There are several different forms of Severe Combined Immune Deficiency (SCID). An altered gene, passed to the baby from one or both parents, is associated with many forms of SCID. However, sometimes the SCID gene shows up for the first time in the newborn without being passed down from a parent (spontaneous occurrence). In fact, in most instances of infants born with SCID there are no other known cases of SCID in the family. Unless there has already been a baby born with SCID in the family, there is no way for a couple to know who could be carrying a gene that causes SCID.
A faulty gene passed from the mother to her son causes most cases of SCID in males. These boys have X-Linked Severe Combined Immune Deficiency (XSCID), referred to previously as the “Bubble Boy” disease. Other types of SCID are caused by two copies of a faulty gene; one copy of the faulty gene being passed down from each parent to the baby. Each parent who carries only one copy of the altered SCID gene is healthy, but when the baby inherits two altered copies, one from each parent, the function of T, B and Natural Killer (NK) cells is seriously impaired. NK cells are other important cells in the immune system that are so named because they easily kill cells infected with viruses.
No matter which gene or genes cause an infant to have SCID, intervention is essential and the sooner it is started the better things will be.
