WGS identifies NOTCH2 mutations in SMZL. (A and B) A representative case of SMZL with typical histopathological features of SMZL at low and high power (Bars: (A) 400 µm; (B) 50 µm) including expansion of pale staining marginal zones surrounding splenic follicles in a biphasic pattern. (C–E) Reverse complement sequence reads (Read Alignment) mapped to the reference genome (Reference Sequence) from three index samples with mutations in NOTCH2 (boxed) with deviations from reference genome highlighted in blue. Bottom panels show Sanger sequencing electropherograms confirming mutations in the index cases (SMZL) and the absence of the mutations in matched normal constitutional tissue (Germline). One frameshift p.I2304fsX9 mutation and two nonsense p.R2400X mutations were identified in three patients among the six index cases (arrows). The total number of reads containing the indicated mutation compared with the total number of reads mapping to this region is shown (C, 11/28; D, 16/44; E, 11/90). Genome sequencing was performed once for each index case. Sanger sequencing confirmation of somatic acquisition was performed in at least two independent replicates.