BCL9 and Neurodevelopmental delay: Similarly, BCL9, a gene important in apoptosis and also one of seven genes in the 1q21.1 region, has a well-known role in cell proliferation in tumors.81 The model of NDD proposed here predicts that human NSC models of either 16p11.2 or 1q21.1 CNVs will have reciprocal effects (for example, increased differentiation markers for the deletion and decreased differentiation markers for the duplication).