Abstract
Germline or somatic variation in the family of KMT2 lysine methyltransferases have been associated with a variety of congenital disorders and cancers. Notably, KMT2A-fusions are prevalent in 70% of infant leukaemias but fail to phenocopy short latency leukaemogenesis in mammalian models, suggesting additional factors are necessary for transformation. Given the lack of additional somatic mutation, the role of epigenetic regulation in cell specification, and our prior results of germline KMT2C variation in infant leukaemia patients, we hypothesized that germline dysfunction of KMT2C altered haematopoietic specification. In isogenic KMT2C KO hPSCs, we found genome-wide differences in histone modifications at active and poised enhancers, leading to gene expression profiles akin to mesendoderm rather than mesoderm highlighted by a significant increase in NODAL expression and WNT inhibition, ultimately resulting in a lack of in vitro hemogenic endothelium specification. These unbiased multi-omic results provide new evidence for germline mechanisms increasing risk of early leukaemogenesis.