Two mutations were found to occur more than once in our families, representing mutational hotspots: The mutation R168X (c.502 C>T) in MECP2 (Rett syndrome; OMIM: #300005) repeated itself in eight different families and G380R (c.1138 C>A) in FGFR3 (Achondroplasia; OMIM: #134934) was found in three different families. This evidence concerns the gene MECP2 and achondroplasia.