The tyrosine kinase receptor ErbB4 (erythroblastic leukemia viral oncogene homolog 4) plays a crucial role in numerous neurobiological processes in the developing and adult brain. Moreover, recent molecular genetics studies implicate ErbB4 in the pathophysiology of schizophrenia. However, the phenotypic consequences of haploinsufficiency of ErbB4 are not known, as no coding mutations have been identified until now. Here, we present a patient with early myoclonic encephalopathy and profound psychomotor delay with a de novo reciprocal translocation t(2;6)(q34;p25.3), disrupting the ErbB4 gene. This patient represents the first case of haploinsufficiency for one of the ErbB family members of tyrosine kinase receptors.