Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to Noonan syndrome ?
    ### Response:
    Mutations in the PTPN11, SOS1, RAF1, KRAS, NRAS and BRAF genes cause Noonan syndrome.  Most cases of Noonan syndrome result from mutations in one of three genes, PTPN11, SOS1, or RAF1. PTPN11 gene mutations account for approximately 50 percent of all cases of Noonan syndrome.
    