Heterozygous loss of function mutations in the KMT2D gene (OMIM 147920) is the major primary cause of KS-1 and individuals who also manifest with intellectual disability and developmental delay and may share physical and behavioral characteristics with individuals with KLEFS-2 (Lavery et al., 2020; Barry et al., 2022). The gene discussed is KMT2C; the disease is Intellectual disability.