CALB1 and essential thrombocythemia: We also investigated calbindin level, a protein specifically expressed by PCs in the cerebellum, and found that ET cases had a lower level of calbindin than controls (0.58±0.18 vs. 1.01±0.26, p<0.01) (Figure 1E), consistent with our previous findings that ET cases had a lower number of PCs [3].