EFL1 variants display somatic mosaicism. (A) All 3 patients demonstrate a partial LOH in chromosome 15, as indicated by the deviation from variant AF (VAF) of 0.5. The variant origin is indicated by red or blue dots; parental samples were not available for II-1. The location of EFL1 is indicated by a red dotted line. (B) Schematic diagram of the single-cell LOH experiment shown in panels C and D, where a red cell symbolizes an LOH-carrying cell. (C-D) Single-cell LOH profiles from I-1 bone marrow (BM) (C) and III-1 buccal swab samples (D); the upper plots denote cells without LOH, and the lower plots represent cells with complete LOH in chromosome 15. The plots on the right show chromosome 15 with the variant origin shown in red or blue dots. (E) VAF of the EFL1 variant in multiple tissue samples from I-1. (F) Genetic process underlying selection of EFL1p.Thr1069Ala cells in the patients. BMT, bone marrow transplantation; gDNA, genomic DNA; SNP, single-nucleotide polymorphism.