TPO and cyclic hematopoiesis: Therefore, animals and humans heterozygous for a variation in TPO do not usually develop clinical signs compatible with CH; however, in this study, we identified two heterozygous variations in TPO of the affected cat, and the presence of clinical signs in this patient may be associated with a monoallelic expression of the mutant TPO allele due to the dominant-negative effect, of which there are few reports in humans [13,14].