Northern blot analysis. The top panel shows RNA from EBV-transformed cell lines (B) and neutrophils (N) from an XLA patient with a 4-bp deletion (1); the patient described in this study (2); an XLA patient with an amino acid substitution (3); and a normal control (4). To control for sample loading, the blot was stripped and rehybridized with a β-actin specific probe, shown in the lower panel.