Existing blood tests may help unlock some of the mysteries surrounding infant immunodeficiency syndromes, according to a speaker at the American Academy of Allergy and Immunology Annual Meeting held in Washington this week.
Performing inexpensive quantitative polymerase chain reaction assays may help avert expensive and ineffective later stage treatments for children with severe combined immunodeficiency, said Jennifer Puck, MD, professor of pediatrics at the University of California, San Francisco.
Infants with severe combined immunodeficiency (SCID) appear healthy at birth, but have few T cells, leaving them susceptible to recurrent and opportunistic infections. Health officials estimate SCID affects about one in 50,000 infants, but the exact number is unknown due to a of lack specific diagnostic tools and an incomplete understanding of the genetic interplay that results in symptoms. Currently, about 80% of infants with SCID go unrecognized until they develop infectious complications due to their immune deficiency, Puck said.
“The best survival and outcomes are achieved if treatment, such as bone marrow transplantation, can be done before infections occur,” she said.
Puck has developed a method for identifying presymptomatic children with SCID using the dried blood spots already obtained from all babies for newborn screening. DNA is extracted and PCR used to determine the number of T-cell receptor excision circles (TRECs) vs. a copy number of a control genomic DNA segment. Patients who lack TRECs may have SCID or other disorders with very low T cells. Pilot screening of newborns is currently ongoing in Wisconsin, Massachusetts and Navajo Indian populations, where SCID incidence is high. The tests cost between $6 and $10 per sample to perform.
The Medical College of Wisconsin recently instituted universal newborn screening, and researchers there noted among 46 children in whom SCID was diagnosed before 3.5 months of age, 96% survived 26 years post transplantation, compared with 66% of 116 children who did not receive an early diagnosis.
“Identifying infants who have low TRECs with screening will improve SCID outcomes, establish SCID incidence, and make identification of further immune defects possible,” Puck said.
The ongoing pilot trials will soon determine the clinical utility of such screening programs. – by Nicole Blazek
For more information:
- Puck J. #3516. American Academy of Allergy, Asthma & Immunology Annual Meeting; March 13-17, 2009; Washington.
- Routes J. #248. American Academy of Allergy, Asthma & Immunology Annual Meeting; March 13-17, 2009; Washington.
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