RATIONALE: Vietnam recently began to diagnose X-linked Agammaglobulinemia (XLA) by quantitative immunoglobulins and flow cytometry. However, genetic analysis is currently not available. We sought to determine whether blood collected by Guthrie cards could be shipped across continents by regular airmail to a CLIA-approved laboratory for confirmatory testing.
METHODS: 20 patients from 19 unrelated families were diagnosed with XLA by physicians at the National Children's Hospital, Hanoi. Blood spots collected on Guthrie cards were shipped to Seattle Children’s Hospital for BTK analysis by Sanger sequencing using the Qiagen Mini kit and a modified protocol to analyze low concentration DNA samples.
RESULTS: Mean patient age was 7.7 (range 2-16.5) years with onset of symptoms at 9.1 months; 12 patients were diagnosed before age 5 years. Nineteen patients had recurrent URI's, 16 experienced pneumonia, 11 patients suffered severe infections including sepsis, meningitis, encephalitis, and 7 had severe gastroenteritis. Eleven cases had positive family histories. Mean IgG level was 58 mg/dl, mean B-cell number was 15.45 cells/mm3. BTK gene mutations were identified in 17/20 patients, all but 2 mothers and 1 of 3 sisters tested were carriers.
CONCLUSIONS: Dried blood spots incorporates a simple collection method with inexpensive transportation at room temperature shipped to a distant laboratory for sophisticated genetic analysis of patients from countries with limited resources.