Analysis of CSR Sμ-Sα junctions in Artemis-deficient patients. (A) Samples of Sμ-Sα CSR junction sequences amplified from whole blood obtained from 14 healthy controls (8 children and 6 adults) and 2 RS-SCID patients (Art1 and Art2) with hypomorphic Artemis mutations. Microhomology at the junction (middle row) is identified by the longest region of sequence homology (1-bp mismatch accepted, underlined nucleotides, gray box) between the Sμ donor sequence (top row) and the Sα acceptor sequence (bottom row). (B) Distribution of microhomology length at Sμ-Sα junctions. Each dot represents a unique Sμ-Sα junction sequence. Vertical lines and numbers indicate the median value of microhomology length in base pairs. The difference in the median length of microhomology between the 2 Artemis patients (13.5 bp and 14.5 bp) and the pool of 8 pediatric controls (6.0 bp) is highly significant (2-tailed Mann-Whitney test, P < .001 for each patient).