Haploinsufficiency of certain genes may contribute to dysmorphic facial features, overgrowth and reduced cognitive capability (RNF135) (Tastet et al., 2015) or heart defects (ADAP2) (Venturin et al., 2014), whereas others might have tumor suppressive function, thus their deletion promote tumor development (SUZ12, ATAD5) (Bell et al., 2011; Zhang et al., 2014). The gene discussed is ADAP2; the disease is neoplasm.