RBL2 and Global developmental delay: Interestingly, RBL1 and RBL2 have been found to regulate neuronal differentiation and the survival of post-mitotic neurons.11 Correspondingly, pathogenic variants in RBL2 have been associated with severe developmental delay, dysmorphic features, microcephaly, seizures and behavioural abnormalities.12-14 However, clinical features associated with RBL2 pathogenic variants have been characterized in only a limited number of individuals, precluding a comprehensive characterization of this disorder.