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 days36 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.
01 Oct 2015 - 03 Oct 2015