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.