PIK3R1 c.1300-2A>G variant causes activated PI3Kδ syndrome 2. (A) Family pedigree with the patient shaded black and the unaffected family members white. (B) Amplification and sequencing of PIK3R1 cDNA between exons 2 and 15; mRNA was extracted from T cell blasts of patient (P) and healthy control subject (Ctrl) 3. PCR products were visualized on an agarose gel (top). Sequencing of the PCR product with Oxford Nanopore Technology showed loss of exon 11 in one of two consensus sequences from P (bottom); the WT sequence is not shown. (C) Representative flow cytometric analysis of PBMC from Ctrl 3 and P (prior to leniolisib therapy). (D) Flow cytometric analysis of the phosphorylation of AKT at threonine residue 308, mTOR at serine residue 2448, and S6 at serine residues 235/236 in expanded T cell blasts from P and Ctrl 1–Ctrl 3 after treatment with DMSO for 30 min (left), and the same analysis of T cell blasts from P after a 30-min incubation with 500 nM leniolisib vs. DMSO (right). Left and right columns in panel D represent the same experiment. DMSO, dimethyl sulfoxide. Source data are available for this figure: SourceData F1.