severe combined immune deficiency

(SCID) rare condition caused by a gene malfunction in which a baby is born unable to produce the enzyme ADA. Without ADA the T cells involved in fighting infection are poisoned; untreated infants usually die before the age of two. The child must be kept within a germ-free ‘bubble’, a transparent plastic tent, until a matched donor can provide a bone-marrow transplant (bone marrow is the source of disease-fighting cells in the body).

There have been promising results from experimental gene therapy for this condition, pioneered in the USA 1990; in 1993 doctors inserted the ADA gene into stem cells from the umbilical cords of three babies born with SCID and reintroduced them. The gene was still present in blood cells 1995, though only in 1% of T cells. The percentage will need to increase to a minimum of 10% for additional drug treatment to become possibly unnecessary.