bubble'. So far the only effective treatment for SCID is a bone-marrow transplant that replaces the white blood cells.