An insertional translocation (IT) can result in pure segmental aneusomy for the inserted genomic segment allowing to define a more accurate clinical phenotype. Here, we report on two siblings sharing an unbalanced IT inherited from the mother with a history of learning difficulty. An 8-year-old girl with developmental delay, speech disability, and attention-deficit hyperactivity disorder (ADHD), showed by GTG banding analysis a subtle interstitial alteration in 21q21. Oligonucleotide array comparative genomic hybridization (array-CGH) analysis showed a 4q13.1–q13.3 duplication spanning 8.6 Mb. Fluorescence in situ hybridization (FISH) with bacterial artificial chromosome (BAC) clones confirmed the rearrangement, a der(21)ins(21;4)(q21;q13.1q13.3). The duplication described involves 50 RefSeq genes including the EPHA5 gene that encodes for the EphA5 receptor involved in embryonic development of the brain and also in synaptic remodeling and plasticity thought to underlie learning and memory. The same rearrangement was observed in a younger brother with behavioral problems and also exhibiting ADHD. ADHD is among the most heritable of neuropsychiatric disorders. There are few reports of patients with duplications involving the proximal region of 4q and a mild phenotype. To the best of our knowledge this is the first report of a duplication restricted to band 4q13. This abnormality could be easily missed in children who have nonspecific cognitive impairment. The presence of this behavioral disorder in the two siblings reinforces the hypothesis that the region involved could include genes involved in ADHD. © 2013 Wiley Periodicals, Inc.