Cost-effective screening for SCID

Two UCLA studies have shown that newborn screening for Severe Combined Immunodeficiency (SCID) a rare, treatable disorder of the immune system commonly known as 'bubble boy disease' is both cost-effective and could be done accurately using a two tiered testing method.

"We wanted to determine whether testing for SCID should be added to the universal screening panel for genetic disorders," said Dr Sean McGhee, clinical instructor of pediatric immunology at Mattel Children's Hospital at UCLA.

"Treatment is now advanced enough that 95% of children can be cured, but newborns must be detected in the first month, before the onset of severe infections."

The current basis for the screening test is measurement of the number of lymphocytes at the time of birth that are normally very high, but very low in SCID infants. The screening is done by using dried blood samples obtained for other newborn screenings.

In the retrospective analysis, investigators measured serum or plasma levels of interleukin-7 (IL-7), a T-cell growth cytokine elevated in SCID, in combination with the previously developed T-cell receptor recombination excision circles assay.

They found that combining the tests in a two-tiered strategy decreased the false positive rate to nearly zero, which would be sufficient to allow cost-effective screening.

McGhee added that this strategy should be addressed in a multi-centre, prospective trial to determine accurately the incidence, specificity, sensitivity and cost of SCID newborn screening.

The incidence of SCID is unknown but may be more common than published estimates because infants frequently die of infection before diagnosis. If an infant is diagnosed preferably within the first month of life and before their first infection, most can be treated with a bone-marrow transplant. About half of the patients can be cured; the other half may require intravenous immune globulin therapy treatments, but can live normal lives.