CONTEXT Acquired insulinomas are rare causes of hyperinsulinemic hypoglycemia in children and are much less common than focal lesions of congenital hyperinsulinism. The latter are known to be associated with isodisomy for paternally-transmitted KATP mutations on 11p15; however, the molecular basis for pediatric insulinomas is not well characterized. OBJECTIVE The purpose of this study was to characterize the histopathologic and molecular defects in a large group of 12 pediatric insulinomas seen at The Children's Hospital of Philadelphia. RESULTS Twelve children with insulinomas were seen between 1971-2013, compared to 201 cases with focal congenital hyperinsulinism seen between 1997-2014. The age of insulinoma patients ranged from 4-16 years at the time of surgery. Features of MEN1 syndrome were present in 5 of the 12, including 4 cases with heterozygous mutations of MEN1 on 11q. Immunohistochemical analysis revealed nuclear loss of p57 staining consistent with loss of the maternal 11p15 allele in 11 of the 12 insulinomas, including all 5 MEN1-associated tumors. Imbalance of the paternal 11p allele was confirmed by SNP genotyping and methylation assays of the 11p imprinting control loci in 4 of 5 MEN1-associated tumors and 6 of 7 sporadic insulinomas. In addition, SNP genotyping revealed extensive tumor aneuploidy beyond chromosome 11. CONCLUSIONS These data indicate that MEN1 mutations are more common in insulinomas in children than in adults. Aneuploidy of chromosome 11 and other chromosomes is common in both MEN1 and non-MEN1 insulinomas. The novel observation of a paternal parent-of-origin effect in all MEN1 and most non-MEN1 tumors suggests a critical role for imprinted growth-regulatory genes in the 11p region in the genesis of β-cell endocrine tumors in children.
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