Exon 2 was targeted with a G>A point mutation and a neomycin resistance gene cassette was inserted into intron 2. The mutation changes codon 99 from serine to asparagine (p.Ser99Asp). This mimics a mutation found in human multiple synostoses syndrome (SYNS) patients. RT-qPCR confirmed that this allele was expressed at the same level as wild-type.