Hyperactive TLT Signaling: Putting the "H" in H syndrome

In this issue of Blood, Shiloh et al uncover a novel mechanism by which dysregulated toll-like receptor (TLR) signaling drives pathologic mitogen-activated protein kinase (MAPK) pathway activity in H syndrome, a rare multisystemic histiocytic disorder. Building on these findings, they demonstrate that MAPK pathway inhibition ameliorates histiocytosis and hyper-inflammation in a patient with H syndrome, providing proof of concept for future clinical studies.1