Mutations in MLL4/KMT2D have been identified as the most common cause of Kabuki syndrome, which is characterized by distinctive facial features, microcephaly, growth delay, cardiac anomalies, and varying degrees of ID (Lehman et al., 2017; Di Candia et al., 2022; Usluer et al., 2022; Table 3). Here, KMT2B is linked to microcephaly.