ESPE Abstracts (2015) 84 LBP--1258

A Distinct Population of Islet Cells Defines Diffuse Congenital Hyperinsulinism in Infancy but not Other Forms of the Disease

Bing Hana, Melanie Newbouldb, Gauri Batrab, Edmund Cheesmanb, Ross Craigieb, Zainab Mohammada,b, Lindsey Rigbyb, Raja Padidelab, Mars Skaeb, Aleksandr Mironova, Tobias Starborga, Karl Kadlera, Karen Cosgrovea, Indraneel Banerjeeb & Mark Dunnea

aUniversity of Manchester, Manchester, UK; bRoyal Manchester Children’s Hospital, Manchester, UK

Background/hypothesis: Congenital hyperinsulinism in infancy (CHI) mainly arises from mutations in ATP-sensitive potassium channel genes. However, the expression pattern of defects can be markedly diverse. In diffuse CHI (CHI-D) all islet cells express gene defects, whereas patients with focal CHI (CHI-F) only express defects in a localised region of islet cells due to loss of a maternally-imprinted locus. Here, we examined the properties of a novel population of CHI islet cells with enlarged nuclei.

Methods: Tissue was obtained from patients with CHI-D (n=9), CHI-F (n=5), and age-matched controls (n=8, 2 days–36 months of age). High-content analysis of histological sections and serial block face-scanning electron microscopy were used to quantify nuclear enlargement and determined the extent of nucleomegaly.

Results: Islet cells with nucleomegaly have; i) an average area of 100.1±3.8 μm2 (n=105), which was 4.3- and 5.3-fold larger than nuclei in endocrine (n=173) and exocrine cells (n=115) respectively; ii) an increased nuclear volume from 157.33±9 μm3 (n=22) to ~420 μm3; and iii) an endocrine phenotype as they stained positive for the neuroendocrine cell marker chromogranin (n=398/405 cells). The incidence of islet cell nucleomegaly was 6.4- and 8.4-fold greater in CHI-D (0.67±0.11% of islet cells, n=40 320) than in age-matched controls and CHI-F, respectively. Overall, 70.5±6% of CHI-D islets contained at least one enlarged nuclei and 45.4±7% of islets (n=179) were found to have more than one affected cell. As nuclear enlargement might be as a consequence of chromatin decondensation, we examined the correlation of Ki67 staining (as a marker of proliferation) with nucleomegaly. In controls (53%, n=16/30) and CHI-F (67%, n=22/33) nucleomegaly was positively-associated with proliferation, whereas only 9% of cells with nucleomegaly in CHI-D islets were Ki67 positive (n=27/291).

Summary: These findings suggest that nucleomegaly is pathognomonic with CHI-D and unrelated to cell proliferation in CHI-D islets.