LAUSR

Abstract Cardio‐facio‐cutaneous (CFC) syndrome, a genetic disorder caused by germline mutations in BRAF, KRAS, MAP2K1 and MAP2K2, is characterized by growth retardation, heart defects, dysmorphic facial appearance and dermatologic abnormalities. We have previously reported that knock‐in mice expressing the CFC syndrome‐associated mutation, Braf Q241R, showed growth retardation because of gastrointestinal dysfunction. However, other factors associated with growth retardation, including chondrogenesis and endocrinological profile, have not been examined. Here, we show that 3‐ and 4‐week‐old BrafQ241R/+ mice have decreased body weight and length, as well as reduced growth plate width in the proximal tibiae. Furthermore, proliferative and hypertrophic chondrocyte zones of the growth plate were reduced in BrafQ241R/+ mice compared with Braf+/+ mice. Immunohistological analysis revealed that extracellular signal‐regulated kinase (ERK) activation was enhanced in hypertrophic chondrocytes in BrafQ241R/+ mice. In accordance with growth retardation and reduced growth plate width, decreased serum levels of insulin‐like growth factor 1 (IGF‐1) and IGF binding protein 3 (IGFBP‐3) were observed in BrafQ241R/+ mice at 3 and 4 weeks of age. Treatment with C‐type natriuretic peptide (CNP), a stimulator of endochondral bone growth and a potent inhibitor of the FGFR3‐RAF1‐MEK/ERK signaling, increased body and tail lengths in Braf+/+ and BrafQ241R/+ mice. In conclusion, ERK activation in chondrocytes and low serum IGF‐1/IGFBP‐3 levels could be associated with the growth retardation observed in BrafQ241R/+ mice. Our data also suggest that CNP is a potential therapeutic target in CFC syndrome.