The third exon of the endogenous RpS23 locus has been replaced with a version that encodes a R67K amino acid substitution. The same amino acid substitution has been identified in the orthologous human RPS23 gene in a patient with growth retardation and mild autism. In addition, the third exon is flanked by loxP sites (a Disc\RFPmCherry.3xP3 marker is also present within this loxP cassette, downstream of the RpS23 coding sequence). An attP site is also present within the second intron, upstream of the first loxP site of the cassette.