Novel familial distal imprinting centre 1 (11p15.5) deletion provides further insights in imprinting regulation.

backgroundDeletions of the imprinting centre 1 (IC1) in 11p15.5 are rare and their clinical significance is not only influenced by their parental origin but also by their exact genomic localization. In case the maternal IC1 allele is affected, the deletion is associated with the overgrowth disorder Beckwith-Wiedemann syndrome (BWS) and a gain of methylation (GOM) of the IC1. The consequences of deletions of the paternal IC1 allele depend on the localization and probably the binding sites of methylation-specific DNA-binding factors affected by the change. It has been suggested that distal deletions of the paternal allele are associated with a normal IC1 methylation and phenotype, whereas proximal alterations cause a loss of methylation (LOM) and Silver-Russell syndrome (SRS) features.

resultsIn a patient referred for molecular BWS testing and his family, a deletion within the IC1 was identified by MLPA. It was associated with a GOM, corresponding to the transmission of the alteration via the maternal germline. Accordingly, the deletion was also detectable in the maternal grandmother, but here the paternal chromosome 11p15.5 was affected and a IC1 LOM was observed. By nanopore sequencing, the localization of the deletion could be precisely determined.

conclusionsWe report for the first time both GOM and LOM of the IC1 in the same family, caused by transmission of a 2.2-kb deletion in 11p15.5. Nanopore sequencing allowed the precise characterization of the change by long-read sequencing and thereby provides further insights in the regulation of imprinting in the IC1.