There are two recent reports of codon 117 mutations – the first in K-Ras in human colorectal tumours (Wojcik et al, 2008) and the second in H-Ras, associated with activation of the RAS–MAPK pathway and the mental retardation Costello syndrome (Denayer et al, 2008). The gene discussed is HRAS; the disease is Costello syndrome.