Germline CSF3R c.1853C>T:p.T618I mutation. (A) Family tree. Arrow indicates the proband. Individuals with CNL and germline T618I mutation are marked in black. (B) BM aspirate in individual II.1 showing granulocytic hyperplasia. (C) Schematic of the CSF3R T618I mutation identified by HTS. Reads carrying the wild-type nucleotide (n = 799) and the variant nucleotide (n = 795) are shown (screenshot from JSI Medical System software). (D) Clonogenic assay. CD34⁺ progenitors (n = 1000) were seeded in methylcellulose in SCF + IL-3 ± G-CSF ± ruxolitinib; CFU-G colonies were counted 14 days later. The results are the means ± SD of 1 representative experiment performed in triplicate. IL-3, interleukin-3; SCF, stem cell factor.