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Prevalence of SCID higher than original estimates
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Severe combined immunodeficiency is twice as common among newborns as previously thought, according to study findings in JAMA.
Antonia Kwan, PhD, MRCPCH, of the University of California, San Francisco, and colleagues assessed 3,030,083 infants screened for severe combined immunodeficiency (SCID) from 11 programs between January 2008 and July 2013. Forty-six percent of data came from programs in California; 16% was from programs in New York; Wisconsin programs accounted for 11%; and Massachusetts programs accounted for 10% of data.
Screening detected 52 cases of SCID, an overall incidence of 1 in 58,000 births. Previous estimates, based on limited data, indicated an incidence of 1 in 100,000 infants. Incidence was not significantly different among states but was higher in the Navajo Nation, where a common mutation causes SCID in approximately 1 in 2,000 births, according to researchers.
Ten of 52 infants with SCID had leaky SCID. Infants with leaky SCID had an incomplete mutation of a typical SCID gene that contributes to a decreased immune function.
“We’re finding that leaky SCID is more common than previously thought. Before screening we’d typically not make the diagnosis for several months or even years, but because of newborn screening they are being treated before they get into any trouble,” study researcher Jennifer Puck, MD, said in a press release.
Forty-nine of 52 infants with SCID received immune-repairing therapies including stem cell transplants, enzyme replacement therapy, and gene therapy. Three infants died before receiving treatment and four died after receiving transplants. Forty-five infants tolerated treatment.
Researchers found population-based testing revealed a wider range of underlying genetic causes of SCID than previously known. Mutations in the X chromosome-linked IL2RG gene, previously thought to account for half of SCID cases, accounted for 19% of cases in this study. Fifteen percent of infants with SCID had an unknown genetic defect.
“The point of newborn screening is to identify conditions that are treatable, and for which early treatment saves lives. The excellent outcomes of SCID infants across the country reported in this study prove that severe combined immunodeficiency is such a condition,” Puck said in the release.
Disclosure: The researchers report no relevant financial disclosures.
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