Primary immunodeficiencies (PID) are the result of defects in the immune system. Many distinct disorders have been discovered, approximately 140 in total, and most have a genetic basis.
The most common PID is hypogammaglobulinaemia in which antibody production is deficient. An antibody is a type of protein. The body’s immune system produces antibodies when it detects harmful substances like bacteria and viruses. Hypogammaglobulinaemia has several causes but prominent are X-linked agammaglobulinaemia (XLA), also known as Bruton’s disease, and common variable immunodeficiency (CVID).
Severe combined immune deficiency (SCID), is a type of PID where T and B lymphocytes (white blood cells that play a key role in our immune system) are deficient.
Medical text written August 1996 by Dr T B Wallington, Consultant Immunologist, Southmead Hospital, Bristol UK. Last updated November 2010 by Professor A Cant, Consultant Paediatric Immunologist, Newcastle General Hospital, Newcastle, UK.
Boys with XLA become unwell after their mother’s antibody protection wears off at around six months old. CVID can occur at any age when an individual suddenly stops producing antibodies. The result of antibody deficiency is severe, recurrent and unusual infections with poor response to antibiotic treatment. These infections can cause permanent damage and may become life threatening without correct treatment. SCID is characterised by a child being unable to fight infection from an early age.
Effective treatments are available for the various different PIDs and early referral to a clinical immunologist is essential in all cases. Hypogammaglobulinaemia cannot presently be cured but replacement antibody, by a subcutaneous infusion (just under the skin) of immunoglobulin, is common practice and must be continued for life.
Certain primary immunodeficiencies such as SCID are so severe that careful protection of the patient from infection until they can be treated is essential. The main method of treatment for this condition is bone marrow transplant (also known as a haemopoetic stem cell transplant). This procedure replaces the stem cells (specialised cells that give rise to other types of cells) in the bone marrow. Stem cells in bone marrow produce the white blood cells T and B lymphocytes, which fight infection.
Gene replacement therapy is also considered for certain diseases where a genetic defect is the cause of a PID, but this is in its infancy and some side effects of the treatment have been noted, including leukaemia (see entry Leukaemia and other Allied Blood disorders).
X-linked inheritance is the most common method by which PIDs are transmitted from parent to child, but some PIDs are autosomal recessive.
This is possible for some PIDs. Expert genetic guidance should be sought in the case of occurrence of a PID in a family.