KMT2D and microcephaly: Mutations in MLL2/KMT2B have been commonly associated with early onset generalized dystonia, which is a disorder characterized by sustained muscle contractions causing abnormal, repetitive movements, and in a small number of cases has been associated with ID, facial dysmorphisms and microcephaly (Albanese et al., 2013; Zech et al., 2016; Meyer et al., 2017; Kawarai et al., 2018).