STK4 and myeloproliferative disorder: Similarly, in another model characterized by del(20q), a frequent cytogenetic abnormality detected in hematologic malignancies such as MDS but also in myeloproliferative neoplasm (MPN), the STK4 gene encoding for the Hippo kinase MST1 was identified as a key 20q deleted gene with a central role in the biology of del(20q)-associated hematologic malignancies.