News Excerpt:

A two-month-old girl with bubble baby syndrome has become one of the youngest patients in the country to undergo a bone marrow transplant (BMT) from an unrelated donor.

About the Bubble Baby Syndrome:

• Severe combined immunodeficiency (SCID) is a group of rare disorders caused by mutations in different genes involved in the development and function of infection-fighting immune cells.
• SCID is often called bubble baby disease.
• Most often, SCID is inherited in an autosomal recessive pattern, in which both copies of a particular gene—one inherited from the mother and one from the father—contain defects.
• Infants with SCID appear healthy at birth but have no functioning immune system, meaning that even a normally mild infection can be fatal.

Types of SCID:

• The best-known form of autosomal recessive SCID is caused by adenosine deaminase (ADA) deficiency, in which infants lack the ADA enzyme necessary for T-cell survival.
• X-linked SCID, which is caused by mutations in a gene on the X chromosome, primarily affects male infants.
• Children with this type of SCID have white blood cells that grow and develop abnormally.
• Consequently, they have low numbers of T cells (white blood cells that identify and attack perceived “invaders”), and their B cells (white blood cells that produce antibodies against infection) do not function.

Symptoms and Diagnosis:

• Symptoms of SCID occur in infancy and include serious or life-threatening infections, especially viral infections, which may result in pneumonia and chronic diarrhoea.
• Research supported by the National Institute of Allergy and Infectious Disease (NIAID), USA and other organisations has shown that early diagnosis of SCID through newborn screening leads to prompt treatment and high survival rates.
• To confirm a SCID diagnosis, a doctor will evaluate the numbers and types of T and B cells present and their ability to function.

Treatment:

• The condition is fatal, usually within the first year or two of life, unless infants receive immune-restoring treatments, such as transplants of blood-forming stem cells, gene therapy, or enzyme therapy.
  • Stem cell transplantation: Hematopoietic (blood-forming) stem cell transplantation is the standard treatment for infants with SCID.
    • Transplants from matched siblings lead to the best restoration of immune function, but if a matched sibling is unavailable, infants may receive stem cells from a parent or an unrelated donor.
    • These transplants are life-saving but often only partially restore immunity.
  • Enzyme replacement therapy: Children with SCID with Adenosine deaminase (ADA) deficiency have been treated somewhat successfully with PEG-ADA enzyme replacement therapy.
  • Gene therapy: Studies also have shown that gene therapy can be an effective treatment for some types of SCID, including X-linked SCID.
    • In gene therapy, stem cells are obtained from the patient’s bone marrow, the normal gene is inserted into the stem cells using a carrier known as a vector, and the corrected cells are returned to the patient.