A Progeroid Syndrome Caused by RAF1 deficiency Underscores the importance of RTK signaling for Human Development

Somatic and germline gain-of-function point mutations in RAF, the first oncogene to be discovered in humans, delineate a group of tumor-prone syndromes known as RASopathies. In this study, we document the first human phenotype resulting from the germline loss of function of the proto-oncogene RAF1 ( a.k.a. CRAF) . In a consanguineous family, we uncovered a homozygous p.Thr543Met mutation segregating with a neonatal lethal progeroid syndrome with cutaneous, craniofacial, cardiac and limb anomalies. Structure-based prediction and functional tests using human knock-in cells showed that threonine 543 is essential to: 1) ensure RAF1’s stability and phosphorylation, 2) maintain its kinase activity towards substrates of the MAPK pathway and 3) protect from stress-induced apoptosis. When injected in Xenopus embryos mutant RAF1 T543M failed to phenocopy the effects of overactive FGF/MAPK signaling confirming its hypomorphic activity. Collectively, our data disclose the genetic and molecular etiology of a novel segmental progeroid syndrome which highlights the importance of RTK signaling for human development and homeostasis. Short summary A germline homozygous recessive loss-of-function mutation p.T453M in RAF1 causes a neonatal lethal progeroid syndrome. In vitro and in vivo tests demonstrate that Thr543 is necessary for RAF1’s protein stability, to transduce signaling to the MAPK pathway and to respond to stress-induced apoptosis.