Integration of genomic analysis and transcript expression of ABCC8 and KCNJ11 in focal form of congenital hyperinsulinism

Abstract

BackgroundThe focal form of CHI is caused by an autosomal recessive pathogenic variant affecting the paternal homologue of genes ABCC8 or KCNJ11 and a second somatic event specifically occurring in the affected islet of Langerhans. The approach of this study was to integrate the genetic changes occurring in pancreatic focal lesions of CHI at the genomic and transcriptional level.Research Design and MethodsPatients receiving therapeutic surgery and with proven ABCC8 or KCNJ11 pathogenic variants were selected and analyzed for loss of heterozygosity (LOH), changes in copy number and uniparental disomy (UPD) on the short am of chromosome 11 by molecular microarray analysis and methylation-specific MLPA. Gene expression was analyzed by RT-PCR and Massive Analysis of cDNA Ends (MACE).ResultsBoth genes, ABCC8 and KCNJ11, are located in proximity to the Beckwith-Wiedemann (BWS) imprinting control region on chromosome 11p15. Somatic paternal uniparental isodisomy (UPD) at chromosome 11p was identified as second genetic event in focal lesions resulting in LOH and monoallelic expression of the mutated ABCC8/KCNJ11 alleles. Of five patients with samples available for microarray analysis, the breakpoints of UPD on chromosome 11p were different. Samples of two patients were analyzed further for changes in gene expression. Profound downregulation of growth suppressing genes CDKN1 and H19 was detected in focal lesions whereas growth promoting gene ASCL2 and pancreatic transcription factors of the endocrine cell lineage were upregulated.ConclusionsPaternal UPD on the short arm of chromosome 11 appears to be the major second genetic event specifically within focal lesions of CHI but no common breakpoint for UDP can be delineated. We show for the first time upregulation of growth promoting ASCL2 (achaete-scute homolog 2) suggestive of a driving factor in postnatal focal expansion in addition to downregulation of growth suppressing genes CDKN1C and H19.

Monogenic diabetes in a Chinese population with young‐onset diabetes: A 17‐year prospective follow‐up study in Hong Kong

“…Notably, no studies have reported neonatal diabetes or MODY due to dominant frameshift variants in ABCC8 , but occurrence of neonatal diabetes in homozygotes with recessive loss‐of‐function variants have been described 42 . In addition, single paternally inherited ABCC8 variants were identified to cause focal form of congenital hyperinsulinism and permanent neonatal diabetes mellitus as a result of the loss of heterozygosity from somatic paternal uniparental isodisomy on chromosome 11 43–45 . For our patients who were heterozygous carriers of frameshift mutations in ABCC8 , we were unable to confirm if the patients had inherited the variants paternally with coexisting loss of heterozygosity, and therefore they were not considered to have monogenic diabetes.…”

Genetic Heterogeneity Correlated with Phenotypic Variability in Congenital Hyperinsulinism Caused by Mutation in ABCC8 Gene Associated with Early‐Onset Persistent Neonatal Hypoglycemia

“…This variant (Arg598Ter) was also reported as pathogenic in ClinVar (VariationID: 434056). Of the 11 affected individuals, at least 4 were compound heterozygotes carrying a reported pathogenic variant in trans, increasing the likelihood that the Arg598Ter variant is pathogenic (Variation ID: 434053) (https://www.ncbi.nlm.nih.gov/clinvar/variation/434053/, accessed on 7 March 2024) (Damaj, 2008;De Vroede, 2004;Bellanné-Chantelot, 2010;[19-22] In vitro functional studies provided evidence that the Arg598Ter variant may slightly affect protein function [21,23].This variant causes a premature stop codon at position 598, leading to a truncated or absent protein. Paternally-inherited loss-of-function (LOF) ABCC8 mutations represent a known mechanism in autosomal recessive hyperinsulinemic hypoglycemia [24,25].…”

Congenital Hyperinsulinism Caused by Mutations in ABCC8 Gene Associated with Early-Onset Neonatal Hypoglycemia: Genetic Heterogeneity Correlated with Phenotypic Variability

“…In vitro functional studies provided evidence that the Arg598Ter variant may slightly affect protein function [26,28]. This variant causes a premature stop codon at position 598, leading to a truncated or absent protein.…”