Beckwith-Wiedemann syndrome: a quantitative, immunohistochemical study of pancreatic islet cell populations

Endocrine hyperplasia and dysplasia in the pathogenesis of gastrointestinal and pancreatic endocrine tumors

Non-neoplastic proliferative lesions of endocrine cells have been described throughout the gastrointestinal tract and pancreas. A multistep continuum from hyperplasia and dysplasia to neoplasia originally was identified and systematically defined for histamine-producing enterochromaffin-like (ECL) cells of the gastric corpus. More recently, a similar classification system was devised for gastrin (G)- and somatostatin (D)-producing cells in the duodenum. Preneoplastic lesions of the endocrine pancreas still lack a solid and widely accepted definition of a multistep growth process. Similarly, in spite of reports of carcinoid-associated endocrine cell hyperplasia, there is no systematic definition of nonneoplastic lesions of the endocrine cells of the ileum, appendix and colorectum.

Congenital hyperinsulinism and mosaic abnormalities of the ploidy

BACKGROUND

Congenital hyperinsulinism and Beckwith-Wiedemann syndrome both lead to beta islet hyperplasia and neonatal hypoglycaemia. They may be related to complex genetic/epigenetic abnormalities of the imprinted 11p15 region. The possibility of common pathophysiological determinants has not been thoroughly investigated.

OBJECTIVE

To report abnormalities of the ploidy in two unrelated patients with congenital hyperinsulinism.

METHODS

Two patients with severe congenital hyperinsulinism, one overlapping with Beckwith-Wiedemann syndrome, had pancreatic histology, ex vivo potassium channel electrophysiological studies, and mutation detection of the encoding genes. The parental genetic contribution was explored using genome-wide polymorphism, fluorescent in situ hybridisation (FISH), and blood group typing studies.

RESULTS

Histological findings diverged from those described in focal congenital hyperinsulinism or Beckwith-Wiedemann syndrome. No potassium channel dysfunction and no mutation of its encoding genes (SUR1, KIR6.2) were detected. In patient 1 with congenital hyperinsulinism and Beckwith-Wiedemann syndrome, paternal isodisomy for the whole haploid set was homogeneous in the pancreatic lesion, and mosaic in the leucocytes and skin fibroblasts (hemihypertrophic segment). Blood group typing confirmed the presence of two erythroid populations (bi-parental v paternal only contribution). Patient 2 had two pancreatic lesions, both revealing triploidy with paternal heterodisomy. Karyotype and FISH analyses done on the fibroblasts and leucocytes of both patients were unremarkable (diploidy).

CONCLUSIONS

Diploid (biparental/paternal-only) mosaicism and diploid/triploid mosaicism were present in two distinct patients with congenital hyperinsulinism. These chromosomal abnormalities led to paternal disomy for the whole haploid set in pancreatic lesions (with isodisomy or heterodisomy), thereby extending the range and complexity of the mechanisms underlying congenital hyperinsulinism, associated or not with Beckwith-Wiedemann syndrome.

p57Kip2 (cdkn1c): sequence, splice variants and unique temporal and spatial expression pattern in the rat pancreas

The cyclin-dependent kinase (CDK) inhibitor p57Kip2 (CDKN1C) is a negative regulator of cell proliferation, binding to a variety of cyclin-CDK complexes and inhibiting their kinase activities in vitro. The p57Kip2 gene is imprinted and the maternal allele is expressed in terminally differentiated cells, including human beta-cells. Somatic loss of p57Kip2 expression is associated with increased beta-cell proliferation in the focal form of Hyperinsulinism of Infancy. We cloned and sequenced the rat ortholog of p57Kip2, and demonstrate that it is highly homologous to the mouse gene. However, the human and rodent genes are quite divergent. Despite having highly homologous C- and N-terminal domains, the mid-portion of the human gene is entirely different from that of its rodent counterparts. Expression of p57Kip2 was evaluated during fetal and postnatal development, and a highly cell-specific, temporal and spatial expression profile was found. In contrast to other tissues, the expression pattern in rat pancreas was entirely opposite from that previously reported in man, with high levels of expression in rodent exocrine cells, but no expression in beta-cells during any stage of development. These findings demonstrate that p57Kip2 expression is highly regulated. In the pancreas, the functional significance of this gene appears to be quite different in humans when compared with rodents, suggesting that a better understanding of the function of this protein may provide new insights into the mechanisms involved in the control of human beta-cell mass.

Beckwith-Wiedemann syndrome with unusual hepatic and pancreatic features: a case expanding the phenotype

We describe an infant with Beckwith-Wiedemann syndrome (BWS) who had hepatic and pancreatic findings not previously described in BWS. These were biliary dysgenesis and enlargement and cystic dysplasia of the pancreas. The biliary dysgenesis was characterized by proliferation of abnormally shaped ducts in the portal tracts. Massive enlargement and cystic dysplasia of the pancreas was associated with ductular proliferation, virtual absence of normal exocrine tissue, and an increase in endocrine tissue.

Wiedemann-Beckwith syndrome

The Wiedemann-Beckwith syndrome (WBS) comprises an accumulation of multiple congenital anomalies. Exomphalos, macroglossia and gigantism are considered the most common manifestations, hence the alternative designation EMG-syndrome. The syndrome carries with it an increased risk of developing specific tumours. One of the more frequent metabolic changes is transient neonatal hypoglycaemia, the result of increased insulin secretion. Inheritance of the syndrome remains uncertain. Most cases are sporadic, but a number of familial cases have been reported. Present evidence suggests that WBS is an autosomal dominant trait with variable expressivity. This review summarizes the abundant literature on the subject and discusses recent molecular genetic developments that may explain the interrelationship between the clinical abnormalities, metabolic disturbances and development of tumours.

Whole embryo morphometry in teratogen screening

Current methodology in embryo evaluation involves qualitative assessment of razor blade and paraffin serial sections. Presently, no one has applied existing computerized morphometric techniques to examine embryos. A technique has been developed that enables investigators to section embryos at 150 mu, thereby greatly reducing the number of sections and making morphometric analysis possible. This type of analysis permits the precise volumetric determination of several developing organ systems. The aim of this study was to evaluate the feasibility and sensitivity of whole embryo morphometry in teratogen screening. Cadmium chloride, a well-established teratogen, was chosen because of its ability to induce exencephaly in approximately one-half of offspring while having no observable effects on the remaining exposed embryos. It was found that both exencephalic and normal-appearing cadmium-exposed embryos had significantly smaller total cellular, neuroepithelial, otic vesicle, optic assembly, limb bud, and cardiac mesenchyme volumes when compared to controls. Also, the neuroepithelial volume of the exencephalic embryos was significantly smaller than the normal-appearing cadmium-exposed embryos. These results suggest that in addition to inducing exencephaly, cadmium chloride has an overall inhibitory effect on embryonic growth. We have shown that whole embryo morphometry is a sensitive means of evaluating embryonic growth that permitted determination of cadmium-induced aberrations not discernable by currently employed techniques. In light of these results, we feel this technique shows promise for future investigations of known and suspected teratogens.