Paternal 132 bp deletion affecting <i>KCNQ1OT1</i> in 11p15.5 is associated with growth retardation but does not affect imprinting.

Abstract

The chromosomal region 11p15.5 harbours two imprinting centres (<i>H19/IGF2</i>:IG-DMR/IC1, <i>KCNQ1OT1</i>:TSS-DMR/IC2). Molecular alterations of the IC2 are associated with Beckwith-Wiedemann syndrome (BWS), whereas only single patients with growth retardation and Silver-Russell syndrome (SRS) features have been reported. CNVs in 11p15.5 account for less than 1% of patients with BWS and SRS, and they mainly consist of duplications of both ICs either affecting the maternal (SRS) or the paternal (BWS) allele. However, this correlation does not apply to smaller CNVs, which are associated with diverse clinical outcomes. We identified a family with a 132 bp deletion within the <i>KCNQ1OT1</i> gene, associated with growth retardation in case of paternal transmission but a normal phenotype when maternally inherited. Comparison of molecular and clinical data with cases from the literature helped to delineate its functional relevance. Microdeletions within the paternal IC2 affecting the <i>KCNQ1OT1</i> gene have been described in only five families, and they all include the differentially methylated region <i>KCNQ1OT1</i>:TSS-DMR/IC2 and parts of the <i>KCNQ1</i> gene. However, these deletions have different impacts on the expression of both genes and the cell-cycle inhibitor <i>CDKN1C</i>. They thereby cause different phenotypes. The 132 bp deletion is the smallest deletion in the IC2 reported so far. It does not affect the IC2 methylation in general and the coding sequence of the <i>KCNQ1</i> gene. Thus, the deletion is only associated with a growth retardation phenotype when paternally transmitted but not with other clinical features in case of maternal inheritance as observed for larger deletions.