Newborn screening performed in numerous states indicates that the incidence of the potentially life-threatening disorder, severe combined immunodeficiency, is higher than previously believed, at 1 in 58,000 births, although there is a high rate of survival, according to a study in the August 20 issue of JAMA.
The purpose of newborn screening is early detection of inborn conditions for which prompt treatments can reduce the risk of death or irreversible damage. The first heritable immune disorders to which newborn screening has been applied are those that together comprise severe combined immunodeficiency (SCID), a disorder that can result in life-threatening infections, making early detection and treatment critical. Population-based screening is the only means to detect SCID prior to the onset of infections in most cases. The incidence of SCID has been estimated to be 1 in 100,000 births. SCID was added to the national recommended uniform panel for newborn screened disorders in 2010, and currently 23 states, the District of Columbia, and the Navajo Nation screen approximately two-thirds of all infants born in the United States for SCID, according to background information in the article.
Antonia Kwan, Ph.D., M.R.C.P.C.H., of the University of California, San Francisco, and colleagues conducted the first combined analysis of more than 3 million infants screened for SCID in 10 states and the Navajo Nation. Infants born from the start of each participating program from January 2008 through the most recent evaluable date prior to July 2013 were included.
There were 52 SCID cases identified during the study period, an overall incidence of 1 in 58,000 births. The incidence was not significantly different in any state program but was higher in the Navajo Nation (1/3,500), attributed to a genetic mutation found in this population. Survival of SCID-affected infants through their diagnosis and immune reconstitution was 87 percent, 92 percent for infants who received transplantation, enzyme replacement, and/or gene therapy. Additional interventions for SCID and non-SCID T-cell lymphopenia (abnormally low level of certain white blood cells) included immunoglobulin infusions, preventive antibiotics, and avoidance of live vaccines.
"These findings support the view that SCID has previously been underdiagnosed in infants with fatal infections," the authors write.
"Now that infants with SCID are being detected at a very young age in diverse medical settings, it is imperative to tailor protocols for their treatment, including choice and pharmacokinetic monitoring of drugs administered to facilitate hematopoietic cell engraftment."
Editorial: Newborn Screening for Severe Combined Immunodeficiency Progress and Challenges
"Infants born with SCID in the 27 states that do not screen for SCID have a greater chance of not being detected promptly, or at all, and are at increased risk of dying, compared with those born in the 23 states that do screen for SCID," writes Neil A. Holtzman, M.D., M.P.H., of the Johns Hopkins Medical Institutions, Baltimore, in an accompanying editorial.
"Although many states require their own pilot programs before a new screening test is added to their battery of tests, no state could amass as much data in a reasonable time frame as have Kwan et al. Before screening becomes universal in the United States, agreement is needed on what constitutes a positive T-cell receptor excision circle [a biomarker used to help identify SCID] screening test, on ensuring referrals to physicians competent to make a diagnosis, and on providing definitive therapy to every infant detected with SCID in every state."