Beckwith–Wiedemann syndrome (BWS) is a disorder of growth regulation exhibiting somatic overgrowth and predisposition to paediatric tumours. With an incidence estimated at 1 in 13,700, it is caused by various epigenetic and/or genetic alterations associated with disturbances within two different 11p15 domains that are controlled by distinct imprinting control regions (ICR), ICR1 and ICR2. The majority of patients have abnormalities within ICR2 presenting hypomethylation, while less frequent aetiologies include mosaic paternal 11p uniparental disomy (11patUPD), maternally inherited mutations of the CDKN1C gene, and hypermethylation of ICR1. A few patients have cytogenetic abnormalities involving 11p15.5. Since the subgroups are associated with different recurrence risks, the identification of the molecular cause of BWS is particularly important for the follow-up of the patient and the genetic counselling of both the patient and the family. Here, we report a 13-year-old girl with clinical diagnosis of BWS presenting macrosomia, umbilical hernia, kidney abnormalities, hydramnius, prematurity, typical face, advanced bone age, moderate developmental delay, prominent occiput and forehead, round face, epicanthus, short nasal bridge, and microretrognathia. Cytogenetic analysis with highresolution banding showed an apparently normal karyotype. Microsatellite analysis and methylationspecific multiplex ligation-dependent probe amplification revealed a de novo microduplication at 11p15.5 of paternal origin. Duplication has a minimum size of 600 kb, covering only ICR1, not affecting ICR2. This sporadic case with a de novo duplication without other chromosomal abnormalities makes genotype–phenotype correlation difficult. As far as we know, this is one of the smallest duplications associated with BWS and is consistent with the independent regulation of ICR1 and ICR2. Our patient presented moderate developmental delay and craniofacial features typical of 11p15 duplication. Future studies exploiting this subtle 11p15.5 rearrangement will provide an important tool to further dissecting the genomics of BWS region and the pathogenesis of this imprinting disorder
