Herein, we report another Japanese patient with a KAT6B-related disorder and a novel de novo heterozygous variant in exon 18 of KAT6B [c.3925dup, p.(Glu1309fs*33)], providing further evidence that truncating variants in exon 17 and in the proximal region of exon 18 are associated with genitopatellar syndrome-like phenotypes. Here, KAT6B is linked to genitopatellar syndrome.