A single nucleotide promoter variant underlying Wiskott-Aldrich disease. (A) Pedigree tree. Male and female individuals are represented by squares and circles, respectively. Each generation is designated by a Roman numeral, and each individual by an Arabic numeral. Individuals with immune dysregulation are shown as closed black symbols, and the index case is indicated by an arrow. Black dots represent heterozygosity. Mut, mutated; WT, wild-type; y, Y chromosome. (B) Summary of the phenotype of the four patients. (C) Counts of platelets in whole blood of the patients. Normal range is displayed in grey. (D) Scheme of WAS promoter adapted from Petrella et al. (4). Arrows indicate transcription factor–binding sites identified by a combination of computational predictions and experimental validation. The c.-64C>T variant is displayed in red, and the 5′UTR and transcription start site of WAS in green and blue, respectively. (E) Electropherograms for the sequencing of representative WAS nucleotide sequences present in the hemizygous state in the four patients, in the heterozygous state in their mothers and sister, and in the homozygous wild-type state in control (CTL) and in their fathers. (F)WAS quantitative PCR (normalized to GUSB) in T-activated cells from three controls and in the four patients. (G) Quantification of WASP protein expression derived from panel D. (H) Intracellular protein expression of WASp (clone 5A5) or isotype, in T-activated cells derived from two controls (CTL1 and CTL2), P1, P2, P3, and P4, and from a patient previously reported as deficient in WASP (1).