Endocrine Abstracts

Background: Congenital hypopituitarism (CH) is characterised by the deficiency of one or more pituitary hormones and can present alone or in association with complex disorders. Congenital hyperinsulinism (CHI) is a disorder of unregulated insulin secretion despite hypoglycaemia that can occur in isolation or as part of a syndrome. The underlying genetic etiology causing the complex phenotype of CH and CHI is unknown.

Patient and Methods: A female baby born to non-consanguineous Caucasian parents at 42 weeks gestation with a birth weight of 4.185 Kg (+1.72SDS) was noted to have high glucose requirement and a hypoglycaemia screen confirmed CHI. 18F-DOPA PET-CT suggested diffuse pancreatic lesion. She also developed TSH, ACTH and GH deficiencies. MRI brain showed a hypoplastic anterior pituitary, absent posterior pituitary, thin pituitary stalk and corpus callosum. Genetic analysis was negative for ABCC8, KCNJ11, HNF4A and GCK mutations. She has solitary median maxillary incisor, congenital nasal pyriform aperture stenosis, pulmonary stenosis, choroidal coloboma, severe gastroesophageal reflux requiring jejunostomy, persistent oxygen requirement and hepatic portal bridging fibrosis. Whole exome sequencing was performed and the identified variant was confirmed by Sanger sequencing. Further functional studies were performed to demonstrate the pathogenicity of the variant.

Results: A de novo heterozygous mutation in FOXA2 (c.505T>C, p.(S169P) was identified which is at a highly conserved DNA binding domain, not present in control databases and predicted to be deleterious to the protein function. We demonstrated strong expression of Foxa2 mRNA in the developing hypothalamus, pituitary, pancreas, lungs and oesophagus of mouse embryos using in situ hybridization. Expression profiling on human embryos by immunohistochemistry showed strong hFOXA2 expression in the neural tube, third ventricle, diencephalon and pancreas. Transient transfection of HEK293T cells with Wt (Wild type) hFOXA2 and mutant hFOXA2 showed impairment in transcriptional reporter activity by mutant hFOXA2. Further analyses using western blot assays showed that hFOXA2 p.(S169P) variant is pathogenic resulting in lower expression levels when compared with Wt hFOXA2.

Conclusion: We have demonstrated, for the first time, the causative role of FOXA2 in a complex congenital syndrome with hypopituitarism, CHI and endoderm-derived organ abnormalities.