To explore whether WDSTS is treatable in utero, we created and characterized a mouse model (Kmt2a+/LSL) that carries a heterozygous insertion of a loxP-stop-loxP (LSL) cassette in intron 1 of Kmt2a resulting in heterozygous KO of the affected allele. This evidence concerns the gene KMT2A and Wiedemann-Steiner syndrome.