Severe Combined Immunodeficiency (SCID) occurs in just one out of every 50,000 to 100,000 births in the United States, yet it is the most serious primary immunodeficiency disorder. A study published January 27 in Blood, the Journal of the American Society of Hematology (ASH), demonstrates that babies with SCID who are diagnosed at birth and receive a hematopoietic stem cell transplant (HSCT), which is the transplantation of blood-forming stem cells, have significantly improved survival.
SCID is a rare group of genetic disorders characterized by severe abnormalities of the development and function of the immune system due to a defect in the specialized white blood cells that defend the body from infection. Patients with SCID lack almost all immune defenses, are prone to serious, life-threatening infections within the first few months of life, and require major treatment for survival beyond infancy. The most effective treatment for SCID is HSCT from the bone marrow of a healthy person. According to the Immune Deficiency Foundation, if a baby with SCID receives a bone marrow transplant in the first 3.5 months of life, the survival rate can be as high as 94 percent.
"If diagnosed early enough, it is probable that every baby with SCID could be treated, and most likely, cured," said Fabio Candotti, MD, Vice Chair of the ASH Scientific Committee on Immunology and Host Defense and Head of the Disorders of Immunity Section in the Genetics and Molecular Biology Branch of the National Human Genome Research Institute at the National Institutes of Health. "Research that promotes early screening and diagnosis is vital for advancing the idea of universal adoption of testing."
The investigators conducted a retrospective cohort study by comparing the outcomes of 60 babies diagnosed at or before birth (between 1982 and 2010) with the outcomes of their relatives who also had the disorder using information gathered from databases from Great Ormond Street Hospital NHS Trust and Newcastle General Hospital in London, U.K.
Results from the study show that, in comparison to the family member with SCID, babies diagnosed at birth had a significantly decreased number of infections (89 percent versus 17 percent, respectively). Patients in the early-diagnosed group were also transplanted earlier and had a dramatically improved survival outcome following HSCT, regardless of donor match, conditioning regimen (chemotherapy or radiation given immediately prior to a transplant to help eliminate the patient's disease and to suppress immune reactions), or type of SCID.
The study showed that 35.4 percent (17 patients) of the 48 family members with SCID died before HSCT, and among the 31 of them who underwent HSCT, 38.7 percent (12 patients) died after the procedure. In comparison, only one patient in the early-diagnosed group died before HSCT and five patients (8.5 percent) died after HSCT. The transplant survival rate of the early-diagnosed group was 91.5 percent (p<.001) compared to 61.3 percent (p<.001) of their relatives with SCID.
"This is the first study that shows formal comparative data to demonstrate that newborn diagnosis can improve survival in SCID patients, regardless of the type of donor or conditioning regimen used," said H. Bobby Gaspar, MD, PhD, senior author of the study and Professor of Pediatrics and Immunology at University College London (UCL) Institute of Child Health in London, U.K. "There is currently no newborn screening for SCID in the U.K.; the United States is the only country that has started screening for SCID, although only a small number of states are screening at this time. Implementation of newborn screening to more states in the U.S. and in other countries would have a major impact on the outcome of SCID."
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