Characterization of a novel KRAS mutation identified in Noonan syndrome

Noonan syndrome (NS) is the most common non‐chromosomal syndrome seen in children and is characterized by short stature, dysmorphic facial features, chest deformity, a wide range of congenital heart defects and developmental delay of variable degree. Mutations in the Ras/mitogen‐activated protein kinase (MAPK) signaling pathways cause about 70% of NS cases with a KRAS mutation present in about 2%. In a cohort of 65 clinically confirmed NS patients of Japanese origin, we screened for mutations in the RAS genes by direct sequencing. We found a novel mutation in KRAS with an amino acid substitution of asparagine to serine at codon 116 (N116S). We analyzed the biological activity of this mutant by ectopic expression of wild‐type or mutant KRAS. NS‐associated KRAS mutation resulted in Erk activation and active Ras–GTP levels, and exhibited mild cell proliferation. In addition, kras‐targeted morpholino knocked‐down zebrafish embryos caused heart and craniofacial malformations, while the expression of mutated kras resulted in maldevelopment of the heart. Our findings implicate that N116S change in KRAS is a hyperactive mutation which is a causative agent of NS through maldevelopment of the heart. © 2012 Wiley Periodicals, Inc.