Three other observations fit this hypothesis: (i) absence of tuft cell morphology, namely of brush-type villi on lung cancer cells [43, 44], (ii) poor expression of rare genes expressed by mature tuft cells (e.g., CHAT [choline acetyltransferase] (Fig. S7), and DCLK1 [not shown]) [45], and (iii) poor expression of genes of mature ionocytes (e.g., CFTR) [20]. The gene discussed is CFTR; the disease is lung cancer.