A to C or G mutation of the third base of U1 snRNA results in mis-splicing of several cancer-related genes such as CD44, Musashi RNA binding protein 2 (MSI2) and DNA polymerase delta 1, catalytic subunit (POLD1) in CLL and Patched 1 (PTCH1) and GLI family zinc finger 2 (GLI2) in SHH medulloblastomas, respectively [58,59]. The gene discussed is PTCH1; the disease is B-cell chronic lymphocytic leukemia.