Congenital Hyperinsulinism and Novel KDM6A Duplications -Resolving Pathogenicity With Genome and Epigenetic Analyses.

Abstract

Hyperinsulinemic hypoglycemia (HI) can be the presenting feature of Kabuki syndrome (KS), which is caused by loss-of-function variants in KMT2D or KDM6A. As these genes play a critical role in maintaining methylation status in chromatin, individuals with pathogenic variants have a disease-specific epigenomic profile-an episignature. We evaluated the pathogenicity of 3 novel partial KDM6A duplications identified in 3 individuals presenting with neonatal-onset HI without typical features of KS at the time of genetic testing. Three different partial KDM6A duplications were identified by routine targeted next-generation sequencing for HI and initially classified as variants of uncertain significance (VUS) as their location, and hence their impact on the gene, was not known. Whole-genome sequencing (WGS) was undertaken to map the breakpoints of the duplications with DNA methylation profiling performed in 2 individuals to investigate the presence of a KS-specific episignature. WGS confirmed the duplication in proband 1 as pathogenic as it caused a frameshift in the normal copy of the gene leading to a premature termination codon. The duplications identified in probands 2 and 3 did not alter the reading frame, and therefore their significance remained uncertain after WGS. Subsequent DNA methylation profiling identified a KS-specific episignature in proband 2 but not in proband 3. Our findings confirm a role for KDM6A partial gene duplications in the etiology of KS and highlight the importance of performing in-depth molecular genetic analysis to properly assess the clinical significance of VUS' in the KDM6A gene.