Figure 3.

Patient fibroblasts demonstrate a defect in NHEJ. Top, Schematic demonstrating a DSB in the middle of a 6-bp repeat. This can be repaired either via NHEJ (left) or microhomology (right). When repaired via microhomology, a BstXI restriction site is introduced that will result in the generation of multiple shorter DNA bands on the gel. Bottom, MMEJ assay performed in fibroblasts from a normal control, a DNA ligase IV-deficient patient, and proband P1. P1 and the DNA ligase IV-deficient fibroblasts both demonstrate multiple smaller DNA bands after the addition of BstXI, indicating preferential use of the MMEJ pathway for DNA repair.